Reducing Body Myopathy, X-Linked 1a, Severe, with Infantile or Early Childhood Onset, also known as myopathy, reducing body, x-linked, early-onset, severe, is related to reducing body myopathy, x-linked 1b, with late childhood or adult onset. An important gene associated with Reducing Body Myopathy, X-Linked 1a, Severe, with Infantile or Early Childhood Onset is FHL1 (Four And A Half LIM Domains 1). Affiliated tissues include skeletal muscle, and related phenotypes are elevated circulating creatine kinase concentration and respiratory insufficiency due to muscle weakness