Homocystinuric Patient with Deficient CBS Activity: Pyridoxine Efficacy and Toxicity?

A patient with homocystinuria, a risk factor of arterial and venous thrombosis, developed cerebral venous thrombophlebitis before the age of twenty years. As she was B6 sensible, she was given 250 mg/d of pyridoxine and homocysteinemia was well controlled. Unfortunately, at the age of 40, she developed progressive weakness, with a major increase of plasma CPK values (4110 UI/l, normal < 160). Severe rhabdomyolysis was observed, and muscle biopsy showed necrotic fibres. She died of pulmonary embolism. B6 vitamin is not known to be toxic. However, excessive intake can cause ataxia and severe neuropathy. But some authors have reported that a short term administration of 500 mg/d of pyridoxine to a one-month old child caused a rhabdomyolysis, and this observation might evocate a particular susceptibility of our homocystinuric patient to B6 vitamin therapy.