Infantile form of carnitine palmitoyltransferase II deficiency with hepatomuscular symptoms and sudden death. Physiopathological approach to carnitine palmitoyltransferase II deficiencies

Experience with carnitine palmitoyltransferase II deficiency: diagnostic challenges in the myopathic form

OBJECTIVES

Carnitine palmitoyltransferase II (CPT II) deficiency is an autosomal recessive disorder of long-chain fatty acid oxidation. Three clinical phenotypes, lethal neonatal form, severe infantile hepatocardiomuscular form, and myopathic form, have been described in CPT II deficiency. The myopathic form is usually mild and can manifest from infancy to adulthood, characterised by recurrent rhabdomyolysis episodes. The study aimed to investigate the clinical features, biochemical, histopathological, and genetic findings of 13 patients diagnosed with the myopathic form of CPT II deficiency at Ege University Hospital.

METHODS

A retrospective study was conducted with 13 patients with the myopathic form of CPT II deficiency. Our study considered demographic data, triggers of recurrent rhabdomyolysis attacks, biochemical metabolic screening, and molecular analysis.

RESULTS

Ten patients were examined for rhabdomyolysis of unknown causes. Two patients were diagnosed during family screening, and one was diagnosed during investigations due to increased liver function tests. Acylcarnitine profiles were normal in five patients during rhabdomyolysis. Genetic studies have identified a c.338C>T (p.Ser113Leu) variant homozygous in 10 patients. One patient showed a novel frameshift variant compound heterozygous with c.338C>T (p.Ser113Leu).

CONCLUSIONS

Plasma acylcarnitine analysis should be preferred as it is superior to DBS acylcarnitine analysis in diagnosing CPT II deficiency. Even if plasma acylcarnitine analysis is impossible, CPT2 gene analysis should be performed. Our study emphasizes that CPT II deficiency should be considered in the differential diagnosis of recurrent rhabdomyolysis, even if typical acylcarnitine elevation does not accompany it.

Normal Thermostability of p.Ser113Leu and p.Arg631Cys Variants of Mitochondrial Carnitine Palmitoyltransferase II (CPT II) in Human Muscle Homogenate

Previous fibroblast and recombinant enzyme studies showed a markedly thermolabile p.Ser113Leu variant compared to the wild-type (WT) in muscle carnitine palmitoyltransferase II (CPT II) deficiency. Additionally, it has been shown that cardiolipin (CLP) stimulated or inhibited the p.Ser113Leu recombinant variant depending on the pre-incubation temperatures. In this study, the thermolabilities of mitochondrial enzyme CPT II in muscle homogenates of patients with the p.Ser113Leu (n = 3) and p.Arg631Cys (n = 2) variants were identified to be similar to that of WT. Pre-incubation with CLP on ice stimulated the WT enzyme more than both variants. However, CLP stimulated the variants and WT at 46 °C to about 6–18-fold. The present data indicate that the thermostability of CPT II variant in muscle homogenate is similar to that of WT. This is in contrast to the increased thermolability of enzymes derived from fibroblast and that of recombinant enzymes. Hence, it can be speculated that the disruption of the compartmentation in muscle homogenate mediates a protective effect on the thermolability of the native variant. However, the exact mechanism remains unclear. However, the activating effect of CLP on CPT II in muscle homogenate seems to align with those on recombinant enzymes.

A Case of Carnitine Palmitoyltransferase II Deficiency in Bahrain With a Novel Mutation

Carnitine palmitoyltransferase II (CPT II) deficiency is a rare genetic metabolic disorder. Three forms of the disease have been described: the lethal neonatal form, the severe infantile hepatocardiomuscular form, and the myopathic form. We report a case of the infantile form of CPT II deficiency with a novel mutation. Our patient is a seven-year-old Bahraini male who was investigated by the pediatric metabolic team following the sudden death of his twin sister in infancy. A fatty acid metabolic disorder was suspected based on his echocardiogram and tandem mass spectrometry (TMS) findings. Genetic analysis was initially inconclusive. Nonetheless, he was started on a fat-free diet, L-carnitine, and medium-chain triglycerides (MCT). At nearly two years of age, the patient had a metabolic crisis precipitated by a viral illness. TMS during this time was consistent with CPT II deficiency. Sanger sequencing then identified the presence of the variant c.161T>G (p.ille54Ser) in a homozygous state, confirming the diagnosis. Although this mutation has not been reported before in previous literature concerning CPT II deficiency, it is extremely likely that this mutation is pathogenic. Although the initial work-up of the patient was inconclusive, our clinical judgment was paramount in managing the patient.

Genotype–phenotype correlations in CPT1A deficiency detected by newborn screening in Pacific populations

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a long chain fatty acid oxidation disorder, typically presenting with hypoketotic hypoglycaemia and liver dysfunction during fasting and intercurrent illness. Classical CPT1A deficiency is a rare disease, although a milder ‘Arctic variant' (p.P479L) is common in the Inuit population. Since the introduction of expanded metabolic screening (EMS), the newborn screening programmes of Hawai'i and New Zealand (NZ) have detected a significant increase in the incidence of CPT1A deficiency. We report 22 individuals of Micronesian descent (12 in NZ and 10 in Hawai'i), homozygous for a CPT1A c.100T>C (p.S34P) variant detected by EMS or ascertained following diagnosis of a family member. No individuals with the Micronesian variant presented clinically with metabolic decompensation prior to diagnosis or during follow‐up. Three asymptomatic homozygous adults were detected following the diagnosis of their children by EMS. CPT1A activity in cultured skin fibroblasts showed residual enzyme activity of 26% of normal controls. Secondly, we report three individuals from two unrelated Niuean families who presented clinically with symptoms of classic CPT1A deficiency, prior to the introduction of EMS. All were found to be homozygous for a CPT1A c.2122A>C (p.S708R) variant. CPT1A activity in fibroblasts of all three individuals was severely reduced at 4% of normal controls. Migration pressure, in part due to climate change may lead to increased frequency of presentation of Pacific peoples to regional metabolic services around the world. Knowledge of genotype–phenotype correlations in these populations will therefore inform counselling and treatment of those detected by newborn screening.

Whole-Exome Sequencing Identifies a Novel CPT2 Mutation in a Pedigree With Gout

Background: Gout is a common inflammatory arthritis, and its exact pathogenesis remains unclear. Multiple studies have demonstrated that genetic factors play important roles in the development of gout. This study aims to investigate the genetic basis of gout in a three-generation pedigree of affected individuals.

Methods: Whole-exome sequencing (WES), comprehensive variant analyses, and co-segregation testing were performed. The effects of candidate variants on protein localization and cellular expression were analyzed, as were interactions with gout-related genes.

Results: After comprehensive bioinformatic analysis, Sanger sequencing validation, and pedigree co-segregation analysis, we identified a rare heterozygous missense variant (c.1891C > T, p.R631C) in CPT2. Although no associated changes in localization were observed, the fluorescence intensity of p.R631C mutants was obviously reduced in comparison to the wild-type protein, suggesting that protein degradation is induced by the mutant. Furthermore, our results also indicate that the c.1891C > T variant influences the ability of CPT2 to bind UCP2.

Conclusion: This study identified a rare CPT2 mutation in a large Chinese pedigree with gout. Functional studies were used to define the effect of this mutant. This study provides novel insight into the genetic etiology of gout.

