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Carnitine-acylcarnitine translocase deficiency (CACTD) is a rare and life-threatening autosomal recessive disorder of fatty acid β-oxidation (FAO). Most patients with CACTD develop severe metabolic decompensation which deteriorates progressively and rapidly, causing death in infancy or childhood. As CACTD in some patients is asymptomatic or only with some nonspecific symptoms, the diagnosis is easy to be ignored, resulting in sudden death, which often triggers medical disputes. Herein, we report a case of neonatal sudden death with CACTD. The neonate showed a series of severe metabolic crisis, deteriorated rapidly and eventually died 3 days after delivery. Tandem mass spectrometry (MS-MS) screening of dry blood spots before death showed that the level of long-chain acylcarnitines, especially C12-C18 acylcarnitine, was increased significantly, and therefore a diagnosis of inherited metabolic disease (IMD) was suspected. Autopsy and histopathological results demonstrated that there were diffuse vacuoles in the heart and liver of the deceased. Mutation analysis revealed that the patient was a compound heterozygote with c.199–10 T > G and a novel c.1A > T mutation in the SLC25A20 gene. Pathological changes such as heart failure, arrhythmia and cardiac arrest related to mitochondrial FAO disorders are the direct cause of death, while gene mutation is the underlying cause of death.

Carnitine-acylcarnitine translocase deficiency (CACTD) is a rare autosomal recessive disorder of mitochondrial fatty acid oxidation that occurs due to mutations in the SLC25A20 gene. Severe CACTD results in neonatal or infantile sudden death. Herein, we reported six patients with CACTD diagnosed based on biochemical and molecular findings from 5 unrelated families in Guangdong from 2016 to 2017. Among them, five patients presented with hypotonia, nonketotic hypoglycemia, and arrhythmia 2 days after birth, while the other patient presented with respiratory distress, hypotonia, and arrhythmia. Five of the patients died in the neonatal period. Blood acylcarnitine concentrations determination from dried blood spots (DBS) were measured by tandem mass spectrometry (MS/MS). The SLC25A20 and CPT2 gene sequences were analyzed by direct Sanger sequencing. SLC25A20 gene analysis revealed a c.199-10T>G (IVS2-10T>G) homozygous variants in four unrelated patients and a novel mutation c.199-10T>G/c.719-8_c.719-1dupCCCACAG compound heterozygous variants in twins. This report describes the clinical characteristics, biochemical findings and molecular analysis of SLC25A20 gene of patients with CACTD in Guangdong. And our results show that the c.199-10T>G is likely the most common variant of CACTD in Guangdong population as it accounts for 83% (10/12) of the observed mutant alleles. Individuals with the c.199-10T>G genotype had a severe CACTD phenotype.

BACKGROUND: Carnitine acyl-carnitine translocase deficiency (CACTD) is a rare autosomal recessive disorder of mitochondrial long-chain fatty-acid transport. Most patients present in the first two days of life, with hypoketotic hypoglycaemia, hyperammonaemia, cardiomyopathy or arrhythmia, hepatomegaly and elevated liver enzymes. METHOD: Multi-centre international retrospective chart review of clinical presentation, biochemistry, treatment modalities including diet, subsequent complications, and mode of death of all patients. RESULTS: Twenty-three patients from nine tertiary metabolic units were identified. Seven attenuated patients of Pakistani heritage, 6 of these homozygous c.82G>T, had later onset manifestations and long-term survival without chronic hyperammonemia. Of the sixteen classical cases, fifteen had cardiac involvement at presentation comprising cardiac arrhythmias (9/15), cardiac arrest (7/15) and cardiac hypertrophy (9/15). Where recorded, ammonia levels were elevated in all but one severe case (13/14 measured) and 14/16 had hypoglycaemia. Nine classical patients survived longer-term - most with feeding difficulties and cognitive delay. Hyperammonaemia appears refractory to ammonia scavenger treatment and carglumic acid, but responds well to high glucose delivery during acute metabolic crises. High-energy intake seems necessary to prevent decompensation. Anaplerosis utilizing therapeutic D,L-3-hydroxybutyrate, Triheptanoin and increased protein intake, appeared to improve chronic hyperammonemia and metabolic stability where trialled in individual cases. CONCLUSION: CACTD is a rare disorder of fatty acid oxidation with a preponderance to severe cardiac dysfunction. Long-term survival is possible in classical early-onset cases with long-chain fat restriction, judicious use of glucose infusions, and medium chain triglyceride supplementation. Adjunctive therapies supporting anaplerosis may improve longer-term outcomes. This article is protected by copyright. All rights reserved.

