Two Case Reports of Spinal Muscular Atrophy(SMA) Confirmed by Molecular Genetic Studies / 대한임상병리학회지

We present two cases of the patients with spinal muscular atrophy(SMA) confirmed by molecular genetic studies. The first one is 1-year-old female child with SMA type II(Dubowitz disease) who visited pediatric outpatient for developmental delay. She presented lower extremity hypotonia which progress to upper extremities and inability to sit alone. Spinal cord MRI showed normal findings but the needle electromyography suggested the possibility of myopathy. Following muscle biopsy findings were consistent with spinal muscular atrophy and PCR-SSCP(polymerase chain reaction-single strand conformation polymorphism) analysis showed homozygous deletion of telomeric SMN(survivor motor neuron) exon 7. The second is a 19-year-old female with SMA type III(Kugelberg-Welander disease) who visited neurologic outpatient for limbs weakness. She presented slowly progressive gait disturbance without muscle atrophy. The significantly decreased motor power of proximal limbs was observed. And findings of electromyography and muscle biopsy were consistent with spinal muscular atrophy. PCR-SSCP analysis revealed homozyous deletion of exon 7 of telomeric SMN and deletion of exon 8 of centromeric SMN gene. PCR analysis for NAIP(neuronal apoptosis inhibitory protein) exon 5 and 13 revealed no deletion in both cases. Molecular genetic analysis for SMN gene will be very useful for rapid diagnosis of spinal muscular atrophy.

Prenatal diagnosis of the spinal muscular atrophy type I using genetic information from archival slides and paraffin-embedded tissues

Spinal muscular atrophy (SMA) type I is a common severe autosomal recessive inherited neuromuscular disorder that has been mapped to chromosome 5q11.2-13.3. The survival motor neuron (SMN) gene, a candidate gene, is known to be deleted in 96% of patients with SMA type I. Presently, PCR and single strand conformation polymorphism (PCR-SSCP) analyses have been made possible for application to both archival slides and paraffin-embedded tissues. Archival materials represent valuable DNA resources for genetic diagnosis. We applied these methods for the identification of SMN gene of SMA type I in archival specimens for the prenatal diagnosis. In this study, we performed the prenatal diagnosis with chorionic villus sampling (CVS) cells on two women who had experienced neonatal death of SMA type I. DNA extraction was done from archival slide and tissue materials and PEP-PCR was performed using CVS cells. In order to identify common deletion region of SMN and neuronal apoptosis-inhibitory protein (NAIP) genes, cold PCR-SSCP and PCR-restriction site assay were carried out. Case 1 had deletions of the exons 7 and 8, and case 2 had exon 7 only on the telomeric SMN gene. Both cases were found to be normal on NAIP gene. These results were the same for both CVS and archival biopsied specimens. In both cases, the fetuses were, therefore, predicted to be at very high risk of being affected and the pregnancy were terminated. These data clearly demonstrate that archival slide and paraffin-embedded tissues can be a valuable source of DNA when the prenatal genetic diagnosis is needed in case any source for genetic analysis is not readily available due to previous death of the fetus or neonate.