Carnitine Palmitoyltransferase 1A Deficiency Research Articles

Expression Variation of CPT1A Induces Lipid Reconstruction in Goat Intramuscular Precursor Adipocytes.

Intramuscular fat (IMF) deposition is one of the most important factors affecting meat quality and is closely associated with the expression of carnitine palmitoyl transferase 1A (CPT1A) which facilitates the transfer of long-chain fatty acids (LCFAs) into the mitochondria. However, the role of how CPT1A regulates the IMF formation remains unclear. Herein, we established the temporal expression profile of CPT1A during the differentiation of goat intramuscular precursor adipocytes. Functionally, the knockdown of CPT1A by siRNA treatment significantly increased the mRNA expression of adipogenic genes and promoted lipid deposition in goat intramuscular precursor adipocytes. Meanwhile, a CPT1A deficiency inhibited cell proliferation and promoted cell apoptosis significantly. CPT1A was then supported by the overexpression of CPT1A which significantly suppressed the cellular triglyceride deposition and promoted cell proliferation although the cell apoptosis also was increased. For RNA sequencing, a total of 167 differential expression genes (DEGs), including 125 upregulated DEGs and 42 downregulated DEGs, were observed after the RNA silencing of CPT1A compared to the control, and were predicted to enrich in the focal adhesion pathway, cell cycle, apoptosis and the MAPK signaling pathway by KEGG analysis. Specifically, blocking the MAPK signaling pathway by a specific inhibitor (PD169316) rescued the promotion of cell proliferation in CPT1A overexpression adipocytes. In conclusion, the expression variation of CPT1A may reconstruct the lipid distribution between cellular triglyceride deposition and cell proliferation in goat intramuscular precursor adipocyte. Furthermore, we demonstrate that CPT1A promotes the proliferation of goat adipocytes through the MAPK signaling pathway. This work widened the genetic regulator networks of IMF formation and delivered theoretical support for improving meat quality from the aspect of IMF deposition.

Clinical features and genetic variants of a case with carnitine palmitoyltransferase 1A deficiency

To identify the possible pathogenesis of a neonate with carnitine palmitoyltransferase 1A (CPT1A) deficiency by analyzing gene variants. Potential variants were detected with an Ion Torrent semiconductor sequencer using a gene panel for inherited diseases, and gene variants were verified by Sanger sequencing. Genetic testing indicated that the neonate has carried c.1895T>A(p.Leu632X) and c.1153G>A (p.Ala385Thr) compound heterozygous variants of the CPT1A gene, which were inherited from his father and mother, respectively. Both variants were verified as novel through the retrieval of HGMD database, ClinVar database and literature. According to the standards and guidelines of the American College of Medical Genetics and Genomics, the c.1895T>A variant was predicted to be pathogenic (PVS1+PM2+PP4) and c.1153G>A as likely pathogenic (PM1+PM2+PM3+PP3). The c.1895T>A and c.1153G>A compound heterozygous variants of the CPT1A gene might underlie the pathogenesis of this child. Above results have provided a basis for clinical diagnosis and genetic counseling, and enriched the variant spectrum of the CPT1 deficiency.

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.

Three Novel and One Potential Hotspot CPT1A Variants in Chinese Patients With Carnitine Palmitoyltransferase 1A Deficiency.

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is an inherited disorder of mitochondrial fatty acid β-oxidation that impairs fasting ketogenesis and gluconeogenesis in the liver. Few studies implementing newborn screening (NBS) for CPT1A deficiency in the Chinese population have been reported. This study aimed to determine the biochemical, clinical, and genetic characteristics of patients with CPT1A deficiency in China. A total of 204,777 newborns were screened using tandem mass spectrometry at Quanzhou Maternity and Children's Hospital between January 2017 and December 2018. Newborns with elevated C0 levels were recruited, and suspected patients were subjected to further genetic analysis. Additionally, all Chinese patients genetically diagnosed with CPT1A deficiency were reviewed and included in the study. Among the 204,777 screened newborns, two patients were diagnosed with CPT1A deficiency; thus, the estimated incidence in the selected population was 1:102,388. In addition to the two patients newly diagnosed with CPT1A deficiency, we included in our cohort 10 Chinese patients who were previously diagnosed. Five of these 12 patients were diagnosed via NBS. All patients exhibited elevated C0 and/or C0/(C16+C18) ratios. No clinical symptoms were observed in the five patients diagnosed via NBS, while all seven patients presented with clinical symptoms, including fever, cough, vomiting, diarrhea, and seizures. Eighteen distinct CPT1A variants were identified, 15 of which have been previously reported. The three novel variants were c.272T>C (p.L91P), c.734G>A (p.R245Q), and c.1336G>A (p.G446S). in silico analysis suggested that all three novel variants were potentially pathogenic. The most common variant was c.2201T>C (p.F734S), with an allelic frequency of 16.67% (4/24). Our findings demonstrated that NBS for CPT1A deficiency is beneficial. The three novel variants expand the mutational spectrum of CPT1A in the Chinese population, and c.2201T>C (p.F734S) may be a potential hotspot CPT1A mutation.