Infantile onset carnitine palmitoyltransferase 2 deficiency: Cortical polymicrogyria, schizencephaly, and gray matter heterotopias in an adolescent with normal development

OBJECTIVE

To report an adolescent with infantile-onset carnitine palmitoyltransferase 2 (CPT2) deficiency and cerebral malformations and to review the occurrence of brain malformations in CPT2 deficiency. The patient presented clinically at age 5 months with dehydration and hepatomegaly. He also has an unrelated condition, X-linked nephrogenic diabetes insipidus. He had recurrent rhabdomyolysis but normal psychomotor development. At age 17 years, he developed spontaneous focal seizures. Cerebral magnetic resonance imaging revealed extensive left temporo-parieto-occipital polymicrogyria, white matter heterotopias, and schizencephaly. Neuronal migration defects were previously reported in lethal neonatal CPT2 deficiency but not in later-onset forms.

DESIGN AND METHODS

We searched PubMed, Google Scholar, and the bibliographies of the articles found by these searches, for cerebral malformations in CPT2 deficiency. All antenatal, neonatal, infantile, and adult-onset cases were included. Exclusion criteria included insufficient information about age of clinical onset and lack of confirmation of CPT2 deficiency by enzymatic assay or genetic testing. For each report, we noted the presence of cerebral malformations on brain imaging or pathological examination.

RESULTS

Of 26 neonatal-onset CPT2-deficient patients who met the inclusion criteria, brain malformations were reported in 16 (61.5%). In 19 infantile-onset cases, brain malformations were not reported, but only 3 of the 19 reports (15.8%) include brain imaging or neuropathology data. In 276 adult-onset cases, no brain malformations were reported.

CONCLUSION

To the best of our knowledge, this is the first report of cerebral malformations in an infantile onset CPT2-deficient patient. Brain imaging should be considered in patients with CPTII deficiency and neurological manifestations, even in those with later clinical onset.

Biochemical Markers for the Diagnosis of Mitochondrial Fatty Acid Oxidation Diseases

Mitochondrial fatty acid β-oxidation (FAO) contributes a large proportion to the body’s energy needs in fasting and in situations of metabolic stress. Most tissues use energy from fatty acids, particularly the heart, skeletal muscle and the liver. In the brain, ketone bodies formed from FAO in the liver are used as the main source of energy. The mitochondrial fatty acid oxidation disorders (FAODs), which include the carnitine system defects, constitute a group of diseases with several types and subtypes and with variable clinical spectrum and prognosis, from paucisymptomatic cases to more severe affectations, with a 5% rate of sudden death in childhood, and with fasting hypoketotic hypoglycemia frequently occurring. The implementation of newborn screening programs has resulted in new challenges in diagnosis, with the detection of new phenotypes as well as carriers and false positive cases. In this article, a review of the biochemical markers used for the diagnosis of FAODs is presented. The analysis of acylcarnitines by MS/MS contributes to improving the biochemical diagnosis, both in affected patients and in newborn screening, but acylglycines, organic acids, and other metabolites are also reported. Moreover, this review recommends caution, and outlines the differences in the interpretation of the biomarkers depending on age, clinical situation and types of samples or techniques.

Schizophrenic Psychosis Symptoms in a Background of Mild-To-Moderate Carnitine Palmitoyltransferase II Deficiency: A Case Report

Schizophrenia is a multifaceted mental illness characterized by cognitive and neurobehavioral abnormalities. Carnitine palmitoyltransferase II (CPT II) deficiency is a metabolic disorder resulting in impaired transport of long-chain fatty acids from the cytosol to the mitochondrial inner membrane, where fatty acid β-oxidation takes place. Here, we present an interesting clinical case of an adolescent male that presented with psychosis and a history of mild-to-moderate CPT II deficiency. To identify germline genetic variation that may contribute to the phenotypes observed, we performed whole-exome sequencing on DNA from the proband, unaffected fraternal twin, and biological parents. The proband was identified to be homozygous for the p.Val368Ile and heterozygous for the p.Met647Val variant in CPT2. Each of these variants are benign on their own; however, their combined effect is unclear. Further, variation was identified in the dopamine β-hydroxylase (DBH) gene (c.339+2T>C), which may contribute to decreased activity of DBH; however, based on the patient’s presentation, severe DBH deficiency is unlikely. In conclusion, the variants identified in this study do not clearly explain the observed patient phenotypes, indicating that the complex phenotypes are likely caused by an interplay of genetic and environmental factors that warrant further investigation.

Licorice flavonoid oil supplementation promotes a reduction of visceral fat in exercised rats

BACKGROUND

The beneficial effect of exercise combined with licorice flavonoid oil supplementation on visceral fat was investigated.

METHODS

Male Sprague-Dawley rats were divided into 4 groups: control, exercise (Ex), control with licorice flavonoid oil supplementation (LFO), and exercise with licorice flavonoid oil supplementation (ExLFO) groups. The rats in the Ex and ExLFO groups ran on a treadmill (20-degree incline at 20 m/min for 30 min/day) 5 times a week for 7 weeks, and those in the LFO and ExLFO groups were orally administered with licorice flavonoid oil daily using a feeding needle.

RESULTS

Exercise or licorice flavonoid oil supplementation resulted in the reduction of the visceral fat mass and adipocyte size, respectively. In addition, exercise combined with licorice flavonoid oil supplementation more effectively decreased both measures. Exercise alone increased the β-hydroxyacyl-CoA dehydrogenase (β-HAD) and citrate synthase (CS) activities in the soleus and plantaris muscles, and licorice flavonoid oil supplementation alone increased the hepatic carnitine palmitoyl transferase-2 (CPT-2) activity. Furthermore, the combination of exercise and licorice flavonoid oil supplementation enhanced the both muscular β-HAD and CS activities, and hepatic CPT-2 activity.

CONCLUSIONS

These results suggest that exercise combined with licorice flavonoid oil supplementation may be effective to decrease visceral adipose tissue via enhancing skeletomuscular and hepatic fatty acids oxidative capacity.

Muscle Carnitine Palmitoyltransferase II (CPT II) Deficiency: A Conceptual Approach

Carnitine palmitoyltransferase (CPT) catalyzes the transfer of long- and medium-chain fatty acids from cytoplasm into mitochondria, where oxidation of fatty acids takes place. Deficiency of CPT enzyme is associated with rare diseases of fatty acid metabolism. CPT is present in two subforms: CPT I at the outer mitochondrial membrane and carnitine palmitoyltransferase II (CPT II) inside the mitochondria. Deficiency of CPT II results in the most common inherited disorder of long-chain fatty acid oxidation affecting skeletal muscle. There is a lethal neonatal form, a severe infantile hepato-cardio-muscular form, and a rather mild myopathic form characterized by exercise-induced myalgia, weakness, and myoglobinuria. Total CPT activity (CPT I + CPT II) in muscles of CPT II-deficient patients is generally normal. Nevertheless, in some patients, not detectable to reduced total activities are also reported. CPT II protein is also shown in normal concentration in patients with normal CPT enzymatic activity. However, residual CPT II shows abnormal inhibition sensitivity towards malonyl-CoA, Triton X-100 and fatty acid metabolites in patients. Genetic studies have identified a common p.Ser113Leu mutation in the muscle form along with around 100 different rare mutations. The biochemical consequences of these mutations have been controversial. Hypotheses include lack of enzymatically active protein, partial enzyme deficiency and abnormally regulated enzyme. The recombinant enzyme experiments that we recently conducted have shown that CPT II enzyme is extremely thermoliable and is abnormally inhibited by different emulsifiers and detergents such as malonyl-CoA, palmitoyl-CoA, palmitoylcarnitine, Tween 20 and Triton X-100. Here, we present a conceptual overview on CPT II deficiency based on our own findings and on results from other studies addressing clinical, biochemical, histological, immunohistological and genetic aspects, as well as recent advancements in diagnosis and therapeutic strategies in this disorder.

