Features of carnitine palmitoyltransferase type I deficiency

Prolonged Cholestatic Jaundice Associated with Carnitine Palmitoyltransferase IA Deficiency

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a type of fatty acid oxidation disorder in which long chain fatty acids cannot be transported into mitochondria for further processing and storage in our body. Typically, the patients present with lethargy, hypoglycemia, and raised serum transaminase levels before 2 years of age. Cholestatic jaundice as manifestation of this deficiency has been reported rarely; here, we report an adolescent male with CPT1A deficiency who developed prolonged cholestatic jaundice following a febrile illness.

Newborn Screening for Mitochondrial Carnitine-Acylcarnitine Cycle Disorders in Zhejiang Province, China

Background: Disorders of mitochondrial carnitine–acylcarnitine cycle is a heterogeneous group of hereditary diseases of mitochondrial β-oxidation of fatty acids tested in NBS program in Zhejiang province, China. Large-scale studies reporting disorders of mitochondrial carnitine–acylcarnitine cycle among Chinese population in NBS are limited. The aim of this study was to explain the incidence and biochemical, clinical, and genetic characteristics of disorders of mitochondrial carnitine–acylcarnitine cycle in NBS.

Methods: From January 2009 to June 2021, 4,070,375 newborns were screened by tandem mass spectrometry. Newborns with elevated C0 levels and/or C0/(C16 + C18) ratios were identified as having CPT1D, whereas those with decreased C0 levels and/or C0/(C16 + C18) ratios and/or elevated C12-C18:1 level were identified as having CPT2D or CACTD. Suspected positive patients were further subjected to genetic analysis. All confirmed patients received biochemical and nutritional treatment, as well as follow-up sessions.

Results: Overall, 20 patients (12 with CPT1D, 4 with CPT2D, and 4 with CACTD) with disorders of mitochondrial carnitine–acylcarnitine cycle were diagnosed by NBS. The overall incidence of these disorders was one in 203,518 newborns. In toal, 11 patients with CPT1D exhibited increased C0 levels and C0/(C16 + C18) ratios. In all patients of CPT2D, all long chain acyl-carnitines levels were elevated except for case 14 having normal C12 levels. In all patients with CACTD, all long chain acyl-carnitines levels were elevated except for case 17 having normal C12, C18, and C18:1 levels. Most patients with CPT1D were asymptomatic. Overall, two of 4 patients with CPT2D did not present any clinical symptom, but other two patients died. In 4 cases with CACTD, the disease was onset after birth, and 75% patients died. In total, 14 distinct mutations were identified in CPT1A gene, of which 11 were novel and c.1910C > A (p.S637T), c.740C > T (p.P247L), and c.1328T > C (p.L443P) were the most common mutations. Overall, 3 novel mutations were identified in CPT2 gene, and the most frequent mutation was c.1711C > A (p.P571T). The most common variant in SLC25A20 gene was c.199-10T > G.

Conclusion: Disorders of mitochondrial carnitine–acylcarnitine cycle can be detected by NBS, and the combined incidence of these disorders in newborns was rare in Zhejiang province, China. Most patients presented typical acylcarnitine profiles. Most patients with CPT1D presented normal growth and development, whereas those with CPT2D/CACTD exhibited a high mortality rate. Several novel CPT1A and CPT2 variants were identified, which expanded the variant spectrum.

Cardiologic evaluation of Turkish mitochondrial fatty acid oxidation disorders

BACKGROUND

Mitochondrial fatty acid oxidation disorders (FAODs) cause impairment in energy metabolism and can lead to a spectrum of cardiac pathologies including cardiomyopathy and arrhythmias. The frequency of underlying cardiac pathologies and the response to recommended treatment in FAODs was investigated.

METHODS

Sixty-eight children (35 males, 33 females) with the diagnosis of a FAOD were included in the study. Cardiac function was evaluated with 12-lead standard electrocardiography, echocardiography, and 24 h Holter monitoring.