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare disorder of long chain fatty acid oxidation with a very high mortality rate due to cardiomyopathy or multiorgan failure. We present the course of a very premature infant with early onset CACT deficiency complicated by multiple episodes of necrotizing enterocolitis, sepsis, and liver insufficiency, followed by eventual demise. The complications of prematurity, potentiated by the overlay of CACT deficiency, contributed to the difficulty of reaching the ultimate diagnosis of CACT deficiency.

Introduction: Carnitine–acylcarnitine translocase deficiency (CACTD) is a rare and life-threatening autosomal recessive disorder of mitochondrial fatty acid oxidation caused by variation of the Solute carrier family 25 member 20 (SLC25A20) gene. Carnitine–acylcarnitine translocase is one of the crucial transport proteins in the oxidation process of mitochondrial fatty acids. In Asia, the c.199-10T>G splice site variation is the most frequently reported variant of SLC25A20. Patients with CACTD with c.199-10T>G variation usually present with a severe clinical phenotype.Materials and Methods: Herein, we report a neonatal case of late-onset CACTD in mainland China. Symptoms emerged 61 days after birth; the patient presented with a severe metabolic crisis, and her clinical condition rapidly deteriorated, and she died of respiratory insufficiency and cardiac arrest at 61 days. We present the clinical and biochemical features of this patient and briefly review previously reported CACTD cases with c.199-10T>G variation.Results: Acylcarnitine profiling by tandem mass spectrometry and high-throughput sequencing revealed that our patient was homozygous for the c.199-10T>G variation, confirming the diagnosis of CACTD. Histopathologic analysis of the liver by Prussian blue staining showed focal iron deposition in hepatocytes, and electron microscopy analysis revealed a large number of lipid droplet vacuoles in diffusely distributed hepatocytes.Conclusion: The development of CACTD in our patient 61 days after birth is the latest reported onset for CACTD with SLC25A20 c.199-10T>G variation. Early recognition of symptoms and timely and appropriate treatment are critical for improving the outcome of this highly lethal disorder. Death from late-onset CACTD may be caused by the accumulation of long-chain fatty acids as well as iron deposition in the heart leading to heart failure.

Introduction Mitochondrial fatty acid oxidation disorders (FAODs) are a heterogeneous group of hereditary autosomal recessive diseases included in newborn screening (NBS) program in Italy. The aim of this study was to analyse FAODs cases, identified either clinically or by NBS,for clinical and genetic characterization and to evaluate a five years' experience of NBS, in the attempt to figure out the complexity of genotype-phenotype correlation and to confirm the clinical impact of NBS in our centre experience. Materials and methods We analysed FAODs patients diagnosed either by NBS or clinically, followed since February 2014 to April 2019 at the Regional Screening Centre and Inherited Metabolic Diseases Unit of Verona. Diagnosis was confirmed by plasma acylcarnitines, urinary organic acids, enzymatic and genetic testing. For not clear genotypes due to the presence of variants of uncertain significance, in silico predictive tools have been used as well as enzymatic activity assays. Patients underwent clinical, nutritional and biochemical follow up. Results We diagnosed 30 patients with FAODs. 20 by NBS: 3 CUD, 6 SCADD, 5 MCADD, 4 VLCADD, 2 MADD. Overall incidence of FAODs diagnosed by NBS was 1:4316 newborns. No one reported complications during the follow up period. 10 patients were diagnosed clinically: 2 CUD, 2 CPT2D, 1 VLCADD, 5 MADD. Mean age at diagnosis was 29.3 years. Within this group, complications or symptoms were reported at diagnosis, but not during follow-up. 12 mutations not previously reported in literature were found, all predicted as pathogenic or likely pathogenic. Discussion and conclusions Our study highlighted the great phenotypic variability and molecular heterogeneity of FAODs and confirmed the importance of a tailored follow up and treatment. Despite the short duration of follow up, early identification by NBS prevented diseases related complications and resulted in normal growth and psycho-motor development as well., Highlights • Early identification by newborn screening prevents disease related complications. • Newborn screening is changing prevalence clinical and molecular heterogeneity of FAODs. • Genotype-phenotype correlation helps to achieve personalized follow-up and treatment. • Enzymatic assay may be pivotal in predicting phenotype and symptoms severity. • Diagnosis on clinical grounds is anyway important to change disease course.