Carnitine palmitoyltransferase II deficiency with a focus on newborn screening

Carnitine palmitoyltransferase (CPT) II deficiency is one of the most common forms of mitochondrial fatty acid oxidation disorder. Its clinical phenotypes are classified into the muscle, severe infantile, and lethal neonatal forms. Among Caucasians, the muscle form predominates, and the c.338C > T (p.S113L) variant is detected in most cases, whereas among the Japanese, c.1148T > A (p.F383Y) is the variant allele occurring with the highest frequency and can apparently cause symptoms of the severe infantile form. Newborn screening (NBS) for this potentially fatal disease has not been established. We encountered an infantile case of CPT II deficiency not detected in NBS using C16 and C18:1 concentrations as indices, and therefore we adopted the (C16 + C18:1)/C2 ratio as an alternative primary index. As a result, the disease was diagnosed in nine of 31 NBS-positive subjects. The values for (C16 + C18:1)/C2 in the affected newborns partly overlapped with those in unaffected ones. Among several other indices proposed previously, C14/C3 has emerged as a more promising index. Based on these findings, nationwide NBS for CPT II deficiency using both (C16 + C18:1)/C2 and C14/C3 as indices was officially approved and started in April 2018. We diagnosed the disease in four young children presenting with symptoms of the muscle form, whose values for the new indices were not elevated. Although it is still difficult to detect all cases of the muscle form of CPT II deficiency in NBS, our system is expected to save many affected children in Japan with the severe infantile form predominating.

Phenotype of carnitine palmitoyltransferase II (CPT II) deficiency: A questionnaire-based survey

Wide spectrums of symptoms besides muscle weakness, different triggering factors and varied muscles involvement are associated with CPT II deficiency. However, systematic clinical characterization of CPT II deficiency is not known. A Questionnaire-based retrospective study on 13 biochemically and genetically confirmed CPT II deficient patients was performed to analyze these aspects. Attacks of myalgia (13/13 patients), weakness (13/13) and rhabdomyolysis (10/13 patients) were most frequently reported. The number of attacks ranged from 1 to 85/year. Common triggers were exercise (13/13), fasting (13/13), cold (12/13) and infections (12/13). Exercise lasting from 15 to 60 min was sufficient for attacks in 9/13 patients, 1-4 h in 3/13 patients and more than 4 h in 1/13 patient. 2/13 patients required dialysis. Limb muscles were affected slightly more often than other muscles. Mean intensity of pain in visual analogue scale (VAS) during regular attack was 4.77 (±1.36). Frequency and severity of attacks did not increase during the course of disease in 10/13 patients. 7/13 patients quit sports after the symptoms emerged. 3/13 patients changed their profession permanently. Increased number of attacks were positively correlated with higher BMI (P = 0.05). Body rest, carbohydrate-rich nutrients and fluid-supplement mitigated the pain. After the first attack [Mean: 9.7 (±4.46) years], diagnosis took an average of 26.7 (± 13.06) years. In myopathic CPT II deficiency, frequencies of attacks are highly variable. Generally, the myopathic form is a mild form. However, severe patients requiring dialysis due to kidney failure could be present. Individuals with higher BMI are at risk of developing more frequent attacks.

Fluxomic assay-assisted diagnosis orientation in a cohort of 11 patients with myopathic form of CPT2 deficiency

Carnitine palmitoyltransferase type 2 (CPT2) deficiency, a mitochondrial fatty acid oxidation disorder (MFAOD), is a cause of myopathy in its late clinical presentation. As for other MFAODs, its diagnosis may be evocated when blood acylcarnitine profile is abnormal. However, a lack of abnormalities or specificity in this profile is not exclusive of CPT2 deficiency. Our retrospective study reports clinical and biological data in a cohort of 11 patients with circulating acylcarnitine profile unconclusive enough for a specific diagnosis orientation. In these patients, CPT2 gene studies was prompted by prior fluxomic explorations of mitochondrial β-oxidation on intact whole blood cells incubated with pentadeuterated ([16-²H₃, 15-²H₂])-palmitate. Clinical indication for fluxomic explorations was at least one acute rhabdomyolysis episode complicated, in 5 of 11 patients, by acute renal failure. Major trigger of rhabdomyolysis was febrile infection. In all patients, fluxomic data indicated deficient CPT2 function showing normal deuterated palmitoylcarnitine (C16-Cn) formation rates associated with increased ratios between generated C16-Cn and downstream deuterated metabolites (Σ deuterated C2-Cn to C14-Cn). Subsequent gene studies showed in all patients pathogenic gene variants in either homozygous or compound heterozygous forms. Consistent with literature data, allelic frequency of the c.338C > T[p.Ser113Leu] mutation amounted to 68.2% in our cohort. Other missense mutations included c.149C > A[p.Pro50His] (9%), c.200C > G[p.Ala200Gly] (4.5%) and previously unreported c.1171A > G[p.ser391Gly] (4.5%) and c.1420G > C[p.Ala474Pro] (4.5%) mutations. Frameshift c.1666-1667delTT[p.Leu556val*16] mutation (9%) was observed in two patients unknown to be related.

Carnitine and septic shock: a review

Most studies have reported reduced carnitine levels in the tissues of patients with sepsis, probably due to increased urinary excretion. Because of the increased utilization of fatty acids and ketone bodies as sources of energy in sepsis, the carnitine deficiency can further impair the fuel metabolism and contribute to the unregulated lipid metabolism in these patients.

Recently, experimental and clinical studies have shown that carnitine and its congeners are able to: (a) downmodulate the spontaneous and endotoxin (LPS)-triggered overproduction of tumor necrosis factor (TNF)-alpha; (b) ameliorate the lipid metabolism; and (c) reduce the severity of illness, accelerate recovery, and, in some cases, improve survival in experimental septic shock.

Many questions concerning the ultimate molecular mechanism of action of these compounds in endotoxaemia are still unanswered. Yet, these compounds may be helpful in patients with sepsis, when associated with conventional therapy, in that they can effectively reduce TNF-alpha levels and ameliorate the host's metabolic processes.

Abbreviated half-lives and impaired fuel utilization in carnitine palmitoyltransferase II variant fibroblasts

Carnitine palmitoyltransferase II (CPT II) deficiency is one of the most common causes of fatty acid oxidation metabolism disorders. However, the molecular mechanism between CPT2 gene polymorphisms and metabolic stress has not been fully clarified. We previously reported that a number of patients show a thermal instable phenotype of compound hetero/homozygous variants of CPT II. To understand the mechanism of the metabolic disorder resulting from CPT II deficiency, the present study investigated CPT II variants in patient fibroblasts, [c.1102 G>A (p.V368I)] (heterozygous), [c.1102 G>A (p.V368I)] (homozygous), and [c.1055 T>G (p.F352C)] (heterozygous) + [c.1102 G>A (p.V368I)] (homozygous) compared with fibroblasts from healthy controls. CPT II variants exerted an effect of dominant negative on the homotetrameric proteins that showed thermal instability, reduced residual enzyme activities and a short half-life. Moreover, CPT II variant fibroblasts showed a significant decrease in fatty acid β-oxidation and adenosine triphosphate generation, combined with a reduced mitochondrial membrane potential, resulting in cellular apoptosis. Collectively, our data indicate that the CPT II deficiency induces an energy crisis of the fatty acid metabolic pathway. These findings may contribute to the elucidation of the genetic factors involved in metabolic disorder encephalopathy caused by the CPT II deficiency.