Clinical features and gene mutations of 6 patients with carnitine palmitoyltransferase 1A deficiency

The clinical and biochemical data and gene sequencing results of patients with carnitine palmitoyltransferase 1A deficiency were analyzed, in order to improve the understanding of the disease. Six patients (5 males and 1 female, aged from 1 to 8 years old) with carnitine palmitoyltransferase 1A deficiency from Department of Pediatric Endocrinology and Genetic Metabolism, Xinhua Hospital between 2008 and 2019 were included. Two cases were detected by neonatal screening and had no clinical symptoms. The remaining 4 cases all showed seizures induced by fever, vomiting or diarrhea. All the 6 patients showed increased serum free carnitine (C0), decreased hexadecanoylcarnitine (C16) and octadecanoylcarnitine (C18), and increased C0/(C16+C18). Meanwhile, compound heterozygous mutations of CPT1A gene were detected in all 6 patients, of which 2 were reported mutations (c.281+1G>A and c.968-8C>T), and 10 were new mutations. The new mutations included 6 missense mutations, 1 nonsense mutation, 1 deletion mutation and 2 splicing mutations. Detection of free carnitine and acyl carnitine by tandem mass spectrometry is helpful for early screening and diagnosis of carnitine palmitoyltransferase 1A deficiency.

Study of a Chinese pedigree carrying a novel variant of α-1, 3-N-acetyl galactosaminyl transferase gene

To explore the genetic basis for a Chinese pedigree with a novel ABO subtype. The proband and his family members were subjected to serological analysis, and their genotypes were determined by fluorescence PCR and direct sequencing of the coding regions of the ABO gene. Exons 6 to 7 of the ABO gene were also subjected to clone sequencing for haplotype analysis. The proband was determined as an AxB subtype. By fluorescence PCR, he was typed as A/B. Clone sequencing has revealed a insertional mutation c.797_798 insT in exon 7 of the ABO gene, which yielded a novel allele. Pedigree analysis confirmed that the novel ABO*A1.02 allele carried by the proband and his sister was inherited from their father. The c.797_798insT mutation has been submitted to GenBank with an accession number of MK125137. The c.797_798insT mutation of exon 7 of the ABO gene probably has led to weakened expression of A antigen.

Three Patients with CPT1A Deficiency: Literature Review and Case Series

Background: Carnitine palmitoyltransferase 1A deficiency is a rare genetic disorder with autosomal recessive inheritance pattern of fatty acid metabolism secondary to CPT1A mutation. Several dozen infants and children have been described with a deficiency of the liver and kidney CPT1 isoenzyme (CPT1-A). Clinical manifestation includes fasting-induced hypoketotic hypoglycemia, occasionally with extremely abnormal liver function test (LFT) and rarely with renal tubular acidosis. Acyl carnitine analysis has been the main method for the diagnosis of CPT1A deficiency. Prompt treatment of hypoglycemia includes intravenous fluid containing 10% dextrose. To prevent hypoglycemia, infants should eat frequently during the day and have cornstarch continuously at night. Fasting should not last more than 12 hours during illness, surgery, or medical procedures.
 Case Presentation: We reported three patients with CPT1A deficiency presented with hypoglycemia and Reye like syndrome in early childhood that with early diagnosis and treatment they are well in follow-up.
 Conclusion: Prognosis of this genetic disorder will be good with appropriate treatment.