Background Patients with severe long-chain fatty acid oxidation disorders (LC-FAODs) experience serious morbidity and mortality despite traditional dietary management including medium-chain triglyceride (MCT)-supplemented, low-fat diets. Triheptanoin is a triglyceride oil that is broken down to acetyl-coenzyme A (CoA) and propionyl-CoA, which replenishes deficient tricarboxylic acid cycle intermediates. We report the complex medical and nutrition management of triheptanoin therapy initiated emergently for 3 patients with LC-FAOD. Methods Triheptanoin (Ultragenyx Pharmaceutical, Inc, Novato, CA, USA) was administered to 3 patients with LC-FAOD on a compassionate-use basis. Triheptanoin was mixed with non-MCT-containing low-fat formula. Patients were closely followed with regular cardiac and laboratory monitoring. Results Cardiac ejection fraction normalized after triheptanoin initiation. Patients experienced fewer hospitalizations related to metabolic crises while on triheptanoin. Patient 1 has tolerated oral administration without difficulty since birth. Patients 2 and 3 experienced increased diarrhea. Recurrent breakdown of the silicone gastrostomy tube occurred in patient 3, whereas the polyurethane nasogastric tube for patient 2 remained intact. Patient 3 experiences recurrent episodes of elevated creatine kinase levels and muscle weakness associated with illness. Patient 3 had chronically elevated C10-acylcarnitines while on MCT supplementation, which normalized after initiation of triheptanoin and discontinuation of MCT oil. Conclusions Triheptanoin can ameliorate acute cardiomyopathy and increase survival in patients with severe LC-FAOD. Substituting triheptanoin for traditional MCT-based treatment improves clinical outcomes. MCT oil might be less effective in carnitine-acylcarnitine translocase deficiency patients compared with other FAODs and needs further investigation.

We report a female infant who was diagnosed to have carnitine–acylcarnitine translocate deficiency (CACTD) and developed ventricular tachycardia followed by cardiac arrest. Following full feeding, the infant developed significant bradycardia, hypothermia, hypotonia, hypoglycemia, metabolic acidosis, and hyperammonemia. The hyperammonemia was successfully treated with continuous renal replacement therapy (CRRT). One day after the CRRT, she developed ventricular tachycardia that was refractory to medical treatment and synchronized cardioversion. She had cardiac arrest that was unresponsive to full cardiopulmonary resuscitation and died. Raising high index of suspicion of CACTD in the deferential diagnosis of infants present with sudden deterioration, hypoglycemia or hyperammonemia is crucial for early recognition and providing appropriate treatment in this highly lethal disorder.

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare long-chain fatty acid oxidation disorder (LC-FAOD) with high mortality due to cardiomyopathy or lethal arrhythmia. Triheptanoin (UX007), an investigational drug composed of synthetic medium odd-chain triglycerides, is a novel therapy in development for LC-FAOD patients. However, cases of its safe and efficacious use to reverse severe heart failure in CACT deficiency are limited. Here, we present a detailed report of an infant with CACT deficiency admitted in metabolic crisis that progressed into severe cardiogenic shock who was successfully treated by triheptanoin. The child was managed, thereafter, on triheptanoin until her death at 3 years of age from a cardiopulmonary arrest in the setting of acute respiratory illness superimposed on chronic hypercarbic respiratory failure.

Rationale Carnitine-acylcarnitine translocate deficiency (CACTD) is a rare and life-threatening, autosomal recessive disorder of fatty acid β-oxidation characterized by hypoketotic hypoglycemia, hyperammonemia, cardiomyopathy, liver dysfunction, and muscle weakness; culminating in early death. To date, CACTD cases screened from the Chinese mainland population, especially patient with compound heterozygote with c.199-10T>G and a novel c.1A>G mutation in the SLC25A20 gene has never been described. Patient concerns Herein, we report 2 neonatal cases of CACTD identified from the mainland China. These 2 patients were presented with severe metabolic crisis and their clinical conditions deteriorate rapidly and both died of cardiorespiratory collapse in the first week of life. We present the clinical and biochemical features of 2 probands and a brief literature review of previously reported CACTD cases with the c.199-10T>G mutation. Diagnoses The acylcarnitine profiles by tandem-mass-spectrometry and the mutation analysis of SLC25A20 gene confirmed the diagnosis of CACTD in both patients. Mutation analysis demonstrated that patient No. 1 was homozygous for c.199-10T>G mutation, while patient No. 2 was a compound heterozygote for 2 mutations, a maternally-inherited c.199-10T>G and a paternally-inherited, novel c.1A>G mutation. Interventions Both patients were treated with an aggressive treatment regimen include high glucose and arginine infusion, respiratory, and circulatory support. Outcomes The first proband died 3 days after delivery due to sudden cardiac arrest. The second patient's clinical condition, at one time, was improved by high glucose infusion, intravenous arginine, and circulatory support. However, the patient failed to wean from mechanical ventilation. Unfortunately, her parents refused further treatment due to fear of financial burdens. The patient died of congestive heart failure in the 6th day of life. Lessons We report the first 2 cases of CACTD identified from the mainland China. Apart from a founder mutation c.199-10T>G, we identified a novel c.1A>G mutation. Patients with CACTD with a genotype of c.199-10T>G mutation usually presents with a severe clinical phenotype. Early recognition and appropriate treatment is crucial in this highly lethal disorder. This case series highlights the importance of screening for metabolic diseases including CACTD in cases of sudden infant death and unexplained abrupt clinical deterioration in the early neonatal period.

