Novel PHKA1 mutation in glycogen storage disease type IXD with typical myotonic discharges

Abstract

Glycogen storage disease type IXD (GSD9D, OMIM 300559) is a rare metabolic myopathy characterized by exercise intolerance, myoglobinuria, myalgia, cramps, and myopathy. 1 The pattern of muscle involvement has been recognized as a phenotype of primarily proximal weakness or primarily distal involvement. GSD9D is caused by muscle phosphorylase kinase deficiency, a key regulator of glycogen metabolism. This PHK protein plays a critical role in regulating glucose release from glycogen to obtain sufficient energy for muscle contrac-