Homocystinuria: Treatment With N-Acetylcysteine

Homocystinuria (MIM 236200) due to CBS deficiency is the most common inborn error of sulfur amino acid metabolism with severe clinical manifestations. We propose: 1. An open-label pilot study of N-acetylcysteine (NAC) to lower plasma homocysteine levels in those that have not responded to conventional treatment which includes betaine (Cystadane®, Orphan Medical Inc.), which while lowering Hcy levels does not normalize it, and is very expensive. There are no known contraindications to NAC used for nutritional supplementation and it is relatively inexpensive. Oral NAC has reduced total plasma homocysteine in healthy subjects in a dose-dependent fashion. 2. Measurement of flow-mediated vasodilation of the brachial artery (endothelial function) in response to NAC treatment. Endothelial dysfunction is a precursor of atherogenesis. 3. Sequencing the CBS gene in these individuals in order to identify novel mutations causing homocystinuria and identify polymorphisms in other genes that may affect response to treatment.