General mitochondrial trifunctional protein (TFP) deficiency as a result of either alpha- or beta-subunit mutations exhibits similar phenotypes because mutations in either subunit alter TFP complex expression and subunit turnover

Inborn errors of energy metabolism associated with myopathies

Inherited neuromuscular disorders affect approximately one in 3,500 children. Structural muscular defects are most common; however functional impairment of skeletal and cardiac muscle in both children and adults may be caused by inborn errors of energy metabolism as well. Patients suffering from metabolic myopathies due to compromised energy metabolism may present with exercise intolerance, muscle pain, reversible or progressive muscle weakness, and myoglobinuria. In this review, the physiology of energy metabolism in muscle is described, followed by the presentation of distinct disorders affecting skeletal and cardiac muscle: glycogen storage diseases types III, V, VII, fatty acid oxidation defects, and respiratory chain defects (i.e., mitochondriopathies). The diagnostic work-up and therapeutic options in these disorders are discussed.

Clinical and molecular aspects of Japanese patients with mitochondrial trifunctional protein deficiency

Mitochondrial trifunctional protein (MTP) deficiency is a rare inherited metabolic disorder of mitochondrial fatty acid oxidation. We newly characterized three novel mutations in 2 Japanese patients with MTP deficiency, and investigated the clinical and molecular aspects of 5 Japanese patients including 3 previously reported cases. Herein, we describe the characterization of four missense mutations, R214C, H346R, R411K, and V422G, in the HADHB gene, which have been identified in Japanese patients, employing a newly developed, sensitive transient expression analysis. Co-transfection of wild-type HADHA and HADHB cDNAs in SV40-transfected fibroblasts from a MTP-deficient patient yielded sufficient enzyme activity to evaluate low-level residual enzyme activity, using two incubation temperatures of 30 degrees C and 37 degrees C. At 30 degrees C, residual enzyme activity was higher than that at 37 degrees C in V422G, R214C, and R411K. However, H346R, which was seen in the most severe case, showed no enzyme activity at both temperatures. Our results demonstrate that a defect of HADHB in MTP deficiency is rather common in Japanese patients, and the mutational spectrum is heterogeneous. The present findings showed that all missense mutations in this study were disease-causing. Although the number of patients is still limited, it is suggested that the phenotype is correlated with the genotype and a combination of two mutant alleles of the HADHB gene in MTP deficiency.

EFFECT OF FEEDING, EXERCISE AND GENOTYPE ON PLASMA 3-HYDROXYACYLCARNITINES IN CHILDREN WITH LCHAD DEFICIENCY

Chronic complications observed in patients with long-chain 3-hydroxyacylCoA dehydrogenase (LCHAD) or trifunctional protein (TFP) deficiency may be mediated by the accumulation of 3-hydroxy fatty acids or 3-hydroxyacylcarnitines. To understand variation in metabolite accumulation, their concentrations were measured by tandem mass spectrometry before and after a mixed meal and moderate intensity exercise. Subjects who were homozygous or heterozygous for the common mutation (c.1528G>C) in the TFP alpha subunit (LCHAD deficiency) had significantly higher 3-hydroxyacylcarnitines than subjects with TFP deficiency. Feeding a mixed meal significantly suppressed and exercise significantly increased plasma 3-hydroxyacylcarnitines concentrations.

Mitochondrial trifunctional protein deficiency with recurrent rhabdomyolysis

Rhabdomyolysis is an important clinical diagnosis. The differential diagnosis is extensive and includes various etiologies, such as infection, inflammation, trauma, endocrinopathies, and congenital muscular and metabolic disorders. Reported here is the case of an infant with recurrent rhabdomyolysis diagnosed as suffering from mitochondrial trifunctional protein deficiency -- a rare beta oxidation defect. The clinical course was unique, and a new mutation in the mitochondrial trifunctional protein gene was identified.