Clinical and Biochemical Heterogeneity in an Italian Family with CPT II Deficiency due to Ser 113 Leu Mutation

Background:

Carnitine palmitoyltransferase II (CPT II) deficiency is an autosomal recessive disorder which presents with recurrent myoglobinuria. Heterozygotes are usually asymptomatic.

Methods:

We correlate the clinical, biochemical and molecular features of a family in which the proband is homozygous for CPT II deficiency, due to the common Ser 113 Leu mutation.

Results:

The 20-year-old female proband presented at age three years with episodic myalgia and myoglobinuria, elevated creatine kinase (CK) of 3600 IU/L and had a 33% residual CPT II activity in cultured skin fibroblasts. Her 25-year-old dizygotic twin brothers presented with muscle stiffness following prolonged exercise but no overt pigmenturia and had interictal CKs up to 662 IU/L. Her parents and a 13-year-old brother are asymptomatic. An elder sister, not investigated, had recurrent pigmenturia and died at eight years with myoglobinuria. Molecular analysis revealed that the proband is homozygous for the Ser 113 Leu mutation. Her parents are heterozygotes with CPT II activities of 55% to 70%. Her younger brother is normal with 83% activity. The symptomatic twin brothers are heterozygous but demonstrated unexpectedly low CPT II activities of 40%, which may explain their phenotype.

Conclusion:

We postulate that there may be genetic, environmental and sex hormonal factors accounting for this manifesting heterozygosity and biochemical heterogeneity in CPT II deficiency.

Carnitine palmitoyltransferase 2 gene polymorphism is a genetic risk factor for sudden unexpected death in infancy

RATIONALE

Carnitine palmitoyltransferase (CPT) II is one of a pivotal enzyme in mitochondrial fatty acid oxidation, which is essential for energy production during simultaneous glucose sparing and a requirement for major energy supply, such as prolonged fasting or exercise. When infants require more energy than provided by the glycolytic system, they rely on the mitochondrial fatty acid oxidation pathway. Mutations of the CPT2 gene have been reported to cause sudden unexpected death in infancy (SUDI). A thermolabile phenotype of a CPT2 polymorphism (F352C) has been recently reported to reduce CPT II enzyme activity. The F352C variant results in energy crisis at high temperature and is suspected as a risk factor for acute encephalopathy. However, a relationship between CPT2 gene polymorphism and SUDI has not been described.

METHODS

Single nucleotide polymorphisms of the CPT2 gene were investigated among 54 SUDI cases and 200 healthy volunteers.

RESULTS

The frequency of the C allele was significantly higher in the SUDI group than in the control group [25.0% vs 16.0%, odds ratio (OR)=1.75, 95% confidence interval (CI)=1.05-2.92, p=0.030). The frequency of the F352C homozygote was significantly higher in the SUDI group than in control group (11.1% vs 3.5%, OR=3.45, 95% CI=1.11-10.73, p=0.036).

CONCLUSION

The F352C CPT2 variant might be a genetic risk factor for SUDI.

Disorders of fatty acid oxidation

Recognition of fatty acid oxidation (FAO) disorders is important for the pediatric neurologist as they present with a spectrum of clinical disorders, including progressive lipid storage myopathy, recurrent myoglobinuria, neuropathy, progressive cardiomyopathy, recurrent hypoglycemic hypoketotic encephalopathy or Reye-like syndrome, seizures, and mental retardation. They constitute a critical group of diseases because they are potentially rapidly fatal and a source of major morbidity. There is frequently a family history of sudden infant death syndrome in siblings. Early recognition and prompt institution of therapy and appropriate preventive measures, and in certain cases specific therapy, may be life-saving and may significantly decrease long-term morbidity, particularly with respect to CNS sequelae. All currently known conditions are inherited as autosomal recessive traits. There are now at least 25 enzymes and specific transport proteins in the β-oxidation pathway and 18 have been associated with human disease. The most common defect is medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, which had an incidence of 1 in 8930 live births in one series. The identification of serum acylcarnitines by electrospray ionization-tandem mass spectrometry of dried blood spots on filter paper in newborn screening programs has significantly enhanced the early recognition of these disorders.

Rhabdomyolysis and Cardiomyopathy in a 20-Year-Old Patient with CPT II Deficiency

Aim. To raise the awareness of adult-onset carnitite palmitoyltransferase II deficiency (CPT II) by describing clinical, biochemical, and genetic features of the disease occurring in early adulthood. Method. Review of the case characteristics and literature review. Results. We report on a 20-year-old man presenting with dyspnea, fatigue, fever, and myoglobinuria. This was the second episode with such symptoms (the previous one being three years earlier). The symptoms occurred after intense physical work, followed by a viral infection resulting in fever treated with NSAIDs. Massive rhabdomyolysis was diagnosed, resulting in acute renal failure necessitating plasmapheresis and hemodialysis, acute hepatic lesion, and respiratory insufficiency. Additionally, our patient had cardiomyopathy with volume overload. After a detailed workup, CPT II deficiency was suspected. We did a sequencing analysis for exons 1, 3, and 4 of the CPT II gene and found that the patient was homozygote for Ser 113 Leu mutation in exon 3 of the CPT II gene. The patient recovery was complete except for the cardiomiopathy with mildly impaired systolic function. Conclusion. Whenever a patient suffers recurrent episodes of myalgia, followed by myoglobinuria due to rhabdomyolysis, we should always consider the possibility of this rare condition. The definitive diagnose of this condition is achieved by genetic testing.

Carnitine palmitoyltransferase II (CPT II) deficiency: genotype-phenotype analysis of 50 patients

Clinical, biochemical and molecular genetic data in a cohort of 50 patients with muscle CPT II deficiency are reported. Attacks of myoglobinuria occurred in 86% of patients. In 94% of patients the triggering factor was exercise. Although the myopathic form is often called the adult from, in 60% of patients, the age of onset was in childhood (1-12 years). All the patients in whom biochemical activity was measured had normal enzyme activity of total CPT I+II but the activity was significantly inhibited by malonyl-CoA and Triton. The p.S113L mutation was detected in 38/40 index patients (95%) in at least one allele. Sixty percent of index patients were homozygous for this mutation. Thirteen other mutations, all in compound heterozygote form, were also identified. There was no significant difference in ages of onset, clinical and biochemical phenotype of patients with p.S113L mutation in homozygous or compound heterozygous form. The exception was a tendency of slightly higher residual enzyme activity upon malonyl-CoA inhibition in compound heterozygotes. Phenotype was also not significantly different in patients with missense mutations on both alleles and patients with truncating mutation on one allele and missense mutation on the other allele. However, the only exception was that, attacks were triggered by fasting in almost all the patients with truncating mutations. In contrast, fasting triggered the attacks only in one third of patients with missense mutations on both alleles. The data indicate that within the muscle form of CPT II deficiency, the various genotypes have only marginal influence on the clinical and biochemical phenotype.

