Combined enzyme defect of mitochondrial fatty acid oxidation

I Walk the Line: Between Basic Science and Paediatric Surgery

The role of a basic scientist working with paediatric surgeons is not an obvious one. However, there are several levels at which science can contribute to the speciality, and also ways that scientists can learn useful lessons from paediatric surgery. As most conditions treated by paediatric surgeons have low case numbers, we need to find ways of defining optimal treatment and developing novel therapies within a challenging number of patients.

Cardioprotective GLP-1 metabolite prevents ischemic cardiac injury by inhibiting mitochondrial trifunctional protein-α

Mechanisms mediating the cardioprotective actions of glucagon-like peptide 1 (GLP-1) were unknown. Here, we show in both ex vivo and in vivo models of ischemic injury that treatment with GLP-1(28-36), a neutral endopeptidase-generated (NEP-generated) metabolite of GLP-1, was as cardioprotective as GLP-1 and was abolished by scrambling its amino acid sequence. GLP-1(28-36) enters human coronary artery endothelial cells (caECs) through macropinocytosis and acts directly on mouse and human coronary artery smooth muscle cells (caSMCs) and caECs, resulting in soluble adenylyl cyclase Adcy10-dependent (sAC-dependent) increases in cAMP, activation of protein kinase A, and cytoprotection from oxidative injury. GLP-1(28-36) modulates sAC by increasing intracellular ATP levels, with accompanying cAMP accumulation lost in sAC-/- cells. We identify mitochondrial trifunctional protein-α (MTPα) as a binding partner of GLP-1(28-36) and demonstrate that the ability of GLP-1(28-36) to shift substrate utilization from oxygen-consuming fatty acid metabolism toward oxygen-sparing glycolysis and glucose oxidation and to increase cAMP levels is dependent on MTPα. NEP inhibition with sacubitril blunted the ability of GLP-1 to increase cAMP levels in coronary vascular cells in vitro. GLP-1(28-36) is a small peptide that targets novel molecular (MTPα and sAC) and cellular (caSMC and caEC) mechanisms in myocardial ischemic injury.

Lipid Myopathies

Disorders of lipid metabolism affect several tissues, including skeletal and cardiac muscle tissues. Lipid myopathies (LM) are rare multi-systemic diseases, which most often are due to genetic defects. Clinically, LM can have acute or chronic clinical presentation. Disease onset can occur in all ages, from early stages of life to late-adult onset, showing with a wide spectrum of clinical symptoms. Muscular involvement can be fluctuant or stable and can manifest as fatigue, exercise intolerance and muscular weakness. Muscular atrophy is rarely present. Acute muscular exacerbations, resulting in rhabdomyolysis crisis are triggered by several factors. Several classifications of lipid myopathies have been proposed, based on clinical involvement, biochemical defect or histopathological findings. Herein, we propose a full revision of all the main clinical entities of lipid metabolism disorders with a muscle involvement, also including some those disorders of fatty acid oxidation (FAO) with muscular symptoms not included among previous lipid myopathies classifications.

Fatal pitfalls in newborn screening for mitochondrial trifunctional protein (MTP)/long-chain 3-Hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency

Background

Mitochondrial trifunctional protein (MTP) and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency are long-chain fatty acid oxidation disorders with particularly high morbidity and mortality. Outcome can be favorable if diagnosed in time, prompting the implementation in newborn screening programs. Sporadic cases missed by the initial screening sample have been reported. However, little is known on pitfalls during confirmatory testing resulting in fatal misconception of the diagnosis.

Results

We report a series of three patients with MTP and LCHAD deficiency, in whom diagnosis was missed by newborn screening, resulting in life-threatening metabolic decompensations within the first half year of life. Two of the patients showed elevated concentrations of primary markers C16-OH and C18:1-OH but were missed by confirmatory testing performed by the maternity clinic. A metabolic center was not consulted. Confirmatory testing consisted of analyses of acylcarnitines in blood and organic acids in urine, the finding of normal excretion of organic acids led to rejection and underestimation of the diagnosis, respectively. The third patient, a preterm infant, was not identified in the initial screening sample due to only moderate elevations of C16-OH and C18:1-OH and normal secondary markers and analyte ratios.

Conclusion

Our observations highlight limitations of newborn screening for MTP/LCHAD deficiency. They confirm that analyses of acylcarnitines in blood and organic acids in urine alone are not suitable for confirmatory testing and molecular or functional analysis is crucial in diagnosing MTP/LCHAD deficiency. Mild elevations of primary biomarkers in premature infants need to trigger confirmatory testing. Our report underscores the essential role of specialized centers in confirming or ruling out diagnoses in suspicious screening results.

Acute Fatty Liver of Pregnancy: A Retrospective Analysis of 56 Cases

Background:

Acute fatty liver of pregnancy (AFLP) is a rare but life-threatening complication occurring in the third trimester. It is often fatal to both mother and fetus. The complicated clinical manifestations as well as an insufficient understanding of the disease make the precise diagnosis and effective treatment of AFLP challenging. A full understanding of the risk factors, clinical features, and test findings of AFLP is critical for its timely diagnosis and treatment.

Methods:

We performed a retrospective study of 56 patients with AFLP between June 2008 and July 2013. We analyzed the clinical features, laboratory results, perioperative management, and patient outcomes.

Results:

The initial symptoms varied considerably, with nausea and vomiting (13/56, 23%) being the most common. Liver-function indexes were remarkable, including elevated levels of serum alanine aminotransferase (262.16 ± 281.71 U/L), aspartate aminotransferase (260.98 ± 237.91 U/L), lactic dehydrogenase (1011.76 ± 530.34 U/L), and direct bilirubin (85.59 ± 90.02 μmol/L). Coagulation disorders were indicated by abnormal levels of fibrinogen (245.95 ± 186.11 mg/dL), D-dimer (2.46 ± 4.01 mg/L), and fibrin degradation products (43.62 ± 48.71 mg/L). The main maternal complications were hypoproteinemia (75%), coagulopathy (54%), and acute renal failure (39%). Multivariate logistic regression analysis identified prothrombin time (PT; odds ratio [OR] = 1.558, 95% confidence interval [CI] =1.248–1.946, P = 0.016) and international normalized ratio (INR; OR = 40.034, 95% CI = 2.517–636.693, P = 0.009) as risk factors. The perinatal infant death rate was related to gestational age at delivery (OR = 1.298, 95% CI = 1.040–1.618, P = 0.021), direct bilirubin (OR = 1.05, 95% CI = 1.008–1.094, P = 0.020), and fibrin degradation products (OR = 0.973, 95% CI = 0.950–0.996, P = 0.021).

