Three novel mutations in the carnitine-acylcarnitine translocase (CACT) gene in patients with CACT deficiency and in healthy individuals

Loss-of-function SLC25A20 variant causes carnitine-acylcarnitine translocase deficiency by reducing SLC25A20 protein stability

BACKGROUND/AIM

Autosomal-recessive carnitine-acylcarnitine translocase deficiency (CACTD) is a rare disorder of long-chain fatty acid oxidation caused by variants in the SLC25A20 gene, leading to energy deficiency and the toxic accumulation of long-chain acylcarnitines. Under fasting conditions, most newborns with severe CACTD experience sudden cardiac arrest and hypotonia, often leading to premature death due to rapid disease progression. The genetic factors and pathogenic mechanisms in CACTD are essential for its diagnosis, treatment, and prevention.

METHODS

Whole-exome sequencing was carried out on the CACTD patients. Bioinformatics analysis predicted the pathogenicity and three-dimensional structure of SLC25A20. Quantitative PCR was employed to detect changes in SLC25A20, CPT1A and CPT2 mRNA levels. The expression and stability of the variant protein were assessed via Western blot. Additionally, the subcellular localization of the variant protein was observed using immunofluorescence.

RESULTS

We identified compound heterozygous pathogenic variants of SLC25A20 (c.476 T > C and c.199-10 T > G) in CACTD families, with patients exhibiting an abnormal carnitine spectrum. In vitro functional studies demonstrated that the c.476 T > C and c.199-10 T > G variants decreased the protein stability of SLC25A20, reduced CPT1A and CPT2 mRNA expression, and caused protein aggregation of SLC25A20.

CONCLUSIONS

We propose that the decreased stability of the SLC25A20 variants c.476 T > C and c.199-10 T > G has the potential to lead to the development of CACTD by affecting the mitochondrial shuttle of acylcarnitine and carnitine, thereby inhibiting the β-oxidation pathway. Therefore, we believe these compound heterozygous variants (c.199-10 T > G and c.476 T > C) are loss-of-function variants. Our findings provide valuable data on CACTD pathogenesis and genotype-phenotype correlations.

Carnitine-Acylcarnitine Translocase Deficiency Masked by Extreme Prematurity

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.

Carnitine-acylcarnitine translocase deficiency caused by SLC25A20 gene heterozygous variants in twins: a case report

The current case report describes the clinical, biochemical and genetic characteristics of carnitine-acylcarnitine translocase deficiency (CACTD) in infant male and female twins that presented with symptoms shortly after elective caesarean delivery. The clinical manifestations were neonatal hypoglycaemia, arrhythmia and sudden death. The age of onset was 1.5 days and the age of the death was 1.5-3.5 days. Dried blood filter paper analysis was used for the detection of acylcarnitine. Peripheral venous blood and skin samples were used for next-generation sequencing. The twins and their parents underwent gene analysis and whole exome sequencing analyses of the solute carrier family 25 member 20 (SLC25A20; also known as carnitine-acylcarnitine translocase) gene. Both infants carried compound heterozygous variants of the SLC25A20 gene: variant M1:c.706_707insT:p.R236L fs*12 and variant M2:c.689C>G:p.P230R. The M1 variant was paternal and had not been previously reported regarding CACTD. The M2 variant was maternal. CACTD has severe clinical manifestations and a poor prognosis, which is manifested as hypoketotic hypoglycaemia, hyperammonaemia, liver function damage and elevated creatine kinase.

Carnitine-acylcarnitine Translocase Deficiency with c.199-10T>G Mutation in Two Filipino Neonates Detected through Parental Carrier Testing

Carnitine-acylcarnitine translocase deficiency (CACTD), a fatty acid oxidation defect (FAOD), can present in the neonatal period with non-specific findings and hypoglycemia. A high index of suspicion is needed to recognize the disorder. The case is of a 24-year-old G2P2(2000) mother who sought consultation for recurrent neonatal deaths. The neonates, born two years apart, were apparently well at birth but had a fair cry and no spontaneous eye opening within the first 24 h of life and died before the 72nd hour of life. Newborn screening of both babies revealed elevated long chain acylcarnitines and hypocarnitinemia suggestive of a FAOD. However, due to their early demise, no confirmatory tests were done. Parental carrier testing was performed, revealing both parents to be heterozygous carriers of a pathogenic variant, c.199 10T>G (intronic), in the SLC25A20 gene associated with autosomal recessive CACTD. This is the first reported case of CACTD in the Filipino population.

PRSS37 deficiency leads to impaired energy metabolism in testis and sperm revealed by DIA-based quantitative proteomic analysis

Our previous studies have reported that a putative trypsin-like serine protease, PRSS37, is exclusively expressed in testicular germ cells during late spermatogenesis and essential for sperm migration from the uterus into the oviduct and sperm-egg recognition via mediating the interaction between PDILT and ADAM3. In the present study, the global proteome profiles of wild-type (wt) and Prss37^-/- mice in testis and sperm were compared employing data independent acquisition (DIA) technology. Overall, 2506 and 459 differentially expressed proteins (DEPs) were identified in Prss37-null testis and sperm, respectively, when compared to control groups. Bioinformatic analyses revealed that most of DEPs were related to energy metabolism. Of note, the DEPs associated with pathways for the catabolism such as glucose via glycolysis, fatty acids via β-oxidation, and amino acids via oxidative deamination were significantly down-regulated. Meanwhile, the DEPs involved in the tricarboxylic acid cycle (TCA cycle) and oxidative phosphorylation (OXPHOS) were remarkably decreased. The DIA data were further confirmed by a markedly reduction of intermediate metabolites (citrate and fumarate) in TCA cycle and terminal metabolite (ATP) in OXPHOS system after disruption of PRSS37. These outcomes not only provide a more comprehensive understanding of the male fertility of energy metabolism modulated by PRSS37 but also furnish a dynamic proteomic resource for further reproductive biology studies.

