PHKA2 and glycogen storage disease IXa1: Mutation of PHKA2 results in GSD type IXa, also known as X-linked liver GSD, which accounts for approximately 75% of all cases of GSD type IX.[4] About 134 cases of GSD type IXa have been reported at present, and 99 types of PHKA2 gene mutation have been documented in the Human Gene Mutation Database, including 47 missense mutations, 28 deletion mutations, 9 insertion mutations, 9 nonsense mutations, and 6 splice-site mutations.[5] Most patients with GSD type IXa are characterized by an enlarged liver and increased aminotransferase levels.