Mutations in human lipoyltransferase gene LIPT1 cause a Leigh disease with secondary deficiency for pyruvate and alpha-ketoglutarate dehydrogenase.

International audienceBACKGROUND: Synthesis and apoenzyme attachment of lipoic acid have emerged as a new complex metabolic pathway. Mutations in several genes involved in the lipoic acid de novo pathway have recently been described, but no mutation was found so far in genes involved in the specific process of attachment of lipoic acid to apoenzymes pyruvate dehydrogenase (PDHc), alpha-ketoglutarate dehydrogenase (alpha-KGDHc) and branched chain alpha-keto acid dehydrogenase (BCKDHc) complexes. METHODS: Exome capture was performed in a boy who developed Leigh disease following a gastroenteritis and had combined PDH and alpha-KGDH deficiency with a unique amino acid profile that partly ressembled E3 subunit (dihydrolipoamide dehydrogenase / DLD) deficiency. Functional studies on patient fibroblasts were performed. Lipoic acid administration was tested on the LIPT1 ortholog lip3 deletion strain yeast and on patient fibroblasts. RESULTS: Exome sequencing identified two heterozygous mutations (c.875C > G and c.535A > G) in the LIPT1 gene that encodes a mitochondrial lipoyltransferase which is thought to catalyze the attachment of lipoic acid on PDHc, alpha-KGDHc, and BCKDHc. Anti-lipoic acid antibodies revealed absent expression of PDH E2, BCKDH E2 and alpha-KGDH E2 subunits. Accordingly, the production of 14CO2 by patient fibroblasts after incubation with 14Cglucose, 14Cbutyrate or 14C 3OHbutyrate was very low compared to controls. cDNA transfection experiments on patient fibroblasts rescued PDH and alpha-KGDH activities and normalized the levels of pyruvate and 3OHbutyrate in cell supernatants. The yeast lip3 deletion strain showed improved growth on ethanol medium after lipoic acid supplementation and incubation of the patient fibroblasts with lipoic acid decreased lactate level in cell supernatants. CONCLUSION: We report here a putative case of impaired free lipoic acid attachment due to LIPT1 mutations as a cause of PDH and alpha-KGDH deficiencies. Our study calls for renewed efforts to understand the mechanisms of pathology of lipoic acid-related defects and their heterogeneous biochemical expression, in order to devise efficient diagnostic procedures and possible therapies

A Thermolabile Aldolase A Mutant Causes Fever-Induced Recurrent Rhabdomyolysis without Hemolytic Anemia

International audienceAldolase A deficiency has been reported as a rare cause of hemolytic anemia occasionally associated with myopathy. We identified a deleterious homozygous mutation in the ALDOA gene in 3 siblings with episodic rhabdomyolysis without hemolytic anemia. Myoglobinuria was always triggered by febrile illnesses. We show that the underlying mechanism involves an exacerbation of aldolase A deficiency at high temperatures that affected myoblasts but not erythrocytes. The aldolase A deficiency was rescued by arginine supplementation in vitro but not by glycerol, betaine or benzylhydantoin, three other known chaperones, suggesting that arginine-mediated rescue operated by a mechanism other than protein chaperoning. Lipid droplets accumulated in patient myoblasts relative to control and this was increased by cytokines, and reduced by dexamethasone. Our results expand the clinical spectrum of aldolase A deficiency to isolated temperature-dependent rhabdomyolysis, and suggest that thermolability may be tissue specific. We also propose a treatment for this severe disease

1A: Family tree showing the 3 affected children.

<p>1B: Crystal structure of human muscle aldolase complexed with fructose 1,6-bisphosphate (isoenzyme A, PDB code 4ALD) superimposed with the tetrameric crystal structure of human brain aldolase (isoenzyme C, PDB code 1XFB), which is similar to the muscle isoenzyme. Chains A, B, C and D of isoenzyme C are shown in orange, light blue, light green and pink, respectively. Monomeric isoenzyme A is shown in grey and is superimposed on chain D of the tetrameric isoenzyme C. Fructose 1,6-bisphosphate co-crystallized with isoenzyme A is shown in yellow. The mutated residue described in this report (red arrow) and the mutated amino acids previously described are highlighted in the magnified structure. The structural and functional consequences of the mutations are described in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1004711#pgen-1004711-t001" target="_blank">Table 1</a>. 1C: aldolase A, glucose-6-phosphate dehydrogenase (G6PD) and hexokinase activities in the erythrocytes of the parents, the healthy sibling and the 3 affected patients (*: patients 2, 3, 4). 1D: in vitro muscle study of anaerobic glycogenolysis and glycolysis (only patient 3); results of lactate production (µmol/g muscle in 30 minutes) after incubation with various substrates.</p

Reported cases of Aldolase A deficiency with the described mutations.

<p>*: normal range. In the first case reported by Beutler et al in 1973 with no described mutation, the red cell aldolase activity was 16% of normal mean.</p><p>Reported cases of Aldolase A deficiency with the described mutations.</p

<i>ALDOA</i> expression and activity.

<p>3A:<i>ALDOA</i> mRNA expression in control myoblasts (C, white bars) and the patient myoblasts (P, grey bars) under basal conditions, with TNFα+Ilβ treatment (left) or at a high temperature (right, 40°C); Aldolase A protein levels (lower panel) under basal conditions, with TNFα+Ilβ treatment or at a high temperature. 3B: Aldolase A activity in control and the patients' myoblasts under the same conditions: basal conditions, TNFα+Ilβ treatment and at different temperatures. The results are shown as the mean value ±SD from 3 independent experiments. 3C: Aldolase A activity in control and patients erythrocytes under basal conditions and at different temperatures. The results are shown as the mean value of two independent experiments. 3D: Aldolase A activity (upper) and protein level (below) in the patient myoblasts under basal condition and after arginine (Arg) treatment.*: p<0,05).</p