One potential hotspot SLC25A20 gene variants in Chinese patients with carnitine-acylcarnitine translocase deficiency

BACKGROUND

Carnitine-acylcarnitine translocase deficiency (CACT deficiency) is a rare and life-threatening autosomal recessive disorder of mitochondrial fatty acid oxidation caused by variant of SLC25A20 gene. The most prevalent missense variant in the SLC25A20 gene in Asia was c.199-10T > G. Due to the c.199-10T > G variant, CACT deficiency is a severe phenotype.

MATERIALS AND METHODS

Herein, we present a neonatal case with c.199-10T > G variant in China and analyze the clinical, biochemical, and genetic aspects of 78 patients previously identified with CACT deficiency.

RESULTS

The patient presented with a series of severe metabolic crises that rapidly deteriorated and eventually died 3 days after delivery. The sequencing of the patient's genome indicated that he was homozygous for the c.199-10T > G variant. 30 patients were found to have the c.199-10T > G mutation, of which 23 were Chinese and 22 were afflicted by the c.199-10T > G splicing variation. In China, c.199-10T > G allele frequency was 82.6%.

CONCLUSION

In CACT deficiency, prompt recognition and treatment are critical. Our data suggested that c.199-10T > G may be a potential hotspot SLC25A20 gene mutation in the Chinese population. Detection of single nucleotide polymorphism is possible for high-risk patients and parents in China.

Neonatal sudden death caused by a novel heterozygous mutation in SLC25A20 gene: A case report and brief literature review

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.

New insights into carnitine-acylcarnitine translocase deficiency from 23 cases: Management challenges and potential therapeutic approaches

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 2 days of life, with hypoketotic hypoglycaemia, hyperammonaemia, cardiomyopathy or arrhythmia, hepatomegaly and elevated liver enzymes. Multi-centre international retrospective chart review of clinical presentation, biochemistry, treatment modalities including diet, subsequent complications, and mode of death of all patients. Twenty-three patients from nine tertiary metabolic units were identified. Seven attenuated patients of Pakistani heritage, six of these homozygous c.82G>T, had later onset manifestations and long-term survival without chronic hyperammonemia. Of the 16 classical cases, 15 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 utilising therapeutic d,l-3-hydroxybutyrate, Triheptanoin and increased protein intake, appeared to improve chronic hyperammonemia and metabolic stability where trialled in individual cases. 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.

Metabolic flexibility via mitochondrial BCAA carrier SLC25A44 is required for optimal fever

Importing necessary metabolites into the mitochondrial matrix is a crucial step of fuel choice during stress adaptation. Branched chain-amino acids (BCAAs) are essential amino acids needed for anabolic processes, but they are also imported into the mitochondria for catabolic reactions. What controls the distinct subcellular BCAA utilization during stress adaptation is insufficiently understood. The present study reports the role of SLC25A44, a recently identified mitochondrial BCAA carrier (MBC), in the regulation of mitochondrial BCAA catabolism and adaptive response to fever in rodents. We found that mitochondrial BCAA oxidation in brown adipose tissue (BAT) is significantly enhanced during fever in response to the pyrogenic mediator prostaglandin E₂ (PGE₂) and psychological stress in mice and rats. Genetic deletion of MBC in a BAT-specific manner blunts mitochondrial BCAA oxidation and non-shivering thermogenesis following intracerebroventricular PGE₂ administration. At a cellular level, MBC is required for mitochondrial BCAA deamination as well as the synthesis of mitochondrial amino acids and TCA intermediates. Together, these results illuminate the role of MBC as a determinant of metabolic flexibility to mitochondrial BCAA catabolism and optimal febrile responses. This study also offers an opportunity to control fever by rewiring the subcellular BCAA fate.

Computational studies of the mitochondrial carrier family SLC25. Present status and future perspectives

The members of the mitochondrial carrier family, also known as solute carrier family 25 (SLC25), are transmembrane proteins involved in the translocation of a plethora of small molecules between the mitochondrial intermembrane space and the matrix. These transporters are characterized by three homologous domains structure and a transport mechanism that involves the transition between different conformations. Mutations in regions critical for these transporters’ function often cause several diseases, given the crucial role of these proteins in the mitochondrial homeostasis. Experimental studies can be problematic in the case of membrane proteins, in particular concerning the characterization of the structure–function relationships. For this reason, computational methods are often applied in order to develop new hypotheses or to support/explain experimental evidence. Here the computational analyses carried out on the SLC25 members are reviewed, describing the main techniques used and the outcome in terms of improved knowledge of the transport mechanism. Potential future applications on this protein family of more recent and advanced in silico methods are also suggested.

Late-Onset Carnitine-Acylcarnitine Translocase Deficiency With SLC25A20 c.199-10T>G Variation: Case Report and Pathologic Analysis of Liver Biopsy

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.

Carnitine-acylcarnitine translocase deficiency with c.199-10 T>G and novel c.1A>G mutation: Two case reports and brief literature review

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: Two neonatal cases with common splicing mutation and in vitro bezafibrate response

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 deficiency: experience with four cases in Spain and review of the literature

BACKGROUND

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.

METHODS

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.

RESULTS

Two cases with neonatal onset, carrying in homozygosity the novel variant sequences p.Gly20Asp (c.59G>A) and p.Arg179Gly (c.536A>G), 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.

CONCLUSION

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.