RESULTS

Forty-five patients (66%) were diagnosed after disease symptoms developed and 23 patients (34%) were diagnosed in the pre-symptomatic period. Among symptomatic patients (n: 45), cardiovascular findings were detected in 18 (40%) patients, including cardiomyopathy in 14 (31.1%) and conduction abnormalities in 4 (8.8%) patients. Cardiac symptoms were more frequently detected in primary systemic carnitine deficiency (57.1%). Patients with multiple acyl-CoA dehydrogenase, long-chain 3-hydroxyacyl-CoA dehydrogenase, and mitochondrial trifunctional protein deficiencies also had an increased frequency of cardiac symptoms. Patients with medium-chain acyl-CoA dehydrogenase, very long-chain acyl-CoA dehydrogenase, and carnitine palmitoyltransferase I deficiencies had a lower prevalence of cardiac symptoms both during admission and during clinical follow up. Cardiomyopathy resolved completely in 8/14 (57%) patients and partially in 2/14 (14.3%) patients with treatment. Two patients with cardiomyopathy died in the newborn period; cardiomyopathy persisted in 1 (7.1%) patient with very long-chain acyl-CoA dehydrogenase deficiency.

CONCLUSION

Early diagnosis, treatment and follow up made a significant contribution to the improvement of cardiac symptoms of patients with FAODs.

L-Carnitine in Drosophila: A Review

L-Carnitine is an amino acid derivative that plays a key role in the metabolism of fatty acids, including the shuttling of long-chain fatty acyl CoA to fuel mitochondrial β-oxidation. In addition, L-carnitine reduces oxidative damage and plays an essential role in the maintenance of cellular energy homeostasis. L-carnitine also plays an essential role in the control of cerebral functions, and the aberrant regulation of genes involved in carnitine biosynthesis and mitochondrial carnitine transport in Drosophila models has been linked to neurodegeneration. Drosophila models of neurodegenerative diseases provide a powerful platform to both unravel the molecular pathways that contribute to neurodegeneration and identify potential therapeutic targets. Drosophila can biosynthesize L-carnitine, and its carnitine transport system is similar to the human transport system; moreover, evidence from a defective Drosophila mutant for one of the carnitine shuttle genes supports the hypothesis of the occurrence of β-oxidation in glial cells. Hence, Drosophila models could advance the understanding of the links between L-carnitine and the development of neurodegenerative disorders. This review summarizes the current knowledge on L-carnitine in Drosophila and discusses the role of the L-carnitine pathway in fly models of neurodegeneration.

Carnitine Inborn Errors of Metabolism

Carnitine plays essential roles in intermediary metabolism. In non-vegetarians, most of carnitine sources (~75%) are obtained from diet whereas endogenous synthesis accounts for around 25%. Renal carnitine reabsorption along with dietary intake and endogenous production maintain carnitine homeostasis. The precursors for carnitine biosynthesis are lysine and methionine. The biosynthetic pathway involves four enzymes: 6-N-trimethyllysine dioxygenase (TMLD), 3-hydroxy-6-N-trimethyllysine aldolase (HTMLA), 4-N-trimethylaminobutyraldehyde dehydrogenase (TMABADH), and γ-butyrobetaine dioxygenase (BBD). OCTN2 (organic cation/carnitine transporter novel type 2) transports carnitine into the cells. One of the major functions of carnitine is shuttling long-chain fatty acids across the mitochondrial membrane from the cytosol into the mitochondrial matrix for β-oxidation. This transport is achieved by mitochondrial carnitine–acylcarnitine cycle, which consists of three enzymes: carnitine palmitoyltransferase I (CPT I), carnitine-acylcarnitine translocase (CACT), and carnitine palmitoyltransferase II (CPT II). Carnitine inborn errors of metabolism could result from defects in carnitine biosynthesis, carnitine transport, or mitochondrial carnitine–acylcarnitine cycle. The presentation of these disorders is variable but common findings include hypoketotic hypoglycemia, cardio(myopathy), and liver disease. In this review, the metabolism and homeostasis of carnitine are discussed. Then we present details of different inborn errors of carnitine metabolism, including clinical presentation, diagnosis, and treatment options. At the end, we discuss some of the causes of secondary carnitine deficiency.

Study of Carnitine/Acylcarnitine and Amino Acid Profile in Children and Adults With Acute Liver Failure

OBJECTIVES

Fatty acid oxidation defects (FAODs) may underlie or modify the course of acute liver failure (ALF). Overall significance of carnitine/acylcarnitine and amino acid profile in ALF is similarly undetermined. Thus, this study was undertaken to study the abnormalities in carnitine/acylcarnitine and amino acid profile in ALF.