Conclusions:

Nausea and vomiting may be the most common symptoms of AFLP. Indexes of liver dysfunction and coagulation disorders should also be considered. PT and INR are risk factors for fatal complications in patients with AFLP, and perinatal mortality is linked to the level of fibrin degradation products. Timely delivery is crucial to controlling the development of AFLP.

Autophagy and ubiquitin-proteasome system contribute to sperm mitophagy after mammalian fertilization

Maternal inheritance of mitochondria and mtDNA is a universal principle in human and animal development, guided by selective ubiquitin-dependent degradation of the sperm-borne mitochondria after fertilization. However, it is not clear how the 26S proteasome, the ubiquitin-dependent protease that is only capable of degrading one protein molecule at a time, can dispose of a whole sperm mitochondrial sheath. We hypothesized that the canonical ubiquitin-like autophagy receptors [sequestosome 1 (SQSTM1), microtubule-associated protein 1 light chain 3 (LC3), gamma-aminobutyric acid receptor-associated protein (GABARAP)] and the nontraditional mitophagy pathways involving ubiquitin-proteasome system and the ubiquitin-binding protein dislocase, valosin-containing protein (VCP), may act in concert during mammalian sperm mitophagy. We found that the SQSTM1, but not GABARAP or LC3, associated with sperm mitochondria after fertilization in pig and rhesus monkey zygotes. Three sperm mitochondrial proteins copurified with the recombinant, ubiquitin-associated domain of SQSTM1. The accumulation of GABARAP-containing protein aggregates was observed in the vicinity of sperm mitochondrial sheaths in the zygotes and increased in the embryos treated with proteasomal inhibitor MG132, in which intact sperm mitochondrial sheaths were observed. Pharmacological inhibition of VCP significantly delayed the process of sperm mitophagy and completely prevented it when combined with microinjection of autophagy-targeting antibodies specific to SQSTM1 and/or GABARAP. Sperm mitophagy in higher mammals thus relies on a combined action of SQSTM1-dependent autophagy and VCP-mediated dislocation and presentation of ubiquitinated sperm mitochondrial proteins to the 26S proteasome, explaining how the whole sperm mitochondria are degraded inside the fertilized mammalian oocytes by a protein recycling system involved in degradation of single protein molecules.

¹H-NMR and MS based metabolomics study of the intervention effect of curcumin on hyperlipidemia mice induced by high-fat diet

Curcumin, a principle bioactive component of Curcuma longa L, is well known for its anti-hyperlipidemia effect. However, no holistic metabolic information of curcumin on hyperlipidemia models has been revealed, which may provide us an insight into the underlying mechanism. In the present work, NMR and MS based metabolomics was conducted to investigate the intervention effect of curcumin on hyperlipidemia mice induced by high-fat diet (HFD) feeding for 12 weeks. The HFD induced animals were orally administered with curcumin (40, 80 mg/kg) or lovastatin (30 mg/kg, positive control) once a day during the inducing period. Serum biochemistry assay of TC, TG, LDL-c, and HDL-c was conducted and proved that treatment of curcumin or lovastatin can significantly improve the lipid profiles. Subsequently, metabolomics analysis was carried out for urine samples. Orthogonal Partial Least Squares-Discriminant analysis (OPLS-DA) was employed to investigate the anti-hyperlipidemia effect of curcumin and to detect related potential biomarkers. Totally, 35 biomarkers were identified, including 31 by NMR and nine by MS (five by both). It turned out that curcumin treatment can partially recover the metabolism disorders induced by HFD, with the following metabolic pathways involved: TCA cycle, glycolysis and gluconeogenesis, synthesis of ketone bodies and cholesterol, ketogenesis of branched chain amino acid, choline metabolism, and fatty acid metabolism. Besides, NMR and MS based metabolomics proved to be powerful tools in investigating pharmacodynamics effect of natural products and underlying mechanisms.

Fatty Acid Accumulation and Resulting PPARα Activation in Fibroblasts due to Trifunctional Protein Deficiency

To examine fatty acid accumulation and its toxic effects in cells, we analyzed skin fibroblasts from six patients with mitochondrial trifunctional protein deficiency, who had abnormalities in the second through fourth reactions in fatty acid β-oxidation system. We found free fatty acid accumulation, enhanced three acyl-CoA dehydrogenases, catalyzing the first reaction in the β-oxidation system and being assumed to have normal activities in these patients, and PPARα activation that was confirmed in the experiments using MK886, a PPARα specific antagonist and fenofibrate, a PPARα specific agonist. These novel findings suggest that the fatty acid accumulation and the resulting PPARα activation are major causes of the increase in the β-oxidation ability as probable compensation for fatty acid metabolism in the patients' fibroblasts, and that enhanced cell proliferation and increased oxidative stress due to the PPARα activation relate to the development of specific clinical features such as hypertrophic cardiomyopathy, slight hepatomegaly, and skeletal myopathy. Additionally, significant suppression of the PPARα activation by means of MK886 treatment is assumed to provide a new method of treating this deficiency.

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.

Urgent metabolic service improves survival in long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency detected by symptomatic identification and pilot newborn screening

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a fatty acid oxidation disorder with especially high mortality and uncertain long-term outcome. The aim of the study was to analyze the influence of diagnostic approach on survival in 59 affected children. Referral to a metabolic center was replaced over time by urine/blood testing in centralized metabolic laboratory (selective screening) and by pilot tandem mass spectrometry newborn screening (NBS). Molecular analysis revealed the prevalent mutation in the HADHA gene in all 58 examined cases. Twenty patients died. The number of detections and number of deaths were respectively 9 and 4 (44%) in the patients recognized by differential diagnosis, 28 and 9 (32%) - by selective screening, and 11 and 1 (9%) - by NBS. In 80% of cases the death occurred before or within 3 weeks from the identification. Urgent and active metabolic service remarkably influenced the surviving. The current age of 39 survivors is 0.5 to 23 yrs (mean 7.2 yrs). The disease frequency estimated on the patients number was 1: 115 450, whereas in the pilot NBS - 1: 109 750 (658 492 neonates tested). Interestingly, the phenylalanine level in asymptomatic neonates frequently exceeded the cut-off values.

