Here, we report a new de novo missense variant (c.803C > A (p.Thr268Lys)) in the KCNA1 gene of a 9-year-old boy with a musculoskeletal phenotype characterized by rhabdomyolysis, lower limb stiffness, neuromyotonia, muscle hypertrophy, short stature, and skeletal deformities. This evidence concerns the gene KCNA1 and Isaacs syndrome.