Carnitine-acylcarnitine translocase deficiency, clinical, biochemical and genetic aspects.Rubio-Gozalbo ME, Bakker JA, Waterham HR, Wanders RJ.Department of Pediatrics, University Hospital Maastricht, Maastricht, The Netherlands. mrub@paed.azm.nlThe carnitine-acylcarnitine translocase (CACT) is one of the components of the carnitine cycle. The carnitine cycle is necessary to shuttle long-chain fatty acids from the cytosol into the intramitochondrial space where mitochondrial beta-oxidation of fatty acids takes place. The oxidation of fatty acids yields acetyl-coenzyme A (CoA) units, which may either be degraded to CO(2) and H(2)O in the citric acid cycle to produce ATP or converted into ketone bodies which occurs in liver and kidneys. Metabolic consequences of a defective CACT are hypoketotic hypoglycaemia under fasting conditions, hyperammonemia, elevated creatine kinase and transaminases, dicarboxylic aciduria, very low free carnitine and an abnormal acylcarnitine profile with marked elevation of the long-chain acylcarnitines. Clinical signs and symptoms in CACT deficient patients, are a combination of energy depletion and endogenous toxicity. The predominantly affected organs are brain, heart and skeletal muscle, and liver, leading to neurological abnormalities, cardiomyopathy and arrythmias, skeletal muscle damage and liver dysfunction. Most patients become symptomatic in the neonatal period with a rapidly progressive deterioration and a high mortality rate. However, presentations at a later age with a milder phenotype have also been reported. The therapeutic approach is the same as in other long-chain fatty acid disorders and includes intravenous glucose (+/- insulin) administration to maximally inhibit lipolysis and subsequent fatty acid oxidation during the acute deterioration, along with other measures such as ammonia detoxification, depending on the clinical features. Long-term strategy consists of avoidance of fasting with frequent meals and a special diet with restriction of long-chain fatty acids. Due to the extremely low free carnitine concentrations, carnitine supplementation is often needed. Acylcarnitine profiling in plasma is the assay of choice for the diagnosis at a metabolite level. However, since the acylcarnitine profile observed in CACT-deficient patients is identical to that in CPT2-deficient patients, definitive identification of CACT-deficiency in a certain patient requires determination of the activity of CACT. Subsequently, mutational analysis of the CACT gene can be performed. So far, 9 different mutations have been identified in the CACT gene.

Carnitine-acylcarnitine translocase CACT deficiency is a very rare autosomal recessive disease. The neonatal phenotype of CACT deficiency is characterized by hypoketotic hypoglycaemia, hyperammonaemia, cardiomyopathy and skeletal muscle weakness culminating in early death. The disease is caused by mutations in the CACT gene, which encodes a protein transporting long-chain fatty acid carnitine esters into the mitochondrial matrix. In this report, we describe the first case of CACT deficiency in the Bedouin population in Israel. The patient, the first son of consanguineous parents, was born at term after uneventful delivery. During the second day of life, he developed clinical signs of an acute metabolic crisis with severe hypoglycaemia and hyperammonaemia. Biochemical investigation suggested the diagnosis of CACT deficiency. Genetic molecular analysis confirmed this diagnosis by demonstrating that the affected child was homozygous for a novel missense mutation 793A>G, substituting glutamine by arginine (Q238R) in exon 7 of the CACT gene. Despite medical treatment and adequate nutrition, the patient died at 6 months of age.

Carnitine-acylcarnitine translocase (CAC) deficiency is a rare autosomal recessive disorder of long-chain fatty acid oxidation with a severe outcome. We report mutation analysis in a cohort of 12 patients. Twelve mutations were identified of which 9 have not been reported so far (G28C, D32N, R178Q, P230R, D231H, 179delG, 802delG, 69–70insTGTGC, and 609−1g > a). Altogether, including our results, 22 mutations of the CAC gene have been published to date in 23 patients demonstrating the allelic heterogeneity of CAC deficiency. DNA-based prenatal diagnosis was performed for the first time in pregnancies at risk for CAC deficiency. Two fetuses were affected and one pregnancy was terminated by family decision. Two other fetuses had normal genotype and five others were heterozygotes. All the offspring of these seven pregnancies are alive and apparently healthy.

