SLC16A1 and tuberous sclerosis: Indeed, we found that SynT-I differentiation deficiencies were the common denominator in all these mutant TSC lines, with lower expression of the monocarboxylate transporter Slc16a1 (MCT1) and the heparin-binding EGF-like growth factor Hbegf consistently providing the most reliable readout (Fig. 7a, b and Supplementary Figs. 8, 9).