Sudden infant death and long-chain 3-hydroxyacyl-CoA dehydrogenase

Sudden Death of a Four-Day-Old Newborn Due to Mitochondrial Trifunctional Protein/Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiencies and a Systematic Literature Review of Early Deaths of Neonates with Fatty Acid Oxidation Disorders

Mitochondrial trifunctional protein (MTP) and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiencies have been a part of the Slovenian newborn screening (NBS) program since 2018. We describe a case of early lethal presentation of MTPD/LCHADD in a term newborn. The girl was born after an uneventful pregnancy and delivery, and she was discharged home at the age of 3 days, appearing well. At the age of 4 days, she was found without signs of life. Resuscitation was not successful. The NBS test performed using tandem mass spectrometry (MS/MS) showed a positive screen for MTPD/LCHADD. Genetic analysis performed on a dried blood spot (DBS) sample identified two heterozygous variants in the HADHA gene: a nucleotide duplication introducing a premature termination codon (p.Arg205Ter) and a nucleotide substitution (p.Glu510Gln). Post-mortem studies showed massive macro-vesicular fat accumulation in the liver and, to a smaller extent, in the heart, consistent with MTPD/LCHADD. A neonatal acute cardiac presentation resulting in demise was suspected. We conducted a systematic literature review of early neonatal deaths within 14 days postpartum attributed to confirmed fatty acid oxidation disorders (FAODs), which are estimated to account for 5% of sudden infant deaths. We discuss the pitfalls of the NBS for MTPD/LCHADD.

Syndromic retinitis pigmentosa

Retinitis pigmentosa (RP) is a progressive inherited retinal dystrophy, characterized by the degeneration of photoreceptors, presenting as a rod-cone dystrophy. Approximately 20-30% of patients with RP also exhibit extra-ocular manifestations in the context of a syndrome. This manuscript discusses the broad spectrum of syndromes associated with RP, pathogenic mechanisms, clinical manifestations, differential diagnoses, clinical management approaches, and future perspectives. Given the diverse clinical and genetic landscape of syndromic RP, the diagnosis may be challenging. However, an accurate and timely diagnosis is essential for optimal clinical management, prognostication, and potential treatment. Broadly, the syndromes associated with RP can be categorized into ciliopathies, inherited metabolic disorders, mitochondrial disorders, and miscellaneous syndromes. Among the ciliopathies associated with RP, Usher syndrome and Bardet-Biedl syndrome are the most well-known. Less common ciliopathies include Cohen syndrome, Joubert syndrome, cranioectodermal dysplasia, asphyxiating thoracic dystrophy, Mainzer-Saldino syndrome, and RHYNS syndrome. Several inherited metabolic disorders can present with RP, including Zellweger spectrum disorders, adult Refsum disease, α-methylacyl-CoA racemase deficiency, certain mucopolysaccharidoses, ataxia with vitamin E deficiency, abetalipoproteinemia, several neuronal ceroid lipofuscinoses, mevalonic aciduria, PKAN/HARP syndrome, PHARC syndrome, and methylmalonic acidaemia with homocystinuria type cobalamin (cbl) C disease. Due to the mitochondria's essential role in supplying continuous energy to the retina, disruption of mitochondrial function can lead to RP, as seen in Kearns-Sayre syndrome, NARP syndrome, primary coenzyme Q10 deficiency, SSBP1-associated disease, and long chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Lastly, Cockayne syndrome and PERCHING syndrome can present with RP, but they do not fit the abovementioned hierarchy and are thus categorized as miscellaneous. Several first-in-human clinical trials are underway or in preparation for some of these syndromic forms of RP.

The LCHADD Mouse Model Recapitulates Early-Stage Chorioretinopathy in LCHADD Patients

Purpose

Recent studies have shown that the retinal pigment epithelium (RPE) relies on fatty acid oxidation (FAO) for energy, however, its role in overall retinal health is unknown. The only FAO disorder that presents with chorioretinopathy is long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD). Studying the molecular mechanisms can lead to new treatments for patients and elucidate the role of FAO in the RPE. This paper characterizes the chorioretinopathy progression in a recently reported LCHADD mouse model.

Methods

Visual assessments, such as optokinetic tracking and fundus imaging, were performed in wildtype (WT) and LCHADD mice at 3, 6, 10, and 12 months of age. Retinal morphology was analyzed in 12-month retinal cross-sections using hematoxylin and eosin (H&E), RPE65, CD68, and TUNEL staining, whereas RPE structure was assessed using transmission electron microscopy (TEM). Acylcarnitine profiles were measured in isolated RPE/sclera samples to determine if FAO was blocked. Bulk RNA-sequencing of 12 month old male WT mice and LCHADD RPE/sclera samples assessed gene expression changes.

