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Research in Developmental Disabilities
Neurodevelopmental outcome in Angelman syndrome: Genotype–phenotype correlations Line Granild Bie Mertz a,*, Per Thaulov b, Anegen Trillingsgaard c, Rikke Christensen d, Ida Vogel d, Jens Michael Hertz e, John R. Østergaard a a
Centre for Rare Diseases, Department of Pediatrics, Aarhus University Hospital, Denmark Psychiatric Hospital for Children and Adolescents, Aarhus University Hospital, Denmark Department of Psychology, Aarhus University, Denmark d Department of Clinical Genetics, Aarhus University Hospital, Denmark e Department of Clinical Genetics, Odense University Hospital, Denmark b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 8 December 2013 Received in revised form 18 February 2014 Accepted 21 February 2014 Available online xxx
Angelman syndrome (AS) is a neurogenetic disorder characterized by intellectual disability, developmental delay, lack of speech, and epileptic seizures. Previous studies have indicated that children with AS due to 15q11.2-q13 deletions have a more severe developmental delay and present more often autistic features than those with AS caused by other genetic etiologies. The present study investigated the neurodevelopmental profiles of the different genetic etiologies of AS, and examined the evolution of mental development and autistic features over a 12-year period in children with a 15q11.2-q13 deletion. This study included 42 children with AS. Twelve had a Class I deletion, 18 had Class II deletions, three showed atypical large deletions, five had paternal uniparental disomy (pUPD) and four had UBE3A mutations. Children with a deletion (Class I and Class II) showed significantly reduced developmental age in terms of visual perception, receptive language, and expressive language when compared to those with a UBE3A mutation and pUPD. Within all subgroups, expressive language performance was significantly reduced when compared to the receptive performance. A follow-up study of seven AS cases with 15q11.2-q13 deletions revealed that over 12 years, the level of autistic features did not change, but both receptive and expressive language skills improved. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Angelman syndrome 15q11.2-q13 Language skills Autism ADOS Mullen Intellectual disability
1. Introduction Angelman syndrome (AS) is a neurogenetic disorder caused by loss of expression of the maternal imprinted gene UBE3A, which codes for the protein ubiquitin-protein ligase E3A. Four known molecular mechanisms lead to deficient maternal UBE3A expression and AS development: Deletion of the AS critical region on the maternal chromosome 15q11.2-q13 (70%), paternal uniparental disomy (pUPD) (2–7%), imprinting defects (3–5%), and mutations in the maternal copy of UBE3A (10%)
* Corresponding author. Tel.: +45 27423551. E-mail address: [email protected] (L.G.B. Mertz). http://dx.doi.org/10.1016/j.ridd.2014.02.018 0891-4222/ß 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mertz, L. G. B., et al. Neurodevelopmental outcome in Angelman syndrome: Genotype– phenotype correlations. Research in Developmental Disabilities (2014), http://dx.doi.org/10.1016/j.ridd.2014.02.018
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(Tan et al., 2011). There are two common types of 15q11.2-q13 deletions, a 5.9-Mb (Class I) deletion, and a 5.0-Mb (Class II) deletion, differing only in the position of the proximal (centromeric) breakpoint (Tan et al., 2011; Mertz et al., 2013). Clinical characteristics of AS include severe developmental delay, ataxia, a low threshold for laughter, and 80–90% of AS patients have epileptic seizures (Conant, Thibert, & Thiele, 2009). In addition, a high percentage of individuals with AS has been found to meet the formal diagnostic criteria of autism, defined as total score above autism cut off in ADOS, (autism diagnostic observation schedule) (Lord et al., 2000). Autism or autism spectrum disorder was previously reported in 50–80 per cent of patients with AS (Bonati et al., 2007; Peters, Horowitz, Barberi-Welge, Taylor, & Hundley, 2012; Sahoo et al., 2007; Trillingsgaard & Østergaard, 2004). Previous studies have indicated that children with AS due to 15q11.2-q13 deletions have a more severe developmental delay and present more often autistic features than those with AS caused by other genetic etiologies (Lossie et al., 2001; Peters et al., 2012; Sahoo et al., 2006, 2007; Varela, Kok, Otto, & Koiffmann, 2004). However, not all studies have used validated standardized instruments, and the total number of investigated individuals remains small. Furthermore, virtually all previous studies have a cross-sectional design, and none have performed longitudinal consecutive assessments of neurodevelopmental parameters in children with AS. The present study investigated the neurodevelopmental profiles of the different genetic etiologies of AS, including Class I and Class II deletions, and examined the evolution of mental development and autistic features over a 12-year period in children with a 15q11.2-q13 deletion. 2. Methods 2.1. Patient recruitment We identified patients with AS who were born in Denmark between 1991 and 2009 through the Danish National Patient Registry (NPR) and the Danish Cytogenetic Central Registry (DCCR), supplemented by personal contact with all pediatric and clinical genetic departments and the Patient Organization of Angelman syndrome in Denmark. NPR contains administrative and clinical data from all hospitalizations and out-patient clinics in Denmark. Reporting data to the NPR is mandatory for all Danish hospitals and is further encouraged by the government funding system. Thus, the data in this registry are known to be of very high validity (Andersen, Madsen, Jorgensen, Mellemkjaer, & Olsen, 1999). The diagnoses are recorded according to the tenth revision of the International Classification of Diseases (ICD-10) from the World Health Organization. The DCCR contains data from every prenatal genetic test and every postnatal karyotype performed in Denmark since 1960. It also contains national postnatal genetic data on selected diseases such as 22q11.2 deletion, Prader-Willi, and Angelman syndromes. Data reporting is self-imposed by all clinical genetic departments that perform these genetic tests, and the registry is administered by representatives from these departments. In total, we identified 51 patients with genetically verified AS (Mertz et al., 2013). The deadline for identification was January, 1 2012. This study was approved by the National Ethic Commitee (M-20090028) and the Danish Data Protection Agency (2009-41-3133). The legal guardian of each participant provided verbal and written informed consent. 