METHODS

A prospective study was performed including all patients with ALF, and detailed evaluation including metabolic testing was done.

RESULTS

A total of 55 patients (33 pediatric and 22 adult patients) were included in the study. Three patients (a 1-year 6-month-old child, a 13-year-old adolescent, and a 21-year-old adult, ie, 5.5% of all) were identified for the study with underlying metabolic etiology, that is, carnitine palmitoyl transferase-1 deficiency, based on the abnormal carnitine/acylcarnitine profile. Almost three-fourths of patients (78%) had evidence of serum hyperaminoacidemia. Thirty-one patients (56%) had evidence of abnormal carnitine/acylcarnitine profile with predominant abnormality being low free carnitine (C0). Higher levels of serum tyrosine (P = 0.002) and lower levels of serum C0 (P = 0.032) in children and higher levels of serum phenyalanine (P = 0.047) in adults predicted poor outcome (death/liver transplant) on univariate analysis.

CONCLUSIONS

FAODs are not uncommon in ALF with a suggested prevalence of approximately 5.5%. FAODs can cause ALF or modify the natural course of ALF caused by other etiologies. Serum hyperaminoacidemia and low serum free carnitine may predict poor outcome in patients with acute liver failure.

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.

Newborn screening and renal disease: where we have been; where we are now; where we are going

Newborn screening (NBS) has rapidly changed since its origins in the 1960s. Beginning with a single condition, then a handful in the 1990 s, NBS has expanded in the past decade to allow the detection of many disorders of amino-acid, organic-acid, and fatty-acid metabolism. These conditions often present with recurrent acute attacks of metabolic acidosis, hypoglycemia, liver failure, and hyperammonemia that may be prevented with initiation of early treatment. Renal disease is an important component of these disorders and is a frequent source of morbidity. Hemodialysis is often required for hyperammonemia in the organic acidemias and urea-cycle disorders. Rhabdomyolysis with renal failure is a frequent complication in fatty-acid oxidation disorders. Newer screening methods are under investigation to detect lysosomal storage diseases, primary immunodeficiencies, and primary renal disorders. These advances will present many challenges to nephrologists and pediatricians with respect to closely monitoring and caring for children with such disorders.

Mitochondrial DNA m.3242G > A mutation, an under diagnosed cause of hypertrophic cardiomyopathy and renal tubular dysfunction?

We present two new patients with the recently described mitochondrial m.3242G > A mutation. Although the mutation is situated next to the well known m.3243A > G mutation, the most common alteration associated with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, the clinical presentation is quite different, but characteristic. All three m.3242G > A patients presented in the neonatal period with hypertrophic and dilated cardiomyopathy, generalized muscle hypotonia and lactic acidosis. Two additionally had creatine kinase elevation, renal tubular acidosis/dysfunction and showed a mild clinical course with a favourable psychomotor development. The third patient had more neurological involvement and died in infancy. The mutation occurred de novo in the two patients where maternal investigations were performed. The combination of hypertrophic cardiomyopathy and renal tubular acidosis/renal tubular dysfunction is clinically distinctive and may represent a separate entity.

Cholestatic Jaundice Associated with Carnitine Palmitoyltransferase IA Deficiency

Liver dysfunction usually accompanies metabolic decompensation in fatty acid oxidation disorders, including carnitine palmitoyltransferase (CPT) Ia deficiency. Typically, the liver is enlarged with raised plasma transaminase activities and steatosis on histological examination. In contrast, cholestatic jaundice is rare, having only been reported in long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency. We report a 3-year-old boy with CPT Ia deficiency who developed hepatomegaly and cholestatic jaundice following a viral illness. No cause for the jaundice could be found, apart from the fatty acid oxidation disorder. Liver histology showed diffuse, predominately macrovesicular steatosis, hepatocellular and canalicular cholestasis but no bile duct paucity or evidence of large duct obstruction. The liver dysfunction resolved in 4-7 weeks.

Carrier frequency of a common mutation of carnitine palmitoyltransferase 1A deficiency and long-term follow-up in Finland

OBJECTIVE

To assess the long-term clinical course of carnitine palmitoyltransferase 1A (CPT1A) deficiency, caused by the c.1364A>C (p.K455T) mutation, and the carrier frequency of this mutation in Finland.

STUDY DESIGN

This was a long-term follow-up of patients in whom the common mutation was detected.

