Glycogen storage disease type XIV (GSDXIV) is a rare metabolic disorder caused by a deficiency in phosphoglucomutase (PGM) enzymatic activity and characterized by recurrent cramps during exercise.
This enzymatic disorder is rare, to date two cases have been reported, but its frequency is probably under-estimated.
The disease manifests during the first years of life with recurrent cramps provoked by exercise. Rhabdomyolysis is also observed after strenuous effort. Biochemical examination shows a normal plasma lactate level but increased ammonia after a standardized forearm-exercise test. The creatinine kinase level is increased by a factor of 10 to 20 after exercise.
GSDXIV is caused by a deficiency in PGM enzymatic activity responsible for the switch between glucose-6-phosphate and glucose-1-phosphate during the first steps of glycogen metabolism, resulting in a metabolic block after glucose-1-phosphate and before glucose-6-phosphate during anaerobic glycogenolysis. This enzymatic step is catalyzed by phosphoglucomutase 1 (PGM1), which carries out about 90% of total PGM activity. The deficiency is caused by autosomal recessive mutations in the PGM1 gene (1p31).
Diagnosis is based on the demonstration of a deficit of muscular PGM activity, necessitating a muscular biopsy. Muscle biopsy shows subsarcolemmal and sarcoplasmic accumulations of normally-structured, free glycogen.
Differential diagnoses include McArdle disease (GSDV; see this term), which can be excluded by the occurrence of a 'second wind' during exercise as no 'second wind' is observed with GSDXIV.
Treatment and management protocols have not yet been established because of the lack of data available on this disease.
Prognosis is thought to be good.
Last update: March 2010