Correlation between the effects of rT3 and IMP dehydrogenase inhibitors on normal and trisomic 21 lymphocyte cultures.

3,3'5'-triiodothyronine (rT3) levels have been documented to be low in patients with Down syndrome but the metabolic implications of this finding remain unknown. A highly significant correlation was found between the in vitro variations of the mitotic index in lymphocyte cultures when rT3 or known inhibitors of inosine monophosphate dehydrogenase: mycophenolic acid, 6-mercaptopurine or 2-3-diphosphoglycerate were added. No significant difference was found between the response of trisomy 21 or normal lymphocytes. The finding suggests that rT3 may be a physiological modulator of inosine monophosphate dehydrogenase. The implications on cellular differentiation are discussed.