Mapping of Simpson-Golabi-Behmel syndrome to Xq25-q27

Simpson-Golabi-Behmel syndrome

The Simpson-Golabi-Behmel syndrome (SGBS; OMIM 312870) is an overgrowth/multiple congenital anomalies/dysplasia condition, inherited as an X-linked semi-dominant trait, with variable expressivity in males and reduced penetrance and expressivity in females. The clinical spectrum is broad, ranging from mild manifestations in both males and females to multiple malformations and neonatal death in the more severely affected cases. An increased risk of neoplasia is reported, requiring periodical surveillance. Intellectual development is normal in most cases. SGBS is caused by a loss-of-function mutation of the GPC3 gene, either deletions or point mutations, distributed all over the gene. Notably, GPC3 deletion/point mutations are not found in a significant proportion of clinically diagnosed SGBS cases. The protein product GPC3 is a glypican functioning as a receptor for Hh at the cell surface, involved in the Hh-Ptc-Smo signaling pathway, a regulator of cellular growth.

Simpson-Golabi-Behmel syndrome in a female: A case report and an unsolved issue

Simpson-Golabi-Behmel syndrome is an X-linked recessive overgrowth condition caused by alterations in GPC3 gene, encoding for the cell surface receptor glypican 3, whose clinical manifestations in affected males are well known. Conversely, there is little information regarding affected females, with very few reported cases, and a clinical definition of this phenotype is still lacking. In the present report we describe an additional case, the first to receive a primary molecular diagnosis based on strong clinical suspicion. Possible explanations for full clinical expression of X-linked recessive conditions in females include several mechanisms, such as skewed X inactivation or homozygosity/compound heterozygosity of the causal mutation. Both of these were excluded in our case. Given that the possibility of full expression of SGBS in females is now firmly established, we recommend that GPC3 analysis be performed in all suggestive female cases. © 2016 Wiley Periodicals, Inc.

Somatic CTNNB1 mutation in hepatoblastoma from a patient with Simpson-Golabi-Behmel syndrome and germline GPC3 mutation

Simpson-Golabi-Behmel syndrome is a rare overgrowth syndrome caused by the GPC3 mutation at Xq26 and is clinically characterized by multiple congenital abnormalities, intellectual disability, pre/postnatal overgrowth, distinctive craniofacial features, macrocephaly, and organomegaly. Although this syndrome is known to be associated with a risk for embryonal tumors, similar to other overgrowth syndromes, the pathogenetic basis of this mode of tumorigenesis remains largely unknown. Here, we report a boy with Simpson-Golabi-Behmel syndrome who had a germline loss-of function mutation in GPC3. At 9 months of age, he developed hepatoblastoma. A comparison of exome analysis results for the germline genome and for the tumor genome revealed a somatic mutation, p.Ile35Ser, within the degradation targeting box of β-catenin. The same somatic mutation in CTNNB1 has been repeatedly reported in hepatoblastoma and other cancers. This finding suggested that the CTNNB1 mutation in the tumor tissue represents a driver mutation and that both the GPC3 and the CTNNB1 mutations contributed to tumorigenesis in a clearly defined sequential manner in the propositus. The current observation of a somatic CTNNB1 mutation in a hepatoblastoma from a patient with a germline GPC3 mutation supports the notion that the mutation in GPC3 may influence one of the initial steps in tumorigenesis and the progression to hepatoblastoma.

Simpson-Golabi-Behmel syndrome associated with cleft palate

We report a very rare case of anomaly in the maxillofacial region. This case is a patient with a cleft palate who had Simpson-Golabi-Behmel syndrome. This X-linked symptom was first described by Simpson et al in 1975 and is characterized by prenatal and postnatal overgrowth, as well as visceral and skeletal anomalies. The syndrome consists of a distinctive facial appearance with wide nasal bridge, anteverted nostrils, wide-open mouth, enlarged tongue, and large protruding maxilla and jaw. The cleft palate was repaired surgically using the push-back method.

The Simpson-Golabi-Behmel syndrome causative glypican-3, binds to and inhibits the dipeptidyl peptidase activity of CD26

Simpson-Golabi-Behmel syndrome (SGBS) is an X-linked condition shown to be the result of deletions of the glypican-3 (GPC3) gene. GPC3 is a proteoglycan localized to the cell membrane via a glycosylphosphatidyl-inositol (GPI) anchor. To further elucidate the GPC3 function(s), we have screened various cell lines for proteins that interact with GPC3, resulting in the isolation of a 115 kDa protein, identified as CD26. The interaction occurred with both the glycosylated and unglycosylated forms of GPC3 and led to the inhibition of CD26 peptidase activity. Moreover, introduction of CD26 into Cos-1 cells was accompanied by the up-regulation of cell growth, while inclusion of recombinant GPC3 in the media reduced the growth of CD26 transfected Cos-1 cells, drastically. Furthermore, HepG2 C3A cells containing CD26 underwent apoptosis in the presence of recombinant GPC3 in both concentration and time-dependant manner. In light of the fact that inhibition of CD26 reduces the rate of cell proliferation, we propose that a number of physical findings observed in SGBS patients may be a consequence of a direct interaction of GPC3 with CD26. Furthermore, GPC3 without the GPI anchor is capable of inducing apoptosis indicating that neither the GPI anchor nor the membrane attachment is required for apoptosis induction.