2.2. Genetic analysis Patients who were previously diagnosed with a deletion were further investigated using a high resolution 1000-kb array CGH. DNA was extracted from peripheral blood with an automated Chemagic Magnetic Separation Module (PerkinElmer, Waltham, MA, USA) and was purified prior to array CGH analysis using the DNeasy Blood & Tissue Kit (Qiagen, Valencia, CA, USA). Deletion breakpoints were determined by microarray-based comparative genomic hybridization with the SurePrint G3 Human CGH microarray 1 M (Agilent Technologies, Santa Clara, CA, USA). Sample and reference genomic DNA (1500 ng) were labeled with Cy5 (reference) or Cy3 (patient) using the Genomic DNA ULS labeling kit (Agilent Technologies) and purified as per the manufacturer’s protocol. Labeled sample and reference DNA were pooled, and mixed with 50 ml of human COT-1 DNA (1 mg/ml), 10 blocking agent, and 2 hybridization buffer were added. Hybridization was performed for 40 h at 65 8C. Scanning and image acquisitions were carried out with an Agilent microarray scanner, and microarray image files were quantified with Agilent’s Feature Extraction software version 10.7. Data analysis was performed using Genomic Workbench version 6.5 (Agilent Technologies). Copy number was determined with the adm-2 algorithm. Profile deviations consisting of six or more neighboring oligonucleotides were considered genomic aberrations, yielding an approximately 12 kb resolution. Deletion breakpoints were based on the positions of the first and last oligonucleotide probes within the region of the deletion that showed a copy number loss. We also identified copy number gains or losses on chromosomes other than 15q11-q13. Copy number variations (CNVs) in areas containing previously reported CNVs in healthy control samples from the database of genomic variants (DGV) were excluded. UCSC hg19 version of the human genome and public CNV databases were used as reference. 2.3. Mental development and autism Mental age was assessed with Mullen Scales of Early Learning (Mullen, 1995) based on four sub-scales: visual perception, receptive language, expressive language and fine motor development. The Mullen Scales assess the cognitive and motor
Please cite this article in press as: Mertz, L. G. B., et al. Neurodevelopmental outcome in Angelman syndrome: Genotype– phenotype correlations. Research in Developmental Disabilities (2014), http://dx.doi.org/10.1016/j.ridd.2014.02.018
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functions of young children from birth to 68 months. Scores on each subscale are converted into an age equivalent in months (Akshoomoff, 2006). The Mullen Scales test was performed by four trained professionals who were blinded to the genetic results. Inter-observer reliability was above 80%. Behavior associated with autism or autism spectrum disorders (ASD) was assessed according to the ADOS (Lord et al., 2000) a semi-structured, standardized assessment of communication, social interaction, play, and imagination. ADOS is one of the most widely used observation instruments for assessing a child for the presence of an Autism Spectrum Disorder. ADOS consists of four modules. Module 1 is intended for children who do not consistently use spontaneous phrase speech and is therefore appropriate for children with AS. The test consists of 10 activities with 29 accompanying ratings. ADOS module 1 consists of semi-structured situations allowing observation of imaginative activities, social role-play, and interactions with the observer and with the parent attending the session (Lord et al., 2000). The ADOS classification is based on cut-off scores from two domains; social behavior and communication. The ADOS examination also includes play, stereotyped behavior and restricted interests, and other abnormal behaviors. Repetitive and stereotyped behaviors in early childhood do not differentiate ASD from other developmental disorders in early childhood and therefore are not part of the algorithm for ADOS module 1 (Lord et al., 2000). The ADOS assessment was performed and evaluated by four ADOS-certified professionals, who were all blinded to the genetic results. The assessments were video-recorded and inter-observer reliability was above 80%. Seven of the participants, all with a 15q11.2-q13 deletion, also participated in a previous study by Trillingsgaard and Østergaard published in 2004 (Trillingsgaard & Østergaard, 2004). The Mullen Scales of Early Learning scores (visual reception, receptive language, and expressive language) and the ADOS scores from that examination were used as baseline scores in a longitudinal follow-up study. 2.4. Statistical analysis Statistical analyses were performed using IBM SPSS 20 software. Differences between diagnostic groups in developmental age and ADOS scores were analyzed using Student’s t-test or Fisher’s exact test for categorical variables. Differences over a 12-year follow up period were analyzed using Student’s paired t-test. All reported p-values were two-sided, and p-values 500 kb. The largest CNV was a 2000 kb duplication on chromosome 22. 3.4. Mental age, fine motor performance, and autism Table 2 presents the Mullen Subscale test results. Children with a deletion (Class I and Class II) showed significantly reduced developmental age in terms of visual perception (p < 0.01), receptive language (p < 0.01), and expressive language (p < 0.05) when compared to those with a UBE3A mutation or pUPD. They also showed a significantly reduced fine motor performance (p < 0.01). We found no differences in cognitive and language development or fine motor performance between children with Class I and Class II deletions. However, in all evaluations, children with Class I deletions showed the lowest scores. Table 3 presents specific language skills; only 3 of 30 (10%) children with a deletion used single words, whereas 6 of 9 (67%) of those having a mutation or pUPD could communicate a few spoken words (p < 0.01). Within all subgroups, expressive language performance was significantly reduced when compared to the receptive performance, and this difference was most evident among children with deletions (data not shown). Additional copy number gains or losses did not have any statistically significant impact on mental age or fine motor performance (data not shown). 3.5. Autism Table 4 shows the ADOS domain scores for each subcategory and for social effect (social interaction + communication) in the different genetic subgroups. Children with Class I deletions showed a non-significant tendency for higher ADOS scores compared to children with the smaller Class II deletion. Compared to children with an UBE3A mutation or pUPD, children with a deletion (Class I and Class II) had significantly higher ADOS scores in all subcategories: communication (p < 0.01), social interaction (p < 0.01), play (p < 0.05), and stereotyped behavior and restricted interests (p < 0.05). Overall, ADOS scores above the cut-off level for autism were demonstrated in 9/12 (75%) patients with Class I deletions, 12/18 (67%) with Class II deletions, and in 1/9 (11%) with mutations or pUPD; when including all autism spectrum disorders, these figures were 11/12 (92%), 15/18 (83%), 5/9 (56%), respectively. The presence of copy number gains or losses did not have any impact on ADOS scores (data not shown). 3.6. Follow-up of autism spectrum features and mental development The follow-up study included seven children: two with Class I deletions and five with Class II deletions. Each had participated in the study of Trillingsgaard and Østergaard (2004). The age range at that initial investigation was 4–7 years of age. Table 5 shows Mullen levels and ADOS module 1 for these seven patients at baseline and twelve years later. We found that both receptive and expressive language skills increased significantly during the follow-up period, whereas no differences were observed regarding their ADOS scores. 4. Discussion By the use of well established, standardized instruments to measure neurodevelopmental outcome in a representative large group of children with genetically verified AS, we demonstrated that children with 15q11.2-q13 deletions were Table 3 Distribution of language skills examined using Mullen’s Scales of Early Learning, presented as the number of patients with the ability to perform each language skill. Groups
Vocal sounds
Consonant sounds
Two-syllable sounds
2–7 words
Class I deletion (n = 12) Class II deletion (n = 18) Non deletion (n = 9)
10 16 9
2 5 7
2 1 6
2 1 6
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Table 4 Mean (SD) Autism Diagnosis Observation Schedule (ADOS) scores.
