Homocystinuria in two South African Negro siblings.

: This, to our knowledge, is the first report of homocystinuria in the South African Negro. Two siblings are presented who developed normally until the age of 5 years but then showed mental retardation. Both were tall and thin, had genu valgum and arachnodactyly. The elder sib also had kyphoscoliosis, pes cavus and bilateral ectopia lentis. The diagnosis was confirmed by the presence of homocystine in the urine, elevated plasma homocystine and methionine and diminished plasma cystine levels.