Mutation Analysis In330Chinese Cases With DMD/BMD And Genetic Analysis In A Fetus With Compound Heterozygous DMD Mutations

Background:Duchenne/Becker muscular dystrophy （DMD/BMD） are common X-linked recessive muscle disorders caused by mutations in the DMD gene. DMD, characterized by a rapidly progressive disease with an incidence of1in3,500male births, is a common and severe form of muscular dystrophy and onset in early childhood. Affected individuals commonly lose their ability to walk before12years old and often die of either cardiac or respiratory failure in their early20s. BMD, the milder and more variable form, has a slower progression. Affected boys, with later onset of muscle weakness, lose their ability to walk after the age of16years and may be almost asymptomatic in their lives. Because of the high incidence and the severity, DMD/BMD bring heavy mental and economic burden to the family and society. So far there is no effective clinical treatment. Gene diagnosis, genetic counseling and accurate prenatal diagnosis screen carriers are important to prevent the birth of children suffering from muscular dystrophy.Objective:1. To find mutations of DMD gene in330Chinese cases, and analyze characteristics of DMD gene mutations in Chinese DMD/BMD patients, investigate the relationship between genotype and phenotype of Chinese patients.2. To analyze mutations in a Chinese family with DMD and to perform prenatal genetic diagnosis for their current pregnancy.Methods:1. Mutation detecting of DMD gene in330Chinese cases was carried out by MLPA and direct sequencing.2. Eight intragenic short tandem repeat polymorphisms, STR-（CA）n, were analyzed, aimed at identifying the fetus inherited his maternal grandfather or grandmother’s DMD allele. MLPA and direct sequencing were used to detect mutations of DMD gene. And the X-chromosome inactivation pattern was determined by PCR analysis of the methylation status of the androgen-receptor （AR） locus.Results:1.300mutations in the DMD gene were identified in330Chinese cases, including201deletions （60.9%）,30duplications （9.1%） and69piont mutations （20.9%）. The detection rate was90.9%.89.2%（206/231） of deletion/duplication mutations fit with the reading-frame rule; among deletion mutations,183comply with the reading frame rule （91.0%）, and23duplication mutations comply with the reading frame rule （76.7%）.2. The fetus had two mutations of the DMD gene inherited from his healthy parents:a novel small deletions/insertion mutation c.1056₁058delinsTCAGAAGTGAAA and a deletion of exons50-51. And the X-chromosome inactivation pattern of the fetus was considered random pattern.Conclusions:1.300patients had a confirmed diagnosis of DMD/BMD based on genetic testing, and distribution characteristics of DMD gene in Chinese DMD/BMD patients are similar to global ethnic populations. The reading-frame rule can explain most of deletion/duplication mutations in Chinese DMD/BMD patients.2. The fetus had the two mutations, consistent with a compound heterozygous state. It was the second case with a compound heterozygous DMD mutation in the world. The novel small deletions/insertion mutation c.1056₁058delins TCAGAAGTGAAA causes a DMD phenotype, and a deletion of exons50-51causes an asymptomatic phenotype. And we could not predict whether the fetus would be affected by DMD.