Since the initial genetic test was negative for spinal muscular atrophy, Charcot–Marie–Tooth disease, SOD1‐linked ALS, spinocerebellar atrophy, and hereditary spastic paraplegia, whole‐exome sequencing was performed and identified a homozygous c.283dupC, resulting in frameshift at position 95 (p.L95fs), mutation in the SIGMAR1 gene (Fig 1B). The gene discussed is SIGMAR1; the disease is proximal spinal muscular atrophy.