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

Compartmental Differences in the Retinal Ganglion Cell Mitochondrial Proteome

Among neurons, retinal ganglion cells (RGCs) are uniquely sensitive to mitochondrial dysfunction. The RGC is highly polarized, with a somatodendritic compartment in the inner retina and an axonal compartment projecting to targets in the brain. The drastically dissimilar functions of these compartments implies that mitochondria face different bioenergetic and other physiological demands. We hypothesized that compartmental differences in mitochondrial biology would be reflected by disparities in mitochondrial protein composition. Here, we describe a protocol to isolate intact mitochondria separately from mouse RGC somatodendritic and axonal compartments by immunoprecipitating labeled mitochondria from RGC MitoTag mice. Using mass spectrometry, 471 and 357 proteins were identified in RGC somatodendritic and axonal mitochondrial immunoprecipitates, respectively. We identified 10 mitochondrial proteins exclusively in the somatodendritic compartment and 19 enriched ≥2-fold there, while 3 proteins were exclusively identified and 18 enriched in the axonal compartment. Our observation of compartment-specific enrichment of mitochondrial proteins was validated through immunofluorescence analysis of the localization and relative abundance of superoxide dismutase ( SOD2 ), sideroflexin-3 ( SFXN3 ) and trifunctional enzyme subunit alpha ( HADHA ) in retina and optic nerve specimens. The identified compartmental differences in RGC mitochondrial composition may provide promising leads for uncovering physiologically relevant pathways amenable to therapeutic intervention for optic neuropathies.

Tracer-based lipidomics enables the discovery of disease-specific candidate biomarkers in mitochondrial β-oxidation disorders

Carnitine derivatives of disease-specific acyl-CoAs are the diagnostic hallmark for long-chain fatty acid β-oxidation disorders (lcFAOD), including carnitine shuttle deficiencies, very-long-chain acyl-CoA dehydrogenase deficiency (VLCADD), long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) and mitochondrial trifunctional protein deficiency (MPTD). The exact consequence of accumulating lcFAO-intermediates and their influence on cellular lipid homeostasis is, however, still unknown. To investigate the fate and cellular effects of the accumulating lcFAO-intermediates and to explore the presence of disease-specific markers, we used tracer-based lipidomics with deuterium-labeled oleic acid (D9-C18:1) in lcFAOD patient-derived fibroblasts. In line with previous studies, we observed a trend towards neutral lipid accumulation in lcFAOD. In addition, we detected a direct connection between the chain length and patterns of (un)saturation of accumulating acylcarnitines and the various enzyme deficiencies. Our results also identified two disease-specific candidate biomarkers. Lysophosphatidylcholine(14:1) (LPC(14:1)) was specifically increased in severe VLCADD compared to mild VLCADD and control samples. This was confirmed in plasma samples showing an inverse correlation with enzyme activity, which was better than the classic diagnostic marker C14:1-carnitine. The second candidate biomarker was an unknown lipid class, which we identified as S-(3-hydroxyacyl)cysteamines. We hypothesized that these were degradation products of the CoA moiety of accumulating 3-hydroxyacyl-CoAs. S-(3-hydroxyacyl)cysteamines were significantly increased in LCHADD compared to controls and other lcFAOD, including MTPD. Our findings suggest extensive alternative lipid metabolism in lcFAOD and confirm that lcFAOD accumulate neutral lipid species. In addition, we present two disease-specific candidate biomarkers for VLCADD and LCHADD, that may have significant relevance for disease diagnosis, prognosis, and monitoring.

Case report: Mitochondrial trifunctional protein deficiency caused by HADHB gene mutation (c.1175C>T) characterized by higher brain dysfunction followed by neuropathy, presented gadolinium enhancement on brain imaging in an adult patient

Mitochondrial trifunctional protein (MTP) deficiency is an autosomal recessive disorder caused by impaired metabolism of long-chain fatty acids (LCFAs). Childhood and late-onset MTP deficiency is characterized by myopathy/rhabdomyolysis and peripheral neuropathy; however, the features are unclear. A 44-year-old woman was clinically diagnosed with Charcot-Marie-Tooth disease at 3 years of age due to gait disturbance. Her activity and voluntary speech gradually decreased in her 40s. Cognitive function was evaluated and brain imaging tests were performed. The Mini-Mental State Examination and frontal assessment battery scores were 25/30 and 10/18, respectively, suggesting higher brain dysfunction. Peripheral nerve conduction studies revealed axonal impairments. Brain computed tomography showed significant calcification. Magnetic resonance imaging revealed an increased gadolinium contrast-enhanced signal in the white matter, suggesting demyelination of the central nervous system (CNS) due to LCFAs. The diagnosis of MTP deficiency was confirmed through genetic examination. Administration of L-carnitine and a medium-chain fatty triglyceride diet was initiated, and the progression of higher brain dysfunction was retarded within 1 year. This patient's presentation was suggestive of CNS demyelination. The presence of brain calcification, higher brain dysfunction, or gadolinium enhancement in the white matter in patients with peripheral neuropathy may be suggestive of MTP deficiency.