RESULTS

Between 1999 and 2010, 6 cases of CPT1A deficiency were diagnosed and treated with a high-carbohydrate, low-fat diet. The patients experienced their first symptoms during the first years of life, provoked by viral illness and/or fasting. The clinical features included hypoketotic hypoglycemia, hepatopathy, and loss of consciousness, ranging from transient unconsciousness to prolonged hyperlipidemic coma. Five cases carried a homozygous c.1364A>C (p.K455T) mutation, whereas 1 case had a compound c.1364A>C/c.1493A>C (p.Y498S) mutation. During dietary therapy, the patients had few transient decompensations. No carriers of mutation c.1364A>C were detected by minisequencing of 150 control samples.

CONCLUSION

Even though CPT1A deficiency may be life-threatening and lead to prolonged coma, the long-term prognosis is good. A genotype-phenotype correlation implies that the mutations detected are disease-causing. Despite Finland's location close to the Arctic polar region, the carrier frequency of the c.1364A>C mutation in Finland is far lower than that of the variants found in Alaskan, Canadian, and Greenland native populations.

A Novel Mutation in CPT1A Resulting in Hepatic CPT Deficiency

The present work presents a "from gene defect to clinics" pathogenesis study of a patient with a hitherto unreported mutation in the CPT1A gene. In early childhood, the patient developed a life-threatening episode (hypoketotic hypoglycemia, liver cytolysis, and hepatomegaly) evocative of a mitochondrial fatty acid oxidation disorder, and presented deficient fibroblast carnitine palmitoyltransferase 1 (CPT1) activity and homozygosity for the c.1783 C > T nucleotide substitution on exon 15 of CPT1A (p.R595W mutant). While confirming CPT1A deficiency, whole blood de novo acylcarnitine synthesis and the levels of carnitine and its esters formally linked intracellular free-carnitine depletion to intracellular carnitine esterification. Sequence alignment and modeling of wild-type and p.*R595W CPT1A proteins indicated that the Arg595 targeted by the mutated codon is phylogenetically well conversed. It contributes to a hydrogen bond network with neighboring residues Cys304 and Met593 but does not participate in the catalysis and carnitine pocket. Its replacement by tryptophan induces steric hindrance with the side chain of Ile480 located in α-helix 12, affecting protein architecture and function. This hindrance with Ile480 is also originally described with tryptophan 304 in the known mutant p.C304W CPT1A, suggesting that the mechanisms that invalidate CPT1A activity and underlie pathogenesis could be common in both the new (p.R595W) and previously described (p.C304W) mutants.

Bezafibrate upregulates carnitine palmitoyltransferase II expression and promotes mitochondrial energy crisis dissipation in fibroblasts of patients with influenza-associated encephalopathy

Influenza-associated encephalopathy (IAE) is characterized by persistently high fever, febrile convulsions, severe brain edema and high mortality. We reported previously that a large proportion of patients with disabling or fatal IAE exhibit a thermolabile phenotype of compound variants for [1055T>G/F352C] and [1102G>A/V368I] of carnitine palmitoyltransferase II (CPT II) and mitochondrial energy crisis during high fever. In the present study, we studied the effect of bezafibrate, a hypolipidemic pan-agonist of peroxisome proliferator-activated receptor (PPAR), on CPT II expression and mitochondrial energy metabolism in fibroblasts of IAE patients and wild type (WT) fibroblasts from a healthy volunteer at 37°C and 41°C. Although heat stress markedly upregulated CPT II, CPT IA and PPAR-δ mRNA expression levels, CPT II activity, β-oxidation and ATP levels in WT and IAE fibroblasts at 41°C were paradoxically downregulated probably due to the thermal instability of the corresponding enzymes. Bezafibrate significantly enhanced the expression levels of the above mRNAs and cellular functions of these enzymes in fibroblasts at 37°C. Bezafibrate-induced increase in CPT II activity also tended to restore the downregulated ATP levels, though moderately, and improved mitochondrial membrane potential even at 41°C to the levels at 37°C in fibroblasts of IAE patients. L-carnitine, a substrate of CPT II, boosted the effects of bezafibrate on cellular ATP levels in WT and IAE fibroblasts, even in severe IAE fibroblasts with thermolabile compound variations of F352C+V368I at 37°C and 41°C. The results suggest the potential usefulness of bezafibrate for the treatment of IAE.

