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.

Cardiac anomalies in the Simpson-Golabi-Behmel syndrome.

Diverse cardiac abnormalities have been reported in patients with the Simpson-Golabi-Behmel syndrome (SGBS), and it is suspected that they are related to the apparently high incidence of early death. To clarify the incidence and significance of the various cardiac abnormalities, we reviewed 101 SGBS patients (89 from the literature, 12 new). All were male, except for one clearly affected female patient with translocation X;1 [Punnett, 1994: Am J Med Genet 50: 391-393]. Ninety-six of 99 (97%) patients had the classic phenotype of macrosomia and typical "coarse" face. Thirty-six patients (36%) had a cardiac abnormality, of whom 26 (26%) had a cardiovascular malformation (CVM). After excluding 24 patients with insufficient clinical data, these percentages among the 77 informative cases were 47% and 34%, respectively. When grouped according to a mechanistic classification, most cases (20/ 26, or 77%) were class II CVMs (attributed to altered embryonic intracardiac flow). Other cardiac abnormalities included cardiomyopathy (n = 4) and electrocardiogram (ECG) conduction or rhythm abnormalities (n = 12); three of the affected patients (25%) also had a CVM. Among 92 informative cases, there were 29 (32%) deaths, a figure that excludes seven elective terminations. Among the 25 patients younger than 3 years, death was associated with a cardiac abnormality in six (23%). GPC3 mutation analysis using Southern blot testing and polymerase chain reaction amplification was performed for 37 of 101 (37%) patients. A mutation was detected in 26 of the 37 patients tested (70%), 12 of whom (46%) had a cardiac abnormality. We conclude that cardiac abnormalities of any type are common in SGBS (almost one-half of informative cases), with CVMs seen in one-third of cases. The heterogeneous ECG abnormalities in this survey must be viewed with caution, since they may represent a genuine component of the syndrome or reporting bias. Determining the true prevalence and natural history of cardiac abnormalities in SGBS will require a larger number of patients and more consistent prospective cardiac evaluations. There are sufficient data to recommend a baseline echocardiogram and ECG in SGBS patients. Data are insufficient to define a cardiac phenotype/molecular correlation.

Simpson-Golabi-Behmel syndrome associated with renal dysplasia and embryonal tumor: localization of the gene to Xqcen-q21.

We report 6 affected males in a 5-generation family with x-linked Simpson-Golabi-Behmel (SGB) syndrome. All had pre- and postnatal overgrowth with 2 adult males attaining heights over 195 cm. Other features included "coarse" face with hypertelorism, broad nasal root, cleft palate, full lips with a midline groove of the lower lip, grooved tongue with tongue tie, prominent mandible, congenital heart defects, arrhythmias, supernumerary nipples, splenomegaly, large dysplastic kidneys, cryptorchidism, hypospadias, skeletal abnormalities and postaxial hexadactyly. All affected individuals were of normal intelligence. One boy died at age 19 months of a neuroblastoma. The putative origin of the gene in this family was the maternal great grandmother of the propositus. Eight carrier females, who showed varying manifestations of the gene, have been identified. Anthropometric analysis has identified preliminary characteristic craniofacial dimensions in this syndrome. Molecular studies have shown a maximal lod score of 2.81 with no recombinants observed for the SGB-DXYS68 pairing, mapping the disorder to Xqcen-Xq21.3.

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.

Ultrasonographic measurements of fetal ear.

OBJECTIVE: To establish nomograms of fetal ear measurements. Newborns with trisomies have smaller ears than the normal population. This observation led us to believe that ear measurements might be useful in the antenatal prediction of fetuses with abnormal karyotypes. METHODS: Fetal ear length and width were obtained ultrasonographically in 124 normal singleton pregnancies between 18-42 weeks' gestation. Regression analyses were used to create the nomograms. RESULTS: Linear relationships were found between ear length and width and gestational age (r = 0.956 and 0.898, respectively). In addition, there were significant correlations between ear measurements and biparietal diameter, head circumference, abdominal circumference, and femur length. The ear width-length ratio and the biparietal diameter-ear length ratio were independent of gestational age. CONCLUSION: These normative data may be helpful in the antenatal prediction of chromosomal abnormalities.

Ocular findings in acromesomelic dysplasia.

We examined an infant who had prenatal onset of a skeletal dysplasia that had many features in common with acromesomelic dysplasia, including the clinical and light and electron microscopic findings of both corneas. Successful lamellar keratoplasty was performed on the left eye when histologic examination of the corneal button from the right eye showed that the corneal scar was only of partial thickness.

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

Simpson-Golabi-Behmel syndrome (SGBS) is an X-linked gigantism syndrome characterized primarily by a coarse facies and somatic overgrowth which we have observed to be associated with an increased risk for embryonal tumors. Genetic linkage analysis for two SGBS kindreds in which X linked dominant inheritance was observed has been conducted for the X chromosome. The closest linkage to SGBS was observed for the Xq26 locus HPRT (Z max = 7.45, theta max = 0.00). SGBS-Xq marker recombinations map the disease locus to the DXS425-DXS1123 interval on Xq25-q27. This maps the disease locus to a region known to contain a previously characterized chromosomal translocation breakpoint found in a young girl with somatic overgrowth. This observation may have implications for the cloning of the SGBS gene.

Simpson-Golabi-Behmel syndrome: disproportionate fetal overgrowth and elevated maternal serum alpha-fetoprotein.

Simpson-Golabi-Behmel (SGB) syndrome is an X-linked condition with pre- and postnatal overgrowth, characteristic facies, and visceral and skeletal anomalies. We report an affected male who presented at 16 weeks' gestation with elevated maternal serum alpha-fetoprotein (MSAFP). Fetal measurements at 20 and 31 weeks' gestation were disproportionate, with marked macrosomia but a low head to abdominal circumference ratio and normal femur length. Fetal overgrowth with elevated MSAFP may prove to be useful markers for the prenatal diagnosis of SGB syndrome.