Thermo-sensitive mitochondrial trifunctional protein deficiency presenting with episodic myopathy

Mitochondrial trifunctional protein (MTP) is involved in long-chain fatty acid β-oxidation (lcFAO). Deficiency of one or more of the enzyme activities as catalyzed by MTP causes generalized MTP deficiency (MTPD), long-chain hydroxyacyl-CoA dehydrogenase deficiency (LCHADD), or long-chain ketoacyl-CoA thiolase deficiency (LCKATD). When genetic variants result in thermo-sensitive enzymes, increased body temperature (e.g. fever) can reduce enzyme activity and be a risk factor for clinical decompensation. This is the first description of five patients with a thermo-sensitive MTP deficiency. Clinical and genetic information was obtained from clinical files. Measurement of LCHAD and LCKAT activities, lcFAO-flux studies and palmitate loading tests were performed in skin fibroblasts cultured at 37°C and 40°C. In all patients (four MTPD, one LCKATD), disease manifested during childhood (manifestation age: 2-10 years) with myopathic symptoms triggered by fever or exercise. In four patients, signs of retinopathy or neuropathy were present. Plasma long-chain acylcarnitines were normal or slightly increased. HADHB variants were identified (at age: 6-18 years) by whole exome sequencing or gene panel analyses. At 37°C, LCHAD and LCKAT activities were mildly impaired and lcFAO-fluxes were normal. Remarkably, enzyme activities and lcFAO-fluxes were markedly diminished at 40°C. Preventive (dietary) measures improved symptoms for most. In conclusion, all patients with thermo-sensitive MTP deficiency had a long diagnostic trajectory and both genetic and enzymatic testing were required for diagnosis. The frequent absence of characteristic acylcarnitine abnormalities poses a risk for a diagnostic delay. Given the positive treatment effects, upfront genetic screening may be beneficial to enhance early recognition.

Charcot-Marie-Tooth Disease With Episodic Rhabdomyolysis Due to Two Novel Mutations in the β Subunit of Mitochondrial Trifunctional Protein and Effective Response to Modified Diet Therapy

A 29-year-old female experienced chronic progressive peripheral neuropathy since childhood and was diagnosed with Charcot–Marie–Tooth disease (CMT) at age 15. She developed recurrent, fever-induced rhabdomyolysis (RM) at age 24. EMG studies showed decreased amplitude of compound muscle action potential, declined motor conductive velocity, and absence of sensor nerve action potential. Acylcarnitine analysis revealed elevated C16-OH, C18-OH, and C18:1-OH. Muscle biopsy showed scattered foci of necrotic myofibers invaded by macrophages, occasional regenerating fibers, and remarkable muscle fiber type grouping. Whole-exome sequencing identified two novel heterozygous mutations: c.490G>A (p.G164S) and c.686G>A (p.R229Q) in HADHB gene encoding the β-subunit of mitochondrial trifunctional protein (MTP). Reduction of long-chain fatty acid via dietary restrictions alleviated symptoms effectively. Our study indicates that the defect of the MTP β-subunit accounts for both CMT and RM in the same patient and expands the clinical spectrum of disorders caused by the HADHB mutations. Our systematic review of all MTPD patients with dietary treatment indicates that the effect of dietary treatment is related to the age of onset and the severity of symptoms.

Hypoparathyroidism, neutropenia and nephrotic syndrome in a patient with mitochondrial trifunctional protein deficiency: A case report and review of the literature

INTRODUCTION

Mitochondrial trifunctional protein (TFP) deficiency is an autosomal recessive disorder that causes a clinical spectrum of diseases ranging from severe infantile cardiomyopathy to mild chronic progressive neuromyopathy, however, parathyroid glands, hematologic system and kidney damage are not the common presentations of this disease.

METHODS

We describe the clinical, biochemical and molecular features of the TFP deficiency patient at our institution. We also provide an extensive literature review of previous published cases with emphasis on the clinical/biochemical phenotype-genotype correlation of this disorder.

