Biochemical evidence for heterozygosity in muscular carnitine palmitoyltransferase deficiency

Carnitine palmitoyltransferase (CPT) was studied in muscle homogenates of four patients with recurrent attacks of rhabdomyolysis due to muscular CPT deficiency and in those of the clinically asymptomatic father and mother of two patients. In controls CPT II was readily solubilized by the addition of Triton X-100 and 1% Tween 20. In contrast, CPT I was inactivated by Triton X-100 but remained catalytically active and membrane bound in the presence of 1% Tween 20. Total CPT activity was normal in patients and in both parents when measured under optimal assay conditions. After addition of 1% Tween 20 the insoluble CPT activity was also normal in patients and in both parents. The soluble CPT activity, however, was almost completely lost in patients but was only partially decreased in both parents. The data indicate that in patients an enzymatically active CPT II exists which is abnormally sensitive to inhibition by Tween 20, and that CPT I activity is not compensatorily increased in patients. A partial CPT II deficiency can be identified in heterozygotes most sensitively by the separate determination of soluble and insoluble CPT activities in the presence of 1% Tween 20.