Regulation of mitochondrial fatty acid β-oxidation in human: what can we learn from inborn fatty acid β-oxidation deficiencies?

The mitochondrial fatty acid β-oxidation (FAO) pathway plays a crucial role in ATP production in many tissues with high-energy demand. This is highlighted by the diverse and possibly severe clinical manifestations of inborn fatty acid β-oxidation deficiencies. More than fifteen genetic FAO enzyme defects have been described to date, forming a large group of rare diseases. Inborn FAO disorders are characterized by a high genetic heterogeneity, with a variety of gene mutations resulting in complete or partial loss-of-function of the corresponding enzyme. The panel of observed phenotypes varies from multi-organ failure in the neonate with fatal outcome, up to milder late onset manifestations associated with significant disabilities. Diagnosis of FAO disorders has markedly improved over the last decades, but few treatments are available. The clinical, biochemical, and molecular analysis of these disorders provided new, and sometimes unexpected, data on the organization and regulation of mitochondrial FAO in humans, in various tissues, and at various stages of development. This will be illustrated by examples of FAO defects affecting enzymes of long-chain fatty acid import into the mitochondria, or Lynen helix enzymes. The involvement of the transcriptional network regulating FAO gene expression, in particular the PGC-1α/PPAR axis, as a target for pharmacological therapy of these genetic disorders, will also be discussed.

Modulation of cytokine production by carnitine

The ability of carnitine congeners to modulate cytokine production by human peripheral blood mononuclear cells (PBMC) was investigated. Modulation of cytokine production by PBMC of young (30 years of age or younger) and old (70 years of age or older) normal donors was first compared. The PBMC were collected over Ficoll–Hypaque and incubated in the presence of various concentrations of acetyl L-carnitine for 24 h. Subsequently the supernatants were collected and examined for cytokine production. The presence of cytokines in tissue culture supernatants was examined by ELISA. The cytokines measured included IL-1α, IL-1β, IL-2, IL-4, IL-6, TNFα, GM–CSF, and IFNγ. The results showed that at 50 μg/ml of acetyl L-carnitine the most significant response was obtained for TNFα. In this regard four of five young donors responded, but only one of five old donors responded. More recently these studies were expanded to examine the ability of L-carnitine to modulate cytokine production at higher doses, 200 and 400 μg/ml, in young donors. The results of these studies showed that in addition to TNFα, significant production of IL-1β and IL-6 was observed. These preliminary studies provide evidence that carnitine may modulate immune functions through the production of selected cytokines.

Characterization of compound missense mutation and deletion of carnitine palmitoyltransferase II in a patient with adenovirus-associated encephalopathy

BACKGROUND

In mammals, carnitine palmitoyltransferase (CPT) system is a pivotal component of energy metabolism through mitochondrial fatty acid oxidation. The majority of patients with fatal or handicapped influenza-associated encephalopathy exhibit thermolabile compound homo/heterozygous mutations of CPT II.

OBJECTIVE

Compound CPT II mutations, [c.647A>G (p.Q216R)], [c.1102G>A (p.V368I)], [c.1939A>G (p.M647V)] and [c.745delG (p.G249EfsX16)], were found in a patient with adenovirus-associated encephalopathy and his family. The properties of these CPT II mutations were analyzed in COS-7 cells.

METHODS

CPT II mutations in the patient and his family were expressed in COS-7 cells and their molecular masses, enzyme activities, thermal instabilities and half-lives were analyzed.

RESULTS

We identified two novel CPT II mutations in the patient, [c.647A>G (p.Q216R)] and [c.745delG (p.G249EfsX16)]. The CPT II Q216R mutation showed mild reduction of activity, thermal instability and short half-life but compound mutations with Q216R+V368I+M647V showed further enhancement of these disabilities, although mutations V368I and M647V had no such effects. CPT II mutation [c.745delG (p.G249EfsX16)] abolished enzyme activity and showed short half-life.

CONCLUSION

The thermal instability and short half-life of the novel CPT II mutations, [c.647A>G (p.Q216R)] and [c.745delG (p.G249EfsX16)], could play important roles in energy crisis in the pathogenesis of virus-associated encephalopathy.

Neonatal muscular manifestations in mitochondrial disorders

During the last decade rapid development has occurred in defining nuclear gene mutations causing mitochondrial disease. Some of these newly defined gene mutations cause neonatal or early infantile onset of disease, often associated with severe progressive encephalomyopathy combined with other multi-organ involvement such as cardiomyopathy or hepatopathy and with early death. Findings suggesting myopathy in neonates are hypotonia, muscle weakness and wasting, and arthrogryposis. We aim to describe the clinical findings of patients with mitochondrial disease presenting with muscular manifestations in the neonatal period or in early infancy and in whom the genetic defect has been characterized. The majority of patients with neonatal onset of mitochondrial disease have mutations in nuclear genes causing dysfunction of the mitochondrial respiratory chain, leading to defective oxidative phosphorylation.

Retrospective review of Japanese sudden unexpected death in infancy: the importance of metabolic autopsy and expanded newborn screening

Sudden unexpected death in infancy is defined as sudden unexpected death occurring before 12 months of age. The common causes of sudden unexpected death in infancy are infection, cardiovascular anomaly, child abuse, and metabolic disorders. However, the many potential inherited metabolic disorders are difficult to diagnose at autopsy and may therefore be underdiagnosed as a cause of sudden unexpected death in infancy. In the present study we retrospectively reviewed 30 Japanese sudden unexpected death in infancy cases encountered between 2006 and 2009 at our institute. With postmortem blood acylcarnitine analysis and histological examination of the liver, we found two cases of long-chain fatty acid oxidation defects. Molecular analysis revealed that the one patient had a compound heterozygote for a novel mutation (p.L644S) and a disease-causing mutation (p.F383Y) in the carnitine palmitoyltransferase 2 gene. Furthermore, retrospective acylcarnitine analysis of the newborn screening card of this patient was consistent with carnitine palmitoyltransferase II deficiency. Metabolic autopsy and expanded newborn screening would be helpful for forensic scientists and pediatricians to diagnose fatty acid oxidation disorders and prevent sudden unexpected death in infancy.

Carnitine palmitoyltransferase 2 deficiency: the time-course of blood and urinary acylcarnitine levels during initial L-carnitine supplementation

Carnitine palmitoyltransferase 2 (CPT2) deficiency is one of the most common mitochondrial beta-oxidation defects. A female patient with an infantile form of CPT2 deficiency first presented as having a Reye-like syndrome with hypoglycemic convulsions. Oral L-carnitine supplementation was administered since serum free carnitine level was very low (less than 10 micromol/L), indicating secondary carnitine deficiency. Her serum and urinary acylcarnitine profiles were analyzed successively to evaluate time-course effects of L-carnitine supplementation. After the first two days of L-carnitine supplementation, the serum level of free carnitine was elevated; however, the serum levels of acylcarnitines and the urinary excretion of both free carnitine and acylcarnitines remained low. A peak of the serum free carnitine level was detected on day 5, followed by a peak of acetylcarnitine on day 7, and peaks of long-chain acylcarnitines, such as C16, C18, C18:1 and C18:2 carnitines, on day 9. Thereafter free carnitine became predominant again. These peaks of the serum levels corresponded to urinary excretion peaks of free carnitine, acetylcarnitine, and medium-chain dicarboxylic carnitines, respectively. It took several days for oral L-carnitine administration to increase the serum carnitine levels, probably because the intracellular stores were depleted. Thereafter, the administration increased the excretion of abnormal acylcarnitines, some of which had accumulated within the tissues. The excretion of medium-chain dicarboxylic carnitines dramatically decreased on day 13, suggesting improvement of tissue acylcarnitine accumulation. These time-course changes in blood and urinary acylcarnitine levels after L-carnitine supplementation support the effectiveness of L-carnitine supplementation to CPT2-deficient patients.

