Beckwith-Wiedemann syndrome, tumourigenesis and imprinting Claudine lunien INSERM U73, University Paris V, Paris, France The concurrent development of cytogenetic, clinical, genetic and molecular studies has led to the recognition that the different hereditary and non-hereditary forms of the Beckwith-Wiedemann syndrome and associated tumours result from an imbalance between maternal and paternal alleles. The most exciting development in the past year was the discovery of uniparental paternal disomy and the increased understanding, arising from studies in the mouse and in hereditary cases, of the role possibly played by imprinting and somatic mosaicism in partial and complete expression of this complex syndrome. Current Opinion in Genetics and Development 1992, 2:431-438

Introdudion The Beckwith-Wiedemann syndrome (BWS), first described in 1964, occurs with an incidence of 1/13700 live births and is characterized by numerous growth abnormalities, including exomphalos, macroglossia, visceromegaly and gigantism [1,2]. Other occasional abnormalities include adrenal cortical cytomegaly, neonatal hypoglycaemia, ear lobe creases and pits, hemihypertrophy and predisposition (7.5-10%) to several childhood malignancies such as Wilms' tumour (or nephroblastoma) (50%), adrenocortical carcinoma (15%), hepatoblastoma, rhabdomyosarcoma, and occasionally pancreatic tumour and neuroblastoma [3]. Interestingly, the same organs that are involved in hemihypertrophy-associated neoplasia are also involved in the hyperplastic visceromegaly of BWS. This connection led to the proposal of a close relationship between Wilms' tumour, adrenocortical carcinoma, hemihypertrophy, hamartoma and the BWS [4]. Considerable variability in expression is observed for all these features. Highly suggestive evidence has been presented for a locus for BWS in the llp15 region of the short arm of chromosome 11 and for differences in parent-of-origin in the different forms of BWS. This review focuses on the major advances made in the past year in terms of understanding: whether the bias in parental origin of allele involvement in the different forms and associated tumours relates to genomic imprinting; which subregion(s) and thus how many and which genes in llp15 are associated with the disease; and what lessons we can learn from the accumulating ev-

idence of imprinting of the homologous mouse region. Identification of the gene, or genes, involved is still required to fully understand the role played by imprinting and somatic mosaicism in the complex genetics of this bizarre syndrome [5"].

Bias in parent-of-origin allele involvement Familial transmission Although 85 % of cases are sporadic, BWS can also occur in familial forms or in association with chromosomal aberrations. The clinical findings in BWS patients are highly variable and tend to become less obvious with age. As such, the syndrome may be underdiagnosed in adults and familial inheritance may therefore be masked. It is now widely accepted that BWS is transmitted via an autosomal dominant mode with reduced penetrance and variable expressivity, and that genomic imprinting most likely accounts for the unusual patterns of transmission [6]. Linkage analysis revealed that the locus for the familial form mapped to region 11p15.5 [7,8]. Based on the excess of female carriers observed, a sexdependent mode of transmission has been postulated [7,9]. It has been statistically demonstrated that this excess can be attributed to two phenomena: first, a reduced fecundity of affected males compared with females (ratio 1:4.6); and second, a reduced risk of being affected (ratio 1:3) for individuals having inherited the gene from their father. These latter findings are probably related to

Abbreviations AS--Angelman syndrome; BWS--Beckwith-Wiedemann syndrome; del~eletion; dup~duplication; IGF2--insulin-like growth factor-2; IGF2R--IGF2 receptor; INS~insulin; LOH--Ioss of heterozygosity; MZ--monozygotic; PWS~Prader-Willi syndrome; TGF-i~--transforming growth factor-[3; TH--tyrosine hydroxylase;UPD~uniparental disomy; WT--Wilms' tumour. (~) Current Biology Ltcl ISSN 0959-437X

431

432

Mammalian genetics

imprinting [10-]. BWS males occasionally display genital abnom~alities that could be responsible for impaired fecundity. Thus in BWS, there are no differences in clinical features, except maybe in severity, between patients born to an affected father or to an affected mother. Fm~ilial BWS differs from two reciprocal deletion syndromes, the Prader-Willi syndrome (PWS) and the Angelman syndrome (AS), for which there is clear evidence that the difference in parent-of-origin leads to different phenotypes. In both cases, a deletion of region 15qll-15q13 c~m be observed. PWS occurs when the deleted chromosome is paternally derived while AS occurs when the deleted chromosome is matem,'dly inherited [ 11 "']. Moreover, if as it is believed, genomic imprinting is a speci,'d aspect of phenotype control by modifier genes, variant ,'tildes of modifier genes can probably modulate the level, timing and cell-specificity of imprinting [ 12,13 "° ]. In addition, as demonstrated for the expression of mouse transgenes, an indMdual could be a somatic mosaic with respect to the proportion of cells that carry the imprinted allele in a given tissue [13",14]. Variability could also be achieved by imprinting of the modifier gene itself [15].

Chromosomal

served that the region in common was 11p15.5 [16,17] (Fig. 1) and that the extra material was of paternal origin [18]. h~ contrast, sLx BWS cases with apparently bal,'mced translocation or inversion with breakpoints in 1 lp15 all involved maternal inheritance [19o']. As demonstrated by wtogenetic and molecular analysis, two different subregions could be involved in BWS. One subregion is near the insulin (INS) and insulin-like growth factor-2 (IGF2) genes at 11p15.5, the other subregion being at 11p15.4 proxim,-d to the !B-globin locus, HBB, and near a gene with zinc-binding finger motifs [19-] (Fig. la). Mternatively, the heterogeneity of translocation breakpoints in BWS might ,-also support the implication of position effects in association with translocations.

