Mutation analysis of the APC gene in unrelated Korean patients with FAP: four novel mutations with unusual phenotype.

Germline mutations within the adenomatous polyposis coli (APC) gene are responsible for most cases of familial adenomatous polyposis (FAP), an autosomal dominantly inherited predisposition to colorectal cancer. To date more than 900 different APC germline mutations have been characterized worldwide demonstrating allelic heterogeneity. Here, we analyzed the APC gene in 23 DNA samples from unrelated Korean patients with the typical clinical symptoms of FAP by denaturing high-performance liquid chromatography (DHPLC) and direct sequencing. We identified 20 different APC sequence variants, including 9 truncating mutations, 1 missense mutation, 7 polymorphisms, and 3 intronic variants. Nine different truncating mutations, including four novel mutations (p.Leu180TyrfsX5, p.Gly567X, p.Ser1275PhefsX13, p.Leu1280CysfsX8), were detected. The most common mutation was a 5 bp deletion at codon 1,309 (p.Glu1309AspfsX4) as in Western studies. The next most common mutation was p.Ser1275PhefsX13 with a severe form of FAP with many extracolonic manifestations; this was a novel mutation identified in our study and may represent the second hot-spot mutation in a Korean population. Novel mutations are of particular interest because of the unusual phenotypic features shown by patients. In present study, we found new positions associated with thyroid cancer (codon 180) and desmoid tumor (codon 1,280), which have not been previously reported. The results of this molecular study have revealed the existence of novel pathogenic mutations in Korean patients with FAP. In addition to allowing phenotype-genotype correlations to be performed, these results are currently being used in genetic counseling and in patient care.

Carrier frequency of GJB2 (connexin-26) mutations causing inherited deafness in the Korean population.

Mutations in the GJB2 gene are associated with hereditary hearing loss. Although most studies of GJB2 mutations have dealt with hearing-impaired patients, there are few reports of the frequency of these mutations in the general population. The purpose of this study is to evaluate the prevalence of GJB2 mutations causing inherited deafness in the general Korean population. Blood samples were obtained from 2,072 newborns with normal hearing. The dried blood samples were subjected to PCR to amplify the entire coding region of the GJB2 gene, which was followed by direct DNA sequencing. A total of 24 different sequence variants were identified in the coding region of GJB2, including eight pathogenic mutations (p.V37I, p.G45E, p.R143 W, c.176_191del16, c.235delC, c.292_298dup7, c.299_300delAT and c.605ins46), four polymorphisms (p.V27I, p.E114G, p.G160S and p.I203T), six unclassified variants (p.G4D, p.S85Y, p.T123 N, p.R127H, p.A171T and p.F191L) and six novel variants (p.W3T, p.I20L, p.K41E, c.147C > T, c.186C > T and c.576A > G). Pathogenic mutations causing inherited deafness were identified in 3% (62/2,072) of the newborns with normal hearing. Of the eight pathogenic mutations found, p.V37I was the most common (1.35%, 28/2,072), followed by c.235delC (1.25%, 26/2,072). These data provide information about carrier frequency for GJB2-based hearing loss and have important implications for genetic diagnostic testing for inherited deafness in the Korean population.