CONCLUSIONS

1) Urgent metabolic intervention decreases mortality of LCHAD-deficient patients, but the prognosis is still uncertain. 2) Emergent metabolic reporting and service are crucial also for the survival of neonates detected by NBS. 3) The nationwide selective screening appeared efficient in LCHADD detection in the country. 4) Transient mild hyperphenylalaninaemia may occur in LCHAD-deficient newborns.

Long-chain 3-hydroxy fatty acids accumulating in LCHAD and MTP deficiencies induce oxidative stress in rat brain

Accumulation of long-chain 3-hydroxy fatty acids is the biochemical hallmark of long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiencies. These disorders are clinically characterized by neurological symptoms, such as convulsions and lethargy, as well as by cardiomyopathy and muscle weakness. In the present work we investigated the in vitro effect of 3-hydroxydodecanoic (3HDA), 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, which accumulate in these disorders, on important oxidative stress parameters in cerebral cortex of young rats in the hope to clarify the mechanisms leading to the brain damage found in patients affected by these disorders. It was first verified that these compounds significantly induced lipid peroxidation, as determined by increased thiobarbituric acid-reactive substances levels. In addition, carbonyl formation was significantly increased and sulfhydryl content decreased by 3HTA and 3HPA, which indicates that these fatty acids elicit protein oxidative damage. 3HTA and 3HPA also diminished the reduced glutathione (GSH) levels, without affecting nitrate and nitrite production. Finally, we observed that the addition of the antioxidants and free radical scavengers trolox and deferoxamine (DFO) was able to partially prevent lipid oxidative damage, whereas DFO fully prevented the reduction on GSH levels induced by 3HTA. Our present data showing that 3HDA, 3HTA and 3HPA elicit oxidative stress in rat brain indicate that oxidative damage may represent an important pathomechanism involved in the neurologic symptoms manifested by patients affected by LCHAD and MTP deficiencies.

Liver disease in pregnancy

Severe liver disease in pregnancy is rare. Pregnancy-related liver disease is the most frequent cause of liver dysfunction in pregnancy and provides a real threat to fetal and maternal survival. A rapid diagnosis differentiating between liver disease related and unrelated to pregnancy is required in women who present with liver dysfunction during pregnancy. Research has improved our understanding of the pathogenesis of pregnancy-related liver disease, which has translated into improved maternal and fetal outcomes. Here, we provide an overview of liver diseases that occur in pregnancy, an update on the key mechanisms involved in their pathogenesis, and assessment of available treatment options.

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.

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.

Mitochondrial fatty acid oxidation defects--remaining challenges

Mitochondrial fatty acid oxidation defects have been recognized since the early 1970s. The discovery rate has been rather constant, with 3-4 'new' disorders identified every decade and with the most recent example, ACAD9 deficiency, reported in 2007. In this presentation we will focus on three of the 'old' defects: medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, riboflavin responsive multiple acyl-CoA dehydrogenation (RR-MAD) deficiency, and short-chain acyl-CoA dehydrogenase (SCAD) deficiency. These disorders have been discussed in many publications and at countless conference presentations, and many questions relating to them have been answered. However, continuing clinical and pathophysiological research has raised many further questions, and new ideas and methodologies may be required to answer these. We will discuss these challenges. For MCAD deficiency the key question is why 80% of symptomatic patients are homozygous for the prevalent ACADM gene variation c.985A > G whereas this is found in only approximately 50% of newborns with a positive screen. For RR-MAD deficiency, the challenge is to find the connection between variations in the ETFDH gene and the observed deficiency of a number of different mitochondrial dehydrogenases as well as deficiency of FAD and coenzyme Q(10). With SCAD deficiency, the challenge is to elucidate whether ACADS gene variations are disease-associated, especially when combined with other genetic/cellular/environmental factors, which may act synergistically.

Mitochondrial trifunctional protein defects: clinical implications and therapeutic approaches

The mitochondrial trifunctional protein (MTP) is a heterotrimeric protein that consists of four alpha-subunits and four beta-subunits and catalyzes three of the four chain-shortening reactions in the mitochondrial beta-oxidation of long-chain fatty acids. Families with recessively inherited MTP defects display a spectrum of maternal and fetal phenotypes. Current management of patients with MTP defects include long-term dietary therapy of fasting avoidance, low-fat/high-carbohydrate diet with restriction of long-chain fatty acid intake and substitution with medium-chain fatty acids. These dietary approaches appear promising in the short-term, but the long-term outcome of patients treated with dietary intervention is largely unknown. Potential therapeutic approaches targeted at correcting the metabolic defect will be discussed. We will discuss the potential use of protein transduction domains that cross the mitochondrial membranes for the treatment of mitochondrial disorders. In addition, we discuss the phenotypes of MTP in a heterozygous state and potential ways to intervene to increase hepatic fatty acid oxidative capacity.

Mitochondrial fatty-acid oxidation disorders

Inherited defects in mitochondrial fatty-acid beta-oxidation comprise a group of at least 12 diseases characterized by distinct enzyme or transporter deficiencies. Most of these diseases have a variable age of onset and clinical severity. Symptoms are often episodic and associated with mild viral illness, physiologic stress, or prolonged exercise that overwhelms the ability of mitochondria to oxidize fatty acids. Depending on the specific genetic defect, patients develop fasting hypoketotic hypoglycemia, cardiomyopathy, rhabdomyolysis, liver dysfunction, or sudden death. Neuropathy and pigmentary retinopathy are seen in some of the diseases. The diagnosis is based on finding an accumulation of specific biochemical markers such as acylcarnitine metabolites in blood and urinary dicarboxylic acids and acylglycines. Confirmatory testing requires enzymatic studies and DNA analysis. Therapeutic approaches are generally effective in preventing severe symptomatic episodes, including sudden death. Newborn screening for fatty-acid oxidation disorders promises to identify many affected patients before the onset of symptoms.

The blind men ‘see’ the elephant-the many faces of fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a group of diseases with excess fat in liver in the absence of a poorly defined limit of alcohol consumption. Most common variety, a universal public health problem, is associated with insulin resistance caused by a host of genetic and epigenetic defects modulated by life style and environmental factors. In fact the term NAFLD is loose to incorporate so many etiologies except alcoholism and few other etiologies, presenting as fat in liver. However as a sign fatty liver is very important in predicting the risk of diabetes, cardiovascular disease, stroke, cirrhosis and cancer. Abnormal fat accumulation can result from several defects in nuclear receptors associated with lipid sensing, synthesis and oxidation like LXR, FXR, SREBP, ChREBP and PPAR; defects in the lipid influx-efflux channels, insulin signaling, proteins involved in fatty acid catabolism, defects in adipose tissue development and function, inappropriate nutrition and finally defects in neural regulatory mechanisms. The progress of the disease is determined by the basic defects which results in fat accumulation, an individual’s immunological response to the accumulated fat and its derivatives and the oxidant stress response. Congregation of unrelated genetic defects under same diagnosis ‘NAFLD’ can result in inefficient patient management. Further studies are required to understand the molecular basis of fatty liver to enable a personalized management of diseases presenting as fatty liver in the absence of alcohol abuse.