Uniparental

In his pioneer work oil uniparental disomy (UPD), Engel [20] ascribed tile name isodisomy to the presence in the genome of a pair of chromosomes with whole sequences of identical alleles that arose from the san~e parental chromosome. Heterodisomy refers to the presence of both homologues from the sanle parent. This new genetic concept was based on karyotypic anomalies stemming mainly from meiotic errors affecting the distributiort of the chromosomes in one of the two ganletes, but ignored the possibility of posffertilization errors. Although not yet encountered in humans, postfertilization errors such as non-disjunction with redupli-

anomalies

A sex-dependent mode of transmission is also the role for BWS cases with different wtogenetic abnom~alities invoMng 11p15. In some fifteen cases with different but overlapping duplication (dup) of l l p it was ob-

(a)

HRAS

//I

telomere

(b)

disomy

TH-INS-IGF2-H19

$12

HBB

$776 CALCA

I

//

11p15.5

matt, inv

I centrOmer

e:

chr 11 p

111)I.5.21

I

pat UPD

I

pat dup (c)

r--

RMS

[

HPB

I

]

TunlOl.lrs

VVT ADCC

[

I

[

]

I t-

Fig. 1. Localization of the chromosomal regions involved in Beckwith-Wiedemann syndrome (BWS) and in tumours whether hereditary or not. (a) The short arm of chromosome 11 (chr 11p) with genetic loci indicated. Acronyms include: HRAS, Harvey-ras oncogene; TH, tyrosine hydroxylase; INS, insulin; IGF2, insulin-like growth factor-2; H19, H19 gene; $12, DllS12; HBB, ~ globin; $776, DllS776; CALCA, calcitonin alpha. (b) Mapping of breakpoints in maternal (mat) translocation (t) or inversion (inv) cases, smallest region of homozygosity in paternal (pat) unipaternal disomy (UPD) cases, and smallest region of overlap in paternal duplication (dup) trisomic cases. (c) Smallest regions of overlap for losses of alleles in the different tumours known to be associated with BWS. Abbreviations include: RMS, rhabdomyosarcomas; HPB, hepatoblastoma; WT, Wilms' tumour; ADCC, adrenocortical carcinoma.

Beckwith-Wiedemannsyndrome,tumourigenesisand imprintingJunien 433 cation, mitotic recombination or gene conversion could also lead to complete or partial isodisomy [21]. In such a case, mosaicism might be frequent, as there would be no selection against the original disomic line. According to Engel's theory UPD-associated homozygosity was expected to result in the phenotypic expression of recessive disorders. There is now, however, striking evidence from observations in man and mice that parent-of-origin differences can also account for phenotypic differences in UPD [22,.]. Two lines of evidence now demonstrate that UPD can account for the sporadic occurrence of BWS. First, sporadic cases of BWS were significantly more frequently homozygous for 1 lp15 markers (Fig. la), including INS/IGF2 and DllS774, than were nomlal controls. As such, uniparental isodisomy was subsequently suggested as a possible cause of sporadic BWS [ 2 3 " , 2 4 " ] . Second, the absence of l l p maternal contribution was indeed demonstrated in 4/16 informative sporadic cases. For all cases, isodisomy rather than heterodisomy was unambiguously demonstrated [24.. ]. Confirmation of these data was recently provided by the demonstration of chromosome l i p uniparental paternal isodisomy in a patient with no clinical features of BWS, but with hemihypertrophy and two neoplasms, a congenital adrenal carcinoma and a Wilms' tumour, which are the hallmarks of BWS [24..]. As previously suggested these findings provide further support for the hypothesis that hemihypertrophy could represent incomplete expression of BWS somatic mosaicism [5--]. These findings raised several interesting questions as to the mechanisms involved and their significance [26-.]. First, is the whole length of chromosome 11 involved or only parts of it? Second, did these events occur during meiosis (I or II) or during mitosis, at a later stage after fertilization and do riley thus lead to somatic mosaicism? Third, are the patients isodisomic, heterodisomic or both as is the case in PWS [26.-]? Finally, are patients with UPD more prone to develop a turnout? The mechanism leading to partial disomy was identified in two cases as a postmeiotic recombinational event that must have occurred after fertilization, as a chromosome 11 maternal contribution was observed for markers outside region 11p15 [24.']. In 3/4 cases, somatic mosaicism was revealed after a longer exposure or DNA overloading in Southern-blot experiments. The proportion of uniparent,-d paternal disomic cells versus biparental cells was approximately 50:50. This provided evidence for the suggestion that, depending on the developmental stage when it occurred, a post-fertilization mitotic recombination m W result in a somatic mosaicism with paternal disomy that may be detectable only in some tissues [24..]. This may explain the many incomplete forms of BWS, the association of hemihypertrophy in sporadic but not fan~ilial BWS, and even some cases of isolated hemihypertrophy due to somatic mosaicism [5,24"'].

Twinning and BWS Interestingly, nine cases of monozygotic (MZ) twins with BWS have been reported [27"]. In each twin pair there

was discordance for the expression of BWS, with one twin showing many classical manifestations of the syndrome and the other twin having few or none. The placenta was monochorionic in three totally discordant cases of which one was also diamniotic, while this aspect was not specified in the other reports [28,29]. This implies that for the three pairs of twins each twin of a pair originated from the same blastocyst and that the twinning was an early event, before amnionic cavity formation in the monochorionic, diamnionic case. This argues against dysmorphogenesis as a causal mechanism of the syndrome [30]. An explanation would be somatic mosaicism for UPD limited to one twin, or with different tissue distribution and proportions of mutated cells in the two twins. It would be interesting to search for the occurrence of UPD and also to compare the placental status of all twins. Alternatively, a mitotic crossing-over could result in a disruption of imprinting in one of the twins [31"']. In addition, all discordant twins were female. Following C6te's hypothesis [31"] of a relationship between mitotic crossing-over and twinning it can be assumed that sex differences, similar to meiotic sex differences, are to be found for mitotic crossing-over. Possibly germane is the observation that the later in embryological time a monozygotic twinning occurs, the more likely it is to be in a female zygote [32°.]. As previously reported, because X-chromosome inactivation and monozygous twinning seem to occur at about the same time in embryological development, autosomal imprinting may also be concerned [27",33"*].

