[Clinical, electrophysiologic and genetic characteristics of childhood onset spinal muscular atrophy]

ABSTRACT

Spinal muscular atrophy[SMA] is one of the most common autosomal recessive disorders characterized by degeneration of anterior born cells in the spinal cords and leads to progressive muscular weakness and atrophy. The last 10 years have seen major advances in the field of diagnosis of SMA, but no curative treatment is available now. This study aimed to analyze the clinical characteristics of different types of SMA, improve the clinical diagnosis of SMA and prenatal diagnosis of SMA by gene analysis. Patients with SMA were recruited from neurologic clinic from January 2004 to March 2006. The diagnosis of SMA was made from clinical history and examination, electro physiologic assessment or molecular studies. The clinical characteristics and changes of electrophysiology were assessed in all patients. The deletion of survival motor neuron [SMN] and neuronal apoptosis inhibitory protein [NAIP] genes was studied by PCR. Based on age of onset, age of death, achievement of motor milestones and ambulatory status patients classified into SMA I, SMA II and SMA III. The 42 patients, including 28[66.7%] males and 14[33.3%] females were enrolled in this study. The patients were subdivided into clinical groups 30 [71.7%] of case with SMA I 9[21.4%] of cases with SMA II, 2[4.8%] of case with SMA III and 1[2.4%] of cases with SMA diaphragmatic. They were all characterized by symmetric muscle weakness [more proximal than distal] associated with atrophy, absence or marked decrease of deep tendon reflexes. Fasciculation of tongue was noted in 59.5% of patients. Electroghsiologic studies showed a neurogenic pattern with denervation potentials on 92.8% of cases. The SMN gene was deleted in 78.5% of patients and the NAIP gene was deleted in 54.8% of cases. Deletion of NAIP gene was more common in SMA I, and its deletion correlated with the severity of diseases [P=0.011]. The definite diagnosis of SMA will relay on typical clinical characteristics and changes of electrophysiologic study and gene deletion gene. Genetic diagnosis of SMA can provide a basis of prenatal diagnosis of SMA