A case series of 7 Sri Lankan patients with type 1 spinal muscular atrophy

Introduction: Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder with an incidence of 1 in 6000 to 1 in 10,000 live births. It is characterized by degeneration of the anterior horn cells of the spinal cord, leading to progressive symmetrical proximal muscle weakness and atrophy. About 95-98% of patients have a homozygous deletion of exons 7 and 8 in the telomeric copy of the survival motor neuron 1 gene (SMN1). Another 2-5% are compound heterozygotes for deletion of exons 7 and 8 of SMN1 and a point mutation in SMN1 gene. The clinical and genetic pattern of SMA has not previously been reported in Sri Lanka. Genetic testing for SMA was introduced in Sri Lanka in 2007 since when 39 patients clinically suspected of SMA were referred for testing. Of these, 7 (18%) had homozygous deletions in exons 7 and 8. We describe the clinical and genetic features of these 7 SMA patients.