RESULTS

Our case is a complete TFP deficiency patient dominated presented with hypoparathyroidism, neutropenia and nephrotic syndrome, which caused by compound heterozygoues variants in HADHB gene. Based on the retrospective study of 157 cases, TFP patients presented with diverse clinical, biochemical and molecular features. The onset age is typically before early childhood. Neuromuscular system is more vulnerable involved. Severe form is generally characterized by multiorgan involvement. A notable feature of severe and intermediate form is respiratory failure. Neuropathy and rhabdomyolysis are the typical manifestations of mild form. Increased long-chain 3-OH-acylcarnitines (C16-OH, C18:1-OH) are the most common biochemical finding. The mortality of the present study is as high as 57.9%, which is linked with the onset age, phenotype, mutation type and muscular histology. Mutations in HADHB are more frequent in Asian descent with complete TFP deficiency and usually presented with atypical presentations. The type of mutation, rather than residual enzyme activity seem to be more related to the phenotype and prognosis. The most common HADHA variant is 1528G > C, no common HADHB variant were detected.

CONCLUSIONS

TFP deficiency is heterogeneous at both the molecular and phenotypic levels, generally a high mortality. Although there is no strict clinical/biochemical phenotype-genotype correlation, difference in ethnic and subunit mutations still have certain characteristics.

MTP deficiency caused by HADHB mutations: Pathophysiology and clinical manifestations

Mutations in the HADHB gene lead to Mitochondrial Trifunctional Protein (MTP) deficiency. MTP deficiency is a rare autosomal recessive disorder affecting long-chain fatty acid oxidation. Patients affected by MTP deficiency are unable to metabolize long-chain fatty-acids and suffer a variety of symptoms exacerbated during fasting. The three phenotypes associated with complete MTP deficiency are an early-onset cardiomyopathy and early death, an intermediate form with recurrent hypoketotic hypoglycemia and a sensorimotor neuropathy with episodic rhabdomyolysis with small amount of residual enzyme activities. This review aims to discuss the pathophysiological mechanisms and clinical manifestations of each phenotype, which appears different and linked to HADHB expression levels. Notably, the pathophysiology of the sensorimotor neuropathy is relatively unknown and we provide a hypothesis on the qualitative aspect of the role of acylcarnitine buildup in Schwann cells in MTP deficiency patients. We propose that acylcarnitine may exit the Schwann cell and alter membrane properties of nearby axons leading to axonal degeneration based on recent findings in different metabolic disorders.

PhenoMIP: High-Throughput Phenotyping of Diverse Caenorhabditis elegans Populations via Molecular Inversion Probes

Whether generated within a lab setting or isolated from the wild, variant alleles continue to be an important resource for decoding gene function in model organisms such as Caenorhabditis elegans. With advances in massively parallel sequencing, multiple whole-genome sequenced (WGS) strain collections are now available to the research community. The Million Mutation Project (MMP) for instance, analyzed 2007 N2-derived, mutagenized strains. Individually, each strain averages ∼400 single nucleotide variants amounting to ∼80 protein-coding variants. The effects of these variants, however, remain largely uncharacterized and querying the breadth of these strains for phenotypic changes requires a method amenable to rapid and sensitive high-throughput analysis. Here we present a pooled competitive fitness approach to quantitatively phenotype subpopulations of sequenced collections via molecular inversion probes (PhenoMIP). We phenotyped the relative fitness of 217 mutant strains on multiple food sources and classified these into five categories. We also demonstrate on a subset of these strains, that their fitness defects can be genetically mapped. Overall, our results suggest that approximately 80% of MMP mutant strains may have a decreased fitness relative to the lab reference, N2. The costs of generating this form of analysis through WGS methods would be prohibitive while PhenoMIP analysis in this manner is accomplished at less than one-tenth of projected WGS costs. We propose methods for applying PhenoMIP to a broad range of population selection experiments in a cost-efficient manner that would be useful to the community at large.

Efficacy of bezafibrate in two patients with mitochondrial trifunctional protein deficiency

Mitochondrial trifunctional protein (TFP) deficiency is a rare inherited metabolic disorder caused by defects in fatty acid β-oxidation (FAO) of long-chain fatty acids, leading to impaired energy production. Fasting avoidance, fatty acid-restricted diets, and supplementation with medium-chain triglycerides are recommended as a treatment, but there are no pharmaceutical treatments available with strong evidence of efficacy. Bezafibrate, which enhances the transcription of FAO enzymes, is a promising therapeutic option for FAO disorders (FAODs). The effectiveness of bezafibrate for FAODs has been reported in some clinical trials, but few clinical studies have investigated its in vivo efficacy toward TFP deficiency.