Adult presentations of medium-chain acyl-CoA dehydrogenase deficiency (MCADD)

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is an autosomal recessive disorder of mitochondrial fatty acid oxidation which is usually diagnosed in infancy or through neonatal screening. In the absence of population screening, adults with undiagnosed MCADD can be expected. This review discusses 14 cases that were identified during adulthood. The mortality of infantile patients is approximately 25% whereas in this adult case series it was shown it to be 50% in acutely presenting patients and 29% in total. Therefore, undiagnosed individuals are at risk of sudden fatal metabolic decompensation with high mortality. This review illustrates the need to consider the possibility of a fatty acid oxidation defect in an adult who presents with unexplained sudden clinical deterioration, particularly if precipitated by fasting or alcohol consumption. A history of unexplained sibling death may also raise the index of suspicion. There also needs to be appropriate clinical support for those patients identified clinically or as a result of family studies (sibling or parent).

The paradox of the carnitine palmitoyltransferase type Ia P479L variant in Canadian Aboriginal populations

Investigation of seven patients from three families suspected of a fatty acid oxidation defect showed mean CPT-I enzyme activity of 5.9+/-4.9 percent of normal controls. The families, two Inuit, one First Nation, live in areas of Canada geographically very distant from each other. The CPT1 and CPT2 genes were fully sequenced in 5 of the patients. All were homozygous for the same P479L mutation in a highly conserved region of the CPT1 gene. Two patients from the first family were also homozygous for the CPT2 F352C polymorphism in the CPT2 gene. Genotyping the patients and their family members confirmed that all seven patients were homozygous for the P479L variant allele in the CPT1 gene, as were 27 of 32 family members. Three of the seven patients and two cousins had hypoketotic hypoglycemia attributable to CPT-Ia deficiency, but adults homozygous for the variant denied hypoglycemia. We screened 422 consecutive newborns from the region of one of the Inuit families for this variant; 294 were homozygous, 103 heterozygous, and only 25 homozygous normal; thus the frequency of this variant allele is 0.81. There was an infant death in one family and at least 10 more deaths in those infants (7 homozygous, 3 heterozygous) consecutively tested for the mutation at birth. Thus there is an astonishingly high frequency of CPT1 P479L variant and, judging from the enzyme analysis in the seven patients, also CPT-I deficiency in the areas of Canada inhabited by these families. Despite the deficiency of CPT-Ia which is the major rate-limiting enzyme for long chain fatty acid oxidation, clinical effects, with few exceptions, were slight or absent. One clue to explaining this paradox is that, judging from the fatty acid oxidation studies in whole blood and fibroblasts, the low residual activity of CPT-Ia is sufficient to allow a reasonable flux through the mitochondrial oxidation system. It is likely that the P479L variant is of ancient origin and presumably its preservation must have conveyed some advantage.

Mutations of the withered (whd) gene in Drosophila melanogaster confer hypersensitivity to oxidative stress and are lesions of the carnitine palmitoyltransferase I (CPT I) gene

Since some oxygen defense mutants of Drosophila melanogaster exhibit a crinkled wing phenotype, a screen was performed on strains bearing mutant alleles conferring a visible wing phenotype to determine whether any were hypersensitive to oxidative stress. One mutant, withered (whd), was found to be sensitive to both dietary paraquat and hyperoxia. New alleles of whd were induced on a defined genetic background and strains carrying these alleles were also found to be sensitive to oxidative stress. To identify the product of the whd gene we used a sequence-based positional candidate approach and by this method we determined that whd encodes carnitine palmitoyltransferase I (CPT I), an enzyme of the outer mitochondrial membrane that is required for the import of long-chain fatty acids into the mitochondria for beta-oxidation. Although this function is not vital under laboratory conditions, whd adults were found to be highly sensitive to starvation and to heavy metal toxicity relative to controls. This work uncovers a novel relationship between fatty acid metabolism and reactive oxygen metabolism. Further, these results in conjunction with past research on whd and on mammalian CPT I support the hypothesis that CPT I serves a vital function in the response to thymine supplementation.

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.

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.