Long-term follow-up of bezafibrate treatment in patients with the myopathic form of carnitine palmitoyltransferase 2 deficiency

Carnitine palmitoyltransferase 2 (CPT2) deficiency is a rare mitochondrial fatty acid oxidation (FAO) disorder characterized by myalgia, exercise intolerance, and rhabdomyolysis. We evaluate the efficacy of bezafibrate (BZ), a hypolipidemic drug, as a treatment for this form of CPT2 deficiency. A pilot trial was conducted with BZ in six patients for 6 months. There was a follow-up period of 3 years. The oxidation rates of the long-chain fatty acid derivative palmitoyl-CoA, measured in the mitochondria of the patients' muscles, were markedly lower than normal before treatment and increased significantly (+39 to +206%; P = 0.028) in all patients after BZ treatment. The evaluation of the therapeutic effects by the patients themselves (using the Short Form Health Survey (SF-36)), as well as by the physicians, indicated an improvement in the condition of the patients; there was an increase in physical activity and a decline in muscular pain. The results suggest that BZ has a therapeutic effect in the muscular form of CPT2 deficiency.

Inborn errors of energy metabolism associated with myopathies

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

Carnitine-palmitoyltransferase 2 deficiency: novel mutations and relevance of newborn screening

We report on a newborn male, born at term after an uneventful pregnancy presenting with a pathological acylcarnitine profile in routine newborn screening on the third day of life. The profile showed characteristic elevations of C14:0-, C16:0-, C16:1- and C18:1-acylcarnitines, while the ratio of (C16 + C18:1)/C2 was increased, suggesting CPT2- or carnitine-acylcarnitine-translocase- deficiency. The acylcarnitine profile in blood taken on day 9 was normal with breast milk feeding. No dicarboxylic aciduria was found. In fibroblasts, the activity of CPT2 was decreased to 25%, overall oxidation of the long-chain fatty acids was reduced to 10% of control values. Sequence analysis of the CPT2 gene showed heterozygosity for two previously undescribed mutations in exon 4: c.748-749delAA (truncating), and c.1436A > G (p.Tyr479Cys; missense) mutations. The asymptomatic parents were found to be heterozygous, the mother carries the c.748-749delAA and the father the c.1436A > G mutation. The boy is now 2.5 years old; no clinical symptoms associated with the marked impairment of long-chain fatty acid oxidation have occurred. Confirmation of mitochondrial fatty acid oxidation defects from an initial abnormal newborn-screening by tandem mass spectrometry should include enzyme and, if possible, molecular genetic analysis despite a normal 2nd screening. Biochemical testing of urine (organic acids) may be unrevealing.

Thermal instability of compound variants of carnitine palmitoyltransferase II and impaired mitochondrial fuel utilization in influenza-associated encephalopathy

Influenza-associated encephalopathy (IAE) is characterized by persistent high fever, febrile convulsions, severe brain edema, and high mortality in otherwise apparently healthy individuals. We have reported that a large proportion of patients suffering from disabling or fatal IAE, with transiently elevated serum acylcarnitine during high fever, exhibit a thermolabile phenotype of compound homo-/heterozygous variants of carnitine palmitoyltransferase II (CPT II, gene symbol CPT2). We characterized the enzymatic properties of five single and three compound CPT II variants in patients with IAE. The kinetic characteristics of WT and variant CPT IIs, expressed in COS-7 cells, indicated that the variants exert a dominant-negative effect on the homotetrameric protein of the enzyme. Among the variants, three compound variations found in patients with severe encephalopathy; [c.1055T>G (p.Phe352Cys); c.1102G>A (p.Val368Ile)], [c.1511C>T (p.Pro504Leu); c.1813G>C (p.Val605Leu)], and [c.1055T>G (p.Phe352Cys); c.1102G>A (p.Val368Ile); c.1813G>C (p.Val605Leu)], showed reduced activities, thermal instability, and short half-lives compared with the WT. Like other disease-causing mutant proteins, these variant proteins were poly-ubiquitinated and rapidly degraded by a lactacystin-sensitive proteasome pathway. COS-7 cells transfected with the compound variants had their fatty acid beta-oxidation decreased to 30-59% and intracellular ATP levels to 48-79%, and a marked reduction of mitochondrial membrane potential at 41 degrees C, compared with control cells transfected with WT at 37 degrees C. The unstable CPT II variants with decreased enzymatic activities may bring mitochondrial fuel utilization below the phenotypic threshold during high fever, and thus may play an important etiopathological role in the development of brain edema of IAE.

Substitutions of three amino acids in human heart/muscle type carnitine palmitoyltransferase I caused by single nucleotide polymorphisms

Heart/muscle type carnitine palmitoyltransferase I (M-CPTI) catalyzes the rate-limiting step of mitochondrial long-chain fatty acid (LCFA) oxidation in muscle and adipose tissue. Three replacements of nucleotides resulting in missense mutations of I66V, S427C, and E531K were observed in the M-CPTI gene of patients showing abnormal fatty acid metabolism. These nucleotide replacements were found to be common single nucleotide polymorphisms (SNPs) of this gene and not specific to patients. The question of whether these missense mutations caused by SNPs alter the functional properties of M-CPTI remains unanswered. Thus, we examined whether these missense mutations are associated with any changes in the enzymatic properties of M-CPTI. None of these mutations was found to cause remarkable alteration of its enzymatic properties. Based on the comparison of amino acid sequences of M-CPTI among different animal species, the roles of these amino acids in the enzyme are discussed.

A novel SLC25A20 splicing mutation in patients of different ethnic origin with neonatally lethal carnitine-acylcarnitine translocase (CACT) deficiency

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare disorder of fatty acid oxidation associated with high mortality. Two female newborns of different ethnic origin (the first Anglo-Celtic and the second Palestinian Arab) both died after sudden collapse on day 2 of life. Both had elevated bloodspot long-chain acylcarnitines consistent with either CACT or carnitine palmitoyltransferase II (CPT2) deficiency; the latter was excluded by demonstrating normal CPT2 activity in fibroblasts. Direct sequencing of all SLC25A20 (CACT) gene exons and exon-intron boundaries revealed that Patient 1 was compound heterozygous for a novel c.609-3c>g (IVS6-3c>g) mutation on the paternal allele and a previously described c.326delG mutation on the maternal allele. Patient 2 was homozygous for the same, novel c.609-3c>g mutation. Previously reported SLC25A20 mutations have been almost exclusively confined to a single family or ethnic group. Analysis of fibroblast cDNA by RT-PCR, agarose gel electrophoresis and sequencing of extracted bands showed that both mutations produce aberrant splicing. c.609-3C>G results in exon 7 skipping leading to a frameshift with premature termination seven amino acids downstream. c.326delG was confirmed to produce skipping of exons 3 or 3 plus 4. CACT activity in both patients' fibroblasts was near-zero. For both families, prenatal diagnosis of an unaffected fetus was performed by mutation analysis on CVS tissue in a subsequent pregnancy. Due to the urgency of prenatal diagnosis in the second family, molecular diagnosis was performed prior to demonstration of CACT enzyme deficiency, illustrating that mutation analysis is a rapid and reliable approach to first-line diagnosis of CACT deficiency.