Herein, we describe two Japanese patients with TFP deficiency. Patient 1 presented with recurrent myalgia since the age of 5 years. Laboratory findings showed increased serum levels of long-chain fatty acids and reduced expression of TFPα and TFPβ in his skin fibroblasts. Based on these findings, he was diagnosed with the myopathic type of TFP deficiency. Patient 2 suddenly exhibited cardiopulmonary arrest one day after birth. Elevated levels of creatine kinase and long-chain acylcarnitines were observed. Genetic analysis identified compound heterozygous variants in HADHB (c.1175C>T/c.1364T>G). He was diagnosed with the lethal type of TFP deficiency. Although both patients were treated with dietary therapy and l-carnitine supplementation, they experienced frequent myopathic attacks associated with respiratory infections and exercise. After the initiation of bezafibrate, their myopathic manifestations were markedly reduced, leading to an improvement in quality of life without any side effects.

Our clinical findings indicate that bezafibrate combined with other treatments such as dietary therapy may be effective in improving myopathic manifestations in TFP deficiency.

Mitochondrial DNA Variants and Common Diseases: A Mathematical Model for the Diversity of Age-Related mtDNA Mutations

The mitochondrion is the only organelle in the human cell, besides the nucleus, with its own DNA (mtDNA). Since the mitochondrion is critical to the energy metabolism of the eukaryotic cell, it should be unsurprising, then, that a primary driver of cellular aging and related diseases is mtDNA instability over the life of an individual. The mutation rate of mammalian mtDNA is significantly higher than the mutation rate observed for nuclear DNA, due to the poor fidelity of DNA polymerase and the ROS-saturated environment present within the mitochondrion. In this review, we will discuss the current literature showing that mitochondrial dysfunction can contribute to age-related common diseases such as cancer, diabetes, and other commonly occurring diseases. We will then turn our attention to the likely role that mtDNA mutation plays in aging and senescence. Finally, we will use this context to develop a mathematical formula for estimating for the accumulation of somatic mtDNA mutations with age. This resulting model shows that almost 90% of non-proliferating cells would be expected to have at least 100 mutations per cell by the age of 70, and almost no cells would have fewer than 10 mutations, suggesting that mtDNA mutations may contribute significantly to many adult onset diseases.

Mitochondrial Genetic Disorders: Cell Signaling and Pharmacological Therapies

Mitochondrial fatty acid oxidation (FAO) and respiratory chain (RC) defects form a large group of inherited monogenic disorders sharing many common clinical and pathophysiological features, including disruption of mitochondrial bioenergetics, but also, for example, oxidative stress and accumulation of noxious metabolites. Interestingly, several transcription factors or co-activators exert transcriptional control on both FAO and RC genes, and can be activated by small molecules, opening to possibly common therapeutic approaches for FAO and RC deficiencies. Here, we review recent data on the potential of various drugs or small molecules targeting pivotal metabolic regulators: peroxisome proliferator activated receptors (PPARs), sirtuin 1 (SIRT1), AMP-activated protein kinase (AMPK), and protein kinase A (PKA)) or interacting with reactive oxygen species (ROS) signaling, to alleviate or to correct inborn FAO or RC deficiencies in cellular or animal models. The possible molecular mechanisms involved, in particular the contribution of mitochondrial biogenesis, are discussed. Applications of these pharmacological approaches as a function of genotype/phenotype are also addressed, which clearly orient toward personalized therapy. Finally, we propose that beyond the identification of individual candidate drugs/molecules, future pharmacological approaches should consider their combination, which could produce additive or synergistic effects that may further enhance their therapeutic potential.

High prevalence of carriers of variant c.1528G>C of HADHA gene causing long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) in the population of adult Kashubians from North Poland

Background/Objectives

The mitochondrial β-oxidation of fatty acids is a complex catabolic pathway. One of the enzymes of this pathway is the heterooctameric mitochondrial trifunctional protein (MTP), composed of four α- and β-subunits. Mutations in MTP genes (HADHA and HADHB), both located on chromosome 2p23, cause MTP deficiency, a rare autosomal recessive metabolic disorder characterized by decreased activity of MTP. The most common MTP mutation is long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency caused by the c.1528G>C (rs137852769, p.Glu510Gln) substitution in exon 15 of the HADHA gene.

Subjects/Methods

We analyzed the frequency of genetic variants in the HADHA gene in the adults of Kashubian origin from North Poland and compared this data in other Polish provinces.

