Ophthalmologic findings in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency caused by the G1528C mutation: a new type of hereditary metabolic chorioretinopathy

Early diagnosis and treatment by newborn screening (NBS) or family history is associated with improved visual outcomes for long-chain 3-hydroxyacylCoA dehydrogenase deficiency (LCHADD) chorioretinopathy

Long chain 3-hydroxyacyl-CoA dehydrogenase (LCHADD) is the only fatty acid oxidation disorder to develop a progressive chorioretinopathy resulting in vision loss; newborn screening (NBS) for this disorder began in the United States around 2004. We compared visual outcomes among 40 participants with LCHADD or trifunctional protein deficiency diagnosed symptomatically to those who were diagnosed via NBS or a family history. Participants completed ophthalmologic testing including measures of visual acuity, electroretinograms (ERG), fundal imaging, contrast sensitivity, and visual fields. Records were reviewed to document medical and treatment history. Twelve participants presented symptomatically with hypoglycemia, failure to thrive, liver dysfunction, cardiac arrest, or rhabdomyolysis. Twenty eight were diagnosed by NBS or due to a family history of LCHADD. Participants diagnosed symptomatically were older but had similar percent males and genotypes as those diagnosed by NBS. Treatment consisted of fasting avoidance, dietary long-chain fat restriction, MCT, C7, and/or carnitine supplementation. Visual acuity, rod- and cone-driven amplitudes on ERG, contrast sensitivity scores, and visual fields were all significantly worse among participants diagnosed symptomatically compared to NBS. In mixed-effects models, both age and presentation (symptomatic vs. NBS) were significant independent factors associated with visual outcomes. This suggests that visual outcomes were improved by NBS, but there was still lower visual function with advancing age in both groups. Early diagnosis and treatment by NBS is associated with improved visual outcomes and retinal function compared to participants who presented symptomatically. Despite the impact of early intervention, chorioretinopathy was greater with advancing age, highlighting the need for novel treatments.

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.

A proposal for an updated staging system for LCHADD retinopathy

OBJECTIVE

To develop an updated staging system for long-chain 3-hydroxyacyl coenzyme A dehydrogenase deficiency (LCHADD) chorioretinopathy based on contemporary multimodal imaging and electrophysiology.

METHODS

We evaluated forty cases of patients with genetically confirmed LCHADD or trifunctional protein deficiency (TFPD) enrolled in a prospective natural history study. Wide-field fundus photographs, fundus autofluorescence (FAF), optical coherence tomography (OCT), and full-field electroretinogram (ffERG) were reviewed and graded for severity.

RESULTS

Two independent experts first graded fundus photos and electrophysiology to classify the stage of chorioretinopathy based upon an existing published system. With newer imaging modalities and improved electrophysiology, many patients did not fit cleanly into a single traditional staging group. Therefore, we developed a novel staging system that better delineated the progression of LCHADD retinopathy. We maintained the four previous delineated stages but created substages A and B in stages 2 to 3 to achieve better differentiation.

DISCUSSION

Previous staging systems of LCHADD chorioretinopathy relied on only on the assessment of standard 30 to 45-degree fundus photographs, visual acuity, fluorescein angiography (FA), and ffERG. Advances in recordings of ffERG and multimodal imaging with wider fields of view, allow better assessment of retinal changes. Following these advanced assessments, seven patients did not fit neatly into the original classification system and were therefore recategorized under the new proposed system.

CONCLUSION

The new proposed staging system improves the classification of LCHADD chorioretinopathy, with the potential to lead to a deeper understanding of the disease's progression and serve as a more reliable reference point for future therapeutic research.

Optical coherence tomography angiography of choroidal neovascularization in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD)

Purpose

To report the clinical utility of optical coherence tomography angiography (OCTA) for demonstrating choroidal neovascularization (CNV) associated with Long-Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency (LCHADD) retinopathy.

Methods

Thirty-three participants with LCHADD (age 7-36 years; median 17) were imaged with OCTA and the Center for Ophthalmic Optics & Lasers Angiography Reading Toolkit (COOL-ART) software was implemented to process OCTA scans.

Results

Seven participants (21 %; age 17-36 years; median 25) with LCHADD retinopathy demonstrated evidence of CNV by retinal examination or presence of CNV within outer retinal tissue on OCTA scans covering 3 × 3 and/or 6 × 6-mm. These sub-clinical CNVs are adjacent to hyperpigmented areas in the posterior pole. CNV presented at stage 2 or later of LCHADD retinopathy prior to the disappearance of RPE pigment in the macula.

Conclusion

OCTA can be applied as a non-invasive method to evaluate the retinal and choroidal microvasculature. OCTA can reveal CNV in LCHADD even when the clinical exam is inconclusive. These data suggest that the incidence of CNV is greater than expected and can occur even in the early stages of LCHADD retinopathy.

IMI-Management and Investigation of High Myopia in Infants and Young Children

Purpose

The purpose of this study was to evaluate the epidemiology, etiology, clinical assessment, investigation, management, and visual consequences of high myopia (≤-6 diopters [D]) in infants and young children.

Findings

High myopia is rare in pre-school children with a prevalence less than 1%. The etiology of myopia in such children is different than in older children, with a high rate of secondary myopia associated with prematurity or genetic causes. The priority following the diagnosis of high myopia in childhood is to determine whether there is an associated medical diagnosis that may be of greater overall importance to the health of the child through a clinical evaluation that targets the commonest features associated with syndromic forms of myopia. Biometric evaluation (including axial length and corneal curvature) is important to distinguishing axial myopia from refractive myopia associated with abnormal development of the anterior segment. Additional investigation includes ocular imaging, electrophysiological tests, genetic testing, and involvement of pediatricians and clinical geneticists is often warranted. Following investigation, optical correction is essential, but this may be more challenging and complex than in older children. Application of myopia control interventions in this group of children requires a case-by-case approach due to the lack of evidence of efficacy and clinical heterogeneity of high myopia in young children.

Conclusions

High myopia in infants and young children is a rare condition with a different pattern of etiology to that seen in older children. The clinical management of such children, in terms of investigation, optical correction, and use of myopia control treatments, is a complex and often multidisciplinary process.

