Mutations in the lipoyltransferaseLIPT1gene cause a fatal disease associated with a specific lipoylation defect of the 2-ketoacid dehydrogenase complexes

Abstract

Cofactor disorders of mitochondrial energy metabolism are a heterogeneous group of diseases with a wide variety of clinical symptoms, particular metabolic profiles and variable enzymatic defects. Mutations in NFU1, BOLA3, LIAS and IBA57 have been identified in patients with deficient lipoic acid-dependent enzymatic activities and defects in the assembly and activity of the mitochondrial respiratory chain complexes. Here, we report a patient with an early onset fatal lactic acidosis presenting a biochemical phenotype compatible with a combined defect of pyruvate dehydrogenase (PDHC) and 2-ketoglutarate dehydrogenase (2-KGDH) activities, which suggested a deficiency in lipoic acid metabolism. Immunostaining analysis showed that lipoylated E2-PDH and E2-KGDH were extremely reduced in this patient. However, the absence of glycine elevation, the normal activity of the glycine cleavage system and the normal lipoylation of the H protein suggested a defect of lipoic acid transfer to particular proteins rather than a general impairment of lipoic acid biosynthesis as the potential cause of the disease. By analogy with yeast metabolism, we postulated LIPT1 as the altered candidate gene causing the disease. Sequence analysis of the human LIPT1 identified two heterozygous missense mutations (c.212C>T and c.292C>G), segregating in different alleles. Functional complementation experiments in patient's fibroblasts demonstrated that these mutations are disease-causing and that LIPT1 protein is required for lipoylation and activation of 2-ketoacid dehydrogenases in humans. These findings expand the spectrum of genetic defects associated with lipoic acid metabolism and provide the first evidence of a lipoic acid transfer defect in humans.

Assembly of Lipoic Acid on Its Cognate Enzymes: an Extraordinary and Essential Biosynthetic Pathway

“…In contrast to the LIAS patients, two children with LIPT1 mutations had normal levels of glycine cleavage activity, H protein lipoylation, and glycine in body fluids (153,154). As seen in the LIAS cases, pyruvate and 2-oxoglutarate dehydrogenase activities were very low.…”

“…As seen in the LIAS cases, pyruvate and 2-oxoglutarate dehydrogenase activities were very low. Both patients showed a severe lack of muscle tone and excreted very high levels of lactate (the product of pyruvate reduction) and 2-oxoglutarate (153,154). The E2 subunits of all three dehydrogenases showed low levels of lipoylation, concomitant with the results of the 2-oxoacid dehydrogenase activity assays, whereas liver tissue glycine cleavage H protein lipoylation appeared to be increased somewhat above control levels in the patient tested (154).…”

“…Both patients showed a severe lack of muscle tone and excreted very high levels of lactate (the product of pyruvate reduction) and 2-oxoglutarate (153,154). The E2 subunits of all three dehydrogenases showed low levels of lipoylation, concomitant with the results of the 2-oxoacid dehydrogenase activity assays, whereas liver tissue glycine cleavage H protein lipoylation appeared to be increased somewhat above control levels in the patient tested (154). The addition of lipoic acid to the growth medium of fibroblasts derived from both patients failed to restore lipoylation (153,154), whereas the introduction of a wild-type LIPT1 gene restored fibroblast 2-oxoacid dehydrogenase activities (153).…”

The spectrum of pyruvate oxidation defects in the diagnosis of mitochondrial disorders

“…It is remarkable that iron-sulphur cluster and lipoic acid defects, especially NFU1, have been associated with pulmonary symptoms like respiratory insufficiency or pulmonary hypertension (Seyda et al 2001;Navarro-Sastre et al 2011;Soreze et al 2013;Mayr et al 2014;Tort et al 2014). All BOLA3 patients published so far suffered from hypertrophic cardiomyopathy (Seyda et al 2001;Haack et al 2013;Baker et al 2014).…”

Drug-target interaction prediction: A Bayesian ranking approach

“…Next, we will illustrate that the predictions of BRDTI may contribute to promising thera- Finally, we point out that Lipoyltransferase 1 gene (LIPT1) defects cause Leigh disease [48] and, in case of severe defects, fatal lactic acidosis [49,50]. We hypothesize that in some cases of LIPT mutations, an agonist could help to increase enzymatic activity.…”