Results

We found a significantly higher frequency of HDHA c.1528G>C (rs137852769, p.Glu510Gln) carriers among Kashubians (1/57) compared to subjects from other regions of Poland (1/187). We found higher frequency of c.652G>C (rs71441018, pVal218Leu) polymorphism in the HADHA gene within population of Silesia, southern Poland (1/107) compared to other regions.

Conclusion

Our study indicate described high frequency of c.1528G>C variant of HADHA gene in Kashubian population, suggesting the founder effect. For the first time we have found high frequency of rs71441018 in the South Poland Silesian population.

Clinical, biochemical and molecular investigation of adult-onset glutaric acidemia type II: Characteristics in comparison with pediatric cases

INTRODUCTION

An increasing number of adult patients have been diagnosed with fatty acid β-oxidation disorders with the rising use of diagnostic technologies. In this study, clinical, biochemical, and molecular characteristics of 2 Japanese patients with adult-onset glutaric acidemia type II (GA2) were investigated and compared with those of pediatric cases.

METHODS

The patients were a 58-year-old male and a 31-year-old male. In both cases, episodes of myopathic symptoms, including myalgia, muscle weakness, and liver dysfunction of unknown cause, had been noted for the past several years. Muscle biopsy, urinary organic acid analysis (OA), acylcarnitine (AC) analysis in dried blood spots (DBS) and serum, immunoblotting, genetic analysis, and an in vitro probe acylcarnitine (IVP) assay were used for diagnosis and investigation.

RESULTS

In both cases, there was no obvious abnormality of AC in DBS or urinary OA, although there was a increase in medium- and long-chain ACs in serum; also, fat deposits were observed in the muscle biopsy. Immunoblotting and gene analysis revealed that both patients had GA2 due to a defect in electron transfer flavoprotein dehydrogenase (ETFDH). The IVP assay indicated no special abnormalities in either case.

CONCLUSION

Late-onset GA2 is separated into the intermediate and myopathic forms. In the myopathic form, episodic muscular symptoms or liver dysfunction are primarily exhibited after later childhood. Muscle biopsy and serum (or plasma) AC analysis allow accurate diagnosis in contrast with other biochemical tests, such as analysis of AC in DBS, urinary OA, or the IVP assay, which show fewer abnormalities in the myopathic form compared to intermediate form.

A fetus with mitochondrial trifunctional protein deficiency: Elevation of 3-OH-acylcarnitines in amniotic fluid functionally assured the genetic diagnosis

Mitochondrial trifunctional protein (TFP) is a multienzyme complex that catalyzes the last three steps of the β-oxidation cycle of long-chain fatty acids. In the prenatal diagnosis of TFP deficiency, acylcarnitine (AC) analysis has been considered difficult because of limited excretion of long-chain ACs into the fetal urine and hence into the amniotic fluid. Here, we report our experience with prenatally diagnosing TFP deficiency using AC analysis of amniotic fluid. The index case was a boy born at 38 weeks gestation and weighing 2588 g. He suddenly became unconscious and hypoglycemic and died on day 6 of life. Postmortem blood AC analysis and gene sequencing revealed TFP deficiency. Therefore, the parents underwent prenatal diagnoses for their subsequent 2 pregnancies. Mutation analysis suggested that one (Case 1) was affected and the other (Case 2) was not. AC analysis also demonstrated identical results, with significantly elevated 3-hydroxy-AC levels in the amniotic fluid of the affected pregnancy compared with those of heterozygotes and normal controls (n = 2 for heterozygotes and n = 8 for normal controls). Our findings suggest that AC analysis can functionally confirm results even in families with unidentified mutations, without raising issues related to maternal cell contamination. During prenatal diagnosis, misdiagnosis has to be avoided, and combining AC analysis with gene sequencing may result in more accurate prenatal diagnosis of TFP deficiency.

Mitochondrial trifunctional protein deficiency due to HADHB gene mutation in a Chinese family

We report an 8-year-old girl with lower limb weakness since birth in whom mitochondrial trifunctional protein (MTP) deficiency, an autosomal recessive fatty acid oxidation disorder caused by HADHA or HADHB mutations, had not been definitively diagnosed before she was referred to our hospital. Repeated blood acylcarnitine analysis revealed slightly increased long-chain 3-OH-acylcarnitine levels; electromyography (EMG) suggested peripheral nerve injury; muscle biopsy confirmed a neurogenic lesion in muscle fibers, as shown by EMG. Analysis of the HADHB, which encodes long-chain 3-ketoacyl-CoA thiolase, one of the enzymes constituting mitochondrial trifunctional protein, identified homozygous missense mutation c.739C > T (p.R247C). Mitochondrial trifunctional protein deficiency is an extremely rare disorder and has not been reported in Chinese people to date. It is likely that neonatal onset, as seen in our patient, has not been reported for the neuromyopathic phenotype of mitochondrial trifunctional protein deficiency.