Background Mitochondrial fatty acid oxidation (FAO) disorders are among the causes of acute encephalopathy- or myopathy-like illness. Carnitine–acylcarnitine translocase (CACT) deficiency is a rare FAO disorder, which represent an energy production insufficiency during prolonged fasting, febrile illness, or increased muscular activity. CACT deficiency is caused by mutations of the SLC25A20 gene. Most patients developed severe metabolic decompensation in the neonatal period and died in infancy despite aggressive treatment. Patients and methods We herein report the clinical findings of two unrelated cases of CACT deficiency with mutation confirmation, and in vitro bezafibrate responses using in vitro probe acylcarnitine (IVP) assay. Patients 1 and 2 are products of nonconsanguineous parents. Both patients developed cardiac arrest at day 3 of life but survived the initial events. Their blood chemistry revealed hypoglycemia and metabolic acidosis. The acylcarnitine profiles in both patients demonstrated increased long-chain acylcarnitines, suggesting CACT or carnitine palmitoyltransferase-2 (CPT2) deficiency. Results The mutation analysis identified homozygous IVS2-10T>G in the SLC25A20 gene in both patients, confirming the diagnosis of CACT deficiency. The IVP assay revealed increased C16, C16:1, but decreased C2 with improvement by bezafibrate in the cultured fibroblasts. The short-term clinical trial of bezafibrate in Patient 1 did not show clinical improvement, and died after starting the trial for 6 months. Conclusion This splicing mutation has been identified in other Asian populations indicating a possible founder effect. IVP assay of cultured fibroblasts could determine a response to bezafibrate treatment. A long-term clinical trial of more enrolled patients is required for evaluation of this therapy.

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare autosomal recessive disease in the mitochondrial transport of long-chain fatty acids. Despite early diagnosis and treatment, the disease still has a high mortality rate.Clinical symptoms, long-term follow-up, and biochemical and molecular results of four cases are described and compared with the reviewed literature data of 55 cases.Two cases with neonatal onset, carrying in homozygosity the novel variant sequences p.Gly20Asp (c.59GA) and p.Arg179Gly (c.536AG), died during an intercurrent infectious process in the first year of life despite adequate dietetic treatment (frequent feeding, high-carbohydrate/low-fat diet, MCT, carnitine). The other two cases, one with infantile onset and the other diagnosed in the newborn period after a previous affected sibling, show excellent development at 4 and 16 years of age under treatment. The review shows that the most frequent presenting symptoms of CACT deficiency are hypoketotic hypoglycemia, hyperammonemia, hepatomegaly, cardiomyopathy and/or arrhythmia, and respiratory distress. The onset of symptoms is predominantly neonatal in 82% and infantile in 18%. The mortality rate is high (65%), most in the first year of life due to myocardiopathy or sudden death. Outcomes seem to correlate better with the absence of cardiac disease and with a higher long-chain fatty acid oxidation rate in cultured fibroblasts than with residual enzyme activity.Diagnosis before the occurrence of clinical symptoms by tandem MS-MS and very early therapeutic intervention together with good dietary compliance could lead to a better prognosis, especially in milder clinical cases.

Carnitine-acylcarnitine translocase (CACT) deficiency is an inherited defect of the co-transport of free and esterified carnitine across the inner mitochondrial membrane. We report a case of CACT deficiency in a newborn who died at 72 h of age from severe, intractable cardiac tachyarrhythmia, despite an improvement in his neurological and biochemical status. Postmortem examination showed marked steatosis of myocardium, liver, and kidney. In addition, electron microscopic studies showed virtually complete elimination of mitochondria from cardiomyocytes. It appears that the correction of the acute metabolic derangements in this condition may not prevent rapid progression to death, suggesting that the rhythm disturbances in CACT deficiency result from prior and ongoing accumulation of toxic metabolites, rather than from an acute metabolic derangement. Furthermore, we speculate that the choice of anti-arrhythmic agent in this patient may paradoxically have contributed to his death.

