Muscle phosphofructokinase (PFK) deficiency (Tarui's disease), or glycogen storage disease type 7 (GSD7), is a rare form of glycogen storage disease characterized by exertional fatigue and muscular exercise intolerance. It occurs in childhood. The disease is glycogen storage disease VII (MONDO_0009295). Also known as: GSD due to muscle phosphofructokinase deficiency, GSD type 7, GSD type VII, GSDVII, Glycogen Storage Disease Type 7, PFKM glycogen storage disease, Tarui disease, glycogen storage disease caused by mutation in PFKM.