Molecular analysis of the SMN gene mutations in spinal muscular atrophy patients in China.

Spinal muscular atrophy (SMA) is one of the most common autosomal recessive diseases. Survival motor neuron1 (SMN1) is the SMA disease-determining gene. We examined the molecular basis of SMA in 113 Chinese SMA patients. Homozygous exon 7 and 8 deletions in SMN1 were detected by PCR-RFLP. Heterozygous deletion of SMN1 was analyzed based on variation of the sequencing peak height of the two different base pairs of exons 7 and 8 between SMN1 and SMN2. Subtle mutation was detected by genomic sequencing in the patients with heterozygous deletion of SMN1. In our study, the rate of deletion of SMN1 exon 7 and/or 8 was 91.2%; the rate of subtle mutations was 1.8%. We detected the same subtle mutation (p.Leu228X) of SMN exon 5 in two patients (one type I, one type III). The p.Ser8LysfsX23 and p.Leu228X mutations accounted for 13 of the 23 families with subtle mutations reported in the SMN1 gene of Chinese SMA. This is the first report where the phenotype of SMA-type III is associated with p.Leu228X. We found two subtle mutation hotspots (p.Ser8LysfsX23 and p.Leu228X) of SMN1 exons 1 and 5 in Chinese SMA patients. These two mutations have not been reported from America or Europe. It is proposed that the distribution of subtle mutations of SMN1 of SMA is associated with ethnicity or geographic origin.