Genomic imprinting and tumourigenesis In the earl), 1970's, Knudson raised the possibili W that in retinoblastoma a hit would have to occur in both alleles of the stone gene on chromosome 13, thereby predicting the recessive nature of this genetic function. In hereditary cases, the germline mutation constitutes the first hit and the tumour can arise when a second somatic mutation hits the other allele. In sporadic cases, both hits occur somatically. Following Knudson's prediction that mechanisms similar to those observed in retinoblastoma were to be expected in Wilms' tumour (WT), the search for loss of heterozygosity (LOH) was undertaken. The situation was, however, complicated by the existence of at least three different loci involved in predisposition to Wilms' tumour [35"]. The first, WT1, is the now cloned gene located at 11p13 and associated with the Denys-Drash and the WAGR (for W-Wilms' tumour, A-anridia, G-genitourinary abnormalities, R-mental retardation) syndromes [36"]. WT1, a gene encoding a protein with four zinc-finger motifs and a proline-glutamine rich region, has properties of a tumour suppressor gene [36"] and behaves, in vitro, as a transcriptional repressor [37"]. Because only a few germline and somatic alterations have been found in the many tumours studied, this gene may be involved in only a small proportion of tumours. Several lines of evidence suggest that the second locus, WT2, is identical to the BWS locus and thus

434

Mammalian genetics maps to 11p15.5, in a region more distal to WT1. A third locus, WT3, involved in rare familial forms is not linked to either 11p13 or llp15 and is as yet unmapped [38"]. The specific losses of alleles for 11p markers observed in about one third of the Wilms' tumour cases suggested that Knudson's two-hit theory [34] applied to this type of tumour [39"]. While some tumours showed LOH that encompassed both 11p13 (WT1) and 11p15 (WT2), only a few, sporadic Wilms' mmours had LOH confined to 11p13 (WT1), and the majority showed LOH for markers within 11p15 (WT2) but not 11p13 (WT1) [40,41]. Furthermore, there are several sporadic and hereditary cases where both genes are involved sequentially. In three deletion (del)-11p13 WAGR patients, the allele loss was limited to region 11p15 [41]. This suggests that WT1 may regulate the expression of WT2 [37"]. Whenever identifiable, the l l p alleles lost in cases of Wilms' tumour (29/30), rhabdomyosarcoma (7/7) and adrenocortical carcinoma (2/2) were of maternal origin and, although not fully demonstrated, the vast majority concemed region 1 lp 15 rather than 1 lp 13 [39",40--43 ]. This preferential retention of paternal alleles could be explained by either hypermutability of paternal gametes or differential genomic imprinting. Studies of the parental origin of d e n o v o chromosome rearrangements or mutations in diseases such as de113q14 retinoblastoma and delllp13 WAGR showed a preferential bias towards a paternal origin for new germline mutations. This is reflected by an excess of loss of maternal alleles in bilateral retinoblastoma corresponding to new germline mutations, while in sporadic unilateral tumours maternal and paternal alleles are lost with equal frequency. In BWS-related childhood tumours, whether hereditary or not, because of the unusual parental "allele involvement in the different forms of BWS, it is genomic imprinting that most probably accounts for the parental bias in allele loss. If a locus involved in tumourigenesis undergoes genomic imprinting, this would suggest that the loss of the second 'inactive' allele is unnecessary. Thus imprinting of the 11p15 locus would require only one additional event, the loss of the maternal allele, for the tumour to develop. In hereditary cases, imprinting could be considered the equivalent of germline mutation

[43]. As LOH for region llp15 is a common event in several childhood and adult tumours [39"], a similar bias in allele loss as a result of genomic imprinting could also be expected in the latter. Surprisingly, while LOH for 11p15 markers has been found in 40% of testes tumours, in 3/3 cases the allele lost was paternal [44-]. This implies that if the gene involved is the same as in childhood tumours, then imprinting may either be different or erased in adult tissues. When the overall frequency of tumours in BWS (7.594) is compared with the figure in cases with UPD (3/4 cases observed = 7594) [23",24..] and in cases with dupllp15 (1/15 observed = 7.594) [16,17], there seems to be an increased risk of turnouts in cases with UPD. Thus the congenital absence of the maternal allele would confer a higher risk than the duplication of the paternal

allele. Although UPD cases are stir too rare to confirm this hypothesis, this would have important consequences both in terms of the surveillance of such children and for genetic counselling.

Learning from the mouse The value of comparative mapping between mouse and man has been anlply demonstrated ,and it has been proposed that tile conservation observed may also apply to imprinting. Important clues to the genetic mechanisms of human diseases can be extrapolated from the phenotypic expression of the mouse UPDs. Care must always be taken not to emphasize such homologies too strongly. To date, differences in expression for paternal and maternal alleles have been demonstrated for three mouse genes, Igf2, H19 and that encoding the Igf2 receptor (Igf2r) [45",46",47"]. Part of the distal region of mouse chromosome 7, which shares syntenic homology with the human 11p15.5 region, carries two of these genes, H19 ,and Igf2. Early prenatal death is associated with paternal disomy of distal 7 whereas late prenatal death is associated with maternal disomy of distal 7. Reminiscent of BWS cases with 11p15 paternal disomy, chimaeric embryos with a distal chromosome 7 dipaternal contribution are larger than normal embryos, while those with a dimaternal contribution are smaller [48-]. Thus the homology between human llp15 and mouse distal 7 may not be complete as the viability of BWS patients disomic or trisomic for 11p15 contrasts with the lethality of paternal ,and maternal disomy for the distal region of mouse chromosome 7. This may be a consequence of the effect of other imprinted genes in this region. Mtematively, the human homologues of H19 ,and Igf2 may not be imprinted the same way, or discontinuity in conserved syntenic blocks may provide different patterns of imprinting in the two species. H19 and Igf2, which are closely linked in both species, show opposite parental imprinting patterns, while there is no evidence for imprinting of adjacent genes such as the tyrosine hydro~,lase (TH) and INS genes. This and the absence of imprint for genes adjacent to the imprinted Igf2r gene on mouse chromosome 15 suggest that bnprinting does not span large blocks of genes [47"]. In the mouse, only the paternal copy of Igf2 is actively transcribed during embryonic growth [45"]. The Igf2 gene expresses several transcripts in many tissues during embryonic and neonatal periods, whereas expression in adult animals and from both the paternal and maternal alleles is confined to the choroid plexus and the leptomeninges. Transgenic mice carrying the Igf2 gene disrupted by homologous recombination in embryonic stem cells have been obtained [49]. HeterozTgous mice that inherited this inactive Igf2 gene from the male parent were smaller than normal and did not express Igf2. Mice homozygous for an inactive Igf2 are viable, although small. H19, a gene of unknown function that transcribes a high level of mRNA during development, is expressed at the blastocyst stage and is abundant in tissues of endodermal and mesodermal origin, with the active copy being derived from the mother [46"]. Moreover, the introduction of additional copies of H19 in transgenic mice