Class I (n = 12) Class II (n = 18) Non deletion (n = 9)
Social effecta
RRB
Communication
Social interaction
Play
14.3 (5.3) 13.4 (4.3) 7.3 (5.5)
2.4 (1.9) 2.0 (1.6) 0.9 (1.7)
5.5 (2.0) 5.7 (1.7) 3.6 (2.3)
8.8 (3.7) 7.7 (2.9) 3.8 (3.4)
3.8 (0.9) 3.7 (0.7) 2.9 (1.5)
Higher scores indicate greater impairment. RRB, restricted, repetitive behaviors; SD, standard deviation. a Social interaction + communication.
Table 5 Mean (SD) scores on Autism Diagnosis Observation Schedule (ADOS) and Mullen test (age equivalents in months) at baseline and after 12 years. Parameters
Baseline
12 years
p-Value
ADOS social effect ADOS play ADOS, RRB Mullen visual reception Mullen receptive language Mullen expressive language
10.3 4.0 0.0 12.0 10.0 5.9
10.3 3.3 0.6 12.0 11.9 8.4
1.00 0.12 0.17 1.00 0.04 0.04
(5.8) (0.0) (0.0) (2.6) (2.9) (2.4)
(5.5) (1.1) (1.0) (1.8) (3.0) (3.8)
Higher ADOS scores indicate greater impairment. ADOS social effect, ADOS communication + ADOS social interaction; RRB, restricted, repetitive behavior.
significantly less advanced than the children with AS on a non-deletion basis. This was applicable in all aspects of development and is consistent with findings in previous studies (Gentile et al., 2010; Lossie et al., 2001; Sahoo et al., 2006, 2007; Varela et al., 2004). Additional deletions/duplications outside the 15q11.2-q13 region, which were demonstrated in more than half of the deletion cases, had no impact on the neurodevelopmental outcome. Consistent with other reports (Gentile et al., 2010; Sahoo et al., 2006, 2007; Trillingsgaard & Østergaard, 2004) our data demonstrated that the cognitive skills in children with a deletion do not appear to develop beyond the age of 12–14 months; as regards the expressive language the developmental age rarely exceed 10 months of age, and generally is between 4 and 8 months of age. There is only sparse published data on developmental changes over time, and it is unclear whether the neurodevelopment in AS continues, stagnates, or even decline. The present study includes the first longitudinal examination of cognitive abilities in AS using standardized measures. The 2004 study (Trillingsgaard & Østergaard, 2004) included 16 children with AS, all diagnosed with a deletion. Seven of these patients were also included in the present study, and each underwent the Mullen test twice, with a 12-year interval. Receptive and expressive language skills improved over the 12 years. These improvements were significant, but modest, and the expressive language skills were still low, with developmental ages around 8 months. The general cognitive ability measured as the visual reception in the Mullen test did not change during the follow-up period. Owing to the small number of investigated participants, the findings have to be confirmed in a larger study population, which, if possible, also should comprise a large group of non-deleted AS children, as their development potential is greater and, according to Gentile et al. (2010), may evolve over a longer period. The development of children with AS due to an UBE3A mutation or pUPD was significantly better corresponding to all the investigated aspects, including fine motor performance, but most striking were the differences between the linguistic properties. This was especially true corresponding to the expressive area where 6 out of 9 children with UBE3A mutation or pUPD could use 2–7 words while it was just the case in 3 out of 30 children with a 15q11.2-q13 deletion. As previously noticed (Gentile et al., 2010), we found that all individuals with AS have expressive language skills that were out of proportion to their receptive language skills; i.e., the age of receptive language skills were about twice as high as the age for their expressive language function, irrespective of the molecular basis. Previous studies (Varela et al., 2004; Sahoo et al., 2006) have reported that patients with the greater (Class I) deletion have lower expressive and total language abilities than those having the smaller (Class II) deletion, and it was hypothesized that the four genes located between breakpoint (BP) 1 and BP 2 (NIPA-1; NIPA-2; CYF1P1, and GCP5) may play a role in the speech impairment. In the present study we did not disclose any difference in language abilities between Class I and Class II patients, nor did we find any cognitive differences between Class I and Class II deleted patients. This is in accordance with the latest reports on genotype–phenotype correlations in AS (Gentile et al., 2010; Peters et al., 2012; Sahoo et al., 2007). Which mechanisms are responsible for the extremely low linguistic competences and the gap between receptive and expressive language in AS have yet to be explored. As the single common molecular mechanism regardless of the molecular subclass is lack of the UBE3A protein in parts of the brain where UBE3A is imprinted, it has been suggested that UBE3A may be essential in development of language skills (Gentile et al., 2010).