Results

LCHADD RPE/sclera samples had a 5- to 7-fold increase in long-chain hydroxyacylcarnitines compared to WT, suggesting an impaired LCHAD step in long-chain FAO. LCHADD mice have progressively decreased visual performance and increased RPE degeneration starting at 6 months. LCHADD RPE have an altered structure and a two-fold increase in macrophages in the subretinal space. Finally, LCHADD RPE/sclera have differentially expressed genes compared to WT, including downregulation of genes important for RPE function and angiogenesis.

Conclusions

Overall, this LCHADD mouse model recapitulates early-stage chorioretinopathy seen in patients with LCHADD and is a useful model for studying LCHADD chorioretinopathy.

New Acylcarnitine Ratio as a Reliable Indicator of Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and mitochondrial trifunctional protein (MTP) deficiencies are rare fatal disorders of fatty acid β-oxidation with no apparent genotype-phenotype correlation. The measurement of acylcarnitines by MS/MS is a current diagnostic workup in these disorders. Nevertheless, false-positive and false-negative results have been reported, highlighting a necessity for more sensitive and specific biomarkers. This study included 54 patients with LCHAD/MTP deficiency that has been confirmed by biochemical and molecular methods. The analysis of acylcarnitines in dried blood spots was performed using ESI-MS/MS. The established "HADHA ratio" = (C16OH + C18OH + C18:1OH)/C0 was significantly elevated in all 54 affected individuals in comparison to the control group. Apart from 54 LCHAD deficiency patients, the "HADHA ratio" was calculated in 19 patients with very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. As VLCAD-deficient patients did not show increased "HADHA ratio", the results emphasized the high specificity of this new ratio. Therefore, the "HADHA ratio" was shown to be instrumental in improving the overall performance of MS/MS-based analysis of acylcarnitine levels in the diagnostics of LCHAD/MTP deficiencies. The ratio was demonstrated to increase the sensitivity and specificity of this method and reduce the chances of false-negative results.

Successful management of rhabdomyolysis with triheptanoin in a child with severe long-chain 3-hydroxyacyl-coenzyme A dehydrogenase (LCHAD) deficiency

Early-onset long-chain 3-hydroxyacyl-coenzyme A dehydrogenase (LCHAD) deficiency is a fatty acid β-oxidation disorder with a poor prognosis. Triheptanoin, an anaplerotic oil with odd-chain fatty acids can improve the disease course. The female patient presented here was diagnosed at the age of 4 months, and treatment was started as fat restriction, frequent feeding, and standard medium-chain triglyceride supplementation. In follow-up, she had frequent rhabdomyolysis episodes (∼8 per year). At the age of six, she had 13 episodes in 6 months, and triheptanoin was started as part of a compassionate use program. Following unrelated hospital stays due to multisystem inflammatory syndrome in children and a bloodstream infection, she had only 3 rhabdomyolysis episodes, and hospitalized days decreased from 73 to 11 during her first year with triheptanoin. Triheptanoin drastically decreased the frequency and severity of rhabdomyolysis, but progression of retinopathy was not altered.

Effectiveness of Robotic-Assisted Gait Training and Aquatic Physical Therapy in a Child With Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency: A Case Report

PURPOSE

The purpose of this case study is to describe the outpatient rehabilitation program for a 15-year-old girl with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD).

SUMMARY OF KEY POINTS

The child presented with sudden-onset muscle weakness and fatigue with resultant dependence for all mobility and self-care. After 12 months of therapy, which included aquatic interventions and robotic-assisted gait training, the patient demonstrated independence with transfers, ambulation with a rolling walker, and stair navigation. Functional mobility, gross motor skills, and participation in activities of daily living significantly improved per the Gross Motor Function Measure and the Pediatric Evaluation of Disability Inventory.

STATEMENT OF CONCLUSION AND RECOMMENDATIONS FOR CLINICAL PRACTICE

This is the first case in the literature to outline an outpatient physical therapy treatment plan to address mobility deficits secondary to exacerbation of LCHADD. This patient's rehabilitative course will hopefully add to future research and provide patients with guidelines for their recovery.

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.

