五个脊肌萎缩症高风险胎儿的产前诊断

目的对5名生育过脊肌萎缩症(spinal muscular atrophy,SMA)患儿的妇女当前所怀胎儿进行产前诊断。方法超声监视下行羊膜腔穿刺术抽取羊水。离心后直接从沉渣中提取胎儿基因组DNA。采用短串联重复序列位点检测法排除母体基因组DNA污染。常规PCR扩增胎儿SMN基因第7外显子。PCR产物经DraⅠ酶切后,行琼脂糖凝胶电泳。通过位点特异性PCR扩增SMN1和SMN2的第7外显子。结果比较各胎儿与父母的16个短串联重复序列位点,未见羊水DNA受母体DNA污染迹象。常规PCR中,胎儿A、C、D的PCR产物(189bp)仅有部分可被DraⅠ切割,而胎儿B、E的PCR产物全部被DraⅠ切割。在位点特异性PCR中,胎儿A、C、D既有SMN1、也有SMN2的第7外显子扩增产物,而胎儿B、E只有SMN2的第7外显子扩增。结论胎儿A、C、D未见SMN1纯合性缺失,出生后患SMA的风险极小;胎儿B、E为SMN1纯合性缺失,出生后患SMA的风险极大。

Prenatal diagnosis of 5 fetuses with high risk of developing spinal muscular atrophy

OBJECTIVE: To perform prenatal diagnosis for 5 pregnant women who had given birth to children with spinal muscular atrophy (SMA). METHODS: Thirty to forty mililiters of amniotic fluid was obtained by amniocentesis under ultrasonic monitoring. DNA was extracted directly from sediment of amniotic fluid. Short tandem repeat (STR) profiling was carried out to evaluate the contamination of amniotic DNA by maternal genomic DNA. Two methods, PCR-restriction fragment length polymorphism (PCR-RFLP) and allele-specific PCR, were used to analyze exon 7 of SMN gene from amniotic DNA. RESULTS: Comparing the 16 STR sites of each fetus with those of his/her parents, there was no or little contamination of amniotic DNA by maternal genomic DNA. In conventional PCR-RFLP, part of the PCR product (189 bp) from amniotic DNA of fetus A, C, or D remained intact after digestion with Dra I, while the PCR product from amniotic DNA of fetus B or E was completely digested by Dra I. In allele-specific PCR, exon 7 of both SMN1 and SMN2 gene could be seen when amniotic DNA of fetuses A, C, or D was analyzed, while only exon 7 of SMN2 could be seen when amniotic DNA of fetuses B or E was analyzed. CONCLUSION: Homozygous deletion of SMN1 is not detected in fetuses A, C, and D, predicting that the risk of developing SMA after birth would be extremely low. Homozygous deletion of SMN1 was present in fetuses B and E suggesting high risk of developing SMA after birth.