ETFDH mutations, CoQ10 levels, and respiratory chain activities in patients with riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency

Disorders of muscle lipid metabolism: diagnostic and therapeutic challenges

Disorders of muscle lipid metabolism may involve intramyocellular triglyceride degradation, carnitine uptake, long-chain fatty acids mitochondrial transport, or fatty acid β-oxidation. Three main diseases leading to permanent muscle weakness are associated with severe increased muscle lipid content (lipid storage myopathies): primary carnitine deficiency, neutral lipid storage disease and multiple acyl-CoA dehydrogenase deficiency. A moderate lipidosis may be observed in fatty acid oxidation disorders revealed by rhabdomyolysis episodes such as carnitine palmitoyl transferase II, very-long-chain acyl-CoA dehydrogenase, mitochondrial trifunctional protein deficiencies, and in recently described phosphatidic acid phosphatase deficiency. Respiratory chain disorders and congenital myasthenic syndromes may also be misdiagnosed as fatty acid oxidation disorders due to the presence of secondary muscle lipidosis. The main biochemical tests giving clues for the diagnosis of these various disorders are measurements of blood carnitine and acylcarnitines, urinary organic acid profile, and search for intracytoplasmic lipid on peripheral blood smear (Jordan's anomaly). Genetic analysis orientated by the results of biochemical investigation allows establishing a firm diagnosis. Primary carnitine deficiency and multiple acyl-CoA dehydrogenase deficiency may be treated after supplementation with carnitine, riboflavine and coenzyme Q10. New therapeutic approaches for fatty acid oxidation disorders are currently developed, based on pharmacological treatment with bezafibrate, and specific diets enriched in medium-chain triglycerides or triheptanoin.

High resolution melting analysis facilitates mutation screening of ETFDH gene: applications in riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD) or gluaric aciduria type II is an autosomal recessive disease caused by defects in mitochondrial electron transfer system and metabolism of fatty acid. Recently, ETFDH mutations were reported to be major causes of riboflavin-responsive MADD. The present study is aimed at screening ETFDH mutations.

METHODS

High resolution melting (HRM) analysis was performed to screen ETFDH mutations. Genomic DNA was extracted from peripheral blood samples of the 9 patients with MADD and normal controls. Total 13 exons of ETFDH were screened by HRM analysis. The results were subsequently confirmed by direct DNA sequencing.

RESULTS

This diagnostic strategy proved to be feasible in detecting 3 known (c.250G>A, c380T>A, c.524G>T) and 1 novel (c.1831G>A) ETFDH mutations. Each mutation could be readily and accurately identified in the difference plot curves. We estimated the carrier frequency of the hotspot mutation, c.250G>A, in the Taiwanese population to be 1:125 (0.8%).

CONCLUSIONS

HRM analysis can be successfully applied to screen ETFDH mutations. Since riboflavin-responsive MADD is often treatable, especially with mutations in ETFDH, identifying ETFDH mutations is crucial for these patients.

Coenzyme Q and mitochondrial disease

Coenzyme Q(10) (CoQ(10)) is an essential electron carrier in the mitochondrial respiratory chain and an important antioxidant. Deficiency of CoQ(10) is a clinically and molecularly heterogeneous syndrome, which, to date, has been found to be autosomal recessive in inheritance and generally responsive to CoQ(10) supplementation. CoQ(10) deficiency has been associated with five major clinical phenotypes: (1) encephalomyopathy, (2) severe infantile multisystemic disease, (3) cerebellar ataxia, (4) isolated myopathy, and (5) nephrotic syndrome. In a few patients, pathogenic mutations have been identified in genes involved in the biosynthesis of CoQ(10) (primary CoQ(10) deficiencies) or in genes not directly related to CoQ(10) biosynthesis (secondary CoQ(10) deficiencies). Respiratory chain defects, ROS production, and apoptosis contribute to the pathogenesis of primary CoQ(10) deficiencies. In vitro and in vivo studies are necessary to further understand the pathogenesis of the disease and to develop more effective therapies.

Characterizing the transcriptional regulation of let-721, a Caenorhabditis elegans homolog of human electron flavoprotein dehydrogenase

LET-721 is the Caenorhabditis elegans ortholog of electron-transferring flavoprotein dehydrogenase (ETFDH). We are studying this protein in C. elegans in order to establish a tractable model system for further exploration of ETFDH structure and function. ETFDH is an inner mitochondrial membrane localized enzyme that plays a key role in the beta-oxidation of fatty acids and catabolism of amino acids and choline. ETFDH accepts electrons from at least twelve mitochondrial matrix flavoprotein dehydrogenases via an intermediate dimer protein and transfers the electrons to ubiquinone. In humans, ETFDH mutations result in the autosomal recessive metabolic disorder, multiple acyl-CoA dehydrogenase deficiency. Mutants of let-721 in C. elegans are either maternal effect lethals or semi-sterile. let-721 is transcribed in the pharynx, body wall muscle, hypoderm, intestine and somatic gonad. In addition, the subcellular localization of LET-721 agrees with predictions that it is localized to mitochondria. We identified and confirmed three cis-regulatory sequences (pha-site, rep-site, and act-site). Phylogenetic footprinting of each site indicates that they are conserved between four Caenorhabditis species. The pha-site mapped roughly 1,300 bp upstream of let-721's translational start site and is necessary for expression in pharyngeal tissues. The rep-site mapped roughly 830 bp upstream of the translational start site and represses expression of LET-721 within pharyngeal tissues. The act-site mapped roughly 800 bp upstream of the translational start site and is required for expression within spermatheca, body wall muscle, pharynx, and intestine. Taken together, we find that LET-721 is a mitochondrially expressed protein that is under complex transcriptional controls.