High vulnerability of the heart and liver to 3-hydroxypalmitic acid-induced disruption of mitochondrial functions in intact cell systems

Patients affected by long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency predominantly present severe liver and cardiac dysfunction, as well as neurological symptoms during metabolic crises, whose pathogenesis is still poorly known. In this study, we demonstrate for the first time that pathological concentrations of 3-hydroxypalmitic acid (3HPA), the long-chain hydroxyl fatty acid (LCHFA) that most accumulates in LCHAD deficiency, significantly decreased adenosine triphosphate-linked and uncoupled mitochondrial respiration in intact cell systems consisting of heart fibers, cardiomyocytes, and hepatocytes, but less intense in diced forebrain. 3HPA also significantly reduced mitochondrial Ca²⁺ retention capacity and membrane potential in Ca²⁺ -loaded mitochondria more markedly in the heart and the liver, with mild or no effects in the brain, supporting a higher susceptibility of the heart and the liver to the toxic effects of this fatty acid. It is postulated that disruption of mitochondrial energy and Ca²⁺ homeostasis caused by the accumulation of LCHFA may contribute toward the severe cardiac and hepatic clinical manifestations observed in the affected patients.

Mitochondrial Fatty Acid Oxidation Disorders Associated with Short-Chain Enoyl-CoA Hydratase (ECHS1) Deficiency

Mitochondrial fatty acid β-oxidation (FAO) is the primary pathway for fatty acid metabolism in humans, performing a key role in liver, heart and skeletal muscle energy homeostasis. FAO is particularly important during times of fasting when glucose supply is limited, providing energy for many organs and tissues, including the heart, liver and brain. Deficiencies in FAO can cause life-threatening metabolic disorders in early childhood that present with liver dysfunction, hypoglycemia, dilated hypertrophic cardiomyopathy and Reye-like Syndrome. Alternatively, FAO defects can also cause ‘milder’ adult-onset disease with exercise-induced myopathy and rhabdomyolysis. Short-chain enoyl-CoA hydratase (ECHS1) is a key FAO enzyme involved in the metabolism of fatty acyl-CoA esters. ECHS1 deficiency (ECHS1D) also causes human disease; however, the clinical manifestation is unlike most other FAO disorders. ECHS1D patients commonly present with Leigh syndrome, a lethal form of subacute necrotizing encephalomyelopathy traditionally associated with defects in oxidative phosphorylation (OXPHOS). In this article, we review the clinical, biochemical and genetic features of the ESHS1D patients described to date, and discuss the significance of the secondary OXPHOS defects associated with ECHS1D and their contribution to overall disease pathogenesis.

Very long-/ and long Chain-3-Hydroxy Acyl CoA Dehydrogenase Deficiency correlates with deregulation of the mitochondrial fusion/fission machinery

Children diagnosed with Long-Chain-3-Hydroxy-Acyl-CoA-Dehydrogenase-Deficiency (LCHADD) or Very-Long-Chain-3-Hydroxy-Acyl-CoA-Dehydrogenase-Deficiency (VLCADD) frequently present with hypertrophic cardiomyopathy or muscle weakness which is caused by the accumulation of fatty acid metabolites due to inactivating mutations in the mitochondrial trifunctional protein. By analyzing mitochondrial morphology we uncovered that mutations within the HADHA or the ACADVL gene not only affect fatty acid oxidation, but also cause significant changes in the DNM1L/MFN2 ratio leading to the significant accumulation of truncated and punctate mitochondria in contrast to network-like mitochondrial morphology in controls. These striking morphological abnormalities correlate with changes in OXPHOS, an imbalance in ROS levels, reduced mitochondrial respiration, reduced growth rates and significantly increased glucose uptake per cell, suggesting that HADHA and ACADVL mutations shift cellular energy household into glycolysis. Experiments using the NOX2-specific inhibitor Phox-I2 suggest that NOX2 is activated by accumulating long-chain fatty acids and generates ROS, which in turn changes mitochondrial morphology and activity. We thereby provide novel insights into the cellular energy household of cells from LCHADD/VLCADD patients and demonstrate for the first time a connection between fatty acid metabolism, mitochondrial morphology and ROS in patients with these rare genetic disorders.