The Biochemistry and Physiology of Mitochondrial Fatty Acid β-Oxidation and Its Genetic Disorders

Mitochondrial fatty acid β-oxidation (FAO) is the major pathway for the degradation of fatty acids and is essential for maintaining energy homeostasis in the human body. Fatty acids are a crucial energy source in the postabsorptive and fasted states when glucose supply is limiting. But even when glucose is abundantly available, FAO is a main energy source for the heart, skeletal muscle, and kidney. A series of enzymes, transporters, and other facilitating proteins are involved in FAO. Recessively inherited defects are known for most of the genes encoding these proteins. The clinical presentation of these disorders may include hypoketotic hypoglycemia, (cardio)myopathy, arrhythmia, and rhabdomyolysis and illustrates the importance of FAO during fasting and in hepatic and (cardio)muscular function. In this review, we present the current state of knowledge on the biochemistry and physiological functions of FAO and discuss the pathophysiological processes associated with FAO disorders.

Acute fatty liver of pregnancy associated with fetal mitochondrial trifunctional protein deficiency

Acute fatty liver of pregnancy (AFLP) is a devastating disorder of the maternal liver in the third trimester. Recent studies have demonstrated an association between AFLP and fetal fatty acid oxidation disorders. Here, we report a case of AFLP caused by fetal mitochondrial trifunctional protein (TFP) deficiency. A 21-year-old parous woman presented with nausea, genital bleeding and abdominal pain at 33 weeks of gestation. Laboratory data revealed hepatic failure and disseminated intravascular coagulopathy. The patient underwent emergency cesarean section and was diagnosed with AFLP from the clinical characteristics. She was successfully treated with frequent plasma exchange. The newborn presented severe heart failure and died on the 39th day after birth. Tandem mass spectrometry indicated long-chain fatty acid oxidation disorder. Gene analysis demonstrated homozygous mutation in exon 13 of HADHB, the gene responsible for mitochondrial TFP deficiency. The parents carried a heterozygous mutation at the same location in HADHB.

Muscle MRI in patients with long-chain fatty acid oxidation disorders

INTRODUCTION

Muscle magnetic resonance imaging (MRI) is a useful tool for visualizing abnormalities in neuromuscular disorders. The value of muscle MRI has not been studied in long-chain fatty acid oxidation (lcFAO) disorders. LcFAO disorders may present with metabolic myopathy including episodic rhabdomyolysis.

OBJECTIVE

To investigate whether lcFAO disorders are associated with muscle MRI abnormalities.

METHODS

Lower body MRI was performed in 20 patients with lcFAO disorders, i.e. three carnitine palmitoyltransferase 2 deficiency (CPT2D), 12 very long-chain acyl-CoA dehydrogenase deficiency (VLCADD), three mitochondrial trifunctional protein deficiency (MTPD) and two isolated long-chain hydroxyacyl-CoA dehydrogenase deficiency (LCHADD).

RESULTS

At the time of MRI, four patients had muscle weakness, 14 had muscle pain and 13 were exercise intolerant. Median creatine kinase (CK) level of patients at the day of MRI was 398 U/L (range 35-12,483). T1W and STIR signal intensity (SI) were markedly increased in MTPD patients from girdle to lower leg. VLCADD patients showed predominantly proximal T1W SI changes, whereas LCHADD patients mostly showed distal T1W SI changes. Prominent STIR weighted signal intensity increases of almost all muscle groups were observed in patients with VLCADD and LCHADD with very high CK (>11.000) levels.

CONCLUSIONS AND RELEVANCE

lcFAO disorders are associated with specific patterns of increased T1W and STIR signal intensity. These patterns may reflect lipid accumulation and inflammation secondary to lcFAO defects and progressive muscle damage. Future studies are needed to investigate whether muscle MRI might be a useful tool to monitor disease course and to study pathogenesis of lcFAO related myopathy.