The crystal structure of carnitine palmitoyltransferase 2 and implications for diabetes treatment

Carnitine palmitoyltransferases 1 and 2 (CPTs) facilitate the import of long-chain fatty acids into mitochondria. Modulation of the catalytic activity of the CPT system is currently under investigation for the development of novel drugs against diabetes mellitus. We report here the 1.6 A resolution structure of the full-length mitochondrial membrane protein CPT-2. The structure of CPT-2 in complex with the generic CPT inhibitor ST1326 ([R]-N-[tetradecylcarbamoyl]-aminocarnitine), a substrate analog mimicking palmitoylcarnitine and currently in clinical trials for diabetes mellitus treatment, was solved at 2.5 A resolution. These structures of CPT-2 provide insight into the function of residues involved in substrate binding and determination of substrate specificity, thereby facilitating the rational design of antidiabetic drugs. We identify a sequence insertion found in CPT-2 that mediates membrane localization. Mapping of mutations described for CPT-2 deficiency, a hereditary disorder of lipid metabolism, implies effects on substrate recognition and structural integrity of CPT-2.

Is sudden death with vitamin C deficiency caused by lack of carnitine?

We investigated the effect of carnitine supplementation during vitamin C (ASC) deficiency by measuring the levels of ASC and carnitine in plasma and cardiac muscle cells (CMC), and histological analysis with electron microscopy. The levels of carnitine were significantly decreased in ASC-deficient rats in plasma and the heart than those in the control. In carnitine supplemented ASC-deficient rats, a significant increase of carnitine levels were observed in both plasma and heart. The number of lipid droplets significantly increased in the ASC-deficient rats compared to the control rats, but did not increase in carnitine supplemented rats. These results indicate that ASC deficiency causes a generalized mitochondrial abnormality and accumulation of lipid droplets in CMC as observed in carnitine deficiency, and supplementation of carnitine prevented these changes even in the presence of ASC deficiency.

Novel metabolic and molecular findings in hepatic carnitine palmitoyltransferase I deficiency

Detection of hepatic carnitine palmitoyltransferase I (CPT IA) deficiency by metabolite screening may be problematic. The urine organic acid profile is generally said to be normal and no abnormal or increased acylcarnitine species are evident on bloodspot tandem MS examination. We diagnosed CPT IA deficiency presenting with acute encephalopathy +/- hypoglycemia and hepatomegaly in one Bukharan Jewish and two Palestinian Arab infants from consanguineous families. CPT1A mutation analysis identified two novel nonsense mutations, c.1737C>A (Y579X) and c.1600delC (L534fsX), extending the known genetic heterogeneity in this disorder. A distinctive organic aciduria was observed in all three patients, even several days after initiation of treatment and resolution of symptoms. Abnormal findings included a hypoketotic dicarboxylic aciduria with prominence of the C12 dicarboxylic (dodecanedioic) acid. This C12 dicarboxylic aciduria suggests that CPT I may play a role in uptake of long-chain dicarboxylic acids by mitochondria after their initial shortening by beta-oxidation in peroxisomes. In addition, increased excretion of 3-hydroxyglutaric acid was detected in all three patients, a finding previously observed only in glutaric aciduria type 1, ketosis, and short-chain hydroxyacyl-CoA dehydrogenase deficiency. Examination of urine organic acids with awareness of these metabolic findings may lead to improved diagnosis of this seemingly rare disorder.

Carnitine palmitoyltransferase II deficiency due to a novel gene variant in a patient with rhabdomyolysis and ARF

Adult patients deficient in carnitine palmitoyltransferase II (CPT II) cannot generate sufficient amounts of energy, which results in rhabdomyolysis and acute renal failure (ARF). Its genetic basis has been recognized; but histopathologic changes, especially electron microscopic changes, have scarcely been described. The study subject is a patient with ARF caused by repetitive nontraumatic rhabdomyolysis. The acylcarnitine profile of serum and enzyme assay on skin fibroblasts confirmed the diagnosis of CPT II deficiency. Renal biopsy specimens were examined microscopically and immunohistochemically. The histological diagnosis was interstitial nephritis with acute tubular necrosis caused by rhabdomyolysis. Myoglobin in tubules was detected by means of immunohistochemistry and electron microscopy. The genetic structure of CPT II was analyzed in the patient and his family. Eight pairs of polymerase chain reaction (PCR) primers were designed to cover the coding region. Each PCR-amplified gene product was subjected to DNA sequencing, which unveiled heterozygosity at the CPT II locus consisting of a deletion of cytosine and thymine at codon 408, resulting in a stop signal at 420, as well as a mutation of arginine to cysteine at codon 631. The frame shift at 408 has never been described before. DNA sequencing of the family showed the deletion mutation from the mother and the point mutation from the father. We describe renopathological findings in a patient with CPT II deficiency associated with rhabdomyolysis, which suggested the pathological role of myoglobin casts in the development of tubular necrosis. Genetic analysis of the patient identified a novel variant of the CPT II gene.

Fuel utilization in subjects with carnitine palmitoyltransferase 2 gene mutations

Patients with the myopathic form of carnitine palmitoyltransferase II (CPT II) deficiency typically experience muscle pain, cramps, and myoglobinuria during prolonged exercise. It has been suggested that carriers of CPT2 gene mutations also may have milder clinical symptoms, but fatty acid oxidation (FAO) has never been investigated in vivo in this group. We studied fuel utilization by indirect calorimetry and stable isotope methodology in four patients with CPT II deficiency, three subjects who carried one CPT2 gene mutation, and five healthy control subjects. Cycle exercise at a constant workload of 50% of maximal oxygen uptake capacity was used to facilitate FAO. We found that in vivo oxidation of long-chain fatty acids was normal at rest but severely impaired during prolonged, low-intensity exercise in patients with CPT II deficiency, and that two of the single CPT2 gene mutation carriers, who displayed symptoms of CPT II deficiency, had an FAO comparable with the patients. These results indicate that residual CPT II activity is sufficient to maintain long-chain FAO at rest in CPT II deficiency but not to increase FAO during exercise. The findings also suggest that single CPT2 gene mutations may exert a dominant-negative effect on the tetrameric CPT II protein.

Prenatal diagnosis of carnitine palmitoyltransferase 2 deficiency in chorionic villi: a novel approach

Carnitine palmitoyltransferase 2 (CPT2) deficiency, the most common autosomal recessive inherited disease of the mitochondrial long-chain fatty acid (LCFA) beta-oxidation, may result in three distinct clinical phenotypes, namely, a mild adult muscular form, a severe infantile hepatocardiomuscular disease, and a neonatal form, which includes dysmorphic features in addition to hepatocardiomuscular symptoms. Both the latter forms are life-threatening diseases, and prenatal diagnosis (PND) can be offered to couples at a one-fourth risk of having an affected child. PND of CPT2 deficiency hitherto relied mostly on mutation detection from fresh chorionic villi (10 weeks' gestation), since CPT2 activity could be assayed on cultured amniocytes only (16-17 weeks' gestation).We devised a CPT2 activity assay from 10 mg of chorionic villi sampling (CVS). Combining this enzymatic assay to haplotype study using polymorphic markers linked to the CPT2 gene, we were able to carry out within 2 days, CPT2 deficiency PND, in two unrelated families, using a CVS performed at the 11th week of gestation.