Disturbed bovine mitochondrial lipid metabolism: a review

In mammals, excess energy is stored primarily as triglycerides, which are mobilized when energy demands arise and cannot be covered by feed intake. This review mainly focuses on the role of long chain fatty acids in disturbed energy metabolism of the bovine species. Long chain fatty acids regulate energy metabolism as ligands of peroxisome proliferator-activated receptors. Carnitine acts as a carrier of fatty acyl groups as long-chain acyl-CoA derivatives do not penetrate the mitochondrial inner membrane. There are two different types of disorders in lipid metabolism which can occur in cattle, namely the hypoglycaemic-hypoinsulinaemic and the hyperglycaemic-hyperinsulinaemic type with the latter not always associated with ketosis. There is general agreement that fatty acid β-oxidation capability is limited in the liver of (ketotic) cows. In accord, supplemental L-carnitine decreased liver lipid accumulation in periparturient Holstein cows. Of note, around parturition concurrent oxidation of fatty acids in skeletal muscle is highly activated. Also peroxisomal β-oxidation in liver of dairy cows may be part of the hepatic adaptations to a negative energy balance (NEB) to break down fatty acids. An elevated blood concentration of nonesterified fatty acids is one of the indicators of NEB in cattle among others like increased β-hydroxy butyrate concentration, and decreased concentrations of glucose, insulin, and insulin-like growth factor-I. Assuming that liver carnitine concentrations might limit hepatic fatty acid oxidation capacity in dairy cows, further study of the role of acyl-CoA dehydrogenases and/or riboflavin in bovine ketosis is warranted.

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.

Peripheral neuropathy in patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency - A follow-up EMG study of 12 patients

BACKGROUND

The neonatal screening and early start of the dietary therapy have improved the outcome of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD). The acute symptoms of LCHADD are hypoketotic hypoglycemia, failure to thrive, hepatopathy and rhabdomyolysis. Long term complications are retinopathy and neuropathy. Speculated etiology of these long term complications are the accumulation and toxicity of hydroxylacylcarnitines and long-chain fatty acid metabolites or deficiency of essential fatty acids.

AIMS

To study the possible development of polyneuropathy in LCHADD patients with current dietary regimen.

METHODS

Development of polyneuropathy in 12 LCHADD patients with the homozygous common mutation c.G1528C was evaluated with electroneurography (ENG) studies. The ENG was done 1-12 times to each patient, between the ages of 3 and 40 years. Clinical data of the patients were collected from the patient records.

RESULTS

The first sign of polyneuropathy was detected between the ages of 6-12 years, the first abnormality being reduction of the sensory amplitudes of the sural nerves. With time, progression was detected by abnormalities in sensory responses extending to upper limbs, as well as abnormalities in motor responses in lower limbs. Altogether, eight of the patients had polyneuropathy, despite good compliancy of the diet.

CONCLUSIONS

This study is the first to report the evolution of polyneuropathy with clinical neurophysiological methods in a relative large LCHADD patient group. Despite early start, and good compliance of the therapy, 6/10 of the younger patients developed neuropathy. However, in most patients the polyneuropathy was less severe than previously described.

Mitochondrial dysfunction in fatty acid oxidation disorders: insights from human and animal studies

Patients affected by FAOD commonly present with hepatopathy, cardiomyopathy, skeletal myopathy and encephalopathy. Human and animal evidences indicate that mitochondrial functions are disrupted by fatty acids and derivatives accumulating in these disorders, suggesting that lipotoxicity may contribute to their pathogenesis.

Mitochondrial fatty acid oxidation (FAO) plays a pivotal role in maintaining body energy homoeostasis mainly during catabolic states. Oxidation of fatty acids requires approximately 25 proteins. Inherited defects of FAO have been identified in the majority of these proteins and constitute an important group of inborn errors of metabolism. Affected patients usually present with severe hepatopathy, cardiomyopathy and skeletal myopathy, whereas some patients may suffer acute and/or progressive encephalopathy whose pathogenesis is poorly known. In recent years growing evidence has emerged indicating that energy deficiency/disruption of mitochondrial homoeostasis is involved in the pathophysiology of some fatty acid oxidation defects (FAOD), although the exact underlying mechanisms are not yet established. Characteristic fatty acids and carnitine derivatives are found at high concentrations in these patients and more markedly during episodes of metabolic decompensation that are associated with worsening of clinical symptoms. Therefore, it is conceivable that these compounds may be toxic. We will briefly summarize the current knowledge obtained from patients and genetic mouse models with these disorders indicating that disruption of mitochondrial energy, redox and calcium homoeostasis is involved in the pathophysiology of the tissue damage in the more common FAOD, including medium-chain acyl-CoA dehydrogenase (MCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and very long-chain acyl-CoA dehydrogenase (VLCAD) deficiencies. We will also provide evidence that the fatty acids and derivatives that accumulate in these diseases disrupt mitochondrial homoeostasis. The elucidation of the toxic mechanisms of these compounds may offer new perspectives for potential novel adjuvant therapeutic strategies in selected disorders of this group.