Beckwith-Wiedemann syndrome, tumourigenesis and imprinting Junien 435 leads to late prenatal lethality, just as in the matemal duplication/paternal deficiency of distal 7 [50"]. More recently, it has been shown that expression of human H19 is largely or exclusively from a single allele [51°o].

Normal Tumour suppressor gene

Interesting clues are also provided by the relative contribution of normal and parthenogenetic cells to different tissues of mouse chimaeras [48.°]. Parthenogenetic cells make a disproportionately small contribution to the extra-embryonic.membranes, and to tissues of mesodermal origin such as the skeletal muscle, and including the tongue, liver and pancreas. Birth weights of chimaeric mice are negatively correlated with the proportion of parthenogenetic cells [52]. This is exactly what can be expected: parthenogenetic cells have two haploid sets of chromosomes of maternal origin while BWS patients have an excess of chromosome region 11p15 of paternal origin. Hence the clinical manifestations of the BWS, namely macroglossia (enlarged tongue), gigantism, and visceromegaly including enlarged liver and pancreas.

Growth promoter gene

Towards a model for BWS?

Maternally inherited translocation, inversion

Whatever the function of the BWS gene and whatever the parental origin of the imprint, the different observations are apparently contradictor}, under a single locus hypothesis. The involvement of either two genes with different roles or a single gene that under different conditions acts either as growth promoter or suppressor, more likely accounts for the different observations (Fig. 2). First let us examine the hypothesis of the involvement of a single locus. The genetic data from BWS patients and biological data from mice strongly suggest that IGF2 is the BWS gene [53"]. What is the evidence supporting this assignation? Although it has not yet been proven in humans that the paternal allele is active, IGF2 is a growthpromoter and is in the correct position at 11p15.5. While the presence of two paternal copies (trisomy and UPD) of IGF2 could result in overgrowth/tumour, it is hard to accept that loss of the maternal inactive allele would lead to a tumour. Moreover, this loss is not consistent with cytogenetic and molecular data showing that LOH can result from either mitotic recombination, with two paternal copies, as well as from deletion with only one 'active' paternal copy and therefore no gene dosage effect [40,41,43]. Similarly, in maternally inherited familial cases the alteration of a silent allele should be harmless, unless the underlying mechanism involved resulted in the switching 'on' of the maternal IGF2 gene. IGF2 is certainly expressed at high levels in all tumours, which fits the growth promoter hypothesis [54]. But how can this hypothesis be reconciled with the simultaneous chromosomal loss of 11p in both childhood and adult tumours, which rather suggests the loss of function of a tumour suppressor gene? Indeed, in vivo functional evidence for the existence of a locus involved in suppressing the tumourigenic phenotype of Wilms' tumour in region 11p14-p15.5 has recently been demonstrated by means of microcell transfer using radiation-damaged chromosomes [55*]. As an alternative hypothesis, it can be proposed that the IGF2 gene products can behave not only as a growth promoter, which has been anlply

BWS Paternally inherited 11 pl 5 trisomy

E3

Paternal 11p15 disomy

Maternally inherited mutation

~

or ~

or

E]

(::2

Tumour Loss of" maternal alleles

Eq

Fig. 2. A hypothetic model for Beckwith-Wiedemann syndrome (BWS) and associated tumours involving two different genes imprinted in opposite directions on the maternally derived (circle) and paternally derived (square) chromosomes. A maternally expressed tumour suppressor gene (shaded circle) and a paternally expressed growth promoter gene (shaded square) are shown in the context of both normal individuals and patients with either BWS or tumours. As described in the text, four different forms of BWS are represented - - the maternally inherited mutation is indicated with a black dot, and the maternally derived translocation/inversion with broken circles. The question-marks indicate that the role of the gene involved in tumour formation is unknown. The different situations observed are incompatible under a single locus hypothesis and rather suggest the involvement of two genes with separate roles, or one gene that acts either as growth promoter or suppressor. See text for details. demonstrated, but also as a tumour suppressor gene, as has recently been suggested [56°]. This duality of function, if proven in vivo, would be reminiscent of similar findings for another tumour suppressor, p53, and another growth factor, transforming growth factor-IB (TGF-I8). Conversely, could the BWS gene be a tumour suppressor gene expressed by a maternal allele such as H19? This proposal is in agreement with all observations except a paternally derived trisomy: it is difficult to accept that the duplication of a silent (paternal) allele could lead to an overgrowth syndrome. A model involving two genes and that would fit all the situations observed is called for (provided imprinting affects all cells of a particular tissue equally). In Fig. 2, the growth promoter (perhaps IGF2) is paternally expressed