Mutations in HADHB, which encodes the β-subunit of mitochondrial trifunctional protein, cause infantile onset hypoparathyroidism and peripheral polyneuropathy

Mitochondrial trifunctional protein (MTP) is a hetero-octamer composed of four α- and four β-subunits that catalyzes the final three steps of mitochondrial β-oxidation of long chain fatty acids. HADHA and HADHB encode the α-subunit and the β-subunit of MTP, respectively. To date, only two cases with MTP deficiency have been reported to be associated with hypoparathyroidism and peripheral polyneuropathy. Here, we report on two siblings with autosomal recessive infantile onset hypoparathyroidism, peripheral polyneuropathy, and rhabdomyolysis. Sequence analysis of HADHA and HADHB in both siblings shows that they were homozygous for a mutation in exon 14 of HADHB (c.1175C>T, [p.A392V]) and the parents were heterozygous for the mutation. Biochemical analysis revealed that the patients had MTP deficiency. Structural analysis indicated that the A392V mutation identified in this study and the N389D mutation previously reported to be associated with hypoparathyroidism are both located near the active site of MTP and affect the conformation of the β-subunit. Thus, the present patients are the second and third cases of MTP deficiency associated with missense HADHB mutation and infantile onset hypoparathyroidism. Since MTP deficiency is a treatable disease, MTP deficiency should be considered when patients have hypoparathyroidism as the initial presenting feature in infancy.

A compound heterozygous mutation in HADHB gene causes an axonal Charcot-Marie-tooth disease

Background

Charcot-Marie-Tooth disease (CMT) is a heterogeneous disorder of the peripheral nervous system. So far, mutations in hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase (trifunctional protein), beta subunit (HADHB) gene exhibit three distinctive phenotypes: severe neonatal presentation with cardiomyopathy, hepatic form with recurrent hypoketotic hypoglycemia, and later-onset axonal sensory neuropathy with episodic myoglobinuria.

Methods

To identify the causative and characterize clinical features of a Korean family with motor and sensory neuropathies, whole exome study (WES), histopathologic study of distal sural nerve, and lower limb MRIs were performed.

Results

WES revealed that a compound heterozygous mutation in HADHB is the causative of the present patients. The patients exhibited an early-onset axonal sensorimotor neuropathy without episodic myoglobinuria, and showed typical clinical and electrophysiological features of CMT including predominant distal muscle weakness and atrophy. Histopathologic findings of sural nerve were compatible with an axonal CMT neuropathy. Furthermore, they didn’t exhibit any other symptoms of the previously reported HADHB patients.

Conclusions

These data implicate that mutation in HADHB gene can also cause early-onset axonal CMT instead of typical manifestations in mitochondrial trifunctional protein (MTP) deficiency. Therefore, this study is the first report of a new subtype of autosomal recessive axonal CMT by a compound heterozygous mutation in HADHB, and will expand the clinical and genetic spectrum of HADHB.

Observations regarding retinopathy in mitochondrial trifunctional protein deficiencies

Although the retina is thought to primarily rely on glucose for fuel, inherited deficiency of one or more activities of mitochondrial trifunctional protein results in a pigmentary retinopathy leading to vision loss. Many other enzymatic deficiencies in fatty acid oxidation pathways have been described, none of which results in retinal complications. The etiology of retinopathy among patients with defects in trifunctional protein is unknown. Trifunctional protein is a heteroctomer; two genes encode the alpha and beta subunits of TFP respectively, HADHA and HADHB. A common mutation in HADHA, c.1528G>C, leads to a single amino acid substitution, p. Glu474Gln, and impairs primarily long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) activity leading to LCHAD deficiency (LCHADD). Other mutations in HADHA or HADHB often lead to significant reduction in all three enzymatic activities and result in trifunctional protein deficiency (TFPD). Despite many similarities in clinical presentation and phenotype, there is growing evidence that they can result in different chronic complications. This review will outline the clinical similarities and differences between LCHADD and TFPD, describe the course of the associated retinopathy, propose a genotype/phenotype correlation with the severity of retinopathy, and discuss the current theories about the etiology of the retinopathy.

Necrotizing enterocolitis and respiratory distress syndrome as first clinical presentation of mitochondrial trifunctional protein deficiency

BACKGROUND

Newborn screening (NBS) for long-chain 3-hydroxy acyl-CoA dehydrogenase (LCHAD) deficiency does not discriminate between isolated LCHAD deficiency, isolated long-chain keto acyl-CoA (LCKAT) deficiency and general mitochondrial trifunctional protein (MTP) deficiency. Therefore, screening for LCHAD deficiency inevitably comprises screening for MTP deficiency, which is much less amenable to treatment. Furthermore, absence of a clear classification system for these disorders is still lacking.

