Carnitine-acylcarnitine translocase deficiency