436

Mammaliangenetics while the tumour suppressor (perhaps H19) is maternally expressed. The existence of two candidate subregions, from INSN/IGF2 to HBB and from HBB to CALCA (Fig. 1), may also support the involvement of two genes one of which, the proximal one, would be different from IGF2 or H19. Evidence for a second more proximal subregion, between HBB and CAt.CA arose from the concordance between breakpoints in two apparently balanced translocations and from losses of alleles in two cases of tumours (Fig. 1) [19..,26"',57.]. The maternally imprinted IGF2 receptor gene, IGF2R, may also be involved in controlling IGF2 levels. Under the self-explanatory tide of 'a parental tug of war', it has recently been argued that the evolution of genon'tic imprinting can be understood as a competition between the reproductive demands of the father and the mother driven by the paternally imprinted IGF2 and the maternally imprinted gene encoding the receptor of this growth factor, IGF2R [58..]. Some BWS patients may show maternal allele loss or paternal UPD for the maternally active IGF2R gene, which lies on the long arm of chromosome 6 at 6q21-27. In humans, the genetics underlying proportional dwarfism may, like PWS and AS, be the reciprocal of those of BWS. A good candidate is the Russell-Silver dwarfism syndrome [59], which is characterized by intrauterine and postnatal growth retardation, lateral asymmetry and triangular face. It will be of interest to search for 11p15 maternal UPD in these patients.

Conclusion Progress in the understanding of the rare, complex disease BWS offers a unique opportunity to decipher the role played by imprinting during development and tumourigenesis. The final significance of such study may be even broader as there is now striking evidence that the locus or loci involved in the different aetiological forms of BWS and in childhood and adult tumours play a central role in these fundamental processes. The need to characterize the gene(s) at defined positions on 11p will lead to the isolation of numerous sequences that should facilitate the identification of regions/sequences involved in germline and somatic rearrangements of this 'unstable' region. These approaches promise the development of new means for diagnosing the disease and for detecting individuals at risk for developing tumours. This should also enable the relationship, if any, between mortality and morbidity and the causal defect to be better evaluated. Bearing in mind that 25% of cases die in early infancy and 7.5% of survivors will develop tumours, the prime importance of improved genetic counselling and accurate prenatal diagnosis is evident.

References and recommended reading Papers of particular interest, published within the annual period of review, have been highlighted as: • of special i n t e r e s t oo of outstanding interest 1.

WIEDEI~uNNHR: C o m p l e x e Malformatif Familial Avec H e m i e Ombilicale et Macroglossie - u n 'Syndrome Nouveau'? J Genet Hum 1964, 13:233-232.

2.

BECKWrrH JB: Macroglossia, Omphalocele, Adrenal Cytomegaly, Gigantism, and Hyperplastic Visceromegaly. Birth Defects 1969, 5:188-190.

3.

WIEDEMANNHR: T u m o r s and Hemihypertropby Associated with Wiedemann.Beckwith Syndrome. Eur J Pediatr 1983, 414-429.

4.

MOLTERS, GADNER H, WEBER B, VOGEl. M, RIEHM H: Wilms' Turnout and Adrenocortical Carcinoma with Hemihypertrophy and Hamartomas. E u r J Pediatr 1978, 127:219-226.

5.

HAIA. JG:

Genomic

Imprinting.

Curr

Biol

1991,

1:

One o f 3th4ee39" latest reviews on the different areas of research on imprinting. The key references cited represent ,an essential complement to the bibliography of this re~4ew. 6.

NIII'L,~\VAN, ISHIKIRIYA/~bkS, TAK.M-IASHIS, INAGAWAH, OHTA Y, HASA N, KAMEI T, KAJI[ T: The Wiedemann-Beckwith Syndrome: Pedigree Studies on Five Families with Evidence for Autosomal Dominant Inheritance with Variable Expressivity. Am J Med Genet 1986, 24:41-55.

7.

KOUFOSA, GRUNDYP, MORG,~I K, ALECKKA, HADROT, LAMPKIN BC, KALBAKJIA, CAVENEE 'k~{.: Familial Wiedemann-Beckwith Syndrome and a Second Wilms' T u m o u r Locus Both Map to I lp15.5. Ant J Hum Genet 1989, 44:711-719.

8.

PING AJ, REEVE AE, L~w DJ, YOUNG MR, BOEHNKE M, FEINBERG AP: Genetic Linkage of Beckwith-Wiedemann Syndrome to l lp15. Am J Httm Genet 1974, 44:720-723.

9.

LtIBINSKYM, HERblANN J, KOSSEF AL, OPITZ JM: Autosomal Dominant Sex D e p e n d e n t Transmission of the WiedemannBeckwith Syndrome. Lancet 1974, 2:932.

10. ..

MOUTOUC, JUNIEN C, HENRY 1, BONMTI-PELLII~ C: Beck'withW i e d e m a n n Syndrome: a Demonstration of the Mechanisms Responsible for the Excess of Transmitting Females. J Med Genet 1992, 29:217-220. Using statistical analysis, the excess of transmitting mothers in BWS can be explained by a lower penetrance when the gene is transmined by an affected father and by a reduced fecundiW of affected males. 11.

HULTENM, ARMSTRONG S, CHALLINORP, GOULD C, HARDY G, LEEDPL,',uMP, LEE T, McKE.OWN C: G e n o m i c Imprinting in an Angelman and Prader-Willi Translocation Family. Lancet 1991, 338:638-639. Malsegregation of a translocation t(15;22)(q13;q11 ) leads to Angelman syndrome when the deleted chromosome 15 derivative, d e l l 5 q l l - q l 3 , is maternally inherited, and to Prader-Willi syndrome when it is paternally inherited. This is the first clear-cut example of genomic imprinting in man with an unequivocal demonstration that the same deletion has different effects dependent upon its parental origin. ee

12.

ALLEN ND, NORRIS ML, SURANI MA: Epigenetic Control of Transgene Expression and Imprinting by Genotype-specific Modifiers. Cell 1990, 61:853-861.

13. ..

