Abstract-An inborn error of metabolism, homocystinuria due to cystathionine -synthase deficiency, results in markedly elevated levels of circulating homocysteine. Premature vascular events are the main life-threatening complication. Half of all untreated patients have a vascular event by 30 years of age. We performed a multicenter observational study to assess the effectiveness of long-term homocysteine-lowering treatment in reducing vascular risk in 158 patients. Vascular outcomes were analyzed and effectiveness of treatment in reducing vascular risk was evaluated by comparison of actual to predicted number of vascular events, with the use of historical controls from a landmark study of 629 untreated patients with cystathionine -synthase deficiency. The 158 patients had a mean (range) age of 29.4 (4.5 to 70) years; 57 (36%) were more than 30 years old, and 10 (6%) were older than 50 years. There were 2822 patient-years of treatment, with an average of 17.9 years per patient. Plasma homocysteine levels were markedly reduced from pretreatment levels but usually remained moderately elevated. There were 17 vascular events in 12 patients at a mean (range) age of 42.5 (18 to 67) years: pulmonary embolism (nϭ3), myocardial infarction (nϭ2), deep venous thrombosis (nϭ5), cerebrovascular accident (nϭ3), transient ischemic attack (nϭ1), sagittal sinus thrombosis (nϭ1), and abdominal aortic aneurysm (nϭ2). Without treatment, 112 vascular events would have been expected, for a relative risk of 0.09 (95% CI 0.036 to 0.228; PϽ0.0001). Treatment regimens designed to lower plasma homocysteine significantly reduce cardiovascular risk in cystathionine -synthase deficiency despite imperfect biochemical control. These findings may be relevant to the significance of mild hyperhomocysteinemia that is commonly found in patients with vascular disease.
Following the introduction 30 years ago of neonatal screening and early dietary treatment for phenylketonuria there has been a dramatic decrease in the severity of neurological dysfunction associated with this disorder. However, there is evidence that subtle neurological impairment remains common in early treated subjects and in the last 3 years there have been a number of reports of overt neurological impairment with white matter abnormalities on MRI. The frequency of white matter changes in phenylketonuria, and the relation of these changes to dietary management, have remained unclear. The present study examines MRI findings in 34 subjects aged 8-33 years. Twenty-five subjects had been detected by routine neonatal screening and nine had been missed in the screening programme. At the time of the investigation 16 of the early treated and two of the late treated subjects were still receiving a diet low in phenylalanine. All but two of the 34 subjects showed abnormalities on MRI. In the early diagnosed group it could be shown that the severity of MRI changes (graded 1-5) was significantly and independently associated with phenylalanine concentrations at the time of investigation and the time since dietary treatment had been withdrawn. These data are consistent with studies in animals showing that hyperphenylalaninaemia increases myelin turnover in a dose dependent manner. It is suggested that the effects of phenylalanine on myelin pose a lifelong hazard to the nervous system.
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