Carrier incidence for spinal muscular atrophy in southern Chinese

A real time quantitative PCR (QPCR) method using TaqMan technology was used to assess the copy number of the two survival motor neuron genes (SMN1 and SMN2) on chromosome 5q13. This allows the accurate determination of carriers for spinal muscular atrophy (SMA), with one copy of SMN1. Analysis of 569 normal southern Chinese individuals revealed a carrier incidence of 1.6%, similar to that found in the western society. Study of 42 obligatory carriers showed a (2 + 0) genotype in two (4.8 %). In 27 SMA patients with homozygous deletion of the SMN1 gene, the number of SMN2 gene correlated with disease phenotype, with 68% of type II and III patients carrying three or more SMN2 genes, whilst the incidence of three or more SMN2 genes in the normal population was 1.57%.