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In accordance with previous studies (Bonati et al., 2007; Peters, Beaudet, Madduri, & Bacino, 2004; Peters et al., 2012; Sahoo et al., 2007; Trillingsgaard & Østergaard, 2004) we found that a high percentage of individuals with AS due to 15q11.2q13 deletion showed ADOS scores above the cut-off level for autism. We could not demonstrate any significant differences in autism level between the two deletion classes, nor did we find any differences in ADOS scores in the seven 15q11.2-q13deleted AS patients who were tested twice with 12 years interval. Identification of autism and autism spectrum disorders (ASD) in children with a profound intellectual disability, as in AS, is a clinical challenge, and it has been discussed whether the observed ASD features in AS merely are attributable to the intellectual disability or whether they reflect presence of autism (Moss & Howlin, 2009; Trillingsgaard & Østergaard, 2004; Williams, 2010). As children with AS show high levels of social enjoyment and a strong motivation to seek out adult contact by positive facial expression and positive vocalization (Oliver et al., 2007; Moss et al., 2013), the pattern of social behavior in AS appears inconsistent with core features of ASD. In addition, children with AS are significantly better functioning in terms of dyadic communication, despite their severe expressive language disability, than are children with autism only (Bonati et al., 2007; Trillingsgaard & Østergaard, 2004). Thus, detailed observations of social interaction, social motivation and communication abilities may better characterize the social behavior and linguistic profiles of individuals with profound levels of intellectual disability, and autism-specific assessment might be less sensitive when evaluating neurodevelopmental outcome in children with severe intellectual disabilities. Some limitations may be considered. The results should be interpreted with the modest sample size and numbers of participants in the subgroups in mind. However, the present number of participants equals or outnumbers the quantity in previously reported series (Lossie et al., 2001; Peters et al., 2012; Sahoo et al., 2006, 2007; Trillingsgaard & Østergaard, 2004; Varela et al., 2004). Furthermore, our cohort was close to complete due to our use of the unique Danish registries and our personal contact with all Danish pediatric and clinical genetic departments, and our cooperation with the AS parent organization, which reduced the loss of potential participants to an absolute minimum. Acknowledgements The authors thank all participating children and families and The Danish Angelman Association, which supported this study. References Akshoomoff, N. (2006). Use of the Mullen Scales of Early Learning for the Assessment of Young Children with Autism Spectrum Disorders. Child Neuropsychology, 12, 269–277. Andersen, T. F., Madsen, M., Jorgensen, J., Mellemkjaer, L., & Olsen, J. H. (1999). The Danish National Hospital Register. A valuable source of data for modern health sciences. Danish Medical Bulletin, 46, 263–268. Bonati, M. T., Russo, S., Finelli, P., Valsecchi, M. R., Cogliati, F., Cavalleri, L., et al. (2007). Evaluation of autism traits in Angelman syndrome: A resource to unfold autism genes. Neurogenetics, 8, 169–178. Conant, K. D., Thibert, R. L., & Thiele, E. A. (2009). Epilepsy and the sleep-wake patterns found in Angelman syndrome. Epilepsia, 50, 2497–2500. Gentile, J. K., Tan, W. H., Horowitz, L. T., Bacino, C. A., Skinner, S. A., & Barberi-Welge, et al. (2010). A neurodevelopmental survey of Angelman syndrome with genotype–phenotype correlations. Journal of Developmental & Behavioral Pediatrics, 31, 592–601. Kim, S. J., Miller, J. L., Kuipers, P. J., German, J. R., Beaudet, A. L., Sahoo, T., et al. (2012). Unique and atypical deletions in Prader-Willi syndrome reveal distinct phenotypes. European Journal of Human Genetics, 20, 283–290. Lord, C., Risi, S., Lambrecht, L., Cook, E. H., Jr., Leventhal, B. L., DiLavore, P. C., et al. (2000). The autism diagnostic observation schedule-generic: A standard measure of social and communication deficits associated with the spectrum of autism. Journal of Autism and Developmental Disorders, 30, 205–223. Lossie, A. C., Whitney, M. M., Amidon, D., Dong, H. J., Chen, P., Theriaque, D., et al. (2001). Distinct phenotypes distinguish the molecular classes of Angelman syndrome. Journal of Medical Genetics, 38, 834–845. Mertz, L. G. B., Christensen, R., Vogel, I., Hertz, J. M., Nielsen, K. B., Grønskov, K., et al. (2013). Angelman syndrome in Denmark. Birth incidence, genetic findings, and age at diagnosis. American Journal of Medical Genetics Part A, 161A, 2197–2203. Moss, J., & Howlin, P. (2009). Autism spectrum disorders in genetic syndromes: Implications for diagnosis, intervention and understanding the wider autism spectrum disorder population. Journal of Intellectual Disability Research, 53, 852–873. Moss, J., Howlin, P., Hastings, R. P., Beaumont, S., Griffith, G. M., Petty, J., et al. (2013). Social behavior and characteristics of autism spectrum disorder in Angelman, Cornelia de lange, and Cri du Chat syndromes. American Journal of Intellectual Developmental Disability, 118, 262–283. Mullen, E. M. (1995). Mullen Scales of Early Learning: AGS edition. Circle Pines, MN: National Academy Press. Oliver, C., Horsler, K., Berg, K., Bellamy, G., Dick, K., & Griffiths, E. (2007). Genomic imprinting and the expression of affect in Angelman syndrome. What’s in the smile? Journal of Child Psychology and Psychiatry, 48, 571–579. Peters, S. U., Beaudet, A. L., Madduri, N., & Bacino, C. A. (2004). Autism in Angelman syndrome: Implications for autism research. Clinical Genetics, 66, 530–536. Peters, S. U., Horowitz, L., Barberi-Welge, R., Taylor, J. L., & Hundley, R. J. (2012). Longitudinal follow-up of autism spectrum features and sensory behaviors in Angelman syndrome by deletion class. Journal of Child Psychology and Psychiatry, 53, 152–159. Sahoo, T., Bacino, C. A., German, J. R., Shaw, C. A., Bird, L. M., & Kimonis, et al. (2007). Identification of novel deletions of 15q11q13 in Angelman syndrome by arrayCGH: Molecular characterization and genotype–phenotype correlations. European Journal of Human Genetics, 15, 943–949. Sahoo, T., Peters, S. U., Madduri, N. S., Glaze, D. G., German, J. R., Bird, L., et al. (2006). Microarray based comparative genomic hybridization testing in deletion bearing patients with Angelman syndrome: Genotype–phenotype correlations. Journal of Medical Genetics, 43, 512–516. Sahoo, T., Shaw, C. A., Young, A. S., Whitehouse, N. L., Schroer, R. J., Stevenson, R. E., et al. (2005). Array-based comparative genomic hybridization analysis of recurrent chromosome 15q rearrangements. American Journal of Medical Genetics A, 139A, 106–113. Tan, W. H., Bacino, C. A., Skinner, S. A., Anselm, I., Barbieri-Welge, R., & Bauer-Carlin, et al. (2011). Angelman syndrome: Mutations influence features in early childhood. American Journal of Medical Genetics A, 155A, 81–90. Trillingsgaard, A., & Østergaard, J. R. (2004). Autism in Angelman syndrome: An exploration of comorbidity. Autism, 8, 163–174. Varela, M. C., Kok, F., Otto, P. A., & Koiffmann, C. P. (2004). Phenotypic variability in Angelman syndrome: Comparison among different deletion classes and between deletion and UPD subjects. European Journal of Human Genetics, 12, 987–992. Williams, C. A. (2010). The behavioral phenotype of the Angelman syndrome. American Journal of Medical Genetics, 154C, 432–437.
