Neurol Sci DOI 10.1007/s10072-014-1727-3
LETTER TO THE EDITOR
Novel splice site mutation of SPG4 in a Chinese family with hereditary spastic paraplegia Xiaomin Liu • Jiyou Tang
Received: 16 December 2013 / Accepted: 18 March 2014 Ó Springer-Verlag Italia 2014
Keywords Mutation
Hereditary spastic paraplegia Spastin gene
Dear Editor-in-Chief, A Chinese family with hereditary spastic paraplegia (HSP) spanning five generations was found to possess an autosomal dominant (AD) inheritance pattern (Fig. 1a). There were five patients, including two deceased individuals, with each generation containing one patient. All three living patients (patient III: 3, patient IV: 2 and patient V: 1) were females, and the symptoms that first appeared in these patients included a weakness and spasticity of the lower limbs that slowly progressed in the subsequent years. Additionally, there hyperreflexia, spasticity in the lower limbs and bilateral Babinski sign were seen at examination. Two of the patients reported urinary frequency. The cranial nerves and the tone and power in the upper limbs were normal. There were no additional neurological abnormalities such as dementia, mental retardation, epilepsy, extrapyramidal disturbances, ataxia, deafness, retinopathy, optic neuropathy, peripheral neuropathy and skin lesions. Therefore, all of the patients were considered to have pure HSP. The mean ± SD of the age of onset was 18.33 ± 2.52 years. The mean ± SD of the duration of the disease was 33.33 ± 23.59 years. Patient III: 3 and patient IV: 2 required a walking stick after 30 years and patient III: 3 required a wheelchair after 50 years of disease duration. Patient V: 1 was able to walk unaided after 11 years of disease duration, but her running ability was decreased. All X. Liu J. Tang (&) Department of Neurology, Qianfoshan Hospital, Shandong University, 16766 Jingshi Road, Jinan 250014, Shandong, People’s Republic of China e-mail: [email protected]
patients were of Han nationality from Shandong province, China. Blood specimens and genomic DNA were obtained from 9 family members and 100 control subjects after informed consent. The 17 exons and flanking intronic splice consensus sequences of SPG4 were amplified by polymerase chain reaction (PCR) and were analyzed by single-strand conformation polymorphism analysis. Abnormal migration was detected in patients III: 3, IV: 2 and V: 1, but not in healthy relatives (III: 4, IV: 1, IV: 3, IV: 4, IV: 5 and V: 2) (Fig. 1b). By sequencing, we identified a potential splice-site mutation in intron 7, namely, c.1098?1*2GT?CTCAGA, which was located at the conserved splice donor site of exon 7 of SPG4 in a heterozygous state (Fig. 1c, d). The mutation was absent in 200 normal chromosomes and not previously reported, thus representing a novel etiology in an AD HSP Chinese family. Hereditary spastic paraplegia is a group of genetically heterogeneous neurodegenerative disorders characterized by progressive spasticity and weakness of both lower extremities. To date, there are over 70 HSP loci and more than 50 SPG genes [1]. Mutations in SPG4, which encodes the spastin protein, are detected in approximately 40 % of all the AD HSP families [2]. In this study, all of the patients from the family presented pure HSP. Based upon our analysis, a novel mutation, c.1098?1*2GT?CTCAGA, was identified at the splice donor site of exon 7 of SPG4, thus suggesting a splice-site mutation. The mutation might cause a skipping of exon 7 or an activation of the potential donor splice site at c.1098?40*41GT. A frame shift may occur in the newly formed spliced transcript that would ultimately encode a truncated and dysfunctional spastin, ultimately leading to HSP. In 2000, a splice site point mutation, c.1098?1G?T, at the same site of SPG4 was detected in an AD HSP family [3], thereby suggesting that
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Neurol Sci Fig. 1 Pedigree of patient and mutation analysis of SPG4. a The HSP family. The proband is indicated (arrow). Squares indicate males, circles females, shaded symbols individuals with HSP, unshaded symbols individuals without HSP, symbols with a slash mark deceased individuals. b Singlestrand conformation polymorphism analysis of exon 7 and the flanking intron sequences of SPG4 in the HSP family members. The abnormal migration alteration is indicated (arrow). N indicates a healthy control subject. c Wild-type sequence. d Sequence analysis identified a c.1098?1 *2GT?CTCAGA mutation in intron 7 of SPG4 in this family. Black frames delineate the c. 1098?1*2 nucleotides. Note the substitution of a normal ‘‘GT’’ peak with a mutant peak
mutations at this site are not rare. In 2009, Kasher et al. [4] generated a mice model bearing the c.1092?2G?T mutation of SPG4 to mimic the human pathogenic mutation c.1098?1G?T. They found that this mutation of spastin specifically disrupted anterograde axonal transport of mitochondria and membrane-bound organelles and thus caused the accumulation of mitochondria together with tubulin and neurofilament proteins, among others, in axonal swelling in cortical neurons. Similar pathological features were also observed in human HSP cases caused by spastin mutations. These results provide strong direct evidence for the involvement of axonal transport defects in the pathogenesis of SPG4. In summary, we report a novel splice-site mutation, c.1098?1*2GT?CTCAGA, in the AAA domain of SPG4 in a Chinese family with pure AD HSP. This finding expands the mutation spectrum of SPG4 and provides an
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opportunity to further study the mechanism causing long axonal neurodegeneration in HSP. Acknowledgments We thank the family members for participating in the study, which was supported by Grants ZR2013HQ016 and Y2008C161 from the Natural Science Foundation of Shandong Province. Conflict of interest
We declare that we have no conflict of interest.