ENGLER P, HAASCH D, PINKERT CA, DOGLIO L, GLYMOUR M, BRINSTERR, STROB U: A Strain Modifier on Mouse Chromos o m e 4 Controls t h e Methylation of Independent Transgene Loci. Cell 1991, 65:939-947. Demonstrates that in addition to the methylated and unmethylated transgenic phenotypes, certain mice exhibit a partial methylation pattern that is a consequence of an unusual cellular mosaicism. 14.

SAPIENZAC: G e n o m a Imprinting and Dominance Modifications. Ann N Y Acad Sci 1989, 564:24-38.

15.

SURANI MA, KOTHARY R, ALLEN ND, SINGH PB, FUNDELE R, FERGUSON-SMITHAC, BARTONSC: G e n o m e Imprinting and Dev e l o p m e n t in the Mouse. Development 1990 (suppl):89-98.

16.

TURI.EAUC, GROUCHYJ DE: Beckwith-Wiedemann Syndrome: Clinical Comparison Between Patients with and w i t h o u t l lp15 Trisomy. H u m Genet 1985, 28:93-96.

17.

HENRY I, COUILLIN P, BARICHARD F, SERRE JL, JOURNEL H, LAMOROUXMA, TURLEAUC, GROUCHYJ DE, JUNIEN C: Molecular Definition of t h e 1 lp15.5 Region Involved in Beckwith-

Beckwith-Wiedemann syndrome, tumourigenesis and imprinting Junien 437 Wiedemann Syndrome and in Predisposition to Adrenocortical Carcinoma. H u m Genet 1989, 81:273-277. 18.

BROWNKW, WILLIAMSJC, MAITLANDNJ, MOTr MG: Genetic Imprinting and the Beckwith-Wiedemann Syndrome. Am J Hu m Genet 1990, 46:1000-1001.

MANNENSM, HOOVERS JM, REDEKER B, BLIEK J, FEINBERG API BOAVIDA M, TOMMERUP N, HENRY l, LITTLE P, LESCHOT NJ, WESTERVEtD A: Characterization of Regions on Human C h r o m o s o m e l l p Involved in the D e v e l o p m e n t of Wilms' T u m o u r Associated Congenital Diseases. A Model to Study Genomic Imprinting in Man. Cytogenet Cell Genet 1991, 58:1967. A molecular analysis of breakpoints in 11p15 in patients with a duplication, translocation or inversion. Two different regions show a clustering of breakpoints, one around the IGF2/INS region, and the other proximal to I-IBB. Interesting models involving imprinting and two different regions are discussed.

28.

BERRY AC, BELTON EM, CHANTLRR C: Monozygotic Twins Discordant for Wiedemann-Beckwith Syndrome and the Implications for Genetic Counselling. J Med Genet 1980, 17:136-138.

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BOSE B, WILKIE RA, MADLOM M, FORS'~WH JS, FAED MJ'W: Wiedemann-Beck'with Syndrome in O n e of Monozygotic Twins. Arch Dis Child 1985, 60:1191-1192.

30.

SCHINZELAAGL, SMITH MDD, MILLERJR: Monozygotic Twinning and Structural Defects. J Pediatr 1979, 95:921-930.

19. ••

20.

ENGEL E: A New Genetic Concept: Uniparental Disomy and its Potential Effect, lsodisomy. Am J Med Genet 1980, 6:137-143.

21.

SPENCEJE, PERCIACCANTE RG, GREIG GM, I-IUNT1NGTON F~(/, LEDBE'I'IER DH, I-|EJTMANCIKJF, POLLACK MS, O'BRIEN WE, BEAUDETAL: Uniparental Disomy as a Mechanism for H u m a n Genetic Disease. Am J Hum Genet 1988, 42:217-226.

22.

SCHINZELAA: Uniparental Disomy and Gene Localization. Am

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J Hum GeneI 1991, 48:424-425.

This paper provides a list of the different unusual genetic counselling situations where the phenomenon of uniparental disomy cam both explain the genetic defect and be used as a useful mapping tool. 23.

I~|ENRY I, BONAIT1-PEUJI~ C, CHEHENSSE V, BELDJORD C, SCHWARTZC, UTERMAN G, JUNIEN C: Uniparental Paternal Disomy in a Genetic Cancer-predisposing Syndrome. Nature 1991, 351:665-667. Demonstrates UPD in 3/8 cases of sporadic BWS. The significantly increased homozygosit3, rate ff)r 11 pl 5 markers in a total of 21 BWS patients suggests that approximately five of them are isodisomic, in cases with WT, 2/3 are shown to present with paternal UPD. ••

24. ••

HENRY 1, PUECH A, RIESE\XqJK A, AHN1NE L, MANNENS M, BELDJORDC, BITOUN P, TOURNADE MF, LANDRIEU P, JUNIEN C: Somatic Mosaicism for Partial Paternal lsodisomy in Beckwith-Wiedemann Syndrome: a Post-fertilization Event. Ettr J Hum Genet 1992, in press. Reports a fourth case of Beckwith-Wiedemann syndrome with paternal isodisomy. Further genetic analysis reveals somatic mosaic|sin and partial paternal isodisomy for 11 p in four cases of Beckwith-Wiedemann ~'ndrome with paternal isodisomy. The close relationship between hem|hypertrophy and Beckwith-Wiedemann syndrome is discussed in the context of a post-fertilization event leading to somatic mos:dcism. 25. •*

GRUNm' P, TELZEROW P, PATERSON MC, HABER D, HERMAN B, LI F, GARBER J: C h r o m o s o m e 11 Uniparental Isodisomy Predisposition to Embryonal Neoplasms. Lancet 1991, 338:1079-1080. Paternal isodisomy in a child with hem|hypertrophy and two neoplasms, Wilms' turnout, and an adrenal carcinoma strongly supports a c o m m o n genetic mechanism for hem|hypertrophy and BWS. 26. WItmE AOM, MALCOLm1S, PEMBREY ME: lsodisomy in BWS •. Chromosomes. Nature 1991, 353:802. Based on the meiotic mechanisms leading to |so- and heterodisomy in PWS and AS, this paper raises interesting questions as to the nature of the mechanisms leading to isodisomy in BWS. In BWS, as discussed here, post-zygotic, mitotic crossing-over most likely accounts for two cases of partial paternal disomy and for nine cases of female MZ twins discordant for BWS. 27. LUBINSKYMS, HALLJG: Genomic Imprinting, Monozygous •• Twinning, and X Inactivation. Lancet 1991, 337:1288. Based on conditions other than BWS that shows examples of discordant MZ twins (also only females), together with pedigree patterns highly suggestive of imprinting, this paper draws attention to indications that MZ twinning in females may affect the manifestations of genomic imprinting.