Acute fatty liver of pregnancy: An update on pathogenesis and clinical implications

Acute fatty liver of pregnancy (AFLP) is a serious maternal illness occurring in the third trimester of pregnancy with significant perinatal and maternal mortality. Till recently, it has been considered a mysterious illness. In this editorial, we review the recent advances in understanding the pathogenesis of AFLP and discuss the studies documenting a fetal-maternal interaction with a causative association between carrying a fetus with a defect in mitochondrial fatty acid oxidation and development of AFLP. Further, we discuss the impact of these recent advances on the offspring born to women who develop AFLP, such that screening for a genetic defect can be life saving to the newborn and would allow genetic counseling in subsequent pregnancies. The molecular basis and underlying mechanism for this unique fetal-maternal interaction causing maternal liver disease is discussed.

ENU mutagenesis identifies mice with cardiac fibrosis and hepatic steatosis caused by a mutation in the mitochondrial trifunctional protein beta-subunit

Using the metabolomics-guided screening coupled to N-ethyl-N-nitrosourea-mediated mutagenesis, we identified mice that exhibited elevated levels of long-chain acylcarnitines. Whole genome homozygosity mapping with 262 SNP markers mapped the disease gene to chromosome 5 where candidate genes Hadha and Hadhb, encoding the mitochondria trifunctional protein (MTP) alpha- and beta-subunits, respectively, are located. Direct sequencing revealed a normal alpha-subunit, but detected a nucleotide T-to-A transversion in exon 14 (c.1210T>A) of beta-subunit (Hadhb) which resulted in a missense mutation of methionine to lysine (M404K). Western blot analysis showed a significant reduction of both the alpha- and beta-subunits, consistent with reduced enzyme activity in both the long-chain 3-hydroxyacyl-CoA dehydrogenase and the long-chain 3-ketoacyl-CoA thiolase activities. These mice had a decreased weight gain and cardiac arrhythmias which manifested from a prolonged PR interval to a complete atrio-ventricular dissociation, and died suddenly between 9 and 16 months of age. Histopathological studies showed multifocal cardiac fibrosis and hepatic steatosis. This mouse model will be useful to further investigate the mechanisms underlying arrhythmogenesis relating to lipotoxic cardiomyopathy and to investigate pathophysiology and treatment strategies for human MTP deficiency.

Differential inhibitory effect of long-chain acyl-CoA esters on succinate and glutamate transport into rat liver mitochondria and its possible implications for long-chain fatty acid oxidation defects

Long-chain fatty acid beta-oxidation defects are associated with a series of clinical and biochemical abnormalities, including accumulation of long-chain acyl-CoA esters which have been shown to inhibit several enzymes and transport systems that may disturb energy metabolism. Using isolated rat liver mitochondria incubated under state 3 conditions, we observed that long-chain acyl-CoA esters and their beta-oxidation intermediates inhibit ATP synthesis and oxygen consumption, both with succinate (plus rotenone) and l-glutamate as respiratory substrates. When an uncoupler (2,4-dinitrophenol) was used instead of ADP, to stimulate respiration maximally, the various CoA esters showed differential effects on the oxidation of succinate and l-glutamate, respectively. With succinate as substrate, there was a strong inhibition of oxygen consumption by palmitoyl-CoA, 2,3-unsaturated, 3-hydroxy, and 3-keto-palmitoyl-CoA, in coupled as well as uncoupled mitochondria. On the other hand, with l-glutamate as substrate, inhibition was only observed under coupled conditions. The finding that acyl-CoA esters inhibit the uncoupler-induced respiration with succinate as substrate but not with glutamate, indicates that the observed inhibitory effect is most probably at the level of the transport of succinate across the mitochondrial membrane as mediated by the mitochondrial dicarboxylate carrier. This conclusion was substantiated by mitochondrial swelling studies, which showed inhibition of succinate transport by the different CoA esters whereas no effect was observed on the phosphate/hydroxyl and glutamate/hydroxyl carriers. Furthermore, long-chain acyl-CoA esters were found to potentiate the inhibitory effect of N-butylmalonate, a known inhibitor of the dicarboxylate carrier, upon oxygen consumption driven by succinate (plus rotenone). We conclude that the inhibitory effects of long-chain acyl-CoA esters on oxidative phosphorylation are dependent on the type of substrate used with the ATP/ADP carrier and the dicarboxylate carrier as targets for inhibition.

Intestinal pseudo-obstruction as a manifestation of impaired mitochondrial fatty acid oxidation

Intestinal pseudo-obstruction can be caused by mitochondrial disorders. Understanding the association between genetic alterations in mitochondrial function and development of intestinal pseudo-obstruction may provide insight into the pathogenesis of this disorder. Although the association between mitochondrial DNA defects and pseudo-obstruction is documented, little is known about the relationship between mitochondrial beta-oxidation disorders, which are caused by defects in nuclear genes, and development of intestinal pseudo-obstruction. Mitochondrial beta-oxidation defects have emerged recently as an important group of recessively inherited inborn errors of metabolism with multiple phenotypes. Here we report the case history of a 25-year-old patient with mitochondrial trifunctional protein (MTP) deficiency, the eldest known living patient with this disorder. MTP is an enzyme complex that consists of 4alpha and 4beta subunits and catalyzes the last three steps in the beta-oxidation cycle. The patient's MTP deficiency is secondary to a compound heterozygosity for two mutations in the MTP beta-subunit. Over the past 5 years, the patient had worsening symptoms consistent with intestinal pseudo-obstruction associated with progressive skeletal myopathy and polyneuropathy. We hypothesize that impairment of mitochondrial beta-oxidation causes intestinal pseudo-obstruction secondary to accumulation of intracellular long chain fatty acids, activation of extramitochondrial fatty acid oxidation pathways, and generation of excessive reactive oxygen species leading to visceral myopathy.