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Contents lists available at ScienceDirect
Research in Developmental Disabilities
Neurodevelopmental outcome in Angelman syndrome: Genotype–phenotype correlations Line Granild Bie Mertz a,*, Per Thaulov b, Anegen Trillingsgaard c, Rikke Christensen d, Ida Vogel d, Jens Michael Hertz e, John R. Østergaard a a
Centre for Rare Diseases, Department of Pediatrics, Aarhus University Hospital, Denmark Psychiatric Hospital for Children and Adolescents, Aarhus University Hospital, Denmark Department of Psychology, Aarhus University, Denmark d Department of Clinical Genetics, Aarhus University Hospital, Denmark e Department of Clinical Genetics, Odense University Hospital, Denmark b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 8 December 2013 Received in revised form 18 February 2014 Accepted 21 February 2014 Available online xxx
Angelman syndrome (AS) is a neurogenetic disorder characterized by intellectual disability, developmental delay, lack of speech, and epileptic seizures. Previous studies have indicated that children with AS due to 15q11.2-q13 deletions have a more severe developmental delay and present more often autistic features than those with AS caused by other genetic etiologies. The present study investigated the neurodevelopmental profiles of the different genetic etiologies of AS, and examined the evolution of mental development and autistic features over a 12-year period in children with a 15q11.2-q13 deletion. This study included 42 children with AS. Twelve had a Class I deletion, 18 had Class II deletions, three showed atypical large deletions, five had paternal uniparental disomy (pUPD) and four had UBE3A mutations. Children with a deletion (Class I and Class II) showed significantly reduced developmental age in terms of visual perception, receptive language, and expressive language when compared to those with a UBE3A mutation and pUPD. Within all subgroups, expressive language performance was significantly reduced when compared to the receptive performance. A follow-up study of seven AS cases with 15q11.2-q13 deletions revealed that over 12 years, the level of autistic features did not change, but both receptive and expressive language skills improved. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Angelman syndrome 15q11.2-q13 Language skills Autism ADOS Mullen Intellectual disability
1. Introduction Angelman syndrome (AS) is a neurogenetic disorder caused by loss of expression of the maternal imprinted gene UBE3A, which codes for the protein ubiquitin-protein ligase E3A. Four known molecular mechanisms lead to deficient maternal UBE3A expression and AS development: Deletion of the AS critical region on the maternal chromosome 15q11.2-q13 (70%), paternal uniparental disomy (pUPD) (2–7%), imprinting defects (3–5%), and mutations in the maternal copy of UBE3A (10%)
* Corresponding author. Tel.: +45 27423551. E-mail address: [email protected] (L.G.B. Mertz). http://dx.doi.org/10.1016/j.ridd.2014.02.018 0891-4222/ß 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mertz, L. G. B., et al. Neurodevelopmental outcome in Angelman syndrome: Genotype– phenotype correlations. Research in Developmental Disabilities (2014), http://dx.doi.org/10.1016/j.ridd.2014.02.018
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(Tan et al., 2011). There are two common types of 15q11.2-q13 deletions, a 5.9-Mb (Class I) deletion, and a 5.0-Mb (Class II) deletion, differing only in the position of the proximal (centromeric) breakpoint (Tan et al., 2011; Mertz et al., 2013). Clinical characteristics of AS include severe developmental delay, ataxia, a low threshold for laughter, and 80–90% of AS patients have epileptic seizures (Conant, Thibert, & Thiele, 2009). In addition, a high percentage of individuals with AS has been found to meet the formal diagnostic criteria of autism, defined as total score above autism cut off in ADOS, (autism diagnostic observation schedule) (Lord et al., 2000). Autism or autism spectrum disorder was previously reported in 50–80 per cent of patients with AS (Bonati et al., 2007; Peters, Horowitz, Barberi-Welge, Taylor, & Hundley, 2012; Sahoo et al., 2007; Trillingsgaard & Østergaard, 2004). Previous studies have indicated that children with AS due to 15q11.2-q13 deletions have a more severe developmental delay and present more often autistic features than those with AS caused by other genetic etiologies (Lossie et al., 2001; Peters et al., 2012; Sahoo et al., 2006, 2007; Varela, Kok, Otto, & Koiffmann, 2004). However, not all studies have used validated standardized instruments, and the total number of investigated individuals remains small. Furthermore, virtually all previous studies have a cross-sectional design, and none have performed longitudinal consecutive assessments of neurodevelopmental parameters in children with AS. The present study investigated the neurodevelopmental profiles of the different genetic etiologies of AS, including Class I and Class II deletions, and examined the evolution of mental development and autistic features over a 12-year period in children with a 15q11.2-q13 deletion. 2. Methods 2.1. Patient recruitment We identified patients with AS who were born in Denmark between 1991 and 2009 through the Danish National Patient Registry (NPR) and the Danish Cytogenetic Central Registry (DCCR), supplemented by personal contact with all pediatric and clinical genetic departments and the Patient Organization of Angelman syndrome in Denmark. NPR contains administrative and clinical data from all hospitalizations and out-patient clinics in Denmark. Reporting data to the NPR is mandatory for all Danish hospitals and is further encouraged by the government funding system. Thus, the data in this registry are known to be of very high validity (Andersen, Madsen, Jorgensen, Mellemkjaer, & Olsen, 1999). The diagnoses are recorded according to the tenth revision of the International Classification of Diseases (ICD-10) from the World Health Organization. The DCCR contains data from every prenatal genetic test and every postnatal karyotype performed in Denmark since 1960. It also contains national postnatal genetic data on selected diseases such as 22q11.2 deletion, Prader-Willi, and Angelman syndromes. Data reporting is self-imposed by all clinical genetic departments that perform these genetic tests, and the registry is administered by representatives from these departments. In total, we identified 51 patients with genetically verified AS (Mertz et al., 2013). The deadline for identification was January, 1 2012. This study was approved by the National Ethic Commitee (M-20090028) and the Danish Data Protection Agency (2009-41-3133). The legal guardian of each participant provided verbal and written informed consent. 