Attempted detection of heterozygotes for maple‐syrup‐urine disease

The production of 14CO2 from [1‐14C] leucine by isolated leucocytes from four females and three males heterozygous for maple‐syrup‐urine disease (M. S. U. D.) of classical phenotypc and from urban and rural control groups was determined. Although not significantly different, values tended to be lower for female than for male controls and for rural than for urban controls. The mean values for females (heterozygotes, and rural and urban controls) were not significantly different, and although the mean value for male heterozygotes was significantly less than the means for male controls and female obligate heterozygotes, some male controls had values within the hetero‐zygote range. Thus, the unambiguous identification of heterozygotes in this kindred was not possible with this assay system.