Deciphering the pathogenesis of retinopathy associated with carnitine palmitoyltransferase I deficiency in zebrafish model

Fatty acid oxidation disorders (FAODs) are a group of rare genetic metabolic disorders caused by mutations in genes responsible for transporting and metabolizing fatty acids in the mitochondria. One crucial enzyme involved in this process is carnitine palmitoyltransferase I (CPT1), which transports long-chain fatty acids to the mitochondrial matrix for beta-oxidation. Defects in beta-oxidation enzymes often lead to pigmentary retinopathy; however, the underlying mechanisms are not entirely understood. To investigate FAOD and its impact on the retina, we employed zebrafish as a model organism. Specifically, we used antisense-mediated knockdown strategies to target the cpt1a gene and examined the resulting retinal phenotypes. We demonstrated that the cpt1a MO-injected fish significantly reduced the length of connecting cilia and severely affected photoreceptor cell development. Moreover, our findings highlight that the loss of functional cpt1a disrupted energy homeostasis in the retina, leading to lipid droplet deposition and promoting ferroptosis, which is likely attributed to the photoreceptor degeneration and visual impairments observed in the cpt1a morphants.

SCP2 variant is associated with alterations in lipid metabolism, brainstem neurodegeneration, and testicular defects

BACKGROUND

The detoxification of very long-chain and branched-chain fatty acids and the metabolism of cholesterol to form bile acids occur largely through a process called peroxisomal β-oxidation. Mutations in several peroxisomal proteins involved in β-oxidation have been reported, resulting in diseases characterized by neurological defects. The final step of the peroxisomal β-oxidation pathway is catalyzed by sterol carrier protein-x (SCPx), which is encoded by the SCP2 gene. Previously, there have been two reports of SCPx deficiency, which resulted from a homozygous or compound heterozygous SCP2 mutation. We report herein the first patient with a heterozygous SCP2 mutation leading to SCPx deficiency.

RESULTS

Clinical presentations of the patient included progressive brainstem neurodegeneration, cardiac dysrhythmia, muscle wasting, and azoospermia. Plasma fatty acid analysis revealed abnormal values of medium-, long-, and very long-chain fatty acids. Protein expression of SCPx and other enzymes involved in β-oxidation were altered between patient and normal fibroblasts. RNA sequencing and lipidomic analyses identified metabolic pathways that were altered between patient and normal fibroblasts including PPAR signaling, serotonergic signaling, steroid biosynthesis, and fatty acid degradation. Treatment with fenofibrate or 4-hydroxytamoxifen increased SCPx levels, and certain fatty acid levels in patient fibroblasts.

CONCLUSIONS

These findings suggest that the patient's SCP2 mutation resulted in decreased protein levels of SCPx, which may be associated with many metabolic pathways. Increasing SCPx levels through pharmacological interventions may reverse some effects of SCPx deficiency. Collectively, this work provides insight into many of the clinical consequences of SCPx deficiency and provides evidence for potential treatment strategies.

A novel HADHA variant associated with an atypical moderate and late-onset LCHAD deficiency

Background

Long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a rare inherited disease caused by pathogenic variants of HADHA gene. Along with signs common to fatty acid oxidation defects (FAOD), specific retina and heart alterations are observed. Because long-chain fatty acid oxidation is selectively affected, supplementations with short/medium-chain fats represent energetic sources bypassing the enzymatic blockade. Here, we report on an atypical presentation of the disease.

Methods

Clinical features were described with medical explorations including ophthalmic and cardiac examination. Biological underlying defects were investigated by measurements of biochemical metabolites and by fluxomic studies of mitochondrial β-oxidation. Whole exome sequencing and molecular validation of variants confirmed the diagnosis.

Results

The patient has developed at nine years an unlabeled maculopathy, and at 28 years, an acute cardiac decompensation without any premise. Blood individual acylcarnitine analysis showed a rise in hydroxylated long-chain fatty acids and fluxomic studies validated enzyme blockade consistent with LCHADD. Genetic analysis revealed the common p.(Glu510Gln) variant in HADHA, in trans with a novel variant c.1108G > A, p.(Gly370Arg) located in the NAD binding domain. Patient pathology was responsive to triheptanoin supplementation.

Conclusion

This atypical LCHADD form report should encourage the early assessment of biochemical and genetic testing as a specific management is recommended (combination with fast avoidance, low fat-high carbohydrate diet, medium-even-chain triglycerides or triheptanoin supplementation).

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Mild hyperpigmented macular dots could be the first and early symptom of moderate LCHAD.

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The novel HADHA c.1108G > A, p.(Gly370Arg) is hypomorphic and associated with moderate LCHAD.

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Atypical and late LCHAD can be deciphered by joint biochemical and genetical investigations.

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Acylcarnitines must be tested in unexplained macular dystrophy and/or dilated cardiomyopathy.

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Supplementation with the triglyceride triheptanoin is effective.

CHOROIDAL NEOVASCULARIZATION ASSOCIATED WITH LONG-CHAIN 3-HYDROXYACYL-CoA DEHYDROGENASE DEFICIENCY

PURPOSE

To report the first case describing choroidal neovascularization in long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency.

METHODS

Case report including multimodal imaging discussion.

RESULTS

A 21-year-old woman affected by LCHAD deficiency (confirmed by 1528 G>C homozygous mutation) was referred to our department for progressive visual decline in both eyes. Best-corrected visual acuities were 20/40 and 20/1,000 in the right and left eye, respectively. Ultra-widefield imaging, fluorescein angiography, structural optical coherence tomography, and optical coherence tomography angiography revealed the presence of macular and midperipheral chorioretinal atrophy complicated by a choroidal neovascularization in the left eye.

CONCLUSION

Ocular changes in LCHAD deficiency are long-term complications and severely affect the quality of life of patients. We report for the first time the evidence that choroidal neovascularization could complicate ocular changes accelerating the progressive vision impairment.

Impact of Newborn Screening and Early Dietary Management on Clinical Outcome of Patients with Long Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency and Medium Chain Acyl-CoA Dehydrogenase Deficiency-A Retrospective Nationwide Study

Long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD/MTPD) and medium chain acyl-CoA dehydrogenase deficiency (MCADD) were included in the expanded neonatal screening program (ENBS) in Czechia in 2009, allowing for the presymptomatic diagnosis and nutritional management of these patients. The aim of our study was to assess the nationwide impact of ENBS on clinical outcome. This retrospective study analysed acute events and chronic complications and their severity in pre-ENBS and post-ENBS cohorts. In total, 28 children (12 before, 16 after ENBS) were diagnosed with LCHADD/MTPD (incidence 0.8/100,000 before and 1.2/100,000 after ENBS). In the subgroup detected by ENBS, a significantly longer interval from birth to first acute encephalopathy was observed. In addition, improvement in neuropathy and cardiomyopathy (although statistically non-significant) was demonstrated in the post-ENBS subgroup. In the MCADD cohort, we included 69 patients (15 before, 54 after ENBS). The estimated incidence rose from 0.7/100,000 before to 4.3/100,000 after ENBS. We confirmed a significant decrease in the number of episodes of acute encephalopathy and lower proportion of intellectual disability after ENBS (p < 0.0001). The genotype-phenotype correlations suggest a new association between homozygosity for the c.1528C > G variant and more severe heart involvement in LCHADD patients.