A patient with atypical presentation of chronic hepatosteatosis harboring a novel variant in the CPT1A gene

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a rare disorder of hepatic long-chain fatty acid oxidation. Most patients with CPT1A deficiency present with hypoketotic hypoglycemia and hepatic encephalopathy. We describe an atypical case of an 8-year-old male with CPT1A deficiency presenting with chronic liver steatosis and cirrhosis. He also had a history of developmental delay, autism spectrum disorder, and mild dysmorphic features of unknown cause. His newborn screening test suggested CPT1A deficiency, but confirmatory biochemical testing was not conclusive. The patient never experienced a metabolic crisis. At age six, hepatomegaly was detected. Further investigations showed transaminitis, hepatosteatosis and cirrhosis. Repeat acylcarnitine profile and total/free carnitine were consistent with CPT1A deficiency. The CPTI enzyme activity was 18% of normal on fibroblast enzyme assay. A novel homozygous variant in the CPT1A gene, c.1394G > A (p.Gly465Glu) was identified from whole-exome sequencing. To our knowledge, the patient is the first reported individual with CPT1A deficiency and chronic liver steatosis and fibrosis. Developmental delay and autistic spectrum disorder are not typical features of CPT1A deficiency, given that the patient never experienced any metabolic decompensation.

Carnitine Palmitoyltransferase 1A Deficiency: A Rare Cause of Chronic Liver Disease with Rare Presentation

Carnitine Palmitoyltransferase 1A (CPT1A) deficiency is a very rare autosomal recessive disorder of fatty acid oxidation (FAO) which presents in children during concurrent febrile or gastrointestinal illness with hepatic encephalopathy (HE), hepatomegaly and rarely acute liver failure. Chronic liver damage is not reported in CPT1A deficiency. A 27-year-old female with history of CPT1A deficiency diagnosed in early childhood and chronic liver disease (CLD) complicated by thrombocytopenia, splenomegaly with model for end stage liver disease (MELD) score of 12; presented to emergency department with massive hematemesis. Vitals signs were stable. Physical exam was unremarkable except splenomegaly. Labs were significant for hemoglobin 7 g/dL, platelets 45 uL, electrolytes and liver enzymes unremarkable, INR 1.42, prothrombin time 17.2 sec, and total bilirubin 1.6 mg/dL. Computed tomography abdomen revealed prominent para-esophageal and peri-splenic varices, marked splenomegaly and fatty infiltration of liver (Image 1). The patient was started on IV fluids, ceftriaxone and octreotide. EGD revealed four columns of Grade IV esophageal varices (EV) that required 10 variceal bands (Image 2). Hospital course was further complicated by HE, thought to be multifactorial i.e. worsening liver function, poor oral intake and underlying defect in FAO. The patient was treated with lactulose, rifaximin with minimum improvement. Liver function continued to worsen with bilirubin 5.2 mg/dL, INR of 1.8 and MELD score of 24. A diagnosis of ACLF was made as her liver function 3 months prior to this admission was with in normal limits. She was high risk for re-bleeding and not a candidate for TIPS, so emergently transferred to a liver transplant center. CPT1A deficiency is a rare disorder with 60 cases reported so far. Either CLD or presentation as ACLF has not been reported in CPT1A deficiency. Our patient did not have history alcohol use or risk factors for NAFLD and Hepatitis B and C, hemochromatosis, Wilson's disease, autoimmune hepatitis were ruled out.2293_A Figure 1 No Caption available.2293_B Figure 2 No Caption available.

Genetic Ablation of Liver CPT-1A Gene Protects Mice against High-Fat Diet–Induced Obesity and Insulin Resistance

Carnitine palmitoyl transferase 1A (CPT-1A) catalyzes the transfer of the acyl group of long-chain fatty acid-CoA moiety onto carnitine, an essential step for the uptake of long-chain fatty acids and their subsequent beta-oxidation in the mitochondrion. It is the rate-limiting step in beta-oxidation and is highly expressed in the liver where it plays an important role in triglyceride metabolism. The physiological consequences of CPT-1A deficiency in liver, however, are yet to be reported. In this study, we have generated mouse model with liver specific deletion of CPT-1A gene. We found that deletion of CPT-1A in liver caused an increased triglyceride content in liver and decreased epididymal adipose tissue weight compared with control mice under high fat diet feeding conditions. RNA-seq analysis between livers of CPT-1A knockout vs. wild type mice revealed altered expression of many metabolic pathways such as steroid hormone biosynthesis and PPAR signaling pathways as well as some novel hepatokines. Further analysis of the significance of these changes is under way but the data so far suggest that a pharmacological agent that alters hepatic fatty acid oxidation (perhaps acting on CPT-1A) could provide a novel approach to target nonalcohol fatty liver disease (NAFLD). Disclosure D. Wu: None.