Study of deep intronic sequence exonization in a Japanese neonate with a mitochondrial trifunctional protein deficiency

Mitochondrial trifunctional protein (MTP) comprises heterooctamer alpha4beta4 and a deficiency in this protein causes a mitochondrial long-chain beta-oxidation defect. Here, we describe the molecular basis of an MTPbeta-subunit deficiency in a Japanese neonate. Mutation screening at the genomic level including all exons and exon-intron boundaries identified a novel c.1136A>G (H346R) mutation in exon 13 of the maternal allele, but none in the paternal allele. Analysis by RT-PCR identified paternal-specific 106- and 56-bp intronic insertions between exons 7 and 8, which introduced premature terminations. This intronic exonization was caused by a deep intronic mutation in intron 7 on the paternal allele that generates a cryptic splice donor site. This is the first report of a deep intronic mutation in MTP deficiency.

Intrauterine cardiomyopathy and cardiac mitochondrial proliferation in mitochondrial trifunctional protein (TFP) deficiency

Because of a switch in energy-producing substrate utilization from glucose in the fetal period to fatty acids postnatally, intrauterine morbidity of fatty acid oxidation defects has widely been denied. We report the intrauterine development of severe cardiomyopathy in a child with mitochondrial trifunctional protein deficiency after 27 weeks of gestation. The child was born at 31 weeks of gestation and died on day 3 of life. Severe cardiac mitochondrial proliferation was observed. Molecular analysis of both TFP genes was performed and confirmed a homozygous mutation in the TFP alpha-subunit introducing a stop codon at amino acid position 256 (g.871C>T, p.R256X). Despite severe intrauterine decompensation in our patient, no HELLP-syndrome or acute fatty liver of pregnancy was observed in the mother. In the pathogenesis of maternal HELLP-syndrome, toxic effects of accumulating long-chain hydroxy-acyl-CoAs or long-chain hydroxy-acylcarnitines are suspected. In our patient, acylcarnitine analysis on day 2 of life during severest metabolic decompensation did not reveal massive accumulation of long-chain hydroxy-acylcarnitines in blood, suggesting other pathogenic factors than toxic effects. The most important pathogenic mechanism for the development of intrauterine cardiomyopathy appears to be significant cardiac energy deficiency. In conclusion, our report implicates that fatty acid oxidation does play a significant role during intrauterine development with special regard to the heart. Severe cardiac mitochondrial proliferation in TFP deficiency suggests pathophysiologically relevant energy deficiency in this condition.

Clinical syndromes with variable pathologic features

Frequently, placentas sent for pathologic examination include a clinical diagnosis that does not suggest a specific placental lesion. Pathologists who do not have great experience in this field may need some assistance with selecting the pertinent placental lesions to look for. This brief outline is included to define these conditions and present a list of the specific placental lesions that deserve consideration. The placental examination should be directed with the goal of identifying or noting and recording specifically the presence or absence of the relevant pathologic lesions. The syndromes or conditions considered in this context include neonatal encephalopathy, preterm birth, fetal growth restriction, maternal diabetes mellitus, thrombophilias, HELLP syndrome, and fetal hydrops.

Genome-wide linkage scans for loci affecting total cholesterol, HDL-C, and triglycerides: the Family Blood Pressure Program

Atherosclerosis accounts for 75% of all deaths from cardiovascular disease and includes coronary heart disease (CHD), stroke, and other diseases of the arteries. More than half of all CHD is attributable to abnormalities in levels and metabolism of lipids. To locate genes that affect total cholesterol, high density lipoprotein cholesterol (HDL-C), and triglycerides, genome-wide linkage scans for quantitative trait loci were performed using variance components methods as implemented in SOLAR on a large diverse sample recruited as part of the Family Blood Pressure Program. Phenotype and genetic marker data were available for 9,299 subjects in 2,953 families for total cholesterol, 8,668 subjects in 2,736 families for HDL, and 7,760 subjects in 2,499 families for triglycerides. Mean lipid levels were adjusted for the effects of sex, age, age2, age-by-sex interaction, body mass index, smoking status, and field center. HDL-C and triglycerides were further adjusted for average total alcoholic drinks per week and estrogen use. Significant linkage was found for total cholesterol on chromosome 2 (LOD=3.1 at 43 cM) in Hispanics and for HDL-C on chromosome 3 (LOD=3.0 at 182 cM) and 12 (LOD=3.5 at 124 cM) in Asians. In addition, there were 13 regions that showed suggestive linkage (LOD >or= 2.0); 7 for total cholesterol, 4 for HDL, and 2 for triglycerides. The identification of these loci affecting lipid phenotypes and the apparent congruence with previous linkage results provides increased support that these regions contain genes influencing lipid levels.

