MTTP and dopa-responsive dystonia due to sepiapterin reductase deficiency: Moreover, the expression of the FA β-oxidation enzyme, Cpt1a (Fig. 3F), the rate-limiting enzyme of very low density lipoprotein (VLDL) secretion, Mttp (Fig. 3G), and the ChREBP target rate-limiting enzyme of glycolysis, Lpk (Fig. 3H), was unaltered in livers of CBA mice during the 3-week period of SRD.