Carnitine-acylcarnitine translocase deficiency is a rare and life-threatening mitochondrial fatty acid beta-oxidation disorder. We describe a patient who, despite a severe clinical course and an extremely low carnitine-acylcarnitine translocase activity, is currently alive and in good health. We performed an extensive analysis of all previously published cases in order to evaluate the clinical features and prognostic factors. Reports on 21 patients with carnitine-acylcarnitine translocase deficiency were obtained. Only 5 out of the 21 patients survived early childhood. At least 20 siblings are reported to have died of sudden unexplained death in the neonatal period. Although phenotype and residual enzyme activity have been suggested to be related to outcome, we were not able to establish such a relationship. CONCLUSION: Phenotype and residual enzyme activity do not appear to be major prognostic factors. Vigorous work-up in order to reach an expedite diagnosis and prompt medical intervention during acute episodes, especially in the neonatal period, may prevent fatal complications

Some 13 different inherited defects of mitochondrial fatty acid β-oxidation have been described (Chalmers et al 1997). Four of these affect the carnitine shuttle for the transport of long-chain fatty acids into the mitochondria, either intracellular uptake of carnitine or the enzymes carnitine palmityoltransferase (EC 2.3.1.21) (CPT) I and II (Pande et al 1993). Carnitine-acylcarnitine translocase is an inner mitochondrial membrane protein that is necessary for the entry of long-chain fatty acids (LCFA) into the mitochondrial matrix, transferring acylcarnitines across the inner mitochondrial membrane in exchange for free carnitine. Translocase deficiency presents either in the neonatal period with hypoketotic hypoglycaemia, hyperammonaemia and cardiac arrhythmia (Pande et al 1993), with cardiomyopathy, or as isolated hyperammonaemia with intracardiac conduction defects but with no hypoglycaemia (Ogier de Baulney et al 1995). It may cause sudden infant death (Brivet et al 1996; Chalmers et al 1997). To our knowledge, 11 cases of carnitine-acylcarnitine translocase deficiency are described in the literature. We describe the twelfth case with neonatal apnoeic attacks, nystagmus and hyperammonaemia.

WB Geven,a KE Niezen-Koning,b A Timmer,c AJ van Loon,d RJA Wanders,e FJ van Spronsenf a Department of Pediatrics, Martini Hospital, Groningen, the Netherlands b Laboratory for Metabolic Diseases and cDepartment of Pathology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands, d Department of Obstetrics, Martini Hospital, Groningen, the Netherlands e Department of Clinical Chemistry and Genetic Metabolic Diseases, Academic Medical Center, Amsterdam, the Netherlands f Department of Pediatrics, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands Correspondence: Dr WB Geven, Department of Pediatrics, Martini Hospital, PO Box 30033,9700 RM Groningen, the Netherlands. Email w.b.geven@MZH.nl

M. HUIZING1, U. WENDEL2, W. RUITENBEEK1*, V. IACOBAZZI3, L. IJLST4, P. VEENHUIZEN1, P. SAVELKOUL1, L. P. VAN DEN HEUVEL1, J. A. M. SMEITINK1, R. J. A. WANDERS4, J. M. F. TRIJBELS1 and F. PALMIERI3 of 1University Hospital, Department Pediatrics, Nijmegen, T he Netherlands ; of of 2University Hospital, Department Pediatrics, DuŽ sseldorf, Germany ; 3University of of Bari, Department Pharmaco-Biology, Bari, Italy ; 4University Amsterdam, of Clinical Chemistry and Departments Pediatrics, Amsterdam, T he Netherlands

A breast-fed female infant died suddenly in the neonatal period at 31 hours of age with profound macrovesicular fatty infiltration of liver, kidney, and muscle on postmortem examination, suggestive of a defect in fatty acid β-oxidation. Fatty acid and palmitoylcarnitine oxidation studies and direct enzyme study of cultured skin fibroblasts suggested a deficiency in the oxidation of long-chain fatty acids distal to carnitine palmitoyltransferase I and before long-chain acyl–coenzyme A dehydrogenases. Deficient activity of carnitine-acylcarnitine translocase was demonstrated with intermediate levels of activity in the infant’s parents, consistent with autosomal recessive inheritance. Fatty acid oxidation studies showed deficient oxidation of fatty acids at all chain lengths from C 10:0 to C 24:0 , with partially reduced oxidation of C 26:0 fatty acid, indicating the occurrence of a single mitochondrial carnitine-acylcarnitine translocase and demonstrating the requirement in vivo for l -carnitine for mitochondrial transport of all medium- and long-chain fatty acyl moieties. The disorder may have been precipitated in this breast-fed infant by poor initial feeding, fasting stress, and the long-chain triglycerides of human milk. The severity of the disorder prompted prenatal diagnosis, and affected siblings were excluded in two subsequent pregnancies by fatty acid oxidation in cultured chorionic villus cells and amniocytes. (J Pediatr 1997;131:220-5)