Impact of newborn screening on the reported incidence and clinical outcomes associated with medium- and long-chain fatty acid oxidation disorders

Fatty acid oxidation disorders (FAODs) are potentially fatal inherited disorders for which management focuses on early disease detection and dietary intervention to reduce the impact of metabolic crises and associated spectrum of clinical symptoms. They can be divided functionally into long-chain (LC-FAODs) and medium-chain disorders (almost exclusively deficiency of medium-chain acyl-coenzyme A dehydrogenase). Newborn screening (NBS) allows prompt identification and management. FAOD detection rates have increased following the addition of FAODs to NBS programs in the United States and many developed countries. NBS-identified neonates with FAODs may remain asymptomatic with dietary management. Evidence from numerous studies suggests that NBS-identified patients have improved outcomes compared with clinically diagnosed patients, including reduced rates of symptomatic manifestations, neurodevelopmental impairment, and death. The limitations of NBS include the potential for false-negative and false-positive results, and the need for confirmatory testing. Although NBS alone does not predict the consequences of disease, outcomes, or management needs, subsequent genetic analyses may have predictive value. Genotyping can provide valuable information on the nature and frequency of pathogenic variants involved with FAODs and their association with specific phenotypes. Long-term follow-up to fully understand the clinical spectrum of NBS-identified patients and the effect of different management strategies is needed.

Photoreceptor metabolic reprogramming: current understanding and therapeutic implications

Acquired and inherited retinal disorders are responsible for vision loss in an increasing proportion of individuals worldwide. Photoreceptor (PR) death is central to the vision loss individuals experience in these various retinal diseases. Unfortunately, there is a lack of treatment options to prevent PR loss, so an urgent unmet need exists for therapies that improve PR survival and ultimately, vision. The retina is one of the most energy demanding tissues in the body, and this is driven in large part by the metabolic needs of PRs. Recent studies suggest that disruption of nutrient availability and regulation of cell metabolism may be a unifying mechanism in PR death. Understanding retinal cell metabolism and how it is altered in disease has been identified as a priority area of research. The focus of this review is on the recent advances in the understanding of PR metabolism and how it is critical to reduction-oxidation (redox) balance, the outer retinal metabolic ecosystem, and retinal disease. The importance of these metabolic processes is just beginning to be realized and unraveling the metabolic and redox pathways integral to PR health may identify novel targets for neuroprotective strategies that prevent blindness in the heterogenous group of retinal disorders.

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency and progressive retinopathy: one case report followed by ERGs, VEPs, EOG over a 17-year period

BACKGROUND

LCHAD (long-chain 3-hydroxyacyl-CoA dehydrogenase) deficiency is a rare genetic disorder of mitochondrial long-chain fatty acid oxidation inherited as a recessive trait. Affected patients can present with hypoglycaemia, rhabdomyolysis and cardiomyopathy. About half of the patients may suffer from retinopathy.

CASE REPORT

A 19-year-old girl was diagnosed as suffering from LCHAD deficiency with recurrent rhabdomyolysis episodes at the age of 7 months by an inaugural coma with hypoglycaemia and hepatomegaly. Appropriate dietary management with carnitine supplementation was initiated. Retinopathy was diagnosed at age two. Ophthalmological assessments including visual acuity, visual field, OCT, flash ERGs, P-ERG, flash VEPs and EOG recordings were conducted over a 17-year period.

RESULTS

Visual acuity was decreased. Fundi showed a progressive retinopathy and chorioretinopathy. Photophobia was noticed 2 years before the decrease in photopic-ERG amplitude with normal scotopic-ERGs. Scotopic-ERG amplitude decreased 10 years after the decrease in photopic-ERG amplitude. No EOG light rise was observed. Flash VEPs remained normal. These results suggest that the cone system dysfunction occurs largely prior to the rod system dysfunction with a relative preservation of the macula function.

COMMENTS

This dysfunction of cones prior to the dysfunction of rods was not reported previously. This could be related to mitochondrial energy failure in cones as cones are greater consumers of ATP than rods. This hypothesis needs to be further confirmed as other long-chain fatty oxidation defective patients (VLCAD and CPT2 deficiencies) do not exhibit retinopathy.

Clinical manifestations and management of fatty acid oxidation disorders

Fatty acid oxidation disorders (FAOD) are a group of rare, autosomal recessive, metabolic disorders caused by variants of the genes for the enzymes and proteins involved in the transport and metabolism of fatty acids in the mitochondria. Those affected by FAOD are unable to convert fatty acids into tricarboxylic acid cycle intermediates such as acetyl-coenzyme A, resulting in decreased adenosine triphosphate and glucose for use as energy in a variety of high-energy-requiring organ systems. Signs and symptoms may manifest in infants but often also appear in adolescents or adults during times of increased metabolic demand, such as fasting, physiologic stress, and prolonged exercise. Patients with FAOD present with a highly heterogeneous clinical spectrum. The most common clinical presentations include hypoketotic hypoglycemia, liver dysfunction, cardiomyopathy, rhabdomyolysis, and skeletal myopathy, as well as peripheral neuropathy and retinopathy in some subtypes. Despite efforts to detect FAOD through newborn screening and manage patients early, symptom onset can be sudden and serious, even resulting in death. Therefore, it is critical to identify quickly and accurately the key signs and symptoms of patients with FAOD to manage metabolic decompensations and prevent serious comorbidities.

Retained visual function in a subset of patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD)

Introduction: LCHADD causes retinopathy associated with low vision, visual field defects, nyctalopia and myopia. We report a retrospective long-term single-center study of 6 LCHADD patients trying to clarify if early diagnosis has an impact on the course and outcome of chorioretinal degeneration. Methods: Long-term follow-up of visual acuity and staging of chorioretinal degeneration by fundus photography, optical coherence tomography (OCT) and autofluorescence (AF) in all six patients. Three patients (2 m/1 f; age 8-14.8 years) were diagnosed by newborn screening, a single patient early within the first year of life and treated promptly while the other two (1 m/1 f; age 23-24 years) were diagnosed later after developing symptoms. All carried HADHA variants; five were homozygous for the common p.E510Q variant, in one from the symptomatically diagnosed group p.[E510Q]; [R291*] was detected. Results: All patients showed retinal alterations, but early diagnosis was associated with a milder phenotype and a longer preservation of visual function. Among symptomatic patients, only one showed mild retinal involvement at the time of diagnosis. Conclusion: Despite the small number our study suggests that early diagnosis does not prevent retinopathy but might contribute to a milder phenotype with retained good visual acuity over time. OCT and AF are reliable non-invasive diagnostic tools to estimate the progression of early-stage retinal changes in LCHADD patients.

