Fung Ki Wong

Birt-Hogg-Dubé syndrome: mapping of a novel hereditary neoplasia gene to chromosome 17p12-q11.2

Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant neoplasia syndrome characterized mainly by benign skin tumors, and to a lesser extent, renal tumors and spontaneous pneumothorax. To map the BHD locus, we performed a genome-wide linkage analysis using polymorphic microsatellite markers on a large Swedish BHD family. Evidence of linkage was identified on chromosome 17p12-q11.2, with a maximum LOD score of 3.58 for marker D17S1852. Further haplotype analysis defined a ∼35 cM candidate interval between the two flanking markers, D17S1791 and D17S798. This information will facilitate the identification of the BHD gene, leading to the understanding of its underlying molecular etiology.

Mapping of the second locus for the Van der Woude syndrome to chromosome 1p34

The Van der Woude syndrome (VWS) is a dominantly inherited developmental disorder characterized by pits and/or sinuses of the lower lip, cleft lip and/or cleft palate. It is the most common cleft syndrome. VWS has shown remarkable genetic homogeneity in all populations, and so far, all families reported have been linked to 1q32-q41. A large Finnish pedigree with VWS was recently found to be unlinked to 1q32-q41. In order to map the disease locus in this family, a genome wide linkage scan was performed. A maximum lod score of 3.18 was obtained with the marker D1S2797, thus assigning the disease locus to chromosomal region 1p34. By analyses of meiotic recombinants an ∼30 cM region of shared haplotypes was identified. The results confirm the heterogeneity of the VWS syndrome, and they place the second disease locus in 1p34. This finding has a special interest because the phenotype in VWS closely resembles the phenotype in non-syndromic forms of cleft lip and palate.

Association of a novel constitutional translocation t(1q;3q) with familial renal cell carcinoma

Four cases of late onset clear cell renal cell carcinoma (RCC), a case of gastric cancer, and a case of exocrine pancreatic cancer were identified in a Japanese family. In order to elucidate the underlying mechanism for tumorigenesis in this family, extensive genetic studies were performed including routine and spectral karyotyping (SKY), fluorescence in situ hybridisation (FISH), comparative genomic hybridisation (CGH), loss of heterozygosity studies (LOH), andVHL mutation analysis. A germline translocation t(1;3)(q32-q41;q13-q21) was identified by karyotyping in five members of the family including all three RCC cases tested. The translocation was refined to t(1;3)(q32;q13.3) by FISH analysis using locus specific genomic clones, and the two breakpoints were mapped to a 5 cM region in 3q13.3 and a 3.6 cM region in 1q32. Both CGH and allelotyping using microsatellite markers showed loss of the derivative chromosome 3 carrying a 1q segment in the three familial RCCs analysed. Additional chromosomal imbalances were identified by CGH, including amplifications of chromosomes 5 and 7 and loss of 8p and 9. No germlineVHL mutation was found but two different somatic mutations, a splice (IVS1-2A>C) and a frameshift (726delG), were identified in two RCCs from the same patient confirming their distinct origin.Taken together, these results firmly support a three step model for tumorigenesis in this family. A constitutional translocation t(1q;3q) increased the susceptibility to loss of the derivative chromosome 3 which is then followed by somatic mutations of the RCC related tumour suppressor gene VHLlocated in the remaining copy of chromosome 3.

Sporadic follicular thyroid tumors show loss of a 200-kb region in 11q13 without evidence for mutations in the MEN1 gene.

Loss of heterozygosity (LOH) in 11q13 where the tumor suppressor gene for multiple endocrine neoplasia type 1 (MEN 1) is located has been demonstrated in several tumor types, including follicular thyroid tumors, but whether the MEN1 gene is actually involved in their tumorigenesis is not known. In the present study, the involvement of the MEN1 gene in follicular thyroid tumors was investigated. By using 14 MEN1‐linked microsatellite markers, LOH was demonstrated in 12 out of 60 follicular thyroid tumors: 2/18 adenomas, 4/15 atypical adenomas, 1/6 Hürthle cell adenomas, 1/9 carcinomas, 3/6 Hürthle cell carcinomas, and 1/6 anaplastic carcinomas. In the tumors with LOH, a single minimal region of overlapping deletions was mapped to the 200‐kb interval between D11S4946 and D11S4939. Tumors that showed 11q13 LOH were screened for mutations of the MEN1 gene using single‐strand conformation analysis. Abnormal shifts detected in seven tumors in two exons were sequenced, which revealed two different polymorphisms present in both tumor and constitutional DNA, but without somatic mutation. Taken together, these results suggest that in this region, a tumor suppressor gene other than MEN1 might be involved in the tumorigenesis of follicular thyroid tumors. Genes Chromosomes Cancer 26:35–39, 1999.

