cblC disease: case report and monitoring of a pregnancy at risk by chorionic villus sampling.

We have studied the uptake of both propionate and leucine in a chorionic villus sample from a fetus at risk for cblC disease. The ratio of propionate to leucine incorporation (x 10(-3] was 3.85 +/- 0.27 (n = 8) in the at risk sample, and 2.8 +/- 0.14, and 3.1 +/- 0.15 (n = 4) in two control samples. The finding of an unaffected fetus was confirmed by the absence of methylmalonic acid in amniotic fluid or maternal urine in the second trimester, and after birth by study of cultured fibroblasts from the baby. Because of the reported variability in propionate incorporation in chorionic villus biopsies, however, we recommend that chorionic villus sampling be confirmed by amniocentesis.