SOD1 mutations in adult-onset distal spinal muscular atrophy.

We read with interest the paper "SOD1 p.D12Y variant is associated with ALS/distal myopathy spectrum", recently published by Tasca et al., where four patients heterozygous for the p.D12Y variant in SOD1 were described. Two of them had a classical ALS phenotype. The other two (patient 1 and patient 4, previously reported in) had, according to the authors, a "concomitant distal myopathy". The authors rely mainly on histologic findings to suggest concomitant involvement of skeletal muscle. However, in our opinion, these changes, including the presence of rimmed vacuoles, cytoplasmic bodies and small foci of necrosis and phagocytosis are not specific of a myopathic process and can be found in slowly progressive motor neuron disorders, as a result of long-standing denervation and reinnervation. They should be considered pseudomyopathic changes, as previously described in the literature.