The Studies And Application Of Gene Diagnosis For Spinal Muscular Atrophy

BackgroundSpinal muscular atropy(SMA) is a common autosomal recessive disorder characterized by degeneration of the anterior horn cells of the spinal cord ,leading to progressive symmetrical limb and trunk paralysis associated with muscular atrophy. With an incidence of 1 in 10 000 live births and a carrier frequency of 1 in 50, SMA is the second most common fatal autosomal recessive disorder. SMA is conventionally classified into three types. Up to now, pathological and physiological of SMA is not very clear. All three forms of SMA were mapped to the long arm of chromosome 5, at 5qll.2-5q 13.3. The survival motor neuron (SMN) is the primary SMA-determining gene. There are two highly homologous copies in this region: SMN1(the telomeric copy)and SMN2 (the centromeric copy). The changes of clinical phenotype maybe associated with the regulation of SMN2 gene. The SMN 1gene exon 7 is homozygous deleted in more than 94 % of SMA patients. So, it is very valuable to detect the homozygous deletion of SMN1 gene exon 7 for the diagnosis of SMA. The disease has no therapy effectively by now. Therefore it is necessary to establish a gene diagnosis method to avoid the birth of defective fetus by confirming the diagnosis of clinical cases or suspicious cases, which also is the basis of prenatal gene diagnosis. The method is the most effective one which is adapted currently to prevention and cure SMA and increase the physical quality of population.Object1.To diagnose and prenatal diagnose SMA.2.To provide evidence for genetic counseling by screening the carriers of SMA. Material and Methods1.Patients: Samples from 26 families were collected. All subjects were referred from the Department of Pediatrics, Shengjing Hospital of China Medical University and the Department of Medical Genetics, Peking Union Medical University between January 2005 and December 2007 with informed consents obtained. The research plan was approved by the ethics committee of both universities. These included 26 patients diagnosed for having SMA, their normal parents and 20 amniotic samples.2.Methods: PCR-restriction enzyme digestion was applied to detect the deletion of the exon 7of SMN1 gene;MultiPCR-DHPLC was applied to study the ratio of the SMN1 and SMN2 gene copies.Results1.25 out of 26 patients were found to delete exon 7 of SMN1 gene.2.12out of 20 infants were found to delete exon 7 of SMN1 gene.3.The results of the ratio of the SMN1 and SMN2 copy number detected by MultiPCR-DHPLC are stable and accurate. Confirmed SMA 27 carriers were detected from 30 normal people and 26 SMA family members.Conclusion1.We have made the gene diagnosis more accurate and more sensitive by the PCR-restriction enzyme digestion and MultiPCR-DHPLC methods.2.We can provide important evidence for genetic counseling by screening the carriers of SMA from normal people and SMA family members.