Prevalence of Congenital Homocystinuria in Denmark

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Abstract
Homocystinuria due to a deficiency of cystathionine β-synthase has been reported to occur with a cumulative overall frequency of 1 in 344,000 worldwide, a value that ranges from 1 in 58,000 to 1 in 1,000,000 in countries that systematically screen newborns.1 Overall, 50 percent of persons with untreated homocystinuria have a thromboembolic event before the age of 30 years, and dislocation of the lens occurs in 50 percent by the age of 8.1 Among mutations causing cystathionine β-synthase deficiency, the 833T→C mutation2 is geographically widespread. We determined the prevalence of this mutation among Danish newborns by screening 500 consecutive Guthrie cards (specimens of an infant's blood collected on filter paper). A frequent genetic insertion variant, 844ins68, was simultaneously sought by polymerase-chain-reaction amplification of exon 8 of the cystathionine β-synthase gene in genomic DNA isolated from the Guthrie cards, followed by incubation of the polymerase-chain-reaction products with the restriction enzyme BsrI.3