Study on established lymphoid cells in maple syrup urine disease. Correlation with clinical heterogeneity.

Branched-chain keto acid dehydrogenase complex (BCKAD) was measured in lymphoid cells established from five patients with maple syrup urine disease (MSUD) and six control subjects. Two other MSUD lymphoid cell lines obtained from The Human Genetic Mutant Cell Repository were used as references. One day after subculture, the cells grew logarithmically up to 4-5 days. With this cell growth, BCKAD activity increased greatly in controls, but not in MSUD cells. The maximum BCKAD activity of MSUD cells was less than 7% and 13%-16% of the control in classic and variant types, respectively. Leucine added to culture medium at the concentration of 10-20 mM significantly inhibited cell growth in MSUD cells alone, and with increasing concentration and impaired enzyme activity in a cell line, the effect became more prominent. The effects of isoleucine and valine were mild and did not differ between control and MSUD cells.