2.2. Genetic analysis Patients who were previously diagnosed with a deletion were further investigated using a high resolution 1000-kb array CGH. DNA was extracted from peripheral blood with an automated Chemagic Magnetic Separation Module (PerkinElmer, Waltham, MA, USA) and was purified prior to array CGH analysis using the DNeasy Blood & Tissue Kit (Qiagen, Valencia, CA, USA). Deletion breakpoints were determined by microarray-based comparative genomic hybridization with the SurePrint G3 Human CGH microarray 1 M (Agilent Technologies, Santa Clara, CA, USA). Sample and reference genomic DNA (1500 ng) were labeled with Cy5 (reference) or Cy3 (patient) using the Genomic DNA ULS labeling kit (Agilent Technologies) and purified as per the manufacturer’s protocol. Labeled sample and reference DNA were pooled, and mixed with 50 ml of human COT-1 DNA (1 mg/ml), 10 blocking agent, and 2 hybridization buffer were added. Hybridization was performed for 40 h at 65 8C. Scanning and image acquisitions were carried out with an Agilent microarray scanner, and microarray image files were quantified with Agilent’s Feature Extraction software version 10.7. Data analysis was performed using Genomic Workbench version 6.5 (Agilent Technologies). Copy number was determined with the adm-2 algorithm. Profile deviations consisting of six or more neighboring oligonucleotides were considered genomic aberrations, yielding an approximately 12 kb resolution. Deletion breakpoints were based on the positions of the first and last oligonucleotide probes within the region of the deletion that showed a copy number loss. We also identified copy number gains or losses on chromosomes other than 15q11-q13. Copy number variations (CNVs) in areas containing previously reported CNVs in healthy control samples from the database of genomic variants (DGV) were excluded. UCSC hg19 version of the human genome and public CNV databases were used as reference. 2.3. Mental development and autism Mental age was assessed with Mullen Scales of Early Learning (Mullen, 1995) based on four sub-scales: visual perception, receptive language, expressive language and fine motor development. The Mullen Scales assess the cognitive and motor
Please cite this article in press as: Mertz, L. G. B., et al. Neurodevelopmental outcome in Angelman syndrome: Genotype– phenotype correlations. Research in Developmental Disabilities (2014), http://dx.doi.org/10.1016/j.ridd.2014.02.018
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functions of young children from birth to 68 months. Scores on each subscale are converted into an age equivalent in months (Akshoomoff, 2006). The Mullen Scales test was performed by four trained professionals who were blinded to the genetic results. Inter-observer reliability was above 80%. Behavior associated with autism or autism spectrum disorders (ASD) was assessed according to the ADOS (Lord et al., 2000) a semi-structured, standardized assessment of communication, social interaction, play, and imagination. ADOS is one of the most widely used observation instruments for assessing a child for the presence of an Autism Spectrum Disorder. ADOS consists of four modules. Module 1 is intended for children who do not consistently use spontaneous phrase speech and is therefore appropriate for children with AS. The test consists of 10 activities with 29 accompanying ratings. ADOS module 1 consists of semi-structured situations allowing observation of imaginative activities, social role-play, and interactions with the observer and with the parent attending the session (Lord et al., 2000). The ADOS classification is based on cut-off scores from two domains; social behavior and communication. The ADOS examination also includes play, stereotyped behavior and restricted interests, and other abnormal behaviors. Repetitive and stereotyped behaviors in early childhood do not differentiate ASD from other developmental disorders in early childhood and therefore are not part of the algorithm for ADOS module 1 (Lord et al., 2000). The ADOS assessment was performed and evaluated by four ADOS-certified professionals, who were all blinded to the genetic results. The assessments were video-recorded and inter-observer reliability was above 80%. Seven of the participants, all with a 15q11.2-q13 deletion, also participated in a previous study by Trillingsgaard and Østergaard published in 2004 (Trillingsgaard & Østergaard, 2004). The Mullen Scales of Early Learning scores (visual reception, receptive language, and expressive language) and the ADOS scores from that examination were used as baseline scores in a longitudinal follow-up study. 2.4. Statistical analysis Statistical analyses were performed using IBM SPSS 20 software. Differences between diagnostic groups in developmental age and ADOS scores were analyzed using Student’s t-test or Fisher’s exact test for categorical variables. Differences over a 12-year follow up period were analyzed using Student’s paired t-test. All reported p-values were two-sided, and p-values 500 kb. The largest CNV was a 2000 kb duplication on chromosome 22. 3.4. Mental age, fine motor performance, and autism Table 2 presents the Mullen Subscale test results. Children with a deletion (Class I and Class II) showed significantly reduced developmental age in terms of visual perception (p < 0.01), receptive language (p < 0.01), and expressive language (p < 0.05) when compared to those with a UBE3A mutation or pUPD. They also showed a significantly reduced fine motor performance (p < 0.01). We found no differences in cognitive and language development or fine motor performance between children with Class I and Class II deletions. However, in all evaluations, children with Class I deletions showed the lowest scores. Table 3 presents specific language skills; only 3 of 30 (10%) children with a deletion used single words, whereas 6 of 9 (67%) of those having a mutation or pUPD could communicate a few spoken words (p < 0.01). Within all subgroups, expressive language performance was significantly reduced when compared to the receptive performance, and this difference was most evident among children with deletions (data not shown). Additional copy number gains or losses did not have any statistically significant impact on mental age or fine motor performance (data not shown). 3.5. Autism Table 4 shows the ADOS domain scores for each subcategory and for social effect (social interaction + communication) in the different genetic subgroups. Children with Class I deletions showed a non-significant tendency for higher ADOS scores compared to children with the smaller Class II deletion. Compared to children with an UBE3A mutation or pUPD, children with a deletion (Class I and Class II) had significantly higher ADOS scores in all subcategories: communication (p < 0.01), social interaction (p < 0.01), play (p < 0.05), and stereotyped behavior and restricted interests (p < 0.05). Overall, ADOS scores above the cut-off level for autism were demonstrated in 9/12 (75%) patients with Class I deletions, 12/18 (67%) with Class II deletions, and in 1/9 (11%) with mutations or pUPD; when including all autism spectrum disorders, these figures were 11/12 (92%), 15/18 (83%), 5/9 (56%), respectively. The presence of copy number gains or losses did not have any impact on ADOS scores (data not shown). 3.6. Follow-up of autism spectrum features and mental development The follow-up study included seven children: two with Class I deletions and five with Class II deletions. Each had participated in the study of Trillingsgaard and Østergaard (2004). The age range at that initial investigation was 4–7 years of age. Table 5 shows Mullen levels and ADOS module 1 for these seven patients at baseline and twelve years later. We found that both receptive and expressive language skills increased significantly during the follow-up period, whereas no differences were observed regarding their ADOS scores. 4. Discussion By the use of well established, standardized instruments to measure neurodevelopmental outcome in a representative large group of children with genetically verified AS, we demonstrated that children with 15q11.2-q13 deletions were Table 3 Distribution of language skills examined using Mullen’s Scales of Early Learning, presented as the number of patients with the ability to perform each language skill. Groups
Vocal sounds
Consonant sounds
Two-syllable sounds
2–7 words
Class I deletion (n = 12) Class II deletion (n = 18) Non deletion (n = 9)
10 16 9
2 5 7
2 1 6
2 1 6
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Table 4 Mean (SD) Autism Diagnosis Observation Schedule (ADOS) scores.
