Spinal Muscular Atrophy from Northern Iran: A Clinical and Genetic Spectrum of Ten Patients

Objective

Autosomal recessive spinal muscular atrophy (SMA) is, after cystic fibrosis, the second most common fatal monogenic disorder and the second most common hereditary neuromuscular disease after duchenne dystrophy. The disease is characterized by degeneration of anterior horn cells leading to progressive paralysis with muscular atrophy. Depending on the clinical type (Werdnig- Hoffmann = type I, intermediate form = type II, Kugelberg-Welander = type III), some workers also have delineated an adult form of SMA (SMA type 4).

SMA causes early death or increasing disability in childhood. The aim of this investigation was to describe the clinical findings of patients with spinal muscular atrophy (SMA) with survival motor neuron (SMN) gene deletion.

Materials & methods

This is a descriptive study conducted on 10 patients of SMA, confirmed by deletion of the SMN gene. All 10 patients had symmetrical muscle weakness, which was diffuse in those with onset of symptoms up to 1 months of age, and either proximal or predominant in lower limbs. Frequency determination of positive clinical and laboratory data was done according to revised diagnostic criteria.

Results

It was found that all patients with SMA had homozygous deletions of exons 7 and 8 of the survival motor neuron 1 (SMN1) gene, which is one of the candidate genes identified within 5q13. Fasciculations, atrophy and decreased DTR were frequent findings. Laboratory metabolic tests and all brain CT scans were normal. EMG and NCV findings, all showed normal motor and Sensory NCV and denervation of muscles of upper and lower extremities were compatible with a diagnosis of spinal muscular atrophy.

Conclusion

Our results confirm that SMN1 copy number analysis is an important parameter for identification of couples at risk of having a child affected with SMA and reduces unwarranted prenatal diagnosis for SMA.