Four steps are required for the transport of long-chain fatty acids (LCFA) into the mitochondrial matrix : a plasma membrane carnitine transporter maintains the intracellular supply of carnitine ; an outer mitochondrial membrane carnitine palmitoyltransferase I (CPT I) converts acyl-CoA compounds to their acylcarnitine analogues ; a carnitine-acylcarnitine translocase (CATR) mediates the transmembrane transfer of acylcarnitines ; an inner mitochondrial membrane carnitine palmitoyltransferase II (CPT II) allows the re-esterification of acylcarnitines to form acyl-CoA esters. Inherited metabolic diseases affecting CATR and CPT II are recognized as a contributing cause of life-threatening events in infancy. In these two disorders, long-chain acylcarnitines are not efficiently converted to their corresponding acyl-CoA esters, and prominent long-chain acylcarnitine species are seen in plasma. It has been speculated that increased concentrations of long-chain acylcarnitines may promote cardiac arrhythmia (Corr et al 1989). Tandem mass spectrometry has enabled quantitative analysis of acylcarnitines in small volumes of blood, including filter paper blood spots used for neonatal screening (Millington et al 1991). Determination of the acylcarnitine profile in the Guthrie card is particularly useful in case of sudden infant death when no other biological specimen had been preserved. The finding of abnormal accumulation of C 18 and C 16 species argues in favour of CATR or profound CPT II deficiency. However, the definitive diagnosis of these two disorders requires documentation of the specific enzymatic defect in cellular material. Both defects are transmitted as autosomal recessive traits. The enzymatic activities of obligate heterozygotes are approximately 50% of normal activity (Stanley et al 1992; Elpeleg et al 1993). Thus, enzymatic determinations in parents' cells can be used to establish the diagnosis.

Deficiency of the enzymes of mitochondrial fatty acid oxidation and related carnitine dependent steps have been shown to be one of the causes of the fasting-induced hypoketotic hypoglycemia. We describe here carnitine-acylcarnitine translocase deficiency in a neonate who died eight days after birth. The proband showed severe fasting-induced hypoketotic hypoglycemia, high plasma creatine kinase, heartbeat disorder, hypothermia, and hyperammonemia. The plasma-free carnitine on day three was only 3 microM, and 92% of the total carnitine (37 microM) was present as acylcarnitine. Treatments with intravenous glucose, carnitine, and medium-chain triglycerides had been tried without improvements. Measurements in fibroblasts confirmed deficient oxidation of palmitate and showed normal activities of the carnitine palmitoyltransferases I and II and of the three acyl-CoA dehydrogenases. A total deficiency of the carnitine-acyl-carnitine translocase was found in fibroblasts using the carnitine acetylation assay (1986. Biochem. J. 236:143-148). This assay has been further simplified by seeking conditions permitting application to permeabilized fibroblasts and lymphocytes.

MITOCHONDRIAL oxidation of fatty acids provides the chief source of energy during prolonged fasting as well as for cardiac muscle and skeletal muscle during exercise. In the past decade, 10 genetic defects of this pathway have been recognized in infants and children.1 2 3 4 5 6 7 Although each of these disorders is rare, failure to recognize them can deprive patients of lifesaving therapy. Patients with these defects present with coma after a period of starvation and have hypoketosis — that is, their serum ketone concentrations are low. They may also have cardiomyopathy and muscle weakness. Three of the disorders affect the carnitine cycle, illustrated . . .

Carnitine plays an essential role in the transfer of long-chain fatty acids across the inner mitochondrial membrane. This transfer requires enzymes and transporters that accumulate carnitine within the cell (OCTN2 carnitine transporter), conjugate it with long chain fatty acids (carnitine palmitoyl transferase 1, CPT1), transfer the acylcarnitine across the inner plasma membrane (carnitine-acylcarnitine translocase, CACT), and conjugate the fatty acid back to Coenzyme A for subsequent beta oxidation (carnitine palmitoyl transferase 2, CPT2). Deficiency of the OCTN2 carnitine transporter causes primary carnitine deficiency, characterized by increased losses of carnitine in the urine and decreased carnitine accumulation in tissues. Patients can present with hypoketotic hypoglycemia and hepatic encephalopathy, or with skeletal and cardiac myopathy. This disease responds to carnitine supplementation. Defects in the liver isoform of CPT1 present with recurrent attacks of fasting hypoketotic hypoglycemia. The heart and the muscle, which express a genetically distinct form of CPT1, are usually unaffected. These patients can have elevated levels of plasma carnitine. CACT deficiency presents in most cases in the neonatal period with hypoglycemia, hyperammonemia, and cardiomyopathy with arrhythmia leading to cardiac arrest. Plasma carnitine levels are extremely low. Deficiency of CPT2 present more frequently in adults with rhabdomyolysis triggered by prolonged exercise. More severe variants of CPT2 deficiency present in the neonatal period similarly to CACT deficiency associated or not with multiple congenital anomalies. Treatment for deficiency of CPT1, CPT2, and CACT consists in a low-fat diet supplemented with medium chain triglycerides that can be metabolized by mitochondria independently from carnitine, carnitine supplements, and avoidance of fasting and sustained exercise.