Clinical and molecular studies on two further families with Simpson-Golabi-Behmel syndrome

The Simpson-Golabi-Behmel syndrome (SGBS) (OMIM 312870) is an overgrowth/multiple congenital anomalies syndrome caused by a semi-dominant X-linked gene encoding glypican 3 (GPC3). It shows great clinical variability, ranging from mild forms in carrier females to lethal forms with failure to thrive in males. The most consistent findings in SGBS are pre- and postnatal macrosomia, characteristic facial anomalies and abnormalities affecting the internal organs, skeleton, and on some occasions, mental retardation of variable degree. SGBS is also associated with an increased risk of developing embryonal tumors, mostly Wilms and liver tumors. We describe two molecularly-confirmed families with SGBS. All patients had typical manifestations of SGBS including some female relatives who had minor manifestations of the disorder. Some patients had novel findings such as a deep V-shaped sella turcica and six lumbar vertebrae. Molecular studies in affected patients showed a deletion of exon 6 in family 1 and an intronic mutation in family 2.

Somatic glypican 3 (GPC3) mutations in Wilms' tumour

Tumour and normal tissue from 41 male cases of Wilms' tumour were screened to determine the presence of sequence variants in the glypican 3 (GPC3) gene. Two non-conservative single base changes were present in tumour tissue only. These findings imply a possible role for GPC3 in Wilms' tumour development.

Linkage study in families with posterior helical ear pits and Wiedemann-Beckwith syndrome

The Wiedemann-Beckwith syndrome (WBS) is defined by a group of anomalies, including macrosomia, macroglossia, omphalocele, and ear creases. Several minor anomalies have also been reported in the syndrome, including posterior helical ear pits (PHEP). Two independent linkage studies of pedigrees with autosomal dominant inheritance have shown linkage of WBS to 11p15.5 markers. Further confirming the location of WBS to this location is the finding of 11p15.5 duplications and translocations, as well as uniparental disomy for a small area of 11p15.5. In this study, members of previously described families exhibiting autosomal dominant inheritance of the PHEP phenotype were genotyped for three markers in the 11p15.5 region. These three markers were in the insulin-like growth factor (IGF2), insulin (INS), and tyrosine hydroxylase (TH) region. The data were examined by linkage analysis using the same genetic model used previously to demonstrate linkage of WBS to markers on chromosome 11p15.5: an autosomal dominant model with a penetrance of 0.90 and a gene frequency of 0.001. In one large pedigree, linkage analysis of the 11p15.5 markers excluded the PHEP phenotype from the IGF2, INS, and TH region. In the four other pedigrees examined, the marker loci were not sufficiently informative or the pedigrees did not provide sufficient power to exclude linkage from this region. The strongest evidence against linkage of the PHEP phenotype to 11p15.5 was evident by inspection of the segregation of the haplotypes of the markers in the pedigrees. In two informative pedigrees, relatives with the PHEP phenotype did not share the same haplotype of markers identical by descent. Our results show that the PHEP phenotype is not linked to chromosome 11p15.5 in the informative families tested. In the families examined, there are not enough individuals with WBS to determine if WBS was linked to 11p15.5 in these families. Although locus heterogeneity has not been demonstrated in WBS, it is possible that a second WBS locus exists and that the PHEP phenotype in these families is linked to a second WBS locus. Alternatively, the PHEP phenotype may occur independently of WBS so that the association of WBS and PHEP in our pedigrees may, in fact, represent causal heterogeneity.