The role of reduced ear size in the prenatal detection of chromosomal abnormalities.

A prospective ultrasound study was performed between 18 and 38 weeks' gestation on 29 fetuses in a high-risk population, defined by the presence of structural anomalies, in order to investigate the usefulness of fetal ear measurements in the prenatal prediction of chromosomal abnormality. The prevalence of abnormal chromosomes was 34 per cent. The sensitivity (SE), specificity (SC), positive predictive values (PPV), and negative predictive values (NPV) of ear length for the detection of chromosomal abnormality were 80, 84.2, 72.7 and 88.9 per cent. The SE, SC, PPV, and NPV of ear width were 40, 94.7, 80 and 75 per cent. Fetal ear measurements may be a useful adjunct to the various ultrasound parameters in the prenatal detection of chromosome abnormality in a high-risk population of fetuses with structural anomaly(ies).

The Aicardi-Goutières syndrome (familial, early onset encephalopathy with calcifications of the basal ganglia and chronic cerebrospinal fluid lymphocytosis).

Aicardi-Goutières syndrome (Mendelian inheritance in man Catalog No *225750) is an autosomal recessive encephalopathy which causes developmental arrest, intracerebral calcification, and white matter disease in the presence of chronic cerebrospinal fluid lymphocytosis, and a raised level of cerebrospinal fluid interferon-alpha (IFN-alpha). Diagnosis requires the presence of progressive encephalopathy with onset shortly after birth, and characteristic clinical neurological and neuroimaging signs together with chronic CSF lymphocytosis. The syndrome has superficial resemblance to the neurological sequelae of congenital infection, thus a rigorous search for microbiological and serological evidence of embryopathic infections should be carried out in each case.

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.

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.

Markedly increased tissue concentrations of 7-dehydrocholesterol combined with low levels of cholesterol are characteristic of the Smith-Lemli-Opitz syndrome.

The Smith-Lemli-Opitz syndrome is an autosomal recessive birth defect (frequency 1:20,000-1:40,000) that results in profound mental retardation, physical deformities, and failure to thrive. It is characterized biochemically by low plasma cholesterol and greatly elevated levels of two dehydrocholesterols, one of which is the cholesterol precursor 7-dehydrocholesterol. To determine whether the block in cholesterol biosynthesis affects tissue sterols, we assayed several organs from two affected individuals, a female who died at 27 hours and a 20-week male fetus. Cholesterol concentrations in abdominal wall, adrenal gland, and kidney from two or three unaffected fetuses, who served as controls, averaged 2.0, 1.5, and 1.4 mg/g wet weight, compared to 0.08, 0.44, and 0.14, respectively, for the homozygous fetus. Cerebral cortex cholesterol concentrations were 2.2 mg/g for two 20-22-week fetal controls but only 0.21 and 0.09 mg/g, respectively, for the homozygous child and fetus. Similarly, tissue cholesterol levels were abnormally low in the homozygous child being less than 1 mg/g in liver, adipose, thymus, muscle, and adrenal and 6.2 mg/dl in plasma. Dehydrocholesterols could not be detected by conventional means in any controls but were elevated enough in tissues from affected individuals to make total sterol concentrations nearly normal. These results suggest that a defect in 3 beta-hydroxysterol delta 7-reductase leads to both a profound lack of cholesterol and its replacement by dehydrocholesterols. Such a combination may be lethal in the most severely affected individuals.

How interested is the public in genetic testing for colon cancer susceptibility? Report of a cross-sectional population survey.

OBJECTIVE: To assess the public's interest in genetic testing for colon cancer susceptibility, to determine whether provision of information about the accuracy of the test or the population risk of inheriting the colon cancer gene influences interest, to determine the reasons for wanting to be tested and to identify the factors related to interest in testing. DESIGN: A cross-sectional random digit dialing telephone survey of 501 adults. SETTING: Ontario. MAIN OUTCOME MEASURES: Proportion of the public interested in genetic testing; reasons for interest in testing. RESULTS: Of the sample, 39.9% (95% confidence interval [CI] 35.5 to 44.3) stated that they would be very interested in taking a simple blood test if a positive result suggested they had an 80% chance of getting colon cancer sometime during their lifetime. When it was suggested that the test might be accurate only 90% of the time, 33.1% of the sample (95% CI 28.7 to 37.5) still said they would be very interested in testing. When informed that less than 1% of the population inherits the gene for colon cancer, the proportion of the sample stating they would still be very interested in genetic testing fell to 19.2% (95% CI 14.8 to 23.6). The main reasons given for wanting genetic testing were to take preventive action, for peace of mind and curiosity. For respondents who remained interested in testing after being given information about the population risk of inheriting the gene, 2 factors were identified by logistic regression analysis as being independently related to interest: worry about cancer and perceived risk of getting colon cancer. CONCLUSIONS: If the public's interest in testing for colon cancer susceptibility has any influence on its eventual request to be tested, then demand for genetic testing may be considerable once such tests become widely available and known to the public. This study reveals that the public's interest in genetic testing is substantial, although modifiable by the provision of information about the population risk of inheriting a colon cancer gene. This finding suggests that genetic researchers and others should be careful to provide the population risk of inheriting cancer genes when discussing the discovery of these genes with the media. Furthermore, public health educators will need to ensure that information aids include material on familial risk criteria, genetic counselling and genetic testing, as well as on the implications of genetic testing, the general population risk of developing colon cancer and the general population risk of carrying the colon cancer gene. This information should also be provided to those who seek assessment, to health care professionals and to the public.