High prevalence of V37I genetic variant in the connexin-26 (GJB2) gene among non-syndromic hearing-impaired and control Thai individuals.

Hearing loss is highly prevalent with a worldwide incidence of 1-2 per 1000 newborns. Several previous studies have demonstrated that mutations of connexin 26 (Cx26 or GJB2) are responsible for most cases of the recessive non-syndromic sensorineural hearing loss (NSSHL). Certain mutations have been described frequently among various populations, which include 35delG, 167delT, and 235delC. Recently, a missense mutation, V37I, was reported as a pathogenic change in East Asian affected individuals. To identify genetic variants associated with NSSHL in Thai population, we performed mutation analysis of Cx26 in 166 unrelated probands with NSSHL and 205 controls. We identified seven novel genetic variants in Cx26. We also identified a high prevalence of the V37I mutation among both affected probands (11.1%) and control subjects (8.5%), which suggests that the pathologic role of V37I may be modified by other genes. Our data support previous studies that show heterogeneity in the frequencies and types of mutations in Cx26 within populations and among ethnicities and that before clinical significance and causality can be attributed to a genetic variant, functional characterization is necessary.

Molecular defect of PKD1 gene resulting in abnormal RNA processing in a Thai family.

Autosomal dominant polycystic kidney disease (ADPKD) is a common human autosomal disorder caused mainly by mutations of the PKD1 gene. In analysis of PKD1 transcripts by long RT-PCR and nested PCR procedures, we observed PKD1-cDNA fragments from three ADPKD siblings from the same family with a size approximately 250 base pairs (bp) shorter than normal. Further investigations showed that the PKD1 transcripts from these patients had been abnormally processed, the nucleotide sequence of exon 43 containing 291 nt was missing from the transcripts, which would result in an abnormal polycystin-1 with an in-frame deletion of 97 amino acids. This splicing defect did not result from a mutation that disrupted the splice donor or acceptor sites adjacent to exon 43 or the branch sites in flanking introns but was most likely due to 20-bp deletion observed in intron 43. The intronic deletion was present in 8 affected members but absent in 11 unaffected members, corresponding with the results of genetic linkage analysis using 5 polymorphic markers in the PKD1 region. Molecular diagnosis of PKD1 in this family could, therefore, be carried out by genomic DNA amplification to directly detect the PKD1 intronic deletion.

Long RT-PCR Amplification of the entire coding sequence of the polycystic kidney disease 1 (PKD1) gene.

Characterization of mutations of the PKD1 gene has been limited by the fact that three-fourths of this gene at its 5' end is homologous to sequences of at least three other genes on the same chromosome. We have therefore developed a method of long reverse transcription PCR for selective amplification of the entire coding sequence of the PKD1 gene from its mRNA. A PCR primer specific to the sequence in the 3' unique region of the PKD1 gene was synthesized for use coupled with a primer binding to sequence in the homologous region at a distance of about 13.6 kb apart. The commercial availability of RNase H-free reverse transcriptase for long cDNA synthesis and of an enzyme mixture containing Taq and Pfu DNA polymerases for long-range PCR have made this development possible. The long PCR product was proven to be derived from PKD1-mRNA. The results clearly indicated that the long PCR product contained the coding sequence derived from PKD1-mRNA. To our knowledge, this is the first report of a procedure that can reproducibly isolate full-length PKD1 coding sequence from its mRNA transcript, which will prove useful for screening and characterization of mutations in the PKD1 gene.