Linkage Analysis of Candidate Regions in Swedish Nonsyndromic Cleft Lip with or without Cleft Palate Families

OBJECTIVE To analyze linkage of five candidate regions for nonsyndromic cleft lip with or without palate (CLP) on chromosome 2p13, 4q, 6p23, and 19q13; in addition chromosome 1q32, the locus for van der Woude syndrome, on Swedish CLP families. DESIGN Three to five linked microsatellite markers were selected from each candidate region. Polymerase chain reaction (PCR) with fluorescent-labeled microsatellite markers was performed on DNA samples from the participating families. Electrophoresis of the PCR products was performed on a laser-fluorescent DNA sequencer. The genotype data were analyzed with multipoint linkage analysis. Modes of inheritance tested included two autosomal dominant, an autosomal recessive, and a nonparametric model. Multipoint logarithm of odds (LOD) scores were also calculated by assuming genetic heterogeneity. PARTICIPANTS Nineteen Swedish multigenerational families with at least two first-degree relatives affected with CLP. Greater than 50% of the families studied show vertical transmission of the clefting phenotype and both inter- and intrafamilial variability were noted. RESULTS Cumulative multipoint LOD scores for the whole group of families calculated under autosomal dominant modes of inheritance were negative in all regions and less than -2 except chromosome 6p23. LOD scores calculated under recessive inheritance and the nonparametric model were inconclusive. There was no significant evidence of genetic heterogeneity among the sample group. CONCLUSIONS The group of Swedish CLP families did not demonstrate significant linkage to any of the five candidate regions examined. This might suggest a new but yet unknown CLP locus or loci in this family group. However, because linkage could not be excluded in some individual families, they should still be tested with candidate genes from these regions.

Clinical and genetic studies of Van der Woude syndrome in Sweden.

Van der Woude syndrome (VWS) is an autosomal dominant craniofacial disorder characterized by pits of the lower lip, hypodontia and cleft lip and/or cleft palate. It has been reported as the most common form of syndromic orofacial clefting with very high penetrance and varied expressivity. The disease locus for VWS has been mapped to chomosome 1q32, but the gene is yet to be cloned. Here we report a total of 11 Swedish VWS patients: 9 familial cases from two families and two isolated cases. Clinical examination of these patients showed phenotypic variability, even between patients from the same family. Genetic studies were performed using four microsatellite markers from chromosome 1q32. Constitutional deletion in this region was not demonstrated in any of the familial or isolated cases. However, in the two VWS families, linkage analysis using these markers showed positive LOD (logarithm of the odds) scores ranging from 2.56 to 2.88 to all individual markers. The highest LOD score of 3.75 was obtained with the combined haplotypes of D1S491 and D1S205, thus confirming linkage of VWS in these two families to 1q32. We conclude that there is varied expressivity but no evidence of genetic heterogeneity in VWS.

Popliteal pterygium syndrome in a Swedish family-clinical findings and genetic analysis with the van der Woude syndrome locus at 1q32-q41

The present study describes a Swedish family in which the mother and her son were affected with signs of popliteal pterygium syndrome (PPS, OMIM 119500). Both individuals had bilateral complete cleft lip and palate, oral synechiae, paramedian pits on the lower lip, toe syndactyly and a piece of triangular skin overgrowth on the great toes. The son also presented with soft tissue syndactyly of the 2nd and 3rd fingers. Although popliteal pterygium was not found, the above clinical features were diagnostic for PPS. Chromosomal abnormalities were not revealed in either case by cytogenetic analyses. A test for microdeletion in the VWS region at 1q32-q41 was performed in the family using 5 polymorphic microsatellite markers from the region. The affected son was found to be heterozygous for all 5 markers, suggesting that microdeletion at the VWS region was unlikely. The VWS locus, however, was not excluded by haplotype analysis of the family.

Serum apolipoprotein(a) concentrations and apo(a) phenotypes in patients with liver cirrhosis

Objective:The liver is the major site of apolipoprotein(a) synthesis, and an inverse correlation between the size of apolipoprotein(a) isoforms and its serum levels have been described. We evaluated the Apo(a) serum levels and its isoforms in patients with liver cirrhosis at different stages of the disease (Childe Turcotte classification), and during the characteristic phase of liver synthesis decline.Methods:We studied 84 patients with liver cirrhosis and 185 control subjects with normal liver function.Results:Apo(a) serum levels were significantly lower (p < 0.01) in cirrhotic patients and, after 24 months, six patients showing a change from class A to class B had a statistically significant decrease in Apo(a) concentrations (p= 0.0313). Moreover, our data showed an inversion of the small/large isoforms ratio in patient with cirrhosis in spite of the reduction in plasma concentration.Conclusion:We showed a reduction of Apo(a) serum concentrations in a large number of patients with cirrhosis and, for the first time, during the characteristic phase of liver synthesis decline, confirming the liver as the major site of Apoliprotein(a) synthesis. Moreover we showed in the cirrhotic patients that the normal correlation between Apo(a) isoforms and Apo(a) concentrations is not conserved and the low levels are not dependent upon a high prevalence of large isoforms.