Ethical standard This study was approved by the Ethical Committee of Shandong University and informed consent was obtained from the family members and control subjects.
References 1. Novarino G, Fenstermaker AG, Zaki MS et al (2014) Exome sequencing links corticospinal motor neuron disease to common neurodegenerative disorders. Science 343:506–511
Neurol Sci 2. Hazan J, Fonknechten N, Mavel D et al (1999) Spastin, a new AAA protein, is altered in the most frequent form of autosomal dominant spastic paraplegia. Nat Genet 23:296–303 3. Fonknechten N, Mavel D, Byrne P et al (2000) Spectrum of SPG4 mutations in autosomal dominant spastic paraplegia. Hum Mol Genet 9:637–644
4. Kasher PR, De Vos KJ, Wharton SB et al (2009) Direct evidence for axonal transport defects in a novel mouse of mutant spastininduced hereditary spastic paraplegia (HSP) and human HSP patients. J Neurochem 110:34–44
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LETTER TO THE EDITOR
Novel splice site mutation of SPG4 in a Chinese family with hereditary spastic paraplegia Xiaomin Liu • Jiyou Tang
Received: 16 December 2013 / Accepted: 18 March 2014 Ó Springer-Verlag Italia 2014
Keywords Mutation
Hereditary spastic paraplegia Spastin gene
Dear Editor-in-Chief, A Chinese family with hereditary spastic paraplegia (HSP) spanning five generations was found to possess an autosomal dominant (AD) inheritance pattern (Fig. 1a). There were five patients, including two deceased individuals, with each generation containing one patient. All three living patients (patient III: 3, patient IV: 2 and patient V: 1) were females, and the symptoms that first appeared in these patients included a weakness and spasticity of the lower limbs that slowly progressed in the subsequent years. Additionally, there hyperreflexia, spasticity in the lower limbs and bilateral Babinski sign were seen at examination. Two of the patients reported urinary frequency. The cranial nerves and the tone and power in the upper limbs were normal. There were no additional neurological abnormalities such as dementia, mental retardation, epilepsy, extrapyramidal disturbances, ataxia, deafness, retinopathy, optic neuropathy, peripheral neuropathy and skin lesions. Therefore, all of the patients were considered to have pure HSP. The mean ± SD of the age of onset was 18.33 ± 2.52 years. The mean ± SD of the duration of the disease was 33.33 ± 23.59 years. Patient III: 3 and patient IV: 2 required a walking stick after 30 years and patient III: 3 required a wheelchair after 50 years of disease duration. Patient V: 1 was able to walk unaided after 11 years of disease duration, but her running ability was decreased. All X. Liu J. Tang (&) Department of Neurology, Qianfoshan Hospital, Shandong University, 16766 Jingshi Road, Jinan 250014, Shandong, People’s Republic of China e-mail: [email protected]
patients were of Han nationality from Shandong province, China. Blood specimens and genomic DNA were obtained from 9 family members and 100 control subjects after informed consent. The 17 exons and flanking intronic splice consensus sequences of SPG4 were amplified by polymerase chain reaction (PCR) and were analyzed by single-strand conformation polymorphism analysis. Abnormal migration was detected in patients III: 3, IV: 2 and V: 1, but not in healthy relatives (III: 4, IV: 1, IV: 3, IV: 4, IV: 5 and V: 2) (Fig. 1b). By sequencing, we identified a potential splice-site mutation in intron 7, namely, c.1098?1*2GT?CTCAGA, which was located at the conserved splice donor site of exon 7 of SPG4 in a heterozygous state (Fig. 1c, d). The mutation was absent in 200 normal chromosomes and not previously reported, thus representing a novel etiology in an AD HSP Chinese family. Hereditary spastic paraplegia is a group of genetically heterogeneous neurodegenerative disorders characterized