Muscle glycerol kinase in Duchenne dystrophy and glycerol kinase deficiency

The complex glycerol kinase deficiency (GKD) syndrome is an X-linked recessive genetic disorder. The syndrome often includes a myopathy that is similar histologically to Duchenne muscular dystrophy (DMD). The glycerol kinase (GK) locus is in the Xp21 region in the midportion of the short arm of the X chromosome and is in close proximity to the DMD locus. We have investigated GK activity and subcellular distribution of muscle GK in DMD patients and in a patient with the complex GKD syndrome presenting with myopathy. We found no abnormality of muscle GK specific activity or subcellular distribution in DMD. In the patient with the complex GKD syndrome the specific activity and kinetics of muscle GK were normal, but the subcellular distribution of muscle GK was altered. Liver GK had less than 10% of normal activity and showed markedly altered kinetics. These findings indicate that there is no abnormality of muscle GK activity in DMD muscle. Furthermore, the normal GK activity in an individual with the complex GKD syndrome suggests that muscle and liver GK are genetically distinct. These findings support the concept that the complex GKD syndrome results from small deletions that affect closely linked but separate loci for DMD, GK and adrenal hypoplasia.