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.

Carnitine palmitoyltransferase II deficiency: a clinical, biochemical, and molecular review

Congenital deficiency of carnitine palmitoyltransferase (CPT) II has been known for at least 30 years now, and its phenotypic variability remains fascinating. Three distinct clinical entities have been described, the adult, the infantile, and the perinatal, all with an autosomal recessive inheritance pattern. The adult CPT II clinical phenotype is somewhat benign and requires additional external triggers such as high-intensity exercise before the predominantly myopathic symptoms are elicited. The perinatal and infantile forms involve multiple organ systems. The perinatal disease is the most severe form and is invariably fatal. The introduction of mass spectrometry to analyze blood acylcarnitine profiles has revolutionized the diagnosis of fatty acid oxidation disorders including CPT II deficiency. Its use in expanded neonatal screening programs has made presymptomatic diagnosis a reality. An increasing number of mutations are being identified in the CPT II gene with a distinct genotype-phenotype correlation in most cases. However, clinical variability in some patients suggests additional genetic or environmental modifiers. Herein, we present a new case of lethal perinatal CPT II deficiency with a rare missense mutation, R296Q (907G>A) associated with a previously described 25-bp deletion on the second allele. We review the clinical features, the diagnostic protocol including expanded neonatal screening, the treatment, and the biochemical and molecular basis of CPT II deficiency.

Correction of fatty acid oxidation in carnitine palmitoyl transferase 2-deficient cultured skin fibroblasts by bezafibrate

Carnitine palmitoyltransferase 2 (CPTII) deficiency is among the most common inborn errors of mitochondrial fatty acid beta-oxidation (FAO). Clinical phenotype varies in relation to the metabolic block, as assessed by studies of FAO in patient fibroblasts. Thus, fibroblasts from patients with mild manifestations have appreciable residual CPTII enzyme activity, in contrast to those from severely affected patients. In the present study, we hypothesized that the hypolipidemic drug bezafibrate, acting as an activator of the peroxisome proliferator-activated receptor alpha might stimulate FAO in CPTII-deficient cells. Data obtained show that bezafibrate treatment of mild-type CPTII-deficient cells resulted in a time- and dose- dependent increase in CPTII mRNA (from +47% to +66%) and residual enzyme activity (from +54% to 135%), and led to normalization of 3H-palmitate and 3H-myristate cellular oxidation rates. Bezafibrate did not correct FAO in fibroblasts from patients with severe phenotype. This study establishes for the first time that peroxisome proliferator-activated receptor activators, acting via stimulation of gene expression, can stimulate CPTII residual activity to a level sufficient to allow normal FAO flux in deficient human fibroblasts, and suggests that this approach should be tested in other inborn errors of mitochondrial beta-oxidation.

Characterization of fatty acid oxidation in human muscle mitochondria and myoblasts

The mitochondrial oxidation of fatty acids (FAO) is the main energy-producing pathway in skeletal and cardiac muscle. Starting from standard muscle biopsies (100-200mg), we determined the optimal conditions of mitochondrial oxygen consumption by the FAO pathway, and in parallel we performed the isolation and primary culture of muscle cells to test their cellular FAO capacities. The determinations of maximal beta-oxidation rates in the presence of palmitoyl-CoA or palmitoyl-L-carnitine (mean+/-SEM: 32.5+/-2.0 and 34.1+/-1.3nmol O(2) min(-1) mg(-1) protein, n=16, respectively) provide a screening method of mitochondrial fatty acid transport system and intra-mitochondrial beta-oxidation. We also determined the conditions of tritiated palmitate oxidation by human myoblasts (mean+/-SEM: 6.6+/-0.1nmol 3H fatty acid h(-1) mg(-1) protein, n=8), and show that beta-oxidation defects can be detected in our experiments. Overall, we propose an original laboratory test to investigate FAO in human skeletal muscle and to screen for FAO disorders in myopathies and cardiomyopathies in human.

Mutation and biochemical analysis in carnitine palmitoyltransferase type II (CPT II) deficiency

Carnitine palmitoyltransferase type II (CPT II) deficiency has three basic phenotypes, late-onset muscular (mild), infantile/juvenile hepatic (intermediate) and severe neonatal. We have measured fatty acid oxidation and CPT II activity and performed mutation studies in 24 symptomatic patients representing the full clinical spectrum of disease. Severe and intermediate phenotypes show a clear correlation with biochemical indices and genetic analysis revealed causative mutations in most patients. Studies of mild phenotypes suggest a more complex interaction, with higher residual fatty acid oxidation, a wider range of CPT II activity (10-60%) but little evidence of genotype-phenotype correlation. Residual CPT II mutant protein from myopathic patients shows thermal instability at 41 degrees C. The common 'polymorphisms' V3681 and M647V are strikingly overrepresented in the myopathic patients, the implication being that they may significantly influence the manifestation of clinical disease and could therefore potentially be considered as a susceptibility variants. Among myopathic individuals, males comprised 88% of patients, suggesting increased susceptibility to clinical disease. A small number of symptomatic patients appear to have significant residual CPT II activity (42-60%) The synergistic interaction of partial deficiencies of CPT II, muscle adenosine monophosphate deaminase and possibly other enzymes of muscle energy metabolism in the aetiology of episodic myopathy deserves wider consideration.

Cardiolipin and apoptosis

Cardiolipin (CL) is recognized to be an essential phospholipid in eukaryotic energy metabolism so that physiological and pathological perturbations in its synthetic and catabolic pathways play key roles in maintaining mitochondrial structure and function, and ultimately cell survival. This review describes potential regulatory mechanisms in CL synthesis and the effects of de-acylation pathways on steady state levels of CL and its interaction with cytochrome c. The latter interaction is significant in the initiation of programmed cell death. Physiological factors that modify CL acylation include ageing, dietary influences and ischemia/reperfusion where the terminal events may be either necrosis or apoptosis. In various pathologies, phospholipase activity increases in response to production of peroxidized CL. The cell may use lysosomal or mitochondrial pathways for CL degradation. However, the manner by which CL and cytochrome c leave the mitochondria is not well understood. The lipid (CL)-bound form of cytochrome c is thought to initiate apoptosis via a lipid transfer step involving mitochondrially targeted Bid. A direct relationship between CL loss and cytochrome c release from the mitochondria has been identified as an initial step in the pathway to apoptosis. An absolute requirement for CL in the function of crucial mitochondrial proteins, e.g., cytochrome oxidase and the adenine nucleotide translocase, are likely additional factors impacting apoptosis and cellular energy homeostasis. This is reflected in the occurrence of both oncotic and apoptotic events in ischemia and reperfusion injury. Other potential clinical manifestations of perturbations of CL synthesis are discussed with particular emphasis on Barth Syndrome where a primary defect can be attributed to CL metabolism and is associated with dilated cardiomyopathy. Finally, the model of fatty acid induced apoptosis is used as a paradigm to our understanding of the temporal relationship between decreased mitochondrial CL, release of cytochrome c, and initiation of apoptosis.