Clinical and genetic characteristics of patients with fatty acid oxidation disorders identified by newborn screening

BackgroundFatty acid oxidation disorders (FAODs) include more than 15 distinct disorders with variable clinical manifestations. After the introduction of newborn screening using tandem mass spectrometry, early identification of FAODs became feasible. This study describes the clinical, biochemical and molecular characteristics of FAODs patients detected by newborn screening (NBS) compared with those of 9 patients with symptomatic presentations.MethodsClinical and genetic features of FAODs patients diagnosed by NBS and by symptomatic presentations were reviewed.ResultsFourteen patients were diagnosed with FAODs by NBS at the age of 54.8 ± 4.8 days: 5 with very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency, 5 with medium chain acyl-CoA dehydrogenase (MCAD) deficiency, 1 with primary carnitine deficiency, 1 with carnitine palmitoyltransferase 1A (CPT1A) deficiency, 1 with long-chain 3-hydroxyacyl-CoA dehydrogenase or mitochondrial trifunctional protein (LCAHD/MTP) deficiency, and 1 with short chain acyl-CoA dehydrogenase (SCAD) deficiency. Three patients with VLCAD or LCHAD/MTP deficiency developed recurrent rhabdomyolysis or cardiomyopathy, and one patient died of cardiomyopathy. The other 10 patients remained neurodevelopmentally normal and asymptomatic during the follow-up. In 8 patients with symptomatic presentation, FAODs manifested as LCHAD/MTP deficiencies by recurrent rhabdomyolysis or cadiomyopathy (6 patients), and VLCAD deficiency by cardiomyopathy (1 patient), and CPT1A deficiency by hepatic failure (1 patient). Two patients with LCHAD/MTP deficiencies died due to severe cardiomyopathy in the neonatal period, and developmental disability was noted in CPT1A deficiency (1 patient).ConclusionsNBS helped to identify the broad spectrum of FAODs and introduce early intervention to improve the clinical outcome of each patient. However, severe clinical manifestations developed in some patients, indicating that careful, life-long observation is warranted in all FAODs patients.

Utility of Genetic Testing for Confirmation of Abnormal Newborn Screening in Disorders of Long-Chain Fatty Acids: A Missed Case of Carnitine Palmitoyltransferase 1A (CPT1A) Deficiency.

An 18-month-old male was evaluated after presenting with disproportionately elevated liver transaminases in the setting of acute gastroenteritis. He had marked hepatomegaly on physical exam that was later confirmed with an abdominal ultrasound. Given this clinical picture, suspicion for a fatty acid oxidation disorder was raised. Further investigation revealed that his initial newborn screen was positive for carnitine palmitoyltransferase 1A (CPT1A) deficiency—a rare autosomal recessive disorder of long-chain fatty acid oxidation. Confirmatory biochemical testing in the newborn period showed carnitine levels to be unexpectedly low with a normal acylcarnitine profile. Thus, it was considered to be a false-positive newborn screen and metabolic follow-up was not recommended. Repeat biochemical testing during this hospitalization revealed a normal acylcarnitine profile. The only abnormalities noted were a low proportion of acylcarnitine species from plasma, an elevated free-to-total carnitine ratio, and mild hypoketotic medium chain dicarboxylic aciduria on urine organic acids. Gene sequencing of CPT1A revealed a novel homozygous splice site variant that confirmed his diagnosis. CPT1A deficiency has a population founder effect in the Inuit and other Arctic groups, but has not been previously reported in persons of Ashkenazi Jewish ancestry.

