First-trimester diagnosis of Hunter syndrome: very low iduronate sulphatase activity in chorionic villi from a heterozygous female fetus.

Iduronate sulphatase activity was determined in uncultured chorionic villi from four fetuses at risk for Hunter syndrome. All fetuses were shown to be female by chromosome analysis. Biopsy material from three fetuses showed iduronate sulphatase activity within normal limits whilst the fourth fetus showed activity reduced to 7 per cent of our control mean. The importance of fetal sexing in prenatal diagnosis of this condition is emphasized as female carrier fetuses may show iduronate sulphatase activity reduced to levels observed in affected males.