Homocystinuria occurring with pneumothorax : a case report

The homocystinurias are a group of autosomal recessive disorders which are caused by various inborn errors of metabolism. Tnese disorders are characterized by high plasma and urinary ieveis of homocysteine and methionine, and low levels of cysteine. The most common cause of homocystinuria is a defect in the enzyme cystathionine f3-synthase (CBS) which converts homocysteine to cystathionine. Patients who are homozygous for CBS deficiency can be responsive or non-responsive to pyridoxine (vitamin B6), a cofactor of CBS. BB-responsive patients usually have a milder clinical phenotype and later onset of symptoms as compared to B6 non-responsive patients. The common clinical manifestations of homocystinuria are ectopia lentis, skeletal abnormalities and osteoporosis, and mental retardation. The skeletal features and eye findings of patients with homocystinuria are very similar to those of patients with the more common genetic disease, Marfan syndrome, an autosomal dominant disorder affecting the connective-tissue fibrillin. Pneumothorax, relatively common in Marfan syndrome, is rarely seen in homocystinuria. In this paper I describe a patient with pyridoxineresponsive homocystinuria and repeated spontaneous pneumothoraces.