OBJECTIVETo study the incidence of homozygous absence of SMN1 exons 7 and 8, SMN gene conversion frequency and SMN subtle mutations in children with spinal muscular atrophy (SMA).

METHODSThe homozygous deletion was detected by PCR-RFLP in 106 Chinese children with SMA, gene conversion by RFLP and subtle mutations by sequencing.

RESULTSThe rate of deletion of SMN1 exons 7 and/or 8 was 91.5%. Deletion of SMN1 exon 8 but existence of exon 7 was noted in one child with SMA. There were no significant differences in the gene conversion frequency among children with different types of SMA and who had homozygous deletion of SMN1 exon 7 but existence of exon 8. The gene conversion frequency was 8.3% in children with homozygous deletion of SMN1 exon 7. No subtle mutations were found around SMN1 exon 7.

CONCLUSIONSDeletion of SMN1 exons 7 and/or 8 is the main cause of SMA in Chinese children. There exists a SMN gene conversion phenomenon in SMA. Deletion of exon 8 might lead to SMA. The hot area of subtle mutations of this disease might not be around SMN1 exon 7.