glycogen storage disease IXd (MONDO_0010362, a Monarch Disease Ontology identifier) is a benign form of phosphorylase kinase deficiency caused by variants in PHKA1, characterized by exercise intolerance, myalgia, muscle cramps, myoglobinuria, and progressive muscle weakness. Also known as: GSD IXd, GSD due to muscle phosphorylase kinase deficiency, GSD type 9D, GSD type IXd, GSD9D, PHKA1 glycogen storage disease, PHKA1-related glycogen storage disease type IX, glycogen storage disease caused by mutation in PHKA1.