31. ..

CO'rg GB, GYI~rODIMOUJ: Twinning and Mitotic Crossingover: Some Possibilities and their Implications. A m J H u m Genet 1991, 49:120-130. A comprehensive review of MZ twin discordance leads the authors to postulate a model that involves both the existence of a sex difference in the rate of mitotic crossing-over and the impossibili .ty for recombined X chromosomes to undergo inactivation. For certain chromosomal regions, a major role of mitotic crossing-over in the induction of the twinning proces itself is suggested. 32. JAMES WH: Genomic Imprinting. Lancet 1991, 338: ** 189. A relevant paper inferring that the excess of late-formed female MZs is associated with anomalous X-chromosome inactivation. 33. "~is

HULTENM, KERR A: Genomic Imprinting. Lancet 1991, 338:188-189. paper suggests that the differential spatial orientation of the maternal and paternal genome during early embryogenesis, and the differential somatic pairing of the sex chromosomes in XX embryos may influence the beha~4our of the rest of the genome, including imprinting and thus also twinning. 34.

KNUDSONAG, STRONG LC: Mutation and Cancer: a Model for Wilms' T u m o r of the Kidney. J Nail Cancer lnst 1972, 48:313-323.

35.

VAN HEYNINGEN V, HAST1E ND: Wilms' Tumour: Reconciling Genetics and Biology. Trends Genet 1992, 8:16-21. The most complete and up-to-date review on the different genes and genetic mechanisms that are involved in urogenital and kidney developmen• and that are also associated with predisposition to Wilms' tumour. 36. *,

PELLETIERJ, BRUENINGW, KASHTANCE, MAUERSM, NDuXIIVELJC, STRIEGELJE, HOUGHTON DC, JUNIEN C, HABIB R, FOUSER L, ET AL: Germline Mutations in the Wilrns' T u m o r Suppressor Gene are Associated with Abnormal Urogenital Developm e n t in Denys.Drash Syndrome. Cell 1991, 67:437-447. Demonstrates that point mutations in the zinc-finger domains II and III ofWT1, including one at Arg366, seven at the Arg394 and two at Asp396, are responsible for Drash syndrome and predisposition to Wilms' tumour and to juvenile granulosa cell tumour (gonadoblastoma). 37.

MADDENSL, COOK DM, MORRIS JF, GASHLER A, SUKHATME

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VP, RAUSHER FJ IIh Transcriptional Repression Mediated

by the WT1 Wilms T u m o r Gene Product. Science 1991, 253:1550-1553. In transient transfection assays, the WT1 protein functioned as a repressor of transcription when bound to the EGR-1 site. The repression function was mapped to the glutamine, and proline-rich amino-terminus of WTI. 38. •

SCHWARTZCE, HABER DA, STANTON VP, STRONG LC, SKOt.N1CK MH, HOUSMmN DE: Familial Predisposition to Wilms T u m o r Does not Segregate with t h e WT1 Gene. Genomics 1991, 10:927-930. This is the first demonstration using WT1 itself that, at least in this large family, WT1 is not implicated in predisposition to WT. 39. •o

SEIZINGER B, KLINGERHP, JUNIEN C, NAK~tURA Y, LE BEAU M, CAVENEEW, ENtANUEL BS, PONDER B, NAYI.OR S, MrITELMAN F, Er AL: Report of the C o m m i t t e e on C h r o m o s o m e and Gene Loss in H u m a n Neoplasia. Cytogenet Cell Genet 1992, 58:1080-1096. A compilation of specific LOH reported for all types of tumours and for all chromosomes with special notes concerning the subregional localization of possible candidate tumour suppressor genes.

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Mammalian genetics 40.

MANNENSM, SL.XTERRM, HE'YTINGC, BLIEKJ, DE KRAKERJ, COAD N, DE PAGTER-HOLTHUIENP, PEARSON PL: Molecular Nature of Genetic Changes Resulting in Loss of Heterozygosity of C h r o m o s o m e 11 in Wilms' Tumor. Hunt Genet 1988, 81:41--48.

41.

HENRY l, GRANDJOU&N 5, COULLIN P, BAPaCHARD F, HUERREJEAN!'IERRE C, GLASER T, LENOIR G, CHAU~AIN JL, JUNIEN C: Tumor-specific Loss of 11p15.5 Allele in dell l p l 3 Wilms' T u m o r and in Familial Adrenocortical Carcinoma. Proc Natl Acad Sci USA 1989, 86:3247-3251.

42.

43.

SCHROEDER'~g'r, CI-L.%.o LY, DAO DD. STRONG LC, PATHAK S, PdCCARDI V, LI:~.xqs\X/H, SAUNDERS GF: Non Random Loss of Maternal C h r o m o s o m e s in Wilms' Tumors. Am J H um Genet 1987, 40:413-420. SCRABLEHJ, CAVENEE ~t, GHAXqMI F, LoxrEu. M, MORG.'M',I K, SAP!ENZA C: A Model for Embryonal Rhabdomyosarcoma Tumorigenesis that Involves G e n o m e Imprinting. Proc Nail Acad Sci USA 1989, 86:7480-7484.

