ABSTRACT
Objective To explore the importance of gene diagnosis and prenatal diagnosis of spinal muscular atrophy(SMA),and improve the clinical diagnosis of SMA by analyzing the electrophysiological and gene characteristics of SMA.Methods Fifteen cases with SMA including 9 male and 6 female were enrolled in this study.The age was 5 months to 12 years.The 15 cases were subdivided into 3 clinical types,5 cases of type Ⅰ including 3 male and 2 female aging 5-18 months;7 cases of type Ⅱ including 4 males and 3 females aging 5 months-3 years;3 cases of type Ⅲ including 2 male and 1 female aging 3-12 years.They were all characterized by symmetric muscle weakness(more proximal than distal)associated with atrophy,absence or marked decrease of deep tendon reflexes,loss of voluntary movement and inability to sit or stand.The clinical characteristics and changes of electromyography(EMG)and nerve conduction velocity were assessed in all cases by using Danish Medoc Keypoint myoelectricity and evoked potentials inducer.The survival of motor neuron(SMN)gene was detected by PCR and restriction endonuclease spectrum analysis in 10 cases.Results EMG analysis found 94% patients had spontaneous potential,90% patients had increased duration of motor unit,and amplitude increased in 89% patients.Motor nerve conduction velocity was determined in 78 nerves.Motor nerve compound action potential wave amplitude decreased in 52 nerves,among them,distal latent period prolonged and motor conduction velocity reduced slightly in 36 nerves.Sensory nerve conduction velocity was determined in 45 nerves and remained normal.The SMN gene detection revealed deletion of exon 7 and 8 in 9 cases,deletion exon 7 in 1 case.The SMN gene detection in 10 patients and their parents didn't find any deletion of exon 7 and 8.Conclusions The definite diagnosis of SMA will rely on the typical clinical characteristics,changes of EMG and gene deletion analysis.Gene diagnosis of SMA lays a basis for prenatal diagnosis.