Defining the Mitochondrial Proteomes from Five Rat Organs in a Physiologically Significant Context Using 2D Blue-Native/SDS-PAGE

In accordance with their manifold tasks, various dysfunctions of mitochondria are critically involved in a large number of diseases and the aging process. This has inspired considerable efforts to identify all the mitochondrial proteins by denaturing approaches, notably, the standard gel-based method employing isoelectric focusing. Because a significant part of the mitochondrial proteome is membrane-associated and/or functions as homo- or heterooligomeric protein complexes, there is an urgent need to detect and identify mitochondrial proteins, both membranous and soluble ones, under conditions preserving protein-protein interactions. Here, we investigated mitochondria of five different rat organs (kidney, liver, heart, skeletal muscle, and brain) solubilized with digitonin, enabling the quantitative extraction of the five oxidative phosphorylation (OXPHOS) complexes. The analysis by blue-native (BN)-PAGE recovered the OXPHOS complexes to a large extent as supercomplexes and separated many other protein complexes and individual proteins which were resolved by subsequent 2D SDS-PAGE revealing the tissue-diverse mitochondrial proteomes. Using MS peptide mass fingerprinting, we identified in all five organs 92 nonredundant soluble and membrane-embedded non-OXPHOS proteins, among them, many as constituents of known mitochondrial protein complexes as well as novel ones such as the putative "stomatin-like protein 2 complex" with an apparent mass of ca. 1800 kDa. Interestingly, the identification list included 36 proteins known or presumed to be localized to nonmitochondrial compartments, for example, glycolytic enzymes, clathrin heavy chain, valosin-containing protein/p97, VoV1-ATPase, and Na,K-ATPase. We expect that more than 200 distinct non-OXPHOS proteins of digitonin-solubilized rat mitochondria separated by 2D BN/SDS-PAGE, representing a partial "protein interactome" map, can be identified.

Isolated mitochondrial long-chain ketoacyl-CoA thiolase deficiency resulting from mutations in the HADHB gene

BACKGROUND

The human mitochondrial trifunctional protein (MTP) complex is composed of 4 hydroacyl-CoA dehydrogenase-alpha (HADHA) and 4 hydroacyl-CoA dehydrogenase-beta (HADHB) subunits, which catalyze the last 3 steps in the fatty acid beta-oxidation spiral of long-chain fatty acids. The HADHB gene encodes long-chain ketoacyl-CoA thiolase (LCTH) activity, whereas the HADHA gene contains the information for the long-chain enoyl-CoA hydratase and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) functions. At present, 2 different biochemical phenotypes of defects in the mitochondrial trifunctional protein complex are known: isolated LCHAD deficiency and generalized MTP deficiency, with decreased activities of all 3 enzymes. Isolated LCTH deficiency with mutations in the HADHB gene has not been reported.

PATIENT AND RESULTS

We report a male newborn who presented with lactic acidosis, pulmonary edema, and cardiomyopathy leading to acute heart failure and death at the age of 6 weeks. Routine newborn screening by tandem mass spectrometry showed increased concentrations of the acylcarnitines tetradecenoylcarnitine, hexadecenoylcarnitine, hydroxypalmitoylcarnitine, and hydroxyoctadecenoylcarnitine, suggesting LCHAD deficiency or complete MTP deficiency. Enzyme investigations revealed very low LCTH (4% of normal) and normal LCHAD activities, whereas molecular analysis showed compound heterozygosity for 185G > A (R62H) and 1292T > C (F431S) mutations in the HADHB gene.

CONCLUSION

We describe the first case of isolated LCTH deficiency based on a mutation in the HADHB gene.