RSMD1 is a rare autosomal recessive disorder. Unlike most congenital muscular dystrophies, early motor improvement and normal CPK are typical, while in contrast to structural myopathies there is no specific muscle morphology. Rigid spine, early scoliosis and joint contractures are characteristic. We diagnosed RSMD1 in a 27-year-old Russian female with previous diagnosis of unspecified myopathy. DNA test detected compound heterozygosity for two SEPN1 mutations: already known missence-mutation c.1397G>A (p.Arg466Gln) and novel frame-shift mutation c.683_689dup7 leading to preterm stop-codon.