Phosphorylase deficiency associated with isometric exercise intolerance.

In the patient reported here, most of the clinical and biochemical correlates of McArdle's disease were present; however, symptoms developed after isometric rather than after isotonic exercise. Histochemical reactions and assay of muscle homogenates confirmed the absence of phosphorylase; however, venous serum lactate increased in the arm after isometric and isotonic ischemic exercise, although the increase was significantly less than in a normal control. Although the symptoms differ significantly from those in McArdle's disease, this disorder could be a variant.