Class I (n = 12) Class II (n = 18) Non deletion (n = 9)
Social effecta
RRB
Communication
Social interaction
Play
14.3 (5.3) 13.4 (4.3) 7.3 (5.5)
2.4 (1.9) 2.0 (1.6) 0.9 (1.7)
5.5 (2.0) 5.7 (1.7) 3.6 (2.3)
8.8 (3.7) 7.7 (2.9) 3.8 (3.4)
3.8 (0.9) 3.7 (0.7) 2.9 (1.5)
Higher scores indicate greater impairment. RRB, restricted, repetitive behaviors; SD, standard deviation. a Social interaction + communication.
Table 5 Mean (SD) scores on Autism Diagnosis Observation Schedule (ADOS) and Mullen test (age equivalents in months) at baseline and after 12 years. Parameters
Baseline
12 years
p-Value
ADOS social effect ADOS play ADOS, RRB Mullen visual reception Mullen receptive language Mullen expressive language
10.3 4.0 0.0 12.0 10.0 5.9
10.3 3.3 0.6 12.0 11.9 8.4
1.00 0.12 0.17 1.00 0.04 0.04
(5.8) (0.0) (0.0) (2.6) (2.9) (2.4)
(5.5) (1.1) (1.0) (1.8) (3.0) (3.8)
Higher ADOS scores indicate greater impairment. ADOS social effect, ADOS communication + ADOS social interaction; RRB, restricted, repetitive behavior.
significantly less advanced than the children with AS on a non-deletion basis. This was applicable in all aspects of development and is consistent with findings in previous studies (Gentile et al., 2010; Lossie et al., 2001; Sahoo et al., 2006, 2007; Varela et al., 2004). Additional deletions/duplications outside the 15q11.2-q13 region, which were demonstrated in more than half of the deletion cases, had no impact on the neurodevelopmental outcome. Consistent with other reports (Gentile et al., 2010; Sahoo et al., 2006, 2007; Trillingsgaard & Østergaard, 2004) our data demonstrated that the cognitive skills in children with a deletion do not appear to develop beyond the age of 12–14 months; as regards the expressive language the developmental age rarely exceed 10 months of age, and generally is between 4 and 8 months of age. There is only sparse published data on developmental changes over time, and it is unclear whether the neurodevelopment in AS continues, stagnates, or even decline. The present study includes the first longitudinal examination of cognitive abilities in AS using standardized measures. The 2004 study (Trillingsgaard & Østergaard, 2004) included 16 children with AS, all diagnosed with a deletion. Seven of these patients were also included in the present study, and each underwent the Mullen test twice, with a 12-year interval. Receptive and expressive language skills improved over the 12 years. These improvements were significant, but modest, and the expressive language skills were still low, with developmental ages around 8 months. The general cognitive ability measured as the visual reception in the Mullen test did not change during the follow-up period. Owing to the small number of investigated participants, the findings have to be confirmed in a larger study population, which, if possible, also should comprise a large group of non-deleted AS children, as their development potential is greater and, according to Gentile et al. (2010), may evolve over a longer period. The development of children with AS due to an UBE3A mutation or pUPD was significantly better corresponding to all the investigated aspects, including fine motor performance, but most striking were the differences between the linguistic properties. This was especially true corresponding to the expressive area where 6 out of 9 children with UBE3A mutation or pUPD could use 2–7 words while it was just the case in 3 out of 30 children with a 15q11.2-q13 deletion. As previously noticed (Gentile et al., 2010), we found that all individuals with AS have expressive language skills that were out of proportion to their receptive language skills; i.e., the age of receptive language skills were about twice as high as the age for their expressive language function, irrespective of the molecular basis. Previous studies (Varela et al., 2004; Sahoo et al., 2006) have reported that patients with the greater (Class I) deletion have lower expressive and total language abilities than those having the smaller (Class II) deletion, and it was hypothesized that the four genes located between breakpoint (BP) 1 and BP 2 (NIPA-1; NIPA-2; CYF1P1, and GCP5) may play a role in the speech impairment. In the present study we did not disclose any difference in language abilities between Class I and Class II patients, nor did we find any cognitive differences between Class I and Class II deleted patients. This is in accordance with the latest reports on genotype–phenotype correlations in AS (Gentile et al., 2010; Peters et al., 2012; Sahoo et al., 2007). Which mechanisms are responsible for the extremely low linguistic competences and the gap between receptive and expressive language in AS have yet to be explored. As the single common molecular mechanism regardless of the molecular subclass is lack of the UBE3A protein in parts of the brain where UBE3A is imprinted, it has been suggested that UBE3A may be essential in development of language skills (Gentile et al., 2010).