Highly thermostable RadA protein from the archaeon Pyrococcus woesei enhances specificity of simplex and multiplex PCR assays

The radA gene of the hyperthermophilic archaeon Pyrococcus woesei (Thermococcales) was cloned and overexpressed in Escherichia coli. The 1050-bp gene codes for a 349-amino-acid polypeptide with an M r of 38,397 which shows 100 % positional amino acid identity to Pyrococcus furiosus RadA and 27.1 % to the E. coli RecA protein. Recombinant RadA was overproduced in Escherichia coli as a His-tagged fusion protein and purified to electrophoretic homogeneity using a simple procedure consisting of ammonium sulfate precipitation and metal-affinity chromatography. In solution RadA exists as an undecamer (11-mer). The protein binds both to ssDNA and dsDNA. RadA has been found to be highly thermostable, it remains almost unaffected by a 4-h incubation at 94 °C. The addition of the RadA protein to either simplex or multiplex PCR assays, significantly improves the specificity of DNA amplification by eliminating non-specific products. Among applications tested the RadA protein proved to be useful in allelic discrimination assay of HADHA gene associated with long-chain 3-hydroxylacyl-CoA dehydrogenase deficiency that in infancy may lead to hypotonia, serious heart and liver problems and even sudden death.

Uncoupling, metabolic inhibition and induction of mitochondrial permeability transition in rat liver mitochondria caused by the major long-chain hydroxyl monocarboxylic fatty acids accumulating in LCHAD deficiency

Patients with long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiency commonly present liver dysfunction whose pathogenesis is unknown. We studied the effects of long-chain 3-hydroxylated fatty acids (LCHFA) that accumulate in LCHAD deficiency on liver bioenergetics using mitochondrial preparations from young rats. We provide strong evidence that 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, the monocarboxylic acids that are found at the highest tissue concentrations in this disorder, act as metabolic inhibitors and uncouplers of oxidative phosphorylation. These conclusions are based on the findings that these fatty acids decreased ADP-stimulated (state 3) and uncoupled respiration, mitochondrial membrane potential and NAD(P)H content, and, in contrast, increased resting (state 4) respiration. We also verified that 3HTA and 3HPA markedly reduced Ca2+ retention capacity and induced swelling in Ca2+-loaded mitochondria. These effects were mediated by mitochondrial permeability transition (MPT) induction since they were totally prevented by the classical MPT inhibitors cyclosporin A and ADP, as well as by ruthenium red, a Ca2+ uptake blocker. Taken together, our data demonstrate that the major monocarboxylic LCHFA accumulating in LCHAD deficiency disrupt energy mitochondrial homeostasis in the liver. It is proposed that this pathomechanism may explain at least in part the hepatic alterations characteristic of the affected patients.

Clinical outcome, biochemical and therapeutic follow-up in 14 Austrian patients with Long-Chain 3-Hydroxy Acyl CoA Dehydrogenase Deficiency (LCHADD)

Background

LCHADD is a long-fatty acid oxidation disorder with immediate symptoms and long-term complications. We evaluated data on clinical status, biochemical parameters, therapeutic regimens and outcome of Austrian LCHADD patients.

Study design

Clinical and outcome data including history, diagnosis, short- and long-term manifestations, growth, psychomotor development, hospitalizations, therapy of 14 Austrian patients with LCHADD were evaluated. Biochemically, we evaluated creatine kinase (CK) and acyl carnitine profiles.

Results

All LCHADD patients are homozygous for the common mutation. Three are siblings. Diagnosis was first established biochemically. Nine/14 (64%) were prematures, with IRDS occurring in six. In nine (64%), diagnosis was established through newborn screening, the remaining five (36%) were diagnosed clinically. Four pregnancies were complicated by HELLP syndrome, one by preeclampsia. In two, intrauterine growth retardation and placental insufficiency were reported. Five were diagnosed with hepatopathy at some point, seven with cardiomyopathy and eight with retinopathy, clinically relevant only in one patient. Polyneuropathy is only present in one. Three patients have a PEG, one is regularly fed via NG-tube. Growth is normal in all, as well as psychomotor development, except for two extremely premature girls. In 11 patients, 165 episodes with elevated creatine kinase concentrations were observed with 6-31 (median 14) per patient; three have shown no elevated CK concentrations. Median total carnitine on therapy was 19 μmol/l (range 11-61). For 14 patients, there have been 181 hospitalizations (median 9 per patient), comprising 1337 in-patient-days. All centres adhere to treatment with a fat-defined diet; patients have between 15% and 40% of their energy intake from fat (median 29%), out of which between 20% and 80% are medium-chain triglycerides (MCT) (median 62%). Four patients have been treated with heptanoate (C7).

