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Classical homocystinuria: newborn screening with early treatment effectively prevents complications
Classical homocystinuria (HCU) due to cystathionine β-synthase deficiency is an inherited disorder of methionine metabolism. HCU has a reported worldwide prevalence ranging from 1 in 344 000 to 1 in 65 000 in Ireland. Molecular studies indicate a much higher incidence of between 1 in 6500–20 000 and as high as 1 in 1800 in a highly consanguinous Qatari population. Recognized complications from the untreated disease affect four major systems: ocular (ectopia lentis), skeletal (osteoporosis), vascular (thromboembolic events) and central nervous systems (intellectual disabilities). The natural history is such that 82% will have ectopia lentis by the age of 10 years, 27% will have had a clinically detected thromboembolic event by the age of 15 years, 64% will have radiological evidence of spinal osteoporosis by the age of 15 years and 23% will not survive to the age of 30 years. Long-term outcome studies on a group of Irish patients detected by newborn screening and commenced on early treatment document that homocysteine-lowering treatment is effective in preventing complications and normal intelligence is achieved. Vascular events are the major cause of morbidity and mortality. The results from a multicentre study show that homocysteine-lowering therapy is effective in significantly reducing the vascular risk during treatment. In the half-century since its discovery in 1962, homocystinuria with its devastating complications has been discovered to be a treatable condition, with the best possible clinical outcome in cases detected early by newborn screening.