RESUMEN
Background & objectives: Duchenne and Becker muscular dystrophies are X-linked allelic disorders which are caused by mutations in the DMD gene. Carrier analysis in DMD is complicated due to the heterozygous nature of the X chromosome. Several techniques have been tried for carrier analysis in families where the mutation is identified including quantitative multiplex PCR (qmPCR), Southern blot, and now multiplex ligation-dependent probe amplification (MLPA). Linkage analysis is used in cases without identifiable mutations. The present study was undertaken to determine the status of probable carriers in families where the DMD deletion/duplication has been identified for the affected index cases. Methods: Carrier status was present in 150 probable carriers from 110 apparently unrelated families where the patients’ mutations were known. Of these 110 families, 100 were deletions, 9 duplications and 1 point mutation. Multiplex ligation-dependent probe amplification (MLPA) was used to assess the copy number changes and direct sequencing was used for the case with the point mutation. Results: Of the 150 cases, 49 were found to be carriers. Among the sporadic cases, it was observed that the rate of de novo mutations was very high (71%) as compared to the hereditary cases (29%), which was higher than the calculated rate (30%). It was observed that this difference was more apparent in deletion mutations than in duplications. Interpretation & conclusions: Identifying the DMD carrier rates in the families with unidentified deletions and duplications and where the causative mutation could be small insertions/deletions or point mutations could throw more light into this observation. MLPA was found to be useful in detecting copy number changes in DMD carriers and this could be the method of choice for DMD carrier analysis, when the mutation is detected in the affected child.
RESUMEN
OBJECTIVE: Linkage analysis is a very useful method for prenatal diagnosis of Hemophilia B, especially when a mutation was not identified. Seven polymorphic markers were studied in Korean populations to evaluate the efficiency for prenatal and carrier diagnosis. METHODS: Subjects of this study was 100 healthy Korean women (200 X-chromosomes). Polymerase chain reacton-restriction fragment length polymorphism (PCR-RFLP) method was used to detect SalI, MseI, NruI, DdeI, XmnI, TaqI and HhaI polymorphisms. RESULTS: SalI (-) allele showed the frequency of 0.355 and SalI(+) allele 0.645. MseI(-) allele was 0.645 in frequency and MseI(+) allele was 0.355. SalI and MseI polymorphisms were in complete linkage disequilibrium. And no increase was expected in overall heterozygosity with these two polymorphisms. NruI(-) allele frequency was 0.855 and NruI(+) was 0.145. There was no polymorphism of DdeI, XmnI and TaqI marker systems in Korean population. In HhaI polymorphism, allele frequencies were estimated that HhaI(-) is 0.82 and HhaI(+) is 0.18. CONCLUSION: Only SalI, NruI and HhaI polymorphisms are useful for the diagnosis of hemophilia B in Korean population. Expected heterozygosity for above 3 poylmorphic markers was estimated to be 0.723, and 71 of 100 female subjects were heterozygous for at least one marker system. Korean population showed relatively low extent of polymorphisms compared to Caucasians, Blacks and Japanese. For the effective prenatal diagnosis of hemophilia B with linkage analysis, other polymorphic markers should be evaluated.