Cryo-EM structure of human mitochondrial trifunctional protein

The mitochondrial trifunctional protein (TFP) catalyzes three reactions in the fatty acid β-oxidation process. Mutations in the two TFP subunits cause mitochondrial trifunctional protein deficiency and acute fatty liver of pregnancy that can lead to death. Here we report a 4.2-Å cryo-electron microscopy α2β2 tetrameric structure of the human TFP. The tetramer has a V-shaped architecture that displays a distinct assembly compared with the bacterial TFPs. A concave surface of the TFP tetramer interacts with the detergent molecules in the structure, suggesting that this region is involved in associating with the membrane. Deletion of a helical hairpin in TFPβ decreases its binding to the liposomes in vitro and reduces its membrane targeting in cells. Our results provide the structural basis for TFP function and have important implications for fatty acid oxidation related diseases.

Role of 3-Hydroxy Fatty Acid-Induced Hepatic Lipotoxicity in Acute Fatty Liver of Pregnancy

Acute fatty liver of pregnancy (AFLP), a catastrophic illness for both the mother and the unborn offspring, develops in the last trimester of pregnancy with significant maternal and perinatal mortality. AFLP is also recognized as an obstetric and medical emergency. Maternal AFLP is highly associated with a fetal homozygous mutation (1528G>C) in the gene that encodes for mitochondrial long-chain hydroxy acyl-CoA dehydrogenase (LCHAD). The mutation in LCHAD results in the accumulation of 3-hydroxy fatty acids, such as 3-hydroxy myristic acid, 3-hydroxy palmitic acid and 3-hydroxy dicarboxylic acid in the placenta, which are then shunted to the maternal circulation leading to the development of acute liver injury observed in patients with AFLP. In this review, we will discuss the mechanistic role of increased 3-hydroxy fatty acid in causing lipotoxicity to the liver and in inducing oxidative stress, mitochondrial dysfunction and hepatocyte lipoapoptosis. Further, we also review the role of 3-hydroxy fatty acids in causing placental damage, pancreatic islet β-cell glucolipotoxicity, brain damage, and retinal epithelial cells lipoapoptosis in patients with LCHAD deficiency.

Most patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency develop pathological or subnormal retinal function

AIM

There have been few studies on long-term electroretinographic findings in patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD). This study correlated long-term electroretinographic findings with age, metabolic control and clinical symptoms.

METHODS

We examined 12 Swedish patients with LCHADD. Visual acuity testing, fundus examinations, optical coherence tomography and electroretinography were performed. The results were correlated to age, the levels of 3-hydroxyacylcarnitine and acylcarnitine and clinical metabolic control.

RESULTS

Blindness or moderate visual impairment was found in two patients. Retinal pigmentation, atrophy and fibrosis were present in 11, seven and one of the patients, respectively, and optical coherence tomography showed retinal thinning in three of the six patients examined. Electroretinography was performed on 11 of the 12 patients. It was pathological, with reduced rod and cone responses, in five patients, subnormal in four and was related to poor clinical metabolic control and severe neonatal symptoms. Repeated electroretinographies revealed reduced function with increasing age.

CONCLUSION

More than 80% of the LCHADD patients developed pathological or subnormal retinal function. This was more pronounced in patients with neonatal symptoms, but ameliorated by strict dietary treatment. Annual ophthalmological follow-ups, with electroretinography every second or third year, are recommended.

Characterization of Chorioretinopathy Associated with Mitochondrial Trifunctional Protein Disorders: Long-Term Follow-up of 21 Cases

PURPOSE

To assess long-term effects of genotype on chorioretinopathy severity in patients with mitochondrial trifunctional protein (MTP) disorders.

DESIGN

Retrospective case series.

PARTICIPANTS

Consecutive patients with MTP disorders evaluated at a single center from 1994 through 2015, including 18 patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) and 3 patients with trifunctional protein deficiency (TFPD).

METHODS

Local records from all visits were reviewed. Every participant underwent a complete ophthalmic examination and was evaluated by a metabolic physician and dietitian. Nine patients underwent ancillary funduscopic imaging including optical coherence tomography (OCT) and OCT angiography.

MAIN OUTCOME MEASURES

The primary outcome measure was best-corrected visual acuity at the final visit. Secondary outcome measures included spherical equivalent refraction, visual fields, electroretinography B-wave amplitudes, and qualitative imaging findings.

RESULTS

Participants were followed up for a median of 5.6 years (range 0.3-20.2 years). The median age of LCHADD participants at initial and final visits was 2.3 and 11.9 years, whereas that for TFPD participants at initial and final visits was 4.7 and 15.5 years, respectively. Four long-term survivors older than 16 years were included (3 with LCHADD and 1 with TFPD). The LCHADD participants demonstrated a steady decline in visual acuity from an average of 0.23 logarithm of the minimum angle of resolution (logMAR; Snellen equivalent, 20/34) at baseline to 0.42 logMAR (Snellen equivalent, 20/53) at the final visit, whereas TFPD patients maintained excellent acuity throughout follow-up. Participants with LCHADD, but not TFPD, showed an increasing myopia with a mean decrease in spherical equivalent refraction of 0.24 diopters per year. Visual fields showed sensitivity losses centrally associated with defects on OCT. Multimodal imaging demonstrated progressive atrophy of the outer retina in LCHADD, often preceded by the formation of outer retinal tubulations and choriocapillaris dropout. Electroretinography findings support the more severe clinical profile of LCHADD patients compared with TFPD patients; the function of both rods and cones are attenuated diffusely in LCHADD patients, but are within normal limits for TFPD patients.

CONCLUSIONS

Despite improved survival with early diagnosis, medical management, and dietary treatment, participants with the LCHADD subtype of MTP disorder continue to demonstrate visually disabling chorioretinopathy. Multimodal imaging is most consistent with choriocapillaris loss exceeding photoreceptor loss.

MULTIMODAL IMAGING AND ELECTRORETINOGRAPHY IN LONG-CHAIN 3-HYDROXYACYL COENZYME A DEHYDROGENASE DEFICIENCY

PURPOSE

To report a case of pigmentary retinopathy in long-chain 3-hydroxyacyl coenzyme A dehydrogenase deficiency using multimodal imaging techniques.

METHODS

Case report.

RESULTS

An 8-year-old boy with a history of failure to thrive and a diagnosis of long-chain 3-hydroxyacyl coenzyme A dehydrogenase deficiency was referred for examination. Examination revealed a pigmentary retinopathy with macular atrophy; electroretinography results were consistent with a rod-cone dystrophy. Fundus autofluorescence and optical coherence tomography revealed retinal pigment epithelium atrophy. Follow-up examination findings showed increased severity of retinopathy on electroretinography, with optical coherence tomography angiography revealing enhanced visualization of choroidal vessels.

