Background:Facioscapulohumeral muscular dystrophy (FSHD),a common autosomal dominant muscular disorder,is caused by contraction of the D4Z4 repeats on 4q35.The complicated genotype-phenotype correlation among different ethnic population remains a controversial subject.We aimed to refine this correlation in order to provide new information for genetic counseling.Methods:Here,a cohort of 136 Chinese families including 178 affected individuals and 137 unaffected members were investigated.Genetic analyses were performed using the pl3E-11,4qA and 4qB probes after pulsed field gel electrophoresis separation and south blotting.A 10-grade FSHD clinical severity scale was adopted for clinical assessment.The genotype-phenotype correlation was established by linear regression analyses.Results:We observed a roughly inversed correlation between the short EcoRI fragment size and age-corrected clinical severity score in 154 symptomatic patients (P ＜ 0.05).Compared to male patients,a significant higher proportion of females in both asymptomatic carriers and severe patients showed larger variation in the size of short EcoRI fragment.A high incidence (19/42,45.2％) of asymptomatic (or minimally affected) carriers was found in familial members.Conclusions:Although the number of D4Z4 repeats is known as one of the critical influences on genotype-phenotype correlation,a majority of phenotypic spectrum was still incompatible with their heterozygous contraction of the D4Z4 repeat,especial in female cases.Our results suggest that there are multi-factors synergistically modulating the phenotypic expression.