Conclusion

Our data show LCHADD outcome can be favourable. Growth and psychomotor development is normal, except in two prematures. Frequency of CK measurements decreases with age, correlating with a decreasing number of hospitalizations. About 50% develop complications affecting different organ systems. There is no relevant difference between the patients treated in the respective centers. Concluding from single case reports, anaplerotic therapy with heptanoate should be further evaluated.

Growth in Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency is an inborn error of fatty acid metabolism that affects the degradation of long chain fatty acids and causes insufficient energy production and accumulation of toxic intermediates. The treatment consists of a diet low in fat, with supplementation of medium-chain triglycerides that bypass the metabolic block. In addition, frequent feeds and extra carbohydrates are given during febrile illnesses to reduce lipolysis. Hence, this diet differs from the general dietary recommendations for growing children. Furthermore, the Swedish dietary instructions for fat intake in LCHAD deficiency are given in grams, which differ from most guidelines that recommend fat intake as percentage shares of total caloric intake.

AIMS

To assess growth in patients with LCHAD deficiency, in relation to dietary treatment and to evaluate if overweight/obesity is more common than in the normal population.

RESULTS

The growth velocity showed acceleration after diagnosis and the start of treatment, followed by a period of stable or decelerated growth. The majority of the patients developed overweight to a greater extent than children without LCHAD deficiency. Several patients also went through a phase of obesity. Data on final height (FH) showed that three out of five patients had grown according to their genetic potential.

CONCLUSIONS

Regular and frequent follow-up and careful monitoring of weight are essential to avoid the development of overweight and obesity. The Swedish dietary instructions defining fat intake in total grams per day may be an alternative approach to achieve a moderate total caloric intake.

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.

Prevalence of Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency in Estonia

The aim of our study was to evaluate the prevalence of long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) in the general Estonian population and among patients with symptoms suggestive of fatty acid oxidation (FAO) defects. We collected DNA from a cohort of 1,040 anonymous newborn blood spot samples. We screened these samples for the presence of the common c.1528G>C mutation in the HADHA gene. Based on the clinical suspicion of FAO defects, we screened suspected individuals since 2004 for the common c.1528G>C mutation in the HADHA gene and since 2008 in addition by tandem mass spectrometric analysis of plasma acylcarnitines. Our results showed that the carrier frequency of the c.1528G>C mutation in the Estonian population is high - 1:173. During the screening of symptomatic patients, we identified five LCHADD patients in four families. Three patients were retrospectively identified by molecular screening of the HADHA gene. One patient was homozygous for the c.1528G>C mutation in the HADHA gene, and two siblings were compound heterozygotes with HADHA genotype c.[1528G>C]+[1690-2A>G]. Among patients tested using acylcarnitine profiling, we identified two cases with an abnormal acylcarnitine profile typical to LCHADD. Molecular analysis showed homozygosity for c.1528G>C mutation. Based on a carrier frequency of 1:173 (95% Confidence Interval 1:76-1:454) and taking into account that the c.1528G>C mutation makes up 87.5% of disease alleles in Estonian LCHADD patients, the estimated prevalence of LCHADD in Estonia would be 1: 91,700.

Fatty acid oxidation disorders: maternal health and neonatal outcomes

Mitochondrial fatty acid beta-oxidation (FAO) disorders have become an important group of inherited metabolic disorders causing serious pediatric and maternal morbidity and mortality. More than 20 defects affecting beta-oxidation have been discovered, characterized by distinct enzyme or transporter deficiencies. This growing number of FAO disorders covers a wide spectrum of phenotypes and are characterized by a wide array of clinical presentations. We discuss the major mitochondrial FAO disorders and the impact they have on maternal health and neonatal outcomes; diagnostic tools and the value of genetic screening are reviewed; and current therapeutic approaches and management strategies are discussed.

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

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

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.

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

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

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.