Peroxisome proliferator-activated receptor delta activates fatty acid oxidation in cultured neonatal and adult cardiomyocytes

Peroxisome proliferator-activated receptors (PPARalpha, -gamma and -delta) are nuclear receptors involved in transcriptional regulations of lipid metabolism. The effect of PPARalpha in regulation of cardiac fatty acid oxidation has been well characterized. Whether PPARdelta also independently regulates fatty acid oxidation in the heart remains unclear. In this study, we tested the hypothesis that PPARdelta activates fatty acids oxidation in cardiomyocytes through transcriptional activation that are independent of PPARalpha. Our results first indicate that PPARdelta abundantly expresses in nucleus of cardiomyocytes. Palmitate oxidation rates were significantly increased in both neonatal and adult cardiomyocytes after treatment of a PPARdelta-selective ligand (GW0742). Further increases of fatty acid oxidation were evident when the treatment was applied to cardiomyocytes overexpressing a wild type PPARdelta, but not a mutant PPARdelta that lacks the intact carboxyl ligand-binding domain. Furthermore, genes of fatty acid oxidation enzymes were significantly upregulated in cultured rat neonatal cardiomyocytes when exposed to GW0742. GW0742 can restore partly the expression of certain key genes of fatty acid oxidation in mouse adult cardiomyocytes isolated from PPARalpha knockout mice. Therefore, while active crosstalk between PPARdelta and -alpha may exist, PPARdelta regulates cardiac fatty acid oxidation in the heart at least partly independent of PPARalpha. We conclude that PPARdelta may play a key role in cardiac energy balance and may serve as a "sensor" of fatty acid of other endogenous ligands in controlling fatty acids oxidation levels in the hearts under normal and pathological conditions.

Diagnosis of inherited disorders of liver metabolism

Diagnosis of the metabolic disorder responsible for liver disease can sometimes be straightforward but it can also present a major challenge, particularly if the liver is sufficiently damaged to produce secondary biochemical abnormalities such as galactosuria, hypoglycaemia with hypoketonaemia, or excretion of 3-oxo-delta4 bile acids. It is important to consider the age of the patient, the nature of the liver disease, any extrahepatic clinical features, the imaging and the first-line laboratory tests when prioritizing diagnostic investigations. This article gives some examples of diagnoses made in our unit for patients with liver disease presenting in utero, in the neonatal period, in infancy and the preschool years, and in the school years. The differential diagnoses that should be considered for different clinical presentations are discussed.

Fatty acid oxidation disorders

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

Hepatic Carnitine Palmitoyltransferase I Deficiency: Acylcarnitine Profiles in Blood Spots Are Highly Specific

Background: In carnitine palmitoyltransferase I (CPT-I) deficiency (MIM 255120), free carnitine can be increased with no pathologic acylcarnitine species detectable. As inclusion of CPT-I deficiency in high-risk and newborn screening could prevent potentially life-threatening complications, we tested whether CPT-I deficiency might be diagnosed by electrospray ionization-tandem mass spectrometry (ESI-MS/MS).

Methods: A 3.2-mm spot of whole blood dried on filter paper was extracted with 150 μL of methanol. After derivatization of carnitine and acylcarnitines to their butyl esters, the samples were analyzed by ESI-MS/MS with 37.5 pmol of l-[2H3]carnitine and 7.5 pmol of l-[2H3]palmitoylcarnitine as internal standards.

Results: In all dried-blood specimens from each of three patients with CPT-I deficiency, we found an invariably increased ratio of free carnitine to the sum of palmitoylcarnitine and stearoylcarnitine [C0/(C16 + C18)]. The ratio in patients was between 175 and 2000, or 5- to 60-fold higher than the ratio for the 99.9th centile of the normal newborn population in Bavaria (n = 177 842). No overlap with the values of children that were known to be supplemented with carnitine was detected [C0/(C16 + C18), 34 ± 30; mean ± SD; n = 27].

Conclusions: ESI-MS/MS provides a highly specific acylcarnitine profile from dried-blood samples. The ratio of free carnitine to the sum of palmitoylcarnitine and stearoylcarnitine [C0/(C16 + C18)] is highly specific for CPT-I deficiency and may allow presymptomatic diagnosis.

Lethal neonatal presentation of carnitine palmitoyltransferase I deficiency

A neonate subsequently diagnosed with carnitine palmitoyltransferase I deficiency died at 34 h of untreatable bradycardia. There was fatty infiltration of the liver and increased free carnitine and reduced acylcarnitines in the blood.