Novel Mutations in theCPT1AGene Identified in the Patient Presenting Jaundice as the First Manifestation of Carnitine Palmitoyltransferase 1A Deficiency

Carnitine palmitoyltransferase 1A (CPT1A) is an enzyme functioning in mitochondrial fatty acid oxidation (FAO) of the liver. Patients with CPT1A deficiency have impaired mitochondrial FAO and display hypoketotic hypoglycemia and hepatic encephalopathy as typical manifestations. In this report, we present a case of CPT1A deficiency presenting jaundice as the first manifestation. A 1.9 years old boy showed jaundice and elevated levels of free and total carnitine were observed. From direct sequencing analysis of CPT1A, two novel mutations, c.1163+1G>A and c.1393G>A (p.Gly465Arg), were identified. At the age of 2.2 years, hypoglycemia, tachycardia, and altered mental status developed just after cranioplasty for craniosynostosis. High glucose infusion rate was required for recovery of his vital signs and mentality. Diet rich in high carbohydrate, low fat and inclusion of medium chain triglyceride oil resulted in improvement in cholestatic hepatitis and since then the boy has shown normal growth velocity and developmental milestones to date.

Atypical Manifestation of Carnitine Palmitoyltransferase 1A Deficiency

Atypical Manifestation of Carnitine Palmitoyltransferase 1A Deficiency

Carnitine Palmitoyltransferase-1A Deficiency

Carnitine palmitoyltransferase-1A (CPT-1A) deficiency is a defect of fatty acid metabolism that presents as an autosomal recessive inheritance. Carnitine palmitoyltransferase-1A is the rate-limiting enzyme that allows the body to process fats to provide energy during times of fasting and illness. Patients usually present between birth and 18 months of age following an illness with various symptoms including hypoketotic hypoglycemia, lethargy, and seizures. Diagnosis can be achieved through newborn metabolic screening. Long-term treatment is managed through dietary management. A milder form has been found to occur at a much higher incidence in the Inuit population. Since the recent discovery of CPT-1A deficiency, much is yet to be learned. Researchers are busy identifying and studying groups of people who are presenting with CPT-1A deficiency at significantly higher rates than the general population. This research will lead to a better understanding and future care of individuals diagnosed with CPT-1A deficiency.

Carrier Frequency of a Common Mutation of Carnitine Palmitoyltransferase 1A Deficiency and Long-Term Follow-Up in Finland

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

Prevalence and Distribution of the c.1436C→T Sequence Variant of Carnitine Palmitoyltransferase 1A among Alaska Native Infants

To use genotype analysis to determine the prevalence of the c.1436C→T sequence variant in carnitine palmitoyltransferase 1A (CPT1A) among Alaskan infants, and evaluate the sensitivity of newborn screening by tandem mass spectrometry (MS/MS) to identify homozygous infants. We compared MS/MS and DNA analyses of 2409 newborn blood spots collected over 3 consecutive months. Of 2409 infants, 166 (6.9%) were homozygous for the variant, all but one of whom were of Alaska Native race. None of the homozygous infants was identified by MS/MS on the first newborn screen using a C0/C16 + C18 cutoff of 130. Among 633 Alaska Native infants, 165 (26.1%) were homozygous and 218 (34.4%) were heterozygous for the variant. The prevalence was highest in Alaska's northern/western regions (51.2% of 255 infants homozygous; allele frequency, 0.7). The CPT1A c.1436C→T variant is prevalent among some Alaska Native peoples, but newborn screening using current MS/MS cutoffs is not an effective means to identify homozygous infants. The clinical consequences of the partial CPT1A deficiency associated with this variant are unknown. If effects are substantial, revision of newborn screening, including Alaska-specific MS/MS cutoffs and confirmatory genotyping, may be needed.

Carnitine palmitoyltransferase 1A (CPT1A) P479L prevalence in live newborns in Yukon, Northwest Territories, and Nunavut