Post-mortem analysis for two prevalent beta-oxidation mutations in sudden infant death

BACKGROUND

Fatty acid oxidation disorders may cause sudden and unexpected infant death and are associated with the histological hallmark of hepatic steatosis. The goal of the present study was to assess the value of post-mortem molecular analysis for medium-chain acyl-coenzyme A dehydrogenase (MCAD) and mitochondrial trifunctional protein (MTP) defects in unexplained sudden infant death (SID) associated with fatty infiltration of the liver. MCAD catalyzes the first step of medium-chain fatty acid oxidation while MTP catalyzes the last three steps of long-chain fatty acid oxidation.

METHODS

In a retrospective study, 220 consecutive cases of sudden and unexplained infant death certified by medical examiners at Wake Forest University Medical Center were assessed for hepatic steatosis. Subjects with evidence of hepatic steatosis were screened for mutations in MCAD and MTPalpha-subunit using DNA isolated from paraffin-embedded liver tissue, single-strand conformation variance, and nucleotide sequence analyses.

RESULTS

Sixteen cases (7.3%) were associated with diffuse micro-vesicular or mixed micro- and macro-vesicular hepatic steatosis. Two of these 16 cases (12.5%) had disease-causing mutations. One was homozygous for the prevalent MCAD A985G mutation. The second was a compound heterozygous for the prevalent MTP G1528C mutation and a novel 1 bp deletion in exon 18 of the MTPalpha-subunit gene.

CONCLUSIONS

A significant proportion (7.3%) of SID is associated with hepatic steatosis. The present data support post-mortem molecular analysis for the MCAD A985G and MTP G1528C prevalent mutations in cases of sudden and unexplained infant death associated with hepatic steatosis.

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.

Immunizations for patients with metabolic disorders

Individuals with underlying metabolic disorders are a potential high-risk group for vaccine-preventable diseases. Newborn metabolic screening has provided a means of early identification and treatment for many of these disorders, whereas childhood immunization is one of the most effective means of decreasing the morbidity and mortality resulting from communicable diseases worldwide. There are very few contraindications to the routine administration of vaccines to the healthy, immunocompetent individual. In certain high-risk groups, such as immunocompromised patients, gravid females, and those with a history of previous anaphylactic reaction to a vaccine or its components, selective withholding of immunizations must be considered to decrease potential adverse events. A detailed analysis of the medical literature revealed few specific recommendations regarding appropriate immunization techniques for patients with metabolic disorders. In this review we detail the major metabolic disorder subtypes, elaborate on the available literature on immunizations for patients with these disorders, and provide suggested vaccine recommendations.

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.

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.

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.

Maternal acute fatty liver of pregnancy and the associated risk for long-chain 3-hydroxyacyl-coenzyme a dehydrogenase (LCHAD) deficiency in infants

Acute fatty liver disease of pregnancy has been recognized as a clinical problem since the 1980s. In the past 8 years, the association of this disease with a genetic inborn error of metabolism in the infant has been recognized. Women who are heterozygous for this disorder are usually asymptomatic until the capacity of their livers to metabolize free fatty acids (FFA) is overwhelmed by a homozygous fetus. The inborn error of metabolism, long-chain 3-hydroxyacyl-coenzyme A dehydrogenase (LCHAD) deficiency, may not be immediately recognizable in the infant. Symptoms in the infant are often triggered by an increased long-chain fatty acid load in the diet, or by illness that results in breakdown of endogenous fat. The following case study reviews the clinical pathophysiology of this perinatal health problem and highlights the priorities for the care of infants born to mothers with acute fatty liver disease of pregnancy.

Molecular and phenotypic heterogeneity in mitochondrial trifunctional protein deficiency due to beta-subunit mutations

The mitochondrial trifunctional protein (TFP) is a multienzyme complex of the fatty acid beta-oxidation cycle. It is composed of four alpha-subunits (HADHA) harboring long-chain enoyl-CoA hydratase and long-chain L-3-hydroxyacyl-CoA dehydrogenase (LCHAD) and four beta-subunits (HADHB) harboring long-chain 3-ketoacyl-CoA thiolase (LKAT). Mutations in either subunit can result in TFP deficiency with reduced activity of all three TFP enzymes. We characterize 15 patients from 13 families with beta-subunit mutations by clinical, biochemical, and molecular features. Three clinical phenotypes are apparent: a severe neonatal presentation with cardiomyopathy, Reye-like symptoms, and early death (n=4); a hepatic form with recurrent hypoketotic hypoglycemia (n=2); and a milder later-onset neuromyopathic phenotype with episodic myoglobinuria (n=9). Maternal HELLP syndrome occurred in two mothers independently of the fetal phenotype. Mutational analysis revealed 16 different mutations, the majority being missense mutations (n=12). The predominance of missense mutations and the milder myopathic phenotype are consistent. Based upon homology to yeast thiolase that has been characterized structurally, the mutation localization within the protein correlates with the clinical phenotype. Outer loop mutations that are expected to alter protein stability less were only present in milder forms. The degree of reduction in thiolase antigen also correlated with the severity of clinical presentation. Although TFP deficiency is highly heterogeneous, there is genotype-phenotype correlation.

