OBJECTIVETo develop a screening program for spinal muscular atrophy (SMA) carriers, and to assess the carrier frequency and detection rate in Shanghai region.

METHODSQuantitative analysis of the SMN1 gene by real-time PCR was developed using specimens from 15 SMA patients and 76 SMA parents from 38 affected nuclear families. A pilot screening was carried out for 1741 asymptomatic pregnant women. Frequencies of SMN1 alleles were determined with the Hardy-Weinberg equilibrium.

RESULTSForty five out of the 1741 women were identified as SMA carriers by the presence of single copy of SMN1. The frequencies of no copy, 1 copy, 2 copy and 3 copy alleles were 1.37 U+00D7 10-2, 9.45 U+00D7 10-1, 2.80 U+00D7 10-2 and 1.27 U+00D7 10-2, respectively. The adjusted SMA carrier frequency was 1:35 with a detection rate of 94.49%. For those with a negative screening result, individuals with 3 copies carried a higher residual risk.

CONCLUSIONThe incidence of SMA carriers in Shanghai region is similar with that in Caucasian populations. Carrier screening has high detection efficiency. An effort should be made to further distinguish SMN1 gene copy numbers for those with more than 2 copies, since accurate determination of 2 and 3 copy allele frequencies is essential for post-screening genetic consulting.