Abstract: Background：There are significant differences in the prognosis, treatment and follow-up of Duchenne muscular dystrophy(DMD) and Becker muscular dystrophy(BMD). At present, there is still no consensus on the diagnosis of presymptomatic progressive muscular dystrophy(PMD) at home and abroad. Objective：To study the clinical and test results of pre symptomatic PMD in infants and analyze the accuracy of serum muscle enzyme level in distinguishing DMD and BMD. Design：Case series report. Methods：Children diagnosed with presymptomatic PMD at Jiangxi Children's Hospital between January 2016 to July 2020 were included in the study to have their clinical and test results of presymptomatic PMD analyzed. The DMD and BMD were distinguished by gene results. The maximum value of yoden index was taken as the diagnostic standard by ROC curve analysis. The consistency and accuracy of gene diagnosis and muscle enzyme diagnosis were compared. Main outcome measures：Clinical manifestations, gene results and serum enzyme(AST, ALT，LDH，CK，CK-MB). Results：The study collected 24 children with 18 cases of DMD and 6 cases of BMD. In total, 91.7%(22/24) came to hospital because of elevated aminotransferase and 8.3%(2/24) came to hospital because one of their relatives was diagnosed as PMD. There was a significant increase in CK-MB, CK, LDH, AST and ALT in PMD children with higher levels in DMD group compared to those of BMD group(P<0.05, except for AST). When ALT>224.5 U·L-1、CK>11 069 IU·L-1、CK-Mb>204 IU·L-1、LDH>1 349.5 IU·L-1, it is more likely to be DMD especially with the high specificity of LDH>1 349.5 IU·L-1. Conclusion：Higher level of muscle enzyme than healthy people is the main manifestation in the early stage of symptoms in PMD children. LDH>1 349.5 IU·L-1 is highly specific for the diagnosis of DMD.

Key words: Duchenne muscular dystrophy（DMD）, Becker muscular dystrophy（BMD）, Dystrophin, Serum muscle enzyme, Gene diagnosis