Prenatal diagnosis of nephropathic cystinosis. Pregnancy at risk ascertained through heterozygote diagnosis of parents.

The biochemical diagnosis of cystinosis in a deceased girl was made indirectly through the demonstration of heterozygote values of free-cystine contents in leukocytes from both parents. Amniocentesis was performed on the mother in the 16th week of two subsequent pregnancies. Amniotic fluid cell lysate from the first fetus had 6-8 times normal levels of radioactivity in the cystine band determined by a 35S-cystine pulse labeling method followed by high voltage electrophoresis on paper. Values for the cystine contents in various organs of the affected fetus are given. The second fetus was found to be not affected, and this was subsequently confirmed by the birth of a healthy child. The results of the laboratory analyses in these two cases were available to the parents 21 and 23 days following amniocentesis, respectively. The interruption of the first pregnancy was performed in the 19th week. This was 4 and 6 weeks earlier, respectively, than in the two previously reported induced abortions of affected fetuses, and should increase the acceptability of the present method for prenatal diagnosis of nephrophatic cystinosis.