44. •

LOTHE R.A, HASTIE N, REITVIK GA, FOSSA SD, BORRESEN AL: Allele Losses in Testicular Cancer Detected with l i p Markers. Cl,togenet Cell Genet 1991, 58:1066. Adult testicular mmours show allele losses for region llp. In contrast with other enlbryonal mmours, the allele lost in 3/3 C:LSeSwas of paternal origin. 45. ••

DECHIARATM, ROBERTSON EJ, EFSTRATIADIASA: Parental Ira. printing of the Mouse Insulin-like Growth Factor II Gene. Cell 1991. 64:849-859. Provides genetic and molecular evidence of parental imprinting.

46.

BARTOLOMEIMS, ZEMEL S, TILGHMANS: Parental Imprinting of the Mouse H19 Gene. 1Vat!!re 1991, 351:153-155. "~Vithan RNAse protection assay that can distinguish between H19 alleles in four subspecies of a.ht.~ the authors conclude that the H19 gene is parentally imprinted with the active copy derived from the mother. The3, ,also show that Int-2, H19 and Igf-2 are tightly linked. 47. •

BAPa.OWDP, STOGER R, HERRI~L.XNNBG, SAITO K, SCHWEIFERN: The Mouse Insulin-like Growth Factor Type-2 Receptor is Imprinted and Closely Linked to the T m e Locus. Nature 1991, 349:84-87. Embryos express lgf2r only' from the maternal chromosome while the adjacent genes Tcp-1, Pig and Sod-2 are expressed from both chromo. somes: imprinting does not necessarily extend to closely linked genes. 48. • ,,

FERGUSON-SMITHAC, CATrANACHBM, BARTONSC. BEECHEY CV, SURANI~ Embryological and Molecular Investigations of Parental Imprinting on Mouse C h r o m o s o m e 7. Nature 1991, 351:667~570. Chimaefic mouse embryos carrying cells with paternal disomy are shown to be abnormally, large. Includes a comparison between the phenotypes resulting from distal chromosome 7 paternal or maternal duplication, and the phenotypes resulting from the duplication of tile entire parental genome. 49.

DECHtARA TM. EFST~TtADIS & ROBERTSON EJ: A Growthdeficiency Phenotype in Heterozygous Mice Carrying an Insulin-like Growth Factor II Gene Disrupted by Target. ing. Nature 1990, 345:78-80.

50. ,,•

BRUNKOWME, TILGHMANSM: Ectopic Expression of the HI9 Gene in Mice Causes Prenatal Lethality. Genes De!' 1991, 5:1092-1101.

The authors suggest that the prenatal lethality of transgenic mouse embryos, which carry one to four copies of a normal or deleted H19 gene and overexpress H19, is the consequence of a disruption in the tightly controlled H19 gene dosage. 51. ZHANGY, T~'CKO B: Monoallelic Expression of the H u m a n ** HI9 Gene. Nature Genel 1992, 1:40-44. Monoallelic expression of HI9 and biallelic expression of W'I'I are demonstrated in human fetal tissues. 52.

FUNDELERH, NOPaUS ML, BARTON SC, FELHAU M, HOWI_E'Vr SK, bllU£ WE, SUR&N! MA: Temporal and Spatial Selection ,against Parthenogenetic CeRs during Development of Fetal Chimeras. Det,elopment 1990, 108:203-211.

53. LITTLEM, VAN HE~INGEN V, HASTIE N: Dads and Disomy and .,, Disease. Nature 1991, 351:609-610. Discussion of the link between the phenotypic consequences of 11 pl 5 paternal disomy in BWS and paternal duplication of distal mouse chronlosome 7. The possible role of IGF2 is anab'zed and arguments favouring models invoMng genomic imprinting of growth/tumour suppressor and promoter genes are discussed. 54.

REEVEAE, ECCLES MR, \X:II.KINSRJ, BEIJ. GI, MILLWJL: Expression of Insulin-like Growth Factor.I! Transcripts in Wilms' Tumour. Nat!!re 1985, 317:258-260.

55. •

DOWDy SF. FAS,CHING CL, ARAtUO D. L4.l CM, 1.1x';~NOS E, WEISSMANE, ST,U,mRIDGE El: Suppression of Tumorigenicity in Wilms T u m o u r by the p15.5-p14 Region of C h r o m o s o m e 11. Science 1991, 254:293-295. Nlicrocell fusion studies show that introduction of chromosome 11 into the tumot, rigenic Wilms' tunlour cell-line G401 results in suppression of mmourigenicit3,. The ability to suppress m m o u r fonnation is due to the \XrF2 gene in 11 pl-~.l-p15.5, and not to the WT1 gene in 111)13. 56.

5CHOFtEt.DPN, LEE A, HIU. DJ, CI-!EE'IlbVXlJE, JAMES D, S'fEWART T u m o u r Suppression Associated with Expression of Human Insulin-like Growth Factor II. B r J Cancer 1991, 63:687~692. An IGFII eDNA is introduced into a retroviral expression vector and used to infect a cloned libroblast cell line in which the endogenous IGFII genes are silent. Expression of IGFII conferred serum independence of growth, although when injected into nude mice a greatly increased latency of sarcoma fomlation was obsetwed. •

C:

57. •

B','RNEJA, LrVrLE NIH, 5,',11"I"I-IPJ: The M1 Subunit of Ribonucleotide Reductase Refines Mapping of Genetic Rearrangem e n t s at C h r o m o s o m e 1 lp15.5. Cancer Genet C I,togenet 1992, in press. Results at tile RR/vll locus, which encodes tile ribonucleotide reductase MI subunit indicate that different regions of 11 p15.5 are involved in one WT and in tile adrenal adenoma from a BWS patient. These findings support tile hypothesis that more than one locus may, exist at 11 pl 5.5. 58. MOORET, HAIG D: G e n o m i c Imprinting in Mammalian De.. velopment: a Parental Tug-of-War. Science 1991, 7:'~5-49. Anmctive speculations from an evolutionary point of view on the role of imprinting. 59.

DUNCANPA, HALLJG, SHm,,tO LR, VIBERT BK: Three-generation Dominant Transmission of the Silver-Russel Syndrome. Am J Med Genet 1990, 35:245-250.

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