Mice heterozygous for a defect in mitochondrial trifunctional protein develop hepatic steatosis and insulin resistance

BACKGROUND & AIMS

Little is known about the role of mitochondrial beta-oxidation in development of nonalcoholic fatty liver disease (NAFLD). Mitochondrial trifunctional protein (MTP) catalyzes long-chain fatty acid oxidation. Recently, we generated a mouse model for MTP deficiency and reported that homozygous (MTPa-/-) mice suffer neonatal death. In this study, we investigated effects of heterozygosity for the MTP defect on hepatic oxidative stress, insulin resistance, and development of NAFLD in mice.

METHODS

We evaluated liver histopathology, serum alanine aminotransferase (ALT), glucose, fatty acids, and insulin levels in MTPa+/- and MTPa+/+ littermates. Insulin resistance was evaluated using glucose tolerance test (GTT) and insulin tolerance test (ITT). Liver tissues were used to measure triglyceride and fatty acid content, activity of superoxide dismutases (SOD) and glutathione peroxidase (GPx), glutathione (GSH), and cytochrome P-450 2E1 expression.

RESULTS

Aging but not young MTPa+/- mice developed hepatic steatosis with elevated ALT, basal hyperinsulinemia, and increased insulin area under curve (AUC) on GTT compared with MTPa+/+ littermates. In response to insulin challenge, aging MTPa+/- mice had slower rate of glucose disappearance and increased glucose AUC. Significant hepatic steatosis and insulin resistance developed concomitantly in the MTPa+/- mice at 9-10 months of age. Aging MTPa+/- mice had higher antioxidant activity of total SOD and GPx, lower GSH, and increased expression of cytochrome P-450 2E1, consistent with increased hepatic oxidative stress.

CONCLUSIONS

Heterozygosity for beta-oxidation defects predisposes to NAFLD and insulin resistance in aging mice. Impairment of mitochondrial beta-oxidation may play an important role in pathogenesis of NAFLD.

Maternal heterozygosity for a mitochondrial trifunctional protein mutation as a cause for liver disease in pregnancy

Acute fatty liver of pregnancy (AFLP) and hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome are serious complications of pregnancy associated with significant maternal and perinatal morbidity and mortality. In previous reports, we have documented an association between AFLP and fetal deficiency of long-chain 3-hydroxyacyl coenzyme A dehydrogenase (LCHAD) [N. Engl. J. Med. 340 (1999) 1723-1731; JAMA 288 (2002) 2163-2166]. LCHAD activity resides in the alpha-subunit of the mitochondrial trifunctional protein (MTP), a complex protein that catalyzes beta-oxidation of long chain fatty acids. In all reported cases, the fetus carried a common alpha-subunit MTP mutation (G1528C, E474Q) on one or both alleles. However, the association between fetal LCHAD deficiency and the maternal HELLP syndrome has been limited. Here, we report a case history of a 27-year-old black female who underwent Cesarean section for placenta previa and fetal distress at 36 weeks gestation. The newborn was a healthy male child. Post-delivery, the mother developed severe HELLP syndrome with complications resulting in death of the patient. We used single strand conformation variance and nucleotide sequence analyses to screen DNA isolated from the mother and the newborn for mutations in the MTP alpha-subunit. The mother was heterozygous for a novel mutation (C1072A, Q322K) in exon 11 of the LCHAD domain of the MTP, while the fetal genotype was completely normal. We hypothesize that, in some cases, maternal heterozygosity for an MTP mutation maybe sufficient to cause the development of maternal liver disease without carrying an affected fetus. Combination of the metabolic stress of pregnancy and other environmental stresses may overwhelm the heterozygous mother's capacity for effective metabolism of long chain fatty acids, leading to an accumulation of potentially toxic fatty acid metabolites in the maternal circulation with subsequent damage to the maternal liver.

Implications of impaired ketogenesis in fatty acid oxidation disorders

Long-chain fatty acids are important sources of respiratory fuel for many tissues and during fasting the rate of hepatic production of ketone bodies is markedly increased. Many extra hepatic tissues utilize ketone bodies in the fasted state with the advantage that glucose is "spared" for more vital tissues like the brain. This glucose sparing effect of ketones is especially important in infants where there is a high proportional glucose utilization in cerebral tissue. The first reported inherited defect affecting fatty acid oxidation was described in 1973 and to date about 15 separate disorders have been described. Although individually rare, cumulatively fatty acid oxidation defects are relatively common, have major consequences for affected individuals and their families, and carry significant health care implications. The major biochemical consequence of fatty acid oxidation defects is an inability of extra hepatic tissues to utilize fatty acids as an energy source with absent or limited hepatic capacity to generate ketones. Clinically patients usually present in infancy with acute life-threatening hypoketotic hypoglycaemia, liver disease, hyperammonaemia and cerebral oedema, with or without cardiac involvement, usually following a period of catabolic stress. Chronically there may be muscle involvement with hypotonia or exercise intolerance with or without cardiomyopathy. Treatment is generally by the avoidance of fasting, frequent carbohydrate rich feeds and for long-chain defects, the replacement of long-chain dietary fats with medium-chain formulae. Novel approaches to treatment include the use of d,l-3-hydoxybutyrate or heptanoate as an alternative energy source.

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

The mitochondrial trifunctional protein (TFP) is a multienzyme complex of the beta-oxidation cycle. Human TFP is an octamer composed of four alpha-subunits harboring long-chain enoyl-CoA hydratase and long-chain L-3-hydroxyacyl-CoA dehydrogenase and four beta-subunits encoding long-chain 3-ketoacyl-CoA thiolase. Mutations in either subunit may result in general TFP deficiency with reduced activity of all three enzymes. We report five new patients with alpha-subunit mutations and compare general TFP deficiency caused by alpha-subunit mutations (n = 15) to that caused by beta-subunit mutations (n = 13) with regard to clinical features, enzyme activity, mutations, thiolase expression, and thiolase protein turnover. Among patients with alpha-subunit mutations, the same three heterogeneous phenotypes reported in patients with beta-subunit mutations were observed: a lethal form with predominating cardiomyopathy; an infancy-onset, hepatic presentation; and a milder, later-onset, neuromyopathic form. Maternal HELLP syndrome (hemolysis, elevated liver enzymes, low platelets) occurred with an incidence of 15 to 20%, as in families with beta-subunit mutations. Enzyme assays in fibroblasts revealed an identical biochemical pattern in both groups. alpha-Subunit mutational analysis demonstrated molecular heterogeneity, with 53% (9 of 17) truncating mutations. In contrast, patients with beta-subunit mutations had predominantly missense mutations. Thiolase expression in fibroblasts was as markedly reduced in alpha-subunit patients as in the beta-subunit group with similarly increased thiolase degradation, presumably secondary to TFP complex instability. TFP deficiency as a result of either alpha- or beta-subunit mutations presents with similar, heterogeneous phenotypes. Both alpha- and beta-subunit mutations result in TFP complex instability, demonstrating that the mechanism of disease is the same in alpha- or beta-mutation-derived disease and explaining the biochemical and clinical similarities.

