Abstract
Deficiency of cystathionine beta-synthase (CBS) is the commonest cause of primary homocystinuria. Homocysteine metabolism is intimately linked with the metabolism of folate, vitamin B12 (cobalamin) and pyridoxine. It is hypothesised that the pathogenesis of neuropsychiatric manifestations in hom ocystinuria, folate and cobalamin deficiencies are related to imbalance neurotransmitters in the CNS through disturbances in the pathways linking the metabolism of hom ocysteine and these vitamins. Although neuropsychiatric disorders are relatively common among patients with homocystinuria, it is not well recognised as the causative factor among patients presenting with neuropsychiatric disorders. A 31 year old woman presented with a three week history of delirium and inappropriate and labile affect. There was no history suggestive of drug or alcohol abuse, nutritional deficiency or organic disorders. EEG, cerebral CT, MRI and microbiological investigations did not reveal any organic causes. Because of a diagnosis of pyridoxine-responsive hom ocystinuria seven years previously, the possibility of hom ocystinuria was considered and investigated. Laboratory tests revealed macrocytosis and a high concentration of urinary total homocystine. Commencement of pyridoxine at 400 mg/day resulted in disappearance of homocystine in urine within four days with remarkable clinical improvement. Homocystinuria should be considered in the differential diagnosis of unexplained neuropsychiatric disorders in patients who have past or family history of homocystinuria, mental retardation, thromboembolic episodes, vascular diseases or clinical and laboratory features resembling folate and/or vitamin B12 deficiencies. Homocystinuria-associated neuropsychiatric disturbances can easily be treated with pyridoxine in 50% of cases.