Carrier Screening and Prenatal Diagnosis for Spinal Muscular Atrophy in 13,069 Chinese Pregnant Women

Spinal muscular atrophy (SMA) is a relatively common, life-shortening, autosomal recessive neuromuscular disease. The carrier frequency of SMA ranges from approximately 0.98% to 2.02%, depending on ethnicity. The American College of Medical Genetics has therefore recommended population screening for SMA carrier status, regardless of race or ethnicity. We performed the largest-scale carrier screening for SMA carriers in mainland China. Carrier screening was offered to 36,470 pregnant women between July 2017 and June 2019, of whom 13,069 women accepted the screening program [35.83%; 95% credibility interval (CI), 35.34%-36.33%]. Copy numbers of exons 7 and 8 in the SMN1 gene were detected by real-time quantitative PCR, and the results were confirmed by multiplex ligation-dependent probe amplification. A total of 231 women were identified as carriers (1.77%; 95% CI, 1.56%-2.01%), indicating a carrier prevalence of approximately 1:56 in the population. After detailed genetic counseling, 207 paternal partners were recalled and tested. Both partners were carriers in 10 couples, of whom prenatal diagnosis was implemented in seven, and one fetus was diagnosed with SMA. Carrier screening could provide couples with informed reproductive choices. Our workflow and experience of carrier screening may facilitate the popularization of SMA carrier screening in mainland China.