Genetic defects in fatty acid beta-oxidation and acyl-CoA dehydrogenases. Molecular pathogenesis and genotype-phenotype relationships

Mitochondrial fatty acid oxidation deficiencies are due to genetic defects in enzymes of fatty acid beta-oxidation and transport proteins. Genetic defects have been identified in most of the genes where nearly all types of sequence variations (mutation types) have been associated with disease. In this paper, we will discuss the effects of the various types of sequence variations encountered and review current knowledge regarding the genotype-phenotype relationship, especially in patients with acyl-CoA dehydrogenase deficiencies where sufficient material exists for a meaningful discussion. Because mis-sense sequence variations are prevalent in these diseases, we will discuss the implications of these types of sequence variations on the processing and folding of mis-sense variant proteins. As the prevalent mis-sense variant K304E MCAD protein has been studied intensively, the investigations on biogenesis, stability and kinetic properties for this variant enzyme will be discussed in detail and used as a paradigm for the study of other mis-sense variant proteins. We conclude that the total effect of mis-sense sequence variations may comprise an invariable--sequence variation specific--effect on the catalytic parameters and a conditional effect, which is dependent on cellular, physiological and genetic factors other than the sequence variation itself.

Morphological investigation of two sibling autopsy cases of mitochondrial trifunctional protein deficiency

Two sibling autopsy cases of type 2 mitochondrial trifunctional protein (MTP) deficiency are described. MTP is an enzyme complex involved in the mitochondrial beta-oxidation of fatty acids, which is the major pathway for energy production in heart and skeletal muscle. Both cases showed similar pathological findings. Numerous small foci of degeneration of muscle cells and cardiac myocytes were detected. Some of these cells had condensed or fragmented nuclei and most of them were positively stained using the deoxyuridine triphosphate nick-end labeling method. The lipid staining of both cases showed a small- to medium-sized fatty, vesicular morphology for liver cells, muscle cells, cardiac myocytes and proximal tubular cells of the kidney. Bone marrow was severely hypoplastic, and cortical thymocytes were markedly reduced in number. Neither case had hepatic fibrosis nor cirrhosis. The definitive diagnosis of type 2 MTP deficiency was made by verifying completely defective MTP-alpha and MTP-beta subunits in cultured skin fibroblasts of one of 2 patients. Our patients' signs indicate that there is a wider pathological spectrum of type 2 MTP deficiency, while very few autopsy cases of type 2 MTP deficiency have been confirmed. Pathologists should consider the possibility of type 2 MTP deficiency or other beta-oxidation defects in cases of sudden infant death, fatty infiltration of viscera or cardiomyopathy.

Mitochondrial trifunctional protein deficiency: a severe fatty acid oxidation disorder with cardiac and neurologic involvement

OBJECTIVE

To determine the spectrum of presentation, including both clinical and biochemical abnormalities, and the clinical course in a cohort of patients with complete mitochondrial trifunctional protein (MTP) deficiency, a rare inborn error of mitochondrial fatty acid oxidation.

STUDY DESIGN

A questionnaire was sent to the referring physicians from 25 unselected MTP-deficient patients.

RESULTS

Twenty-one patients could be included. Questionnaires about four patients were not returned. Nine (43%) patients presented with rapidly progressive clinical deterioration; six (67%) of them had hypoketotic hypoglycemia. The remaining 12 patients presented with a much more insidious disease with nonspecific chronic symptoms, including hypotonia (100%), cardiomyopathy (73%), failure to thrive, or peripheral neuropathy. Ten patients (48%) presented in the neonatal period. Mortality was high (76%), mostly attributable to cardiac involvement. Two patients who were diagnosed prenatally died despite treatment.

CONCLUSION

Complete MTP deficiency often presents with nonspecific symptomatology, which makes clinical recognition difficult. Hypotonia and cardiomyopathy are common presenting features, and the differential diagnosis of an infant with these signs should include MTP deficiency. In spite of early diagnosis and treatment, only a few patients with this condition have survived.

Fetal genotypes and pregnancy outcomes in 35 families with mitochondrial trifunctional protein mutations

OBJECTIVE

The purpose of this study was to evaluate the effects of fetal genotype on maternal and fetal outcomes in families with mitochondrial trifunctional protein mutations in the United States. Trifunctional protein has 3 enzymatic activities that include long-chain 3-hydroxyacyl-CoA dehydrogenase, which catalyzes long-chain fatty acid beta-oxidation.

STUDY DESIGN

We analyzed pregnancy history and offspring genotypes in 35 families with heterogeneous mutations. The fetal genotype was determined in utero in 11 pregnancies and after birth in 50 pregnancies.

RESULTS

Forty-nine percent of the women who carried affected fetuses had acute fatty liver of pregnancy. Another 11% of the women had the syndrome of hemolysis, elevated liver enzymes, and low platelets, or preeclampsia. All women who had the maternal illness carried fetuses with isolated long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Sixty-eight percent and 43% of the affected pregnancies also were associated with premature delivery and intrauterine growth retardation, respectively. No maternal or fetal complications were associated with heterozygous or wild-type fetal genotypes.

CONCLUSION

Fetal mitochondrial trifunctional protein defects should be considered a cause for maternal liver disease, preterm labor, and intrauterine growth retardation.

Fatty acid oxidation disorders

Genetic disorders of mitochondrial fatty acid beta-oxidation have been recognized within the last 20 years as important causes of morbidity and mortality, highlighting the physiological significance of fatty acids as an energy source. Although the mammalian mitochondrial fatty acid-oxidizing system was recognized at the beginning of the last century, our understanding of its exact nature remains incomplete, and new components are being identified frequently. Originally described as a four-step enzymatic process located exclusively in the mitochondrial matrix, we now recognize that long-chain-specific enzymes are bound to the inner mitochondrial membrane, and some enzymes are expressed in a tissue-specific manner. Much of our new knowledge of fatty acid metabolism has come from the study of patients who were diagnosed with single-gene autosomal recessive defects, a situation that seems to be further evolving with the emergence of phenotypes determined by combinations of multiple genetic and environmental factors. This review addresses the normal process of mitochondrial fatty acid beta-oxidation and discusses the clinical, metabolic, and molecular aspects of more than 20 known inherited diseases of this pathway that have been described to date.

