SMN1 and neuromuscular disease: Spinal muscular atrophy type 1 (SMA1), also known as Werdnig–Hoffman disease, is an autosomal recessive neuromuscular disease caused by a homozygous mutation or deletion in the survival motor neuron 1 gene (SMN1), which is located on chromosome 5 together with another gene involved in the production of SMN protein, named SMN2 [1,2].