by progressive spasticity and weakness of both lower extremities. To date, there are over 70 HSP loci and more than 50 SPG genes [1]. Mutations in SPG4, which encodes the spastin protein, are detected in approximately 40 % of all the AD HSP families [2]. In this study, all of the patients from the family presented pure HSP. Based upon our analysis, a novel mutation, c.1098?1*2GT?CTCAGA, was identified at the splice donor site of exon 7 of SPG4, thus suggesting a splice-site mutation. The mutation might cause a skipping of exon 7 or an activation of the potential donor splice site at c.1098?40*41GT. A frame shift may occur in the newly formed spliced transcript that would ultimately encode a truncated and dysfunctional spastin, ultimately leading to HSP. In 2000, a splice site point mutation, c.1098?1G?T, at the same site of SPG4 was detected in an AD HSP family [3], thereby suggesting that
123
Neurol Sci Fig. 1 Pedigree of patient and mutation analysis of SPG4. a The HSP family. The proband is indicated (arrow). Squares indicate males, circles females, shaded symbols individuals with HSP, unshaded symbols individuals without HSP, symbols with a slash mark deceased individuals. b Singlestrand conformation polymorphism analysis of exon 7 and the flanking intron sequences of SPG4 in the HSP family members. The abnormal migration alteration is indicated (arrow). N indicates a healthy control subject. c Wild-type sequence. d Sequence analysis identified a c.1098?1 *2GT?CTCAGA mutation in intron 7 of SPG4 in this family. Black frames delineate the c. 1098?1*2 nucleotides. Note the substitution of a normal ‘‘GT’’ peak with a mutant peak
mutations at this site are not rare. In 2009, Kasher et al. [4] generated a mice model bearing the c.1092?2G?T mutation of SPG4 to mimic the human pathogenic mutation c.1098?1G?T. They found that this mutation of spastin specifically disrupted anterograde axonal transport of mitochondria and membrane-bound organelles and thus caused the accumulation of mitochondria together with tubulin and neurofilament proteins, among others, in axonal swelling in cortical neurons. Similar pathological features were also observed in human HSP cases caused by spastin mutations. These results provide strong direct evidence for the involvement of axonal transport defects in the pathogenesis of SPG4. In summary, we report a novel splice-site mutation, c.1098?1*2GT?CTCAGA, in the AAA domain of SPG4 in a Chinese family with pure AD HSP. This finding expands the mutation spectrum of SPG4 and provides an
123
opportunity to further study the mechanism causing long axonal neurodegeneration in HSP. Acknowledgments We thank the family members for participating in the study, which was supported by Grants ZR2013HQ016 and Y2008C161 from the Natural Science Foundation of Shandong Province. Conflict of interest
We declare that we have no conflict of interest.
Ethical standard This study was approved by the Ethical Committee of Shandong University and informed consent was obtained from the family members and control subjects.
References 1. Novarino G, Fenstermaker AG, Zaki MS et al (2014) Exome sequencing links corticospinal motor neuron disease to common neurodegenerative disorders. Science 343:506–511
Neurol Sci 2. Hazan J, Fonknechten N, Mavel D et al (1999) Spastin, a new AAA protein, is altered in the most frequent form of autosomal dominant spastic paraplegia. Nat Genet 23:296–303 3. Fonknechten N, Mavel D, Byrne P et al (2000) Spectrum of SPG4 mutations in autosomal dominant spastic paraplegia. Hum Mol Genet 9:637–644
4. Kasher PR, De Vos KJ, Wharton SB et al (2009) Direct evidence for axonal transport defects in a novel mouse of mutant spastininduced hereditary spastic paraplegia (HSP) and human HSP patients. J Neurochem 110:34–44
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