Control of mitochondrial beta-oxidation flux

The control of mitochondrial beta-oxidation, including the delivery of acyl moieties from the plasma membrane to the mitochondrion, is reviewed. Control of beta-oxidation flux appears to be largely at the level of entry of acyl groups to mitochondria, but is also dependent on substrate supply. CPTI has much of the control of hepatic beta-oxidation flux, and probably exerts high control in intact muscle because of the high concentration of malonyl-CoA in vivo. beta-Oxidation flux can also be controlled by the redox state of NAD/NADH and ETF/ETFH(2). Control by [acetyl-CoA]/[CoASH] may also be significant, but it is probably via export of acyl groups by carnitine acylcarnitine translocase and CPT II rather than via accumulation of 3-ketoacyl-CoA esters. The sharing of control between CPTI and other enzymes allows for flexible regulation of metabolism and the ability to rapidly adapt beta-oxidation flux to differing requirements in different tissues.

Lack of mitochondrial trifunctional protein in mice causes neonatal hypoglycemia and sudden death

Mitochondrial trifunctional protein (MTP) is a hetero-octamer of four alpha and four beta subunits that catalyzes the final three steps of mitochondrial long chain fatty acid beta-oxidation. Human MTP deficiency causes Reye-like syndrome, cardiomyopathy, or sudden unexpected death. We used gene targeting to generate an MTP alpha subunit null allele and to produce mice that lack MTP alpha and beta subunits. The Mtpa(-/-) fetuses accumulate long chain fatty acid metabolites and have low birth weight compared with the Mtpa(+/-) and Mtpa(+/+) littermates. Mtpa(-/-) mice suffer neonatal hypoglycemia and sudden death 6-36 hours after birth. Analysis of the histopathological changes in the Mtpa(-/-) pups revealed rapid development of hepatic steatosis after birth and, later, significant necrosis and acute degeneration of the cardiac and diaphragmatic myocytes. This mouse model documents that intact mitochondrial long chain fatty acid oxidation is essential for fetal development and for survival after birth. Deficiency of MTP causes fetal growth retardation, neonatal hypoglycemia, and sudden death.

Molecular prenatal diagnosis in families with fetal mitochondrial trifunctional protein mutations

OBJECTIVES

To evaluate the feasibility of molecular prenatal diagnosis in families with mitochondrial trifunctional protein (TFP) mutations and prospectively study the effects of fetal genotype on pregnancy outcome. TFP catalyzes the last 3 steps in mitochondrial long-chain fatty acid oxidation.

STUDY DESIGN

We performed molecular prenatal diagnosis in 9 pregnancies, 8 in 6 families with isolated long-chain 3-hydroxyacyl-coenzyme A dehydrogenase (LCHAD) deficiency and one in a family with complete TFP deficiency. Analyses were performed on chorionic villous samples in 7 pregnancies and on amniocytes in 2.

RESULTS

Molecular prenatal diagnosis successfully identified the fetal genotype in all 9 pregnancies. Two fetuses were affected, and both pregnancies were terminated by family decision. Two other fetuses had normal genotype and 5 others were heterozygotes. These 7 pregnancies were uncomplicated, and all the offspring are alive and apparently healthy. Genotypes of the aborted fetuses and neonates were confirmed by molecular analysis and enzymatic assays.

CONCLUSIONS

Molecular prenatal diagnosis is possible and valid in guiding management of pregnancies in families with known TFP defects. Women heterozygous for TFP alpha-subunit mutations who carry fetuses with wild-type or heterozygous genotypes have uncomplicated pregnancies.

Liver disease in pregnancy and fetal fatty acid oxidation defects

Acute fatty liver of pregnancy (AFLP) and the syndrome of hemolysis, elevated liver enzymes, and low platelets (the HELLP syndrome) are serious disorders of the third trimester with high maternal and perinatal morbidity and mortality. Over the past decade, several clinical observations have demonstrated an association between these maternal syndromes and a recessively inherited fatty acid oxidation disorder, long chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency. Many women who carried LCHAD-deficient fetuses developed maternal liver disease. Over the past few years, we and others have made significant progress in understanding the molecular basis for this fetal-maternal interaction. Here, we review the studies in literature that led to the establishment of this causative association with particular emphasis on the molecular analysis that delineated the molecular basis of this association. The likely mechanisms for the genotype-phenotype correlations in pediatric LCHAD deficiency and the fetal-maternal interaction are discussed. Finally, the potential implications of our current knowledge for families with pediatric LCHAD deficiency and for women who develop AFLP and HELLP syndrome are discussed.

Do NSAIDs contribute to acute fatty liver of pregnancy?

Acute fatty liver of pregnancy (AFLP) and the childhood encephalopathy known as Reye's syndrome are both characterised by microvesicular steatosis. Mothers with AFLP are frequently heterozygous for a mutation which reduces the activity of the trifunctional protein (TP) of fatty-acid oxidation. Several lines of evidence suggest that blockade of fatty-acid oxidation may also be the underlying cause of Reye's syndrome, and epidemiological studies have identified aspirin taken during a viral illness as a contributing factor to the development of the disease. The hypotheses are presented:* that children with Reye's syndrome may also be heterozygous for TP mutation, and* that inhibition of the residual long-chain fatty-acid oxidation by NSAIDs including aspirin precipitates the similar symptoms observed in patients with Reye's syndrome and AFLP. Identification of NSAIDs as candidates for the unidentified factor which precipitates AFLP suggests that avoidance of NSAIDs during pregnancy may lead to a reduction in the incidence of this life-threatening disease.

Metabolic myopathies: a clinical approach; part II

Major recent advances in the field of metabolic myopathies have helped delineate the genetic and biochemical basis of these disorders. This progress has also resulted in the development of new diagnostic and therapeutic methodologies. In this second part, we present an updated review of the main nonlysosomal and lysosomal glycogenoses and lipid metabolism defects that manifest with signs of transient or permanent muscle dysfunction. Our intent is to increase the pediatric neurologist's familiarity with these conditions and thus improve decision making in the areas of diagnosis and treatment.

