Secondary respiratory chain defect in a boy with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: possible diagnostic pitfalls

We report on a boy who suffered from microcephaly, growth retardation, cardiomyopathy and hepatic dysfunction. When he had his first febrile infection at the age of 3 months he showed metabolic decompensation. Laboratory parameters and clinical features were compatible with a beta-oxidation defect or a respiratory chain disorder. Measurement of beta-oxidation enzymes showed long-chain 3-hydroxyacyl CoA dehydrogenase (LCHAD) deficiency; determination of respiratory chain complex activities revealed complete absence of complex I, II, III and IV activities in skeletal muscle and reduced activities of complexes II and IV in cultured fibroblasts, with secondary dysregulation of ATP synthase. The patient was found to be homozygous for the MTP:G1528 C mutation (LCHAD-deficiency). Conclusion This patient had LCHAD deficiency as his primary metabolic disorder, leading to secondary inhibition of respiratory chain enzymes by 'toxic' metabolites.