Simpson Golabi Behmel syndrome: progress toward understanding the molecular basis for overgrowth, malformation, and cancer predisposition

Simpson Golabi Behmel syndrome (SGBS) is a complex congenital overgrowth syndrome with features that include macroglossia, macrosomia, and renal and skeletal abnormalities as well as an increased risk of embryonal cancers. Most cases of SGBS appear to arise as a result of either deletions or point mutations within the glypican-3 (GPC3) gene at Xq26, one member of a multigene family encoding for at least six distinct glycosylphophatidylinositol-linked cell surface heparan sulfate proteoglycans. As a class of molecules, heparan sulfate proteoglycans have been found to play essential roles in development by modulating cellular responses to growth factors and morphogens. Specifically, mutations in both the murine GPC3 gene and the Drosophila glypican, dally, have been found to modify cellular responses to bone morphogenetic proteins, providing important clues to the molecular basis of SGBS in humans. Despite these advances, there remains a paucity of information about the natural history of SGBS and optimal medical management strategies, and whether select mutations influence the SGBS phenotype and risk of cancer. To this end, an International SGBS Registry has been created and is being maintained to improve the clinical care and understanding of the pathogenesis of SGBS. Using an integrated approach employing epidemiology, molecular genetic characterization of specific GPC3 mutations, and the use of model organisms should rapidly expand the understanding of this complex disorder.

Mapping of a new SGBS locus to chromosome Xp22 in a family with a severe form of Simpson-Golabi-Behmel syndrome

Simpson-Golabi-Behmel syndrome (SGBS) is an X-linked overgrowth syndrome with associated visceral and skeletal abnormalities. Alterations in the glypican-3 gene (GPC3), which is located on Xq26, have been implicated in the etiology of relatively milder cases of this disorder. Not all individuals with SGBS have demonstrated disruptions of the GPC3 locus, which raises the possibility that other loci on the X chromosome could be responsible for some cases of this syndrome. We have previously described a large family with a severe form of SGBS that is characterized by multiple anomalies, hydrops fetalis, and death within the first 8 wk of life. Using 25 simple tandem-repeat polymorphism markers spanning the X chromosome, we have localized the gene for this disorder to an approximately 6-Mb region of Xp22, with a maximum LOD score of 3.31 and with LOD scores <-2.0 for all of Xq. These results demonstrate that neither the GPC3 gene nor other genes on Xq26 are responsible for all cases of SGBS and that a second SGBS locus resides on Xp22.

A small interstitial deletion in the GPC3 gene causes Simpson-Golabi-Behmel syndrome in a Dutch-Canadian family

Deletions in the heparan sulphate proteoglycan encoding glypican 3 (GPC3) gene have recently been documented in several Simpson-Golabi-Behmel syndrome (SGBS) families. However, no precisely defined SGBS mutation has been published. We report here a 13 base pair deletion which causes a frameshift and premature termination of the GPC3 gene in the Dutch-Canadian SGBS family in whom the trait was originally mapped. Our analysis shows that a discrete GPC3 disabling mutation is sufficient to cause SGBS. Furthermore, our finding of a GPC3 normal daughter of an SGBS carrier with skeletal abnormalities and Wilms tumour raises the possibility of a trans effect from the maternal carrier in SGBS kindreds.

Clinical and molecular aspects of the Simpson-Golabi-Behmel syndrome

The Simpson-Golabi-Behmel syndrome (SGBS) is an overgrowth/multiple congenital anomalies/dysplasia syndrome caused by a mutant X-linked gene. The spectrum of its clinical manifestations is broad, varying from very mild forms in carrier females to infantile lethal forms in affected males. A typically affected male will show tall stature, "coarse" face, supernumerary nipples, congenital heart defect, and generalized muscular hypotonia. Mental development is normal in most cases. There is an increased risk of neoplasia in infancy, especially Wilms tumor. The SGBS gene spans 500 kilobases in the Xq26 region and contains eight exons. It encodes an extracellular proteoglycan, designated glypican 3 (GPC3), capable of interacting with the insulin-like growth factor IGF2. At present, only deletions of various sizes have been found in a number of affected families.

A patient with Simpson-Golabi-Behmel syndrome and hepatocellular carcinoma

Simpson-Golabi-Behmel syndrome (SGBS) is an X linked disorder characterised by pre- and postnatal overgrowth, coarse facial features, and visceral and skeletal abnormalities. Like other overgrowth syndromes, in the SGBS there is an increased risk for developing neoplasia, mainly embryonic, such as Wilms tumour. We report a 3 year old male patient with SGBS and hepatocellular carcinoma, a previously undescribed tumour associated with the syndrome.

Simpson-Golabi-Behmel syndrome: genotype/phenotype analysis of 18 affected males from 7 unrelated families

Simpson-Golabi-Behmel syndrome (SGBS) is an X-linked overgrowth disorder recently shown to be caused by mutations in the heparan sulfate proteoglycan GPC3 [Pilia et al., Nat Genet; 12:241-247 1996]. We have used Southern blot analysis and polymerase chain reaction amplification of intra-exonic sequences to identify four new GPC3 mutations and further characterize three previously reported SGBS mutations. De novo GPC3 mutations were identified in 2 families. In general, the mutations were unique deletions ranging from less than 0.1 kb to more than 300 kb in length with no evidence of a mutational hot spot discerned. The lack of correlation between the phenotype of 18 affected males from these 7 families and the location and size of the GPC3 gene mutations suggest that SGBS is caused by a nonfunctional GPC3 protein.

