Evaluation of an in-house protocol for prenatal molecular diagnosis of SMA in Chinese.

Background: Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder characterized by degeneration of the anterior horn of the spinal cord, leading to symmetric muscle weakness and atrophy. About 95% of SMA patients have homozygous loss of SMN1 which can be detected by conventional PCR-RFLP testing. However, the method cannot distinguish heterozygous healthy carriers. A quantitative method named multiple ligation-dependent probe amplification (MLPA) was introduced in our protocol for prenatal molecular diagnosis of SMA in our laboratory.

Methods: DNA was extracted from amniotic fluid cells of 13 fetuses from 11 Chinese SMA families. STR profiling was carried out to evaluate the contamination of amniotic DNA by maternal genomic DNA. Three methods, PCR-RFLP, allele-specific PCR and MLPA, were used to analyze SMN1 exon 7 of amniotic DNA.

Results: There was no contamination of amniotic DNA by maternal genomic DNA. In conventional PCR-RFLP, allele-specific PCR, and MLPA, homozygous loss of SMN1 was observed in 4 fetuses. Among the remaining 9 fetuses, 6 with 1 copy of SMN1 and 3 with 2 copies of SMN1 were showed by MLPA.

Conclusion: This in-house protocol was reliable and efficient for prenatal molecular diagnosis of SMA.