Carnitine palmitoyltransferase 1A (CPT1A), encoded by the gene CPT1A, is the hepatic isoform of CPT1 and is a major regulatory point in long-chain fatty acid oxidation. CPT1A deficiency confers risk for hypoketotic hypoglycaemia, hepatic encephalopathy, seizures, and sudden unexpected death in infancy (SUDI). It remains controversial whether the CPT1A gene variant, c.1436C>T (p.P479L), identified in Inuit, First Nations, and Alaska Native infants, causes susceptibility to decompensation, in particular during times of fever and intercurrent illness. Although newborn screening for the P479L variant occurs in some jurisdictions, background knowledge about the presence of the variant in Canadian Aboriginal populations is lacking. In an effort to understand the population implications of the variant in northern Canada, overall frequencies of the variant were assessed. Further studies are underway to determine associated risk. Ethics approval was obtained from university REBs, local research institutes, and with consultation with territorial Aboriginal groups. Newborn screening blood spots from all infants born in 2006 in the three territories were genotyped for the p.P479L variant. p.P479L (c.1436C>T) allele frequencies in the three territories were 0.02, 0.08, and 0.77 in Yukon (n=325), Northwest Territories (n=564), and Nunavut (n=695), respectively. Homozygosity rates were 0%, 3%, and 64%. Aboriginal status was available only in NWT, with allele frequencies of 0.04, 0.44, 0.00, and 0.01 for First Nations, Inuvialuit/Inuit, Métis, and non-Aboriginal populations. Although individual blood spots were not identified for Aboriginal ethnicity in Nunavut infants, ~90% of infants in Nunavut are born to Inuit women. The allele frequency and rate of homozygosity for the CPT1A P479L variant were high in Inuit and Inuvialuit who reside in northern coastal regions. The variant is present at a low frequency in First Nations populations, who reside in areas less coastal than the Inuit or Inuvialuit in the two western territories. The significance of the population and geographic distribution remains unclear, but the high population frequencies of the variant suggest a historically low penetrance for adverse outcomes. Further evidence is needed to determine if there is an increased risk for infant mortality and morbidity and whether newborn screening will be indicated on a population basis.

Molecular assay for detection of the common carnitine palmitoyltransferase 1A 1436(C>T) mutation

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is a metabolic disorder that occurs at a key checkpoint of fatty acid metabolism. A new form of CPT1A deficiency caused by a mutation at nucleotide 1436 (C>T), resulting in an amino acid substitution of leucine for proline at position 479 (P479L), has been isolated in Canadian First Nations and Inuit populations. The present study offers a molecular method for assessing CPT1A 1436 (C>T) mutation status. CPT1A-deficient fibroblasts from four patient fibroblast cell lines and ten patient peripheral blood spots were all analyzed by polymerase chain reaction (PCR) coupled to restriction endonuclease (RE) treatment. Genomic DNA was PCR-amplified and treated with an RE specific for normal DNA. CPT1A 1436 (C>T) mutations were identified by resistance to RE treatment. The RE-PCR assay identified homozygosity for the 1436 (C>T) mutation in four fibroblast cell lines and nine blood spots with CPT1A enzyme deficiency. In addition, the assay identified one blood spot that corresponded to the heterozygous genotype. RE-PCR assay for the 1436 (C>T) mutation provides a rapid assay for the diagnosis of CPT1A deficiency resulting from this mutation. The assay will have utility in screening populations with a high prevalence of this genotype.

Functional and Structural Basis of Carnitine Palmitoyltransferase 1A Deficiency

Carnitine palmitoyltransferase 1A (CPT1A) is the key regulatory enzyme of hepatic long-chain fatty acid beta-oxidation. Human CPT1A deficiency is characterized by recurrent attacks of hypoketotic hypoglycemia. We presently analyzed at both the functional and structural levels five missense mutations identified in three CPT1A-deficient patients, namely A275T, A414V, Y498C, G709E, and G710E. Heterologous expression in Saccharomyces cerevisiae permitted to validate them as disease-causing mutations. To gain further insights into their deleterious effects, we localized these mutated residues into a three-dimensional structure model of the human CPT1A created from the crystal structure of the mouse carnitine acetyltransferase. This study demonstrated for the first time that disease-causing CPT1A mutations can be divided into two categories depending on whether they affect directly (functional determinant) or indirectly the active site of the enzyme (structural determinant). Mutations A275T, A414V, and Y498C, which exhibit decreased catalytic efficiency, clearly belong to the second class. They are located more than 20 A away from the active site and mostly affect the stability of the protein itself and/or of the enzyme-substrate complex. By contrast, mutations G709E and G710E, which abolish CPT1A activity, belong to the first category. They affect Gly residues that are essential not only for the structure of the hydrophobic core in the catalytic site, but also for the chain-length specificity of CPT isoforms. This study provides novel insights into the functionality of CPT1A that may contribute to the design of drugs for the treatment of lipid disorders.