Molecular biology of Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome associated with a predisposition to embryonal tumors, most commonly Wilms' (WT). Overlapping clinical phenotypes are seen in two other disorders, Simpson-Golabi-Behmel syndrome (SGBS) and Perlman syndrome (PS). BWS is a genetically heterogeneous disorder most often associated with normal chromosomes and a negative family history. However, autosomal dominant transmission of BWS is reported, as are chromosome 11p15.5 abnormalities, uniparental paternal disomy (UPD) of chromosome 11p15.5, and altered expression of the imprinted gene insulin-like growth factor 2 (IGF2) from the normally repressed maternal allele. Crucial to our understanding of the large variety of genetic presentations in BWS is the concept of genomic imprinting, a process in which gene expression specific to parent-of-origin is observed. The current genetic and molecular data for BWS are best explained by a model assuming an imprinted domain for 11p15.5, whereby altered expression of one or more genes in this region contributes to the BWS phenotype. In this model, a defined chromatin structure is reflected in coordinated control of multiple genes in the domain, as well as specific patterns of replication timing and gene expression. Data supporting this viewpoint include the maternally derived 11p15.5 translocation breakpoints associated with BWS, and the recent finding that the normally asynchronous pattern of replication timing for the imprinted gene IGF2 can be disrupted, shifted by a BWS-associated translocation 400 kh from IGF2. As we unravel the molecular basis of the different BWS patient subgroups, we will achieve a better understanding of this overgrowth syndrome and its relationship to WT.

Mutations in GPC3, a glypican gene, cause the Simpson-Golabi-Behmel overgrowth syndrome

Simpson-Golabi-Behmel syndrome (SGBS) is an X-linked condition characterized by pre- and postnatal overgrowth with visceral and skeletal anomalies. To identify the causative gene, breakpoints in two female patients with X;autosome translocations were identified. The breakpoints occur near the 5' and 3' ends of a gene, GPC3, that spans more than 500 kilobases in Xq26; in three families, different microdeletions encompassing exons cosegregate with SGBS. GPC3 encodes a putative extracellular proteoglycan, glypican 3, that is inferred to play an important role in growth control in embryonic mesodermal tissues in which it is selectively expressed. Initial western- and ligand-blotting experiments suggest that glypican 3 forms a complex with insulin-like growth factor 2 (IGF2), and might thereby modulate IGF2 action.

Infantile lethal variant of Simpson-Golabi-Behmel syndrome associated with hydrops fetalis

Simpson-Golabi Behmel syndrome (SGBS) is an X-linked disorder characterized by pre- and postnatal macrosomia, minor facial anomalies, and variable visceral, skeletal, and neurological abnormalities. Since its first description by Simpson et al. [1975: BD:OA XI(2):18-24], a wide clinical range of cases has been reported. There is great variability in severity, ranging from a mild form associated with long-term survival to an early lethal form with multiple congenital anomalies and severe mental retardation. In 8 reported families, affected individuals died in infancy. Here we present 4 maternally related, male cousins with a severe variant of SGBS. One of these males was aborted therapeutically at 19 weeks of gestation following the detection of multicystic kidneys on ultrasound. The 3 liveborn males were hydropic at birth with a combination of craniofacial anomalies including macrocephaly; apparently low-set, posteriorly angulated ears; hypertelorism; short, broad nose with anteverted nares; large mouth with thin upper vermilion border; prominent philtrum; high-arched or cleft palate; short neck; redundant skin; hypoplastic nails; skeletal defects involving upper and lower limbs; gastrointestinal and genitourinary anomalies. All 3 patients were hypotonic and neurologically impaired from birth. With the exception of a trilobate left lung in one patient, the cardiorespiratory system was structurally normal. All patients died within the first 8 weeks of life of multiple complications including pneumonia and sepsis. Two SGBS kindreds, with moderate expression of the condition, have been mapped to Xq27. It is not known whether severe, familial cases, such as ours, are genetically distinct from and map to another locus. Final resolution of the genetic basis of the phenotypic variability in SGBS must await cloning and mutation analysis of the SGBS gene(s).

Finding genes involved in human developmental disorders

Recent advances in the human genome initiative have accelerated positional cloning efforts toward identification of a number of genes responsible for human developmental anomalies, particularly those involving the skeletal system. Genotype/phenotype comparison and functional analysis of these genes will further elucidate pathways of normal and abnormal human development of the skeletal and other organ systems.