The enzyme carnitine-acylcarnitine translocase (CACT) is involved in the transport of long-chain fatty acids into mitochondria. CACT deficiency is a life-threatening, recessively inherited disorder of lipid beta-oxidation which manifests in early infancy with hypoketotic hypoglycemia, cardiomyopathy, liver failure, and muscle weakness. We report here the clinical, biochemical, and molecular features of six CACT-deficient patients from Italy, Spain, and North America who exhibited significant clinical heterogeneity. In five patients (Patients 1, 2, 4, 5, and 6) the disease manifested in the neonatal period, while the remaining patient (Patient 3), the younger sibling of an infant who had died with clinical suspicion of fatty acid oxidation defect, has been treated since birth and was clinically asymptomatic at 4.5 years of age. Patients 1 and 4 were deceased within 6 months from the onset of this study, while the remaining four are still alive at 8, 4.5, 3.5, and 2 years, respectively. Sequence analysis of the CACT gene (SLC25A20) disclosed five novel mutations and three previously reported mutations. Three patients were homozygous for the identified mutations. Two of the novel mutations (c.718+1G>C and c.843+4_843+50del) altered the donor splice site of introns 7 and 8, respectively. The 47-nt deletion in intron 8 caused both skipping of exon 8 only and skipping of exons 6-8. Four mutations [[c.159dupT;c.163delA] ([p.Gly54Trp;p.Thr55Ala]) c.397C>T (p.Arg133Trp), c.691G>C (p.Asp231His), and c.842C>T (p.Ala281Val)] resulted in amino acid substitutions affecting evolutionarily conserved regions of the protein. Interestingly, one of these exonic mutations (p.Ala281Val) was associated with a splicing defect also characterized by skipping of exons 6-8. The deleterious effect of the p.Arg133Trp substitution was demonstrated by measuring CACT activity upon expression of the normal and the mutant protein in E. coli and functional reconstitution into liposomes. Combined analysis of clinical, biochemical, and molecular data failed to indicate a correlation between the phenotype and the genotype.

Carnitine-acylcarnitine translocase deficiency: case report and review of the literature.Rubio-Gozalbo ME, Vos P, Forget PP, Van Der Meer SB, Wanders RJ, Waterham HR, Bakker JA.Departments of Pediatrics, University Hospital Maastricht, The Netherlands. mrub@groupwise.azm.nlAIM: Carnitine-acylcarnitine translocase (CACT) deficiency is an inborn error of metabolism involving the mitochondrial beta-oxidation of long-chain fatty acids. The aim of this study was to report on a new case (neonatal phenotype) and review the literature data on 24 previously reported cases. METHODS: Clinical data of the new case are described and compared with the previous reports. RESULTS: The patient with a novel mutation had clinical features and biochemical findings similar to those of the other reported patients. CONCLUSION: CACT is an entity in which clinical encephalopathy, hepatomegaly and arrythmias are common. Hyperammonaemia and elevation of creatine kinase seem to be constant findings as in other disorders of mitochondrial beta-oxidation of long-chain fatty acids. The mortality rate is very high.

This report describes three infants with genetic defects of carnitine-acylcarnitine translocase (CACT), an inner mitochondrial membrane carrier that is essential for long-chain fatty acid oxidation. Two of the patients were of European and Chinese origin; the third was from consanguineous Turkish parents. CACT activity was totally deficient in cultured skin fibroblasts from all three patients. Patient 1 was heterozygous for a paternal frameshift mutation (120 del T in exon 1) and a maternal lariat branch point mutation (-10 T --> G in intron 2). Patient 2 was heterozygous for the same lariat branch point (-10T --> G intron 2) mutation, derived from the father, and a maternal frameshift mutation (362 del G in exon 3). Patient 3 was homozygous for a frameshift mutation (306 del C in exon 3). All of the three frameshift mutations give rise to the same stop codon at amino acid residue 127 which is predicted to cause premature protein truncation. In addition, cDNA transcript analysis showed that these coding sequence mutations also increase the amount of aberrant mRNA splicing and exon skipping at distances up to 7.7 kb nucleotides from mutation sites. The data suggest that the stability of mRNA transcripts is decreased or the frequency of aberrant splicing is increased in the presence of CACT coding sequence mutations. These results confirm that CACT is the genetic locus of the recessive mutations responsible for the fatal defects of fatty acid metabolism previously associated with deficiency of translocase activity in these three cases.