CONCLUSION

This report reveals that long-chain 3-hydroxyacyl coenzyme A dehydrogenase deficiency can be characterized as a progressive rod-cone dystrophy, with multi-modal imaging techniques used to describe this condition. In particular, optical coherence tomography angiography can be used to further characterize this condition.

Earlier diagnosis and strict diets improve the survival rate and clinical course of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

AIM

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a severe metabolic disease that, without treatment, often leads to premature death or serious handicap. The aim of this study was to evaluate the clinical course of LCHADD with the homozygous 1528G>C (E510Q) mutation when patients underwent strict dietary treatment.

METHODS

From 1997 to 2010, 16 patients with LCHADD were diagnosed in Finland. They were followed up, and data were prospectively collected as they emerged. Clinical data before diagnosis were retrospectively collected from hospital records. This cohort was compared with an earlier cohort of patients diagnosed from 1976 to 1996.

RESULTS

The disease presented from birth to five months of age with failure to thrive, hypotonia, hepatomegaly, metabolic acidosis, cardiomyopathy and hypoketotic hypoglycaemia. In this cohort, the therapeutic delay was 0-30 days and the survival rate at the end of the study was 62.5% compared with 10-year survival rate of 14.3% for the earlier cohort. The survivors were in good overall condition, but some of them had developed mild retinopathy or mild neuropathy.

CONCLUSION

Earlier diagnosis and stricter dietary regimes improved the survival rates and clinical course of patients with LCHADD in Finland. However, improvements in therapy are still needed to prevent the development of long-term complications, such as retinopathy and neuropathy.

Increased and early lipolysis in children with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency during fast

Children with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHAD) have a defect in the degradation of long-chain fatty acids and are at risk of hypoketotic hypoglycemia and insufficient energy production as well as accumulation of toxic fatty acid intermediates. Knowledge on substrate metabolism in children with LCHAD deficiency during fasting is limited. Treatment guidelines differ between centers, both as far as length of fasting periods and need for night feeds are concerned. To increase the understanding of fasting intolerance and improve treatment recommendations, children with LCHAD deficiency were investigated with stable isotope technique, microdialysis, and indirect calometry, in order to assess lipolysis and glucose production during 6 h of fasting. We found an early and increased lipolysis and accumulation of long chain acylcarnitines after 4 h of fasting, albeit no patients developed hypoglycemia. The rate of glycerol production, reflecting lipolysis, averaged 7.7 ± 1.6 µmol/kg/min, which is higher compared to that of peers. The rate of glucose production was normal for age; 19.6 ± 3.4 µmol/kg/min (3.5 ± 0.6 mg/kg/min). Resting energy expenditure was also normal, even though the respiratory quotient was increased indicating mainly glucose oxidation. The results show that lipolysis and accumulation of long chain acylcarnitines occurs before hypoglycemia in fasting children with LCHAD, which may indicate more limited fasting tolerance than previously suggested.

Pathophysiology of fatty acid oxidation disorders and resultant phenotypic variability

Fatty acids are a major fuel for the body and fatty acid oxidation is particularly important during fasting, sustained aerobic exercise and stress. The myocardium and resting skeletal muscle utilise long-chain fatty acids as a major source of energy. Inherited disorders affecting fatty acid oxidation seriously compromise the function of muscle and other highly energy-dependent tissues such as brain, nerve, heart, kidney and liver. Such defects encompass a wide spectrum of clinical disease, presenting in the neonatal period or infancy with recurrent hypoketotic hypoglycaemic encephalopathy, liver dysfunction, hyperammonaemia and often cardiac dysfunction. In older children, adolescence or adults there is often exercise intolerance with episodic myalgia or rhabdomyolysis in association with prolonged aerobic exercise or other exacerbating factors. Some disorders are particularly associated with toxic metabolites that may contribute to encephalopathy, polyneuropathy, axonopathy and pigmentary retinopathy. The phenotypic diversity encountered in defects of fat oxidation is partly explained by genotype/phenotype correlation and certain identifiable environmental factors but there remain many unresolved questions regarding the complex interaction of genetic, epigenetic and environmental influences that dictate phenotypic expression. It is becoming increasingly clear that the view that most inherited disorders are purely monogenic diseases is a naive concept. In the future our approach to understanding the phenotypic diversity and management of patients will be more realistically achieved from a polygenic perspective.

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.

Pathophysiology of fatty acid oxidation disorders

Mitochondrial fatty acid oxidation represents an important pathway for energy generation during periods of increased energy demand such as fasting, febrile illness and muscular exertion. In liver, the primary end products of the pathway are ketone bodies, which are released into the circulation and provide energy to tissues that are not able to oxidize fatty acids such as brain. Other tissues, such as cardiac and skeletal muscle are capable of direct utilization of the fatty acids as sources of energy. This article provides an overview of the pathogenesis of fatty acid oxidation disorders. It describes the different tissue involvement with the disease processes and correlates disease phenotype with the nature of the genetic defect for the known disorders of the pathway.

Mitochondrial fatty acid oxidation disorders: clinical presentation of long-chain fatty acid oxidation defects before and after newborn screening

The different long-chain fatty acid oxidation defects present with similar heterogeneous clinical phenotypes of different severity. Organs mainly affected comprise the heart, liver, and skeletal muscles. All symptoms are reversible with sufficient energy supply. In some long-chain fatty acid oxidation defects, disease-specific symptoms occur. Only in disorders of the mitochondrial trifunctional protein (TFP) complex, including long-chain 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase (LCHAD) deficiency, neuropathy and retinopathy develop that are progressive and irreversible despite current treatment measures. In most long-chain fatty acid oxidation defects, no clear genotype-phenotype correlation exists due to molecular heterogeneity. However, some isolated mutations have been identified to be associated with only mild phenotypes, e.g., the V243A mutation in very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. LCHAD deficiency is due to the prevalent homozygous 1528G>C mutation and presents with heterogeneous clinical phenotypes, suggesting the importance of other environmental and genetic factors. For some disorders, it was shown that residual enzyme activity measured in fibroblasts or lymphocytes correlated with severity of clinical phenotype. Implementation of newborn screening has significantly reduced morbidity and mortality of long-chain fatty acid oxidation defects. However, the severest forms of TFP deficiency are still highly associated with neonatal death. Newborn screening also identifies a great number of mildly affected patients who may never develop clinical symptoms throughout life. However, later-onset exercise-induced myopathic symptoms remain characteristic clinical features of long-chain fatty acid oxidation defects. Disease prevalence has increased with newborn screening.