Inborn errors of mitochondrial fatty acid oxidation

Inborn errors of the mitochondrial beta-oxidation of long-chain fatty acids represent an evolving field of inherited metabolic disease. Fatty acid oxidation defects demonstrate an abnormal response to the process of fasting adaptation and affect those tissues that utilize fatty acids as an energy source. These tissues include cardiac and skeletal muscle and liver. Muscle directly uses fatty acids as an energy source whilst hepatic metabolism of fatty acids is mostly directed toward the synthesis of ketone bodies for energy utilization by tissues such as brain. The clinical phenotypes of fatty acid oxidation disorders include disease of one or more of these fatty acid-metabolizing tissues. In this review, we provide an overview of the pathway, discuss the disorders that are well established, and describe recent advances in the field. Currently available diagnostic procedures are critically evaluated.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: variable expressivity of maternal illness during pregnancy and unusual presentation with infantile cholestasis and hypocalcaemia

Patients with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency present with a Reye-like syndrome, cardiomyopathy, or sudden unexpected death. We describe an unusual presentation in a patient with unsuspected LCHAD deficiency. The proband presented at 2 months of age with an acute infantile hypocalcaemia and vitamin D deficiency associated with occult, unexplained cholestatic liver disease. Sudden, unexpected death occurred at 8 months. Molecular analysis revealed homozygosity for the prevalent LCHAD (1528G > C, E474Q) mutation. The mother had pre-eclampsia during the third trimester of her pregnancy. In a subsequent pregnancy, she developed severe acute fatty liver of pregnancy (AFLP) and intrauterine fetal death at 33 weeks of gestation. In conclusion, infantile hypocalcaemia is an unusual phenotype associated with LCHAD deficiency. The maternal pregnancy history documents that fetal LCHAD deficiency is associated with a spectrum of maternal illnesses ranging from pre-eclampsia to life-threatening AFLP.

Fatal hepatic short-chain L-3-hydroxyacyl-coenzyme A dehydrogenase deficiency: clinical, biochemical, and pathological studies on three subjects with this recently identified disorder of mitochondrial beta-oxidation

This report describes the clinical, biochemical, and pathological findings in three infants with hepatic short-chain L-3-hydroxyacyl-coenzyme A dehydrogenase (SCHAD) deficiency, a recently recognized disorder of the mitochondrial oxidation of straight-chain fatty acids. Candidate subjects were identified from an ongoing study of infant deaths. SCHAD analysis was performed on previously frozen liver and skeletal muscle on subjects with a characteristic urine organic acid profile. Autopsy findings were correlated with the biochemical abnormalities. Enzyme analysis in liver revealed marked deficiency in SCHAD with residual activities of 3-11%. All subjects had normal activity in skeletal muscle. However, Western blot analysis of SCHAD revealed an identical truncated protein in both liver and muscle from one patient, suggesting that SCHAD is similar in liver and muscle and that the normal activity in muscle may be due to other enzymes with C4 activity. Autopsy findings revealed marked steatosis and a muscle pattern consistent with spinal muscular atrophy in one patient. Lipid storage was less pronounced in one patient and not detected in the third patient who had a well-documented history of recurrent hypoglycemia. This is the initial pathological characterization of this enzyme defect, and our observations suggest that SCHAD deficiency is a very severe disorder contributing to early infant death.

A fetal fatty-acid oxidation disorder as a cause of liver disease in pregnant women

BACKGROUND

Acute fatty liver of pregnancy and the HELLP syndrome (hemolysis, elevated liver-enzyme levels, and a low platelet count) are serious hepatic disorders that may occur during pregnancy in women whose fetuses are later found to have a deficiency of long-chain 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase. This enzyme resides in the mitochondrial trifunctional protein, which also contains the active site of long-chain 2,3-enoyl-CoA hydratase and long-chain 3-ketoacyl-CoA thiolase. We undertook this study to determine the relation between mutations in the trifunctional protein in infants with defects in fatty-acid oxidation and acute liver disease during pregnancy in their mothers.

METHODS

In 24 children with 3-hydroxyacyl-CoA dehydrogenase deficiency, we used DNA amplification and nucleotide-sequence analyses to identify mutations in the alpha subunit of the trifunctional protein. We then correlated the results with the presence of liver disease during pregnancy in the mothers.

RESULTS

Nineteen children had a deficiency only of long-chain 3-hydroxyacyl-CoA dehydrogenase and presented with hypoketotic hypoglycemia and fatty liver. In eight children, we identified a homozygous mutation in which glutamic acid at residue 474 was changed to glutamine. Eleven other children were compound heterozygotes, with this mutation in one allele of the alpha-subunit gene and a different mutation in the other allele. While carrying fetuses with the Glu474Gln mutation, 79 percent of the heterozygous mothers had fatty liver of pregnancy or the HELLP syndrome. Five other children, who presented with neonatal dilated cardiomyopathy or progressive neuromyopathy, had complete deficiency of the trifunctional protein (loss of activity of all three enzymes). None had the Glu474Gln mutation, and none of their mothers had liver disease during pregnancy.

CONCLUSIONS

Women with acute liver disease during pregnancy may have a Glu474Gln mutation in long-chain hydroxyacyl-CoA dehydrogenase. Their infants are at risk for hypoketotic hypoglycemia and fatty liver.

Disorders of mitochondrial fatty acyl-CoA beta-oxidation

In recent years tremendous progress has been made with respect to the enzymology of the mitochondrial fatty acid beta-oxidation machinery and defects therein. Firstly, a number of new mitochondrial beta-oxidation enzymes have been identified, including very-long-chain acyl-CoA dehydrogenase (VLCAD) and mitochondrial trifunctional protein (MTP). Secondly, the introduction of tandem MS for the analysis of plasma acylcarnitines has greatly facilitated the identification of patients with a defect in fatty acid oxidation (FAO). These two developments explain why the number of defined FAO disorders has increased dramatically, making FAO disorders the most rapidly growing group of inborn errors of metabolism. In this review we describe the current state of knowledge of the enzymes involved in the mitochondrial oxidation of straight-chain, branched-chain and (poly)unsaturated fatty acyl-CoAs as well as disorders of fatty acid oxidation. The laboratory diagnosis of these disorders is described, with particular emphasis on the methods used to identify the underlying enzyme defect and the molecular mutations. In addition, a simple flowchart is presented as a guide to the identification of mitochondrial FAO-disorders. Finally, treatment strategies are discussed briefly.