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.

Strategies for the diagnosis of mitochondrial fatty acid beta-oxidation disorders

Mitochondrial fatty acid beta-oxidation disorders (FAOD) are a group of clinically and biochemically heterogeneous inherited metabolic defects. The spectrum of phenotypes has expanded from hepatic encephalopathy to encompass myopathy, cardiomyopathy, peripheral neuropathy, sudden death and pregnancy complicated by fetal FAOD. Pre-symptomatic diagnosis is important to prevent morbidity and this is now achievable through newborn screening using tandem mass spectrometry (MS/MS). Moreover, most of the diagnosed defects are treatable and the prognosis is generally favourable. This article reviews the features of FAOD, critically evaluates methods of investigation including metabolite analyses in body fluids, in vitro oxidation rates and acylcarnitine profiling studies, enzymatic and mutational tests, and discusses genotype-phenotype correlation, treatment and monitoring options. Based on this knowledge, strategies for the biochemical investigation and differential diagnosis of patients presenting clinically, asymptomatic neonates detected by newborn screening, infants born after complications during late pregnancy, and cases of sudden death with suspected FAOD are presented. Laboratory investigation commonly begins with a search for diagnostic metabolites in physiological fluids, followed by in vitro functional studies if the initial findings are inconclusive, and confirmation by enzymology and molecular analyses. Occasionally a stress test in vivo may be required. At other times there may be no firm diagnosis achieved.

Long-chain L-3-hydroxyacyl-coenzyme a dehydrogenase deficiency: a molecular and biochemical review

Since the first report of long-chain L-3-hydroxyacyl-coenzyme A dehydrogenase deficiency a little more than a decade ago, its phenotypic and genotypic heterogeneity in individuals homozygous for the enzyme defect has become more and more evident. Even more interesting is its association with pregnancy-specific disorders, including preeclampsia, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), hyperemesis gravidarum, acute fatty liver of pregnancy, and maternal floor infarct of the placenta. In this review we discuss the biochemical and molecular basis, clinical features, diagnosis, and management of long-chain L-3-hydroxyacyl-coenzyme A dehydrogenase deficiency.

Mutation analysis in mitochondrial fatty acid oxidation defects: Exemplified by acyl-CoA dehydrogenase deficiencies, with special focus on genotype-phenotype relationship

Mutation analysis of metabolic disorders, such as the fatty acid oxidation defects, offers an additional, and often superior, tool for specific diagnosis compared to traditional enzymatic assays. With the advancement of the structural part of the Human Genome Project and the creation of mutation databases, procedures for convenient and reliable genetic analyses are being developed. The most straightforward application of mutation analysis is to specific diagnoses in suspected patients, particularly in the context of family studies and for prenatal/preimplantation analysis. In addition, from these practical uses emerges the possibility to study genotype-phenotype relationships and investigate the molecular pathogenesis resulting from specific mutations or groups of mutations. In the present review we summarize current knowledge regarding genotype-phenotype relationships in three disorders of mitochondrial fatty acid oxidation: very-long chain acyl-CoA dehydrogenase (VLCAD, also ACADVL), medium-chain acyl-CoA dehydrogenase (MCAD, also ACADM), and short-chain acyl-CoA dehydrogenase (SCAD, also ACADS) deficiencies. On the basis of this knowledge we discuss current understanding of the structural implications of mutation type, as well as the modulating effect of the mitochondrial protein quality control systems, composed of molecular chaperones and intracellular proteases. We propose that the unraveling of the genetic and cellular determinants of the modulating effects of protein quality control systems may help to assess the balance between genetic and environmental factors in the clinical expression of a given mutation. The realization that the effect of the monogene, such as disease-causing mutations in the VLCAD, MCAD, and SCAD genes, may be modified by variations in other genes presages the need for profile analyses of additional genetic variations. The rapid development of mutation detection systems, such as the chip technologies, makes such profile analyses feasible. However, it remains to be seen to what extent mutation analysis will be used for diagnosis of fatty acid oxidation defects and other metabolic disorders.

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.