Association of genetically proven deficiencies of myophosphorylase and AMP deaminase: a second case of 'double trouble'.

We studied a 25-year-old man with paresis of the limbs and neck, scapular atrophy, facial weakness, exercise intolerance and frequent episodes of myoglobinuria. Muscle histochemistry and biochemistry revealed a combined defect of myophosphorylase and AMP deaminase. Molecular genetic analysis showed that the patient was homozygous for the two most common mutations associated with myophosphorylase and AMP deaminase deficiencies. This is the second documented case of genetic 'double trouble', which should be looked for in patients with unusual severe phenotypes.