MATERIALS AND METHODS

Two newborns screened positive for LCHAD deficiency died at the age of 10 and 31 days, respectively. One due to severe necrotizing enterocolitis (NEC), cardiomyopathy and multiorgan failure and the other due to severe infant respiratory distress syndrome (IRDS) and hypertrophic cardiomyopathy. (Keto)-acylcarnitine concentration and enzymatic analysis of LCHAD and LCKAT suggested MTP deficiency in both patients. Mutation analysis revealed a homozygous HADHB c.357+5delG mutation in one patient and a homozygous splice-site HADHB mutation c.212+1G>C in the other patient.Data on enzymatic and mutation analysis of 40 patients with presumed LCHAD, LCKAT or MTP deficiency were used to design a classification to distinguish between these disorders.

DISCUSSION

NEC as presenting symptom in MTP deficiency has not been reported previously. High expression of long-chain fatty acid oxidation enzymes reported in lungs and gut of human foetuses suggests that the severe NEC and IRDS observed in our patients are related to the enzymatic deficiency in these organs during crucial stages of development.Furthermore, as illustrated by the cases we propose a classification system to discriminate LCHAD, LCKAT and MTP deficiency based on enzymatic analysis.

A patient with mitochondrial trifunctional protein deficiency due to the mutations in the HADHB gene showed recurrent myalgia since early childhood and was diagnosed in adolescence

Mitochondrial trifunctional protein (MTP) is a multienzyme complex involved in the metabolism of long-chain hydroxyacyl-CoA, a product of the fatty acid β-oxidation cycle. MTP is an α4β4 hetero-octomer encoded by two different genes: HADHA (OMIM 600890) and HADHB (OMIM 143450). MTP deficiency induces three different types of presentation: (1) a lethal phenotype with neonatal onset (severe); (2) a hepatic phenotype with infant onset (intermediate); and (3) a neuromyopathic phenotype with late-adolescent onset (mild). While acylcarnitine analysis has revealed increased levels of long-chain hydroxyacylcarnitine in blood when an MTP deficiency exists, the neuromyopathic type is usually asymptomatic and does not always result in an abnormality in acylcarnitine analysis results. We report here the case of a 13-year-old girl with recurrences of intermittent myalgia since her early childhood, for whom the disorder had not been definitely diagnosed. Since she was referred to our hospital because of rhabdomyolysis, we have repeatedly performed blood acylcarnitine analysis and found slight increases in long-chain 3-OH-acylcarnitine levels, on the basis of which we made a chemical diagnosis of MTP deficiency. Immunoblot analysis of skin fibroblasts revealed loss of α- and β-subunits of MTP. In addition, analysis of the HADHB gene, which encodes long-chain 3-ketoacyl-CoA thiolase, one of the enzymes constituting MTP, identified compound heterozygous mutations of c.520C>T (p.R141C) and c.1331G>A (p.R411K). MTP deficiency is considered an extremely rare disorder, as only five cases (lethal phenotype, two patients; hepatic phenotype, two patients; and neuromyopathic phenotype, one patient) have thus far been reported in Japan. However, it is likely that the neuromyopathic phenotype of MTP deficiency has not yet been diagnosed among patients with recurrences of intermittent myalgia and rhabdomyolysis, as in our patient reported here.

Comprehensive cDNA study and quantitative analysis of mutant HADHA and HADHB transcripts in a French cohort of 52 patients with mitochondrial trifunctional protein deficiency

BACKGROUND

Deficiency of mitochondrial trifunctional protein (MTP) is caused by mutations in the HADHA and HADHB genes, which have been mostly delineated at the genomic DNA level and have not been always elucidated.

AIM

To identify mutations in a French cohort of 52 MTP deficient patients and the susceptibility of mutations generating premature termination codons (PTCs) to the nonsense mRNA mediated decay (NMD).

METHODS

Mutation screening in fibroblasts was performed at the cDNA level and real-time RT-PCR was used to compare the levels of the different PTC-bearing mRNAs before and after a treatment of fibroblasts by emetine, a translation inhibitor.

RESULTS

A mutation detection rate of 100% was achieved. A total of 22 novel mutations were identified, including a large-sized genomic deletion in HADHB gene. A high proportion of all identified mutations were non-sense, frameshift and splicing mutations, generating (PTCs), distributed essentially on HADHA coding regions. We could demonstrate that the majority of mutations resulting in PTCs conform to the established rules governing the susceptibility to NMD.

CONCLUSION

Our results emphasize the value of cDNA analysis in the characterization of HADHA and HADHB mutations and further strengthen the model of haploinsufficiency as a major pathomechanism in MTP defects.