ABSTRACT
The inborn errors of fatty acid oxidation, including carnitine transporter deficiency [1], represent a newly recognized area of human disease. The rate of discovery of distinct disorders has increased rapidly since the discovery of medium-chain acyl CoA dehydrogenase (MCAD) deficiency in 1982 (Chapter 40). Deficiency of carnitine is common in these disorders in which fatty acyl CoA compounds accumulate which then form esters with carnitine and are preferentially excreted in the urine. Carnitine deficiency may also be profound in organic acidemias such as propionic acidemia for the same reason. The transport of carnitine into fibroblasts is inhibited by long and medium chain acylcarnitines [2], and this may be an additional factor in carnitine deficiency in disorders of fatty acid oxidation. Primary carnitine deficiency resulting from an abnormality in the synthesis of carnitine from proteinbound lysine has not yet been observed. Many of the patients reported early as primary carnitine deficiency have turned out to have MCAD deficiency. Deficiency of carnitine as a result of abnormality in the transporter (Figure 37.1) that facilitates its entry into certain cells has been referred to as primary carnitine deficiency [1]. The gene for the carnitine transporter SLC22A5 has been cloned, and a small number of mutations have been defined [3].
