[Myoadenylate deaminase deficiency in a child with myalgias induced by physical exercise]

Myoadenylate deaminase deficiency (MAD) constitutes the most common genetically determined enzymatic defect of the skeletal muscle (2% of the population), however, it causes clinical symptoms such us exercise-related muscle cramps and pain in quite a lower number of patients, being exceptional in children.

A 7 year old boy is referred with intense myalgias after physical exertion associating increased creatin kinase level 3,273 UI/L (normal 24-195) which goes down in rest period to increase again with myalgias during exercise. The ischemic forearm exercise test shows a flat ammonia curve with a normal lactate rise in relation to control. In muscle biopsy, an absence of the enzymatic activity of myoadenylate deaminase is observed and the genetic analysis proves the 'nonsense' Q12X mutation which he has in a homozygous status.

MAD deficiency must be ruled out in every patient with exertional myalgia and increased CK which normalizes when asymptomatic. The ischemic forearm exercise test guides about the muscle metabolic disorder type, although the definitive diagnosis is obtained through the muscle biopsy histoenzymatic analysis and genetic techniques. Although rarely diagnosed in children, MAD deficiency must be included in the differential diagnosis of syndromes with exercise intolerance