Progressive myalgias and polyarthralgias in a patient with myoadenylate deaminase deficiency

Molecular basis of AMP deaminase deficiency in skeletal muscle

AMP deaminase (AMPD; EC 3.5.4.6) is encoded by a multigene family in mammals. The AMPD1 gene is expressed at high levels in skeletal muscle, where this enzyme is thought to play an important role in energy metabolism. Deficiency of AMPD activity in skeletal muscle is associated with symptoms of a metabolic myopathy. Eleven unrelated individuals with AMPD deficiency were studied, and each was shown to be homozygous for a mutant allele characterized by a C----T transition at nucleotide 34 (codon 12 in exon 2) and at nucleotide 143 (codon 48 in exon 3). The C----T transition at codon 12 results in a nonsense mutation predicting a severely truncated AMPD peptide. Consistent with this prediction, no immunoreactive AMPD1 peptide is detectable in skeletal muscle of these patients. This mutant allele is found in 12% of Caucasians and 19% of African-Americans, whereas none of the 106 Japanese subjects surveyed has this mutant allele. We conclude from these studies that this mutant allele is present at a sufficiently high frequency to account for the 2% reported incidence of AMPD deficiency in muscle biopsies. The restricted distribution and high frequency of this doubly mutated allele suggest it arose in a remote ancestor of individuals of Western European descent.

Myoadenylate deaminase deficiency

Myoadenylate deaminase (MAD) is the rate-limiting enzyme in the purine nucleotide cycle which is biochemically linked to glycolysis and the citric cycle and thereby providing energy during intense muscular activity. In muscle fibers, myoadenylate deaminase operates at considerably higher activity levels than in other organs. First detected using enzyme-histochemical methods, it now appears that deficiency of myoadenylate deaminase is one of the most frequent enzyme defects in muscle. The primary defect may occur as an isolated nosological entity or not infrequently it is also associated with a large spectrum of different neuromuscular conditions. It seems to be the primary unassociated MAD deficiency that has recently become amenable to successful treatment with D-ribose in high doses. Secondary MAD deficiency may occur in muscle fibers and muscles that have undergone structural damage as seen, for instance, in polymyositis, muscular dystrophy, and denervation. The wealth of biochemical, morphological, and clinical data that has accumulated since the discovery of MAD deficiency during the past decade provides nosological significance of MAD deficiency as a real entity.

Myoadenylate deaminase deficiency: successful symptomatic therapy by high dose oral administration of ribose

A 55 years old patient suffering from exercise-induced muscle pain and stiffness due to primary myoadenylate deaminase deficiency has been successfully treated with D-ribose since 1984: single doses of 4 grams administered at the beginning of exercise prevented the symptoms completely; on continuation of exercise this dose had to be repeated all 10-30 min. Total doses of 50-60 g per day were tolerated without side-effects.