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In accordance with previous studies (Bonati et al., 2007; Peters, Beaudet, Madduri, & Bacino, 2004; Peters et al., 2012; Sahoo et al., 2007; Trillingsgaard & Østergaard, 2004) we found that a high percentage of individuals with AS due to 15q11.2q13 deletion showed ADOS scores above the cut-off level for autism. We could not demonstrate any significant differences in autism level between the two deletion classes, nor did we find any differences in ADOS scores in the seven 15q11.2-q13deleted AS patients who were tested twice with 12 years interval. Identification of autism and autism spectrum disorders (ASD) in children with a profound intellectual disability, as in AS, is a clinical challenge, and it has been discussed whether the observed ASD features in AS merely are attributable to the intellectual disability or whether they reflect presence of autism (Moss & Howlin, 2009; Trillingsgaard & Østergaard, 2004; Williams, 2010). As children with AS show high levels of social enjoyment and a strong motivation to seek out adult contact by positive facial expression and positive vocalization (Oliver et al., 2007; Moss et al., 2013), the pattern of social behavior in AS appears inconsistent with core features of ASD. In addition, children with AS are significantly better functioning in terms of dyadic communication, despite their severe expressive language disability, than are children with autism only (Bonati et al., 2007; Trillingsgaard & Østergaard, 2004). Thus, detailed observations of social interaction, social motivation and communication abilities may better characterize the social behavior and linguistic profiles of individuals with profound levels of intellectual disability, and autism-specific assessment might be less sensitive when evaluating neurodevelopmental outcome in children with severe intellectual disabilities. Some limitations may be considered. The results should be interpreted with the modest sample size and numbers of participants in the subgroups in mind. However, the present number of participants equals or outnumbers the quantity in previously reported series (Lossie et al., 2001; Peters et al., 2012; Sahoo et al., 2006, 2007; Trillingsgaard & Østergaard, 2004; Varela et al., 2004). Furthermore, our cohort was close to complete due to our use of the unique Danish registries and our personal contact with all Danish pediatric and clinical genetic departments, and our cooperation with the AS parent organization, which reduced the loss of potential participants to an absolute minimum. Acknowledgements The authors thank all participating children and families and The Danish Angelman Association, which supported this study. References Akshoomoff, N. (2006). Use of the Mullen Scales of Early Learning for the Assessment of Young Children with Autism Spectrum Disorders. Child Neuropsychology, 12, 269–277. Andersen, T. F., Madsen, M., Jorgensen, J., Mellemkjaer, L., & Olsen, J. H. (1999). The Danish National Hospital Register. A valuable source of data for modern health sciences. Danish Medical Bulletin, 46, 263–268. Bonati, M. T., Russo, S., Finelli, P., Valsecchi, M. R., Cogliati, F., Cavalleri, L., et al. (2007). Evaluation of autism traits in Angelman syndrome: A resource to unfold autism genes. Neurogenetics, 8, 169–178. Conant, K. D., Thibert, R. L., & Thiele, E. A. (2009). Epilepsy and the sleep-wake patterns found in Angelman syndrome. Epilepsia, 50, 2497–2500. Gentile, J. K., Tan, W. H., Horowitz, L. T., Bacino, C. A., Skinner, S. A., & Barberi-Welge, et al. (2010). A neurodevelopmental survey of Angelman syndrome with genotype–phenotype correlations. Journal of Developmental & Behavioral Pediatrics, 31, 592–601. Kim, S. J., Miller, J. L., Kuipers, P. J., German, J. R., Beaudet, A. L., Sahoo, T., et al. (2012). Unique and atypical deletions in Prader-Willi syndrome reveal distinct phenotypes. European Journal of Human Genetics, 20, 283–290. Lord, C., Risi, S., Lambrecht, L., Cook, E. H., Jr., Leventhal, B. L., DiLavore, P. C., et al. (2000). The autism diagnostic observation schedule-generic: A standard measure of social and communication deficits associated with the spectrum of autism. Journal of Autism and Developmental Disorders, 30, 205–223. Lossie, A. C., Whitney, M. M., Amidon, D., Dong, H. J., Chen, P., Theriaque, D., et al. (2001). Distinct phenotypes distinguish the molecular classes of Angelman syndrome. Journal of Medical Genetics, 38, 834–845. Mertz, L. G. B., Christensen, R., Vogel, I., Hertz, J. M., Nielsen, K. B., Grønskov, K., et al. (2013). Angelman syndrome in Denmark. Birth incidence, genetic findings, and age at diagnosis. American Journal of Medical Genetics Part A, 161A, 2197–2203. Moss, J., & Howlin, P. (2009). Autism spectrum disorders in genetic syndromes: Implications for diagnosis, intervention and understanding the wider autism spectrum disorder population. Journal of Intellectual Disability Research, 53, 852–873. Moss, J., Howlin, P., Hastings, R. P., Beaumont, S., Griffith, G. M., Petty, J., et al. (2013). Social behavior and characteristics of autism spectrum disorder in Angelman, Cornelia de lange, and Cri du Chat syndromes. American Journal of Intellectual Developmental Disability, 118, 262–283. Mullen, E. M. (1995). Mullen Scales of Early Learning: AGS edition. Circle Pines, MN: National Academy Press. Oliver, C., Horsler, K., Berg, K., Bellamy, G., Dick, K., & Griffiths, E. (2007). Genomic imprinting and the expression of affect in Angelman syndrome. What’s in the smile? Journal of Child Psychology and Psychiatry, 48, 571–579. Peters, S. U., Beaudet, A. L., Madduri, N., & Bacino, C. A. (2004). Autism in Angelman syndrome: Implications for autism research. Clinical Genetics, 66, 530–536. Peters, S. U., Horowitz, L., Barberi-Welge, R., Taylor, J. L., & Hundley, R. J. (2012). Longitudinal follow-up of autism spectrum features and sensory behaviors in Angelman syndrome by deletion class. Journal of Child Psychology and Psychiatry, 53, 152–159. Sahoo, T., Bacino, C. A., German, J. R., Shaw, C. A., Bird, L. M., & Kimonis, et al. (2007). Identification of novel deletions of 15q11q13 in Angelman syndrome by arrayCGH: Molecular characterization and genotype–phenotype correlations. European Journal of Human Genetics, 15, 943–949. Sahoo, T., Peters, S. U., Madduri, N. S., Glaze, D. G., German, J. R., Bird, L., et al. (2006). Microarray based comparative genomic hybridization testing in deletion bearing patients with Angelman syndrome: Genotype–phenotype correlations. Journal of Medical Genetics, 43, 512–516. Sahoo, T., Shaw, C. A., Young, A. S., Whitehouse, N. L., Schroer, R. J., Stevenson, R. E., et al. (2005). Array-based comparative genomic hybridization analysis of recurrent chromosome 15q rearrangements. American Journal of Medical Genetics A, 139A, 106–113. Tan, W. H., Bacino, C. A., Skinner, S. A., Anselm, I., Barbieri-Welge, R., & Bauer-Carlin, et al. (2011). Angelman syndrome: Mutations influence features in early childhood. American Journal of Medical Genetics A, 155A, 81–90. Trillingsgaard, A., & Østergaard, J. R. (2004). Autism in Angelman syndrome: An exploration of comorbidity. Autism, 8, 163–174. Varela, M. C., Kok, F., Otto, P. A., & Koiffmann, C. P. (2004). Phenotypic variability in Angelman syndrome: Comparison among different deletion classes and between deletion and UPD subjects. European Journal of Human Genetics, 12, 987–992. Williams, C. A. (2010). The behavioral phenotype of the Angelman syndrome. American Journal of Medical Genetics, 154C, 432–437.
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