The mitochondrial proteome and human disease

For nearly three decades, the sequence of the human mitochondrial genome (mtDNA) has provided a molecular framework for understanding maternally inherited diseases. However, the vast majority of human mitochondrial disorders are caused by nuclear genome defects, which is not surprising since the mtDNA encodes only 13 proteins. Advances in genomics, mass spectrometry, and computation have only recently made it possible to systematically identify the complement of over 1,000 proteins that comprise the mammalian mitochondrial proteome. Here, we review recent progress in characterizing the mitochondrial proteome and highlight insights into its complexity, tissue heterogeneity, evolutionary origins, and biochemical versatility. We then discuss how this proteome is being used to discover the genetic basis of respiratory chain disorders as well as to expand our definition of mitochondrial disease. Finally, we explore future prospects and challenges for using the mitochondrial proteome as a foundation for systems analysis of the organelle.

Carnitine palmitoyltransferase 2: New insights on the substrate specificity and implications for acylcarnitine profiling

Over the last years acylcarnitines have emerged as important biomarkers for the diagnosis of mitochondrial fatty acid beta-oxidation (mFAO) and branched-chain amino acid oxidation disorders assuming they reflect the potentially toxic acyl-CoA species, accumulating intramitochondrially upstream of the enzyme block. However, the origin of these intermediates still remains poorly understood. A possibility exists that carnitine palmitoyltransferase 2 (CPT2), member of the carnitine shuttle, is involved in the intramitochondrial synthesis of acylcarnitines from accumulated acyl-CoA metabolites. To address this issue, the substrate specificity profile of CPT2 was herein investigated. Saccharomyces cerevisiae homogenates expressing human CPT2 were incubated with saturated and unsaturated C2-C26 acyl-CoAs and branched-chain amino acid oxidation intermediates. The produced acylcarnitines were quantified by ESI-MS/MS. We show that CPT2 is active with medium (C8-C12) and long-chain (C14-C18) acyl-CoA esters, whereas virtually no activity was found with short- and very long-chain acyl-CoAs or with branched-chain amino acid oxidation intermediates. Trans-2-enoyl-CoA intermediates were also found to be poor substrates for CPT2. Inhibition studies performed revealed that trans-2-C16:1-CoA may act as a competitive inhibitor of CPT2 (K(i) of 18.8 microM). The results obtained clearly demonstrate that CPT2 is able to reverse its physiological mechanism for medium and long-chain acyl-CoAs contributing to the abnormal acylcarnitines profiles characteristic of most mFAO disorders. The finding that trans-2-enoyl-CoAs are poorly handled by CPT2 may explain the absence of trans-2-enoyl-carnitines in the profiles of mitochondrial trifunctional protein deficient patients, the only defect where they accumulate, and the discrepancy between the clinical features of this and other long-chain mFAO disorders such as very long-chain acyl-CoA dehydrogenase deficiency.

Role of carnitine in disease

Carnitine is a conditionally essential nutrient that plays a vital role in energy production and fatty acid metabolism. Vegetarians possess a greater bioavailability than meat eaters. Distinct deficiencies arise either from genetic mutation of carnitine transporters or in association with other disorders such as liver or kidney disease. Carnitine deficiency occurs in aberrations of carnitine regulation in disorders such as diabetes, sepsis, cardiomyopathy, malnutrition, cirrhosis, endocrine disorders and with aging. Nutritional supplementation of L-carnitine, the biologically active form of carnitine, is ameliorative for uremic patients, and can improve nerve conduction, neuropathic pain and immune function in diabetes patients while it is life-saving for patients suffering primary carnitine deficiency. Clinical application of carnitine holds much promise in a range of neural disorders such as Alzheimer's disease, hepatic encephalopathy and other painful neuropathies. Topical application in dry eye offers osmoprotection and modulates immune and inflammatory responses. Carnitine has been recognized as a nutritional supplement in cardiovascular disease and there is increasing evidence that carnitine supplementation may be beneficial in treating obesity, improving glucose intolerance and total energy expenditure.

[Long-chain 3-hydroxyacyl CoA dehydrogenase deficiency and choroidal neovascularization]

We report the case of a 9-year-old girl with a long-chain 3-hydroxyacyl CoA dehydrogenase (LCHAD) deficiency. This enzyme participates in mitochondrial fatty acid B-oxidation. Genetic fatty acid oxidation defects induce cellular energetic deficiency, and thus early life-threatening manifestations. An appropriate diet prevents these severe disorders. Nevertheless, LCHAD deficiency is the only B-oxidation enzymatic disorder that induces a chorioretinopathy, predominating at the posterior pole. We describe the first case of bilateral macular choroidal neovascularization. One eye presented a fibrovascular lesion. The other eye presented an active neovascularization stabilized by two dynamic phototherapies. The specificity of choroidal degeneration related to LCHAD deficiency remains unknown. Reviewing of literature and biochemical mechanisms suggests that fatty acid oxidative stress rather than a mitochondrial energetic defect is involved. For practical purposes, this report emphasizes the importance of ophthalmological follow-up of these patients.

Ocular characteristics in 10 children with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: a cross-sectional study with long-term follow-up

PURPOSE

To present long-term ocular complications and electroretinographic (ERG) findings in children with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency - a life-threatening metabolic disease - and the relation to age at diagnosis, treatment and other clinical parameters.

METHODS

Ten children with LCHAD deficiency underwent repeated ophthalmological evaluations including ERG.

RESULTS

All 10 children developed chorioretinal pathology. Regardless of age at diagnosis, initiation of treatment and age at examination, inter-individual differences were present. Profound chorioretinal atrophy, severe visual impairment and progressive myopia had developed in two teenagers. Milder chorioretinopathy with or without subnormal visual acuity was present in all other children. ERG was pathological in seven children. The chorioretinopathy often started in the peripapillary or perimacular areas. In one patient, unilateral visual impairment was associated with fibrosis.

CONCLUSION

Early diagnosis and adequate therapy might delay but not prevent the progression of retinal complications. Late diagnosis with severe symptoms at diagnosis, neonatal hypoglycaemia and frequent decompensations may increase the progression rate of the chorioretinopathy. LCHAD deficiency, a potentially lethal disease, is sometimes difficult to diagnose. Unusual chorioretinal findings should alert the ophthalmologist to the long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, especially if there is a history of neonatal hypoglycaemia or failure to thrive.

Long chain fatty acid oxidation defects in children: importance of detection and treatment options

BACKGROUND

Mitochondrial beta oxidation plays a major role in energy production. Long chain fatty acid oxidation defects include deficiency of the trifunctional protein (rare) or more commonly defects of the long chain 3-hydroxy acyl-CoA dehydrogenase enzyme (LCHAD). These long chain defects have variable presentations, they may present in the neonate or infant with sudden death, hepatopathy (Reyes disease), hypoketotic hypoglycaemia, rhabdomyolysis, myopathy, cardiomyopathy and with late complications such as peripheral neuropathy, pigmentary retinopathy, retinal degeneration and progressive visual loss. The correct diagnosis at presentation is not only life saving but also allows for the appropriate dietary and other intervention, which may have major effects on outcome.

AIM

Three case reports of patients with long chain fatty acid oxidation defects who have shown significant benefits from treatment are reported.

CONCLUSIONS

These paediatric presentations illustrate the clinical heterogeneity of long chain fatty acid oxidation defects and opportunities for effective management if correctly diagnosed.

Effect of optimal dietary therapy upon visual function in children with long-chain 3-hydroxyacyl CoA dehydrogenase and trifunctional protein deficiency

The objective of this prospective cohort study was to determine if dietary therapy including docosahexaenoic acid (DHA; C22:6omega-3) supplementation prevents the progression of the severe chorioretinopathy that develops in children with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) or trifunctional protein (TFP) deficiency. Physical, biochemical, and ophthalmological evaluations, including electroretinogram (ERG) and visual acuity by evoked potential (VEP), were performed at baseline and annually following the initiation of 65-130 mg/day DHA supplementation and continued treatment with a low-fat diet. Fourteen children with LCHAD or TFP deficiency, 1-12 years of age at enrollment, were followed for 2-5 years. Three subjects with TFP beta-subunit mutations had normal appearance of the posterior pole of the ocular fundi at enrollment and no changes over the course of the study. Eleven subjects who were homozygote and heterozygote for the common mutation, c.1528G>C, had no change to severe progression of atrophy of the choroid and retina with time. Of these, four subjects had marked to severe chorioretinopathy associated with high levels of plasma hydroxyacylcarnitines and decreased color, night and/or central vision during the study. The plasma level of long-chain 3-hydroxyacylcarnitines, metabolites that accumulate as a result of LCHAD and TFP deficiency, was found to be negatively correlated with maximum ERG amplitude (Rmax) (p=0.0038, R2=0.62). In addition, subjects with sustained low plasma long-chain 3-hydroxyacylcarnitines maintained higher ERG amplitudes with time compared to subjects with chronically high 3-hydroxyacylcarnitines. Visual acuity, as determined with the VEP, appeared to increase with time on DHA supplementation (p=0.051) and there was a trend for a positive correlation with plasma DHA concentrations (p=0.075, R2=0.31). Thus, optimal dietary therapy as indicated by low plasma 3-hydroxyacylcarnitine and high plasma DHA concentrations was associated with retention of retinal function and visual acuity in children with LCHAD or TFP deficiency.

Neonatal screening for defects of the mitochondrial trifunctional protein

Long-chain l-3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency has been included in the routine neonatal screening program by the German screening commission. As tandem mass spectrometry (TMS) does not discriminate between the different defects of the mitochondrial trifunctional protein (MTP) screening for isolated LCHAD deficiency includes the detection of long-chain 3-ketoacyl-CoA thiolase and complete MTP deficiencies as well. We identified 11 patients with abnormalities of the MTP out of 1.2 million newborns screened in our laboratory during the last 6 years. Treatment was started on the day the screening result was obtained (day 3 to day 9 of life). Seven of these newborns developed satisfactorily during an observation period of up to 64 months. They had isolated LCHAD deficiency, four of them caused by the typical mutation (1528 G>C), three others had no molecular genetic analysis done or were shown to have previously unknown mutations. Four children did not survive, two of them showing complete deficiency of MTP and two showing deficiency of long-chain 3-ketoacyl-CoA thiolase. We conclude that, despite the rarity of the disease, screening for MTP deficiencies is justified based on the following criteria: improved quality of life for patients with isolated LCHAD deficiency, absence of stigmatisation of babies showing mild variants without necessity of treatment, no significant increase of the total number of false positive screening results, no false negative results to our knowledge. Finally, extension of analysis to MTP deficiencies is achieved without additional costs for screening laboratories already using TMS.

Lack of correlation between fatty acid oxidation disorders and haemolysis, elevated liver enzymes, low platelets (HELLP) syndrome?

AIM

Fatty acid beta-oxidation defects comprise a heterogeneous group of disorders that may precipitate acute life threatening metabolic crises particularly during catabolic episodes. Several studies have demonstrated a possible association between fatty acid beta-oxidation defects, including long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency and severe pregnancy complications. However, the precise percentage of women with haemolysis, elevated liver enzymes, low platelets (HELLP) syndrome associated with foetal fatty acid beta-oxidation defects is not known.

METHODS

We carried out a multicentre retrospective study on 88 infants, born to women with HELLP syndrome. Acylcarnitine profiles from blood dried on filter paper cards were analysed by tandem mass spectrometry for the diagnosis of fatty acid beta-oxidation defects. In addition, we screened for the common long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency mutation using a standard restriction fragment length polymorphism polymerase chain reaction method.

RESULTS

None of the infants studied carried the common long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency mutation. There was no evidence of fatty acid beta-oxidation defects, including long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, as expected by unremarkable acylcarnitine profiles, while three infants with fatty acid beta-oxidation defects were diagnosed in the control group.

CONCLUSIONS

Neither foetal long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency, including heterozygosity for the common long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency mutation, nor fatty acid beta-oxidation defects in general are a major risk factor for HELLP syndrome in Austria.

Mitochondrial fatty acid beta-oxidation in the human eye and brain: implications for the retinopathy of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

The retinal pigment epithelium (RPE) and the choriocapillaris are affected early in the retinopathy associated with long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency. RPE in culture possesses the machinery needed for mitochondrial fatty acid beta-oxidation in vitro. To further elucidate pathogenesis of LCHAD retinopathy, we performed immunohistochemistry of the human eye and brain with antibodies to beta-oxidation enzymes. Human eye and brain sections were stained with antibodies to medium-chain (MCAD) and very long-chain acyl-CoA dehydrogenase (VLCAD), short-chain 3-hydroxyacyl-CoA dehydrogenase (SCHAD), and mitochondrial trifunctional protein (MTP) harboring LCHAD. Antibodies to 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) and cytochrome c oxidase subunit I (COX I) were used as a reference. VLCAD, MTP, MCAD, SCHAD, MHBD, and COX I antibodies labeled most retinal layers and tissues of the human eye actively involved in oxidative metabolism (extraocular and intraocular muscle, the RPE, the corneal endothelium, and the ciliary epithelium). MTP and COX I antibodies labeled the inner segments of photoreceptors. The choriocapillaris was labeled only with SCHAD and MCAD antibodies. In the brain, the choroid plexus and nuclei of the brain stem were most intensely labeled with beta-oxidation antibodies, whereas COX I antibodies strongly labeled neurons in several regions of the brain. Mitochondrial fatty acid beta-oxidation likely plays a role in ocular energy production in vivo. The RPE rather than the choriocapillaris could be the critical affected cell layer in LCHAD retinopathy. Reduced energy generation in the choroid plexus may contribute to the cerebral edema observed in patients with beta-oxidation defects.

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.

Cataract in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD)

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a rare metabolic disorder that can lead to acute encephalopathy, liver disease, cardiomyopathy, rhabdomyolysis, and long-term complications involving the eye and peripheral nerves. LCHADD is a peroxisome biogenesis disorder (PBD). Except for the series presented by Tyni and colleagues (Ophthalmology 1998;105:810-824), which described visually insignificant lens opacities in association with LCHADD, previous ophthalmic papers have only reported retinal complications. We report on one case with progressive asymmetrical cataract. The more mildly affected eye had a similar morphology to that previously reported and the more severely affected eye had an unusual morphology we believe is unique to LCHADD. We discuss the range of ophthalmic presentations in our cases and in the literature. The variability of the severity of ocular complications, even between eyes in one individual, makes it difficult to test the effectiveness of therapeutic options upon the ophthalmic complications.

What is the role of medium-chain triglycerides in the management of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency?

Cardiomyopathy is common in infants with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Resolution of the cardiomyopathy can often be achieved by avoidance of fasting and changing from a conventional infant formula to one in which most long-chain fat is replaced by medium-chain triglycerides (MCT). It is uncertain whether the clinical improvement is due to the restriction of long-chain fat or whether the MCT have specific beneficial effects. To clarify this, the metabolic effects of MCT were examined in 5 patients. When given at around the level found in MCT-based infant formula, MCT had no effect on blood concentrations of ketone bodies, specific fatty acids or acylcarnitines. The present study cannot, however, exclude the possibility that MCT per se may have beneficial effects.

Plasma and erythrocyte fatty acid concentrations in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

Plasma and erythrocyte fatty acids have been measured in 9 patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency being treated with a low-fat diet. No significant abnormality was detected and in particular docosahexaenoic acid was not deficient.

Mitochondrial fatty acid beta-oxidation in the retinal pigment epithelium

Pigmentary retinopathy is an important feature of long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, a disorder of mitochondrial fatty acid beta-oxidation. Pathogenesis of this complication remains unknown. The retinal pigment epithelium (RPE) is affected early in this retinopathy. We wanted to determine whether there is evidence of mitochondrial fatty acid beta-oxidation in the RPE cells. Fatty acid oxidation was measured from cultured porcine RPE cells by incubating them with [U-13C]-hexadecanoic acid. Acylcarnitine esters were analyzed by tandem mass spectrometry. The activity of LCHAD and carnitine uptake capacity were measured from the cultured cells. Antibodies to the human mitochondrial trifunctional protein (MTP) containing LCHAD activity were used to analyze the expression of the MTP in the cultured RPE cell lysate and in human retinal sections by immunoblotting and immunohistochemistry. Fatty acid oxidation analysis showed normal chain shortening of hexadecanoic acid and production of acetylcarnitine in cultured RPE cells. Immunoblotting revealed expression of the MTP and enzyme assay showed the activity of LCHAD in the RPE cells. RPE cells were also capable of carnitine uptake. Positive labeling to the MTP antibodies was detected in the RPE, photoreceptors, and ganglion cells. The results give strong in vitro evidence for the presence of mitochondrial fatty acid beta-oxidation in RPE cells and the expression of the MTP in the RPE and other layers of the retina. Further studies are required to clarify whether this pathway acts also in vivo in the retina.

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.

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.

Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency: clinical presentation and follow-up of 50 patients

OBJECTIVES

To assess the mode of presentation, biochemical abnormalities, clinical course, and effects of therapy in patients of long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency.

BACKGROUND

LCHAD deficiency is a rare, autosomal recessive inborn error of fatty acid oxidation. Although case reports and small series of patients have been published, these may not give a true picture of the clinical and biochemical spectrum associated with this disorder. To improve the early recognition and management of this potentially lethal disorder, we have reviewed a large cohort of LCHAD-deficient patients.

METHODS

A questionnaire was sent to the referring physicians of 61 unselected patients with LCHAD deficiency diagnosed in our center. The standardized questionnaire requested information about the clinical signs and symptoms at presentation, the clinical history, family history, pregnancy, biochemical parameters at presentation, treatment, and clinical outcome.

RESULTS

Questionnaires on 50 patients (82%) were returned and included in this study. The mean age of clinical presentation was 5.8 months (range: 1 day-26 months). Seven (15%) of the patients presented in the neonatal period. Thirty-nine patients (78%) presented with hypoketotic hypoglycemia, the classical features of a fatty acid oxidation disorder. Eleven patients (22%) presented with chronic problems, consisting of failure to thrive, feeding difficulties, cholestatic liver disease, and/or hypotonia. In retrospect, most (82%) of the patients presenting with an acute metabolic derangement also suffered from a combination of chronic nonspecific symptoms before the metabolic crises. Mortality in this series was high (38%), all dying before or within 3 months after diagnosis. Morbidity in the surviving patients is also high, with recurrent metabolic crises and muscle problems despite therapy.

CONCLUSIONS

LCHAD deficiency often presents with a combination of chronic nonspecific symptoms. Early diagnosis is difficult in the absence of the classical metabolic derangement. Survival can be improved by prompt diagnosis, but morbidity remains alarmingly high despite current therapeutic regimes.

Visually evoked potentials in respiratory chain disorders

OBJECTIVES

Little is known about the frequency of abnormal visually evoked potentials (VEPs) in patients with respiratory chain disorders (RCDs). We thus wanted to investigate the frequency of abnormal VEPs in RCDs, how often VEPs are abnormal despite normal visual acuity, and which of the VEP variables are most often abnormal.

MATERIAL AND METHODS

Reversal checkerboard VEPs of 26 patients with RCDs, aged 32-74 years, were evaluated.

RESULTS

VEPs were abnormal in 17 of the 26 cases (65%). The P100 latency was prolonged at least unilaterally in 16 patients. The P100/N145 amplitude was decreased in a single patient. VEPs were abnormal without visual impairment in 9 cases (53%).

CONCLUSION

VEPs prove useful to detect clinical or subclinical impairment of the optical tract in patients with RCDs. In the majority of the cases, the P100 latencies are prolonged while the P100/N145 amplitude remains normal.