OBJECTIVESpinal muscular atrophy (SMA) is one of common autosomal recessive diseases and is characterized by degeneration of the anterior horn cells of the spinal cord. The reported prevalence is 1/10,000 live births with a carrier rate of one in 50. It is important in genetic counseling to identify the carriers with one copy deletion for the survival motor neuron (SMN(1)) gene. However, the duplication of the SMA locus makes the detection of SMA carriers difficult. This study aimed to determine the potential of the quantitative PCR analysis in the identification of SMA carriers.

METHODSThe SMN(1) gene copy number was detected by realdouble ended arrowtime PCR with TaqMan technology in 109 SMA parents of affected children and 40 normal controls.

RESULTSThe average copy numbers of SMN(1) in the individuals with known one copy of the SMN(1) gene and with the two copies were 0.777 +/-0.035 (CV=4.5%) and 2.064 +/-0.120 (CV= 5.8%) respectively. The average copy number of SMN(1) in all of the parents with affected individuals was 0.798 +/-0.108 (CV=13.5%), and that of normal controls was 2.106 +/-0.18 (CV=8.5%). About 98% of SMA patients' parents carried 1 copy SMN(1), and 95% of normal controls carried 2 copies.

CONCLUSIONSThe gene copy numbers for SMN(1) were one and two for SMA carriers and non-carriers, respectively. Our results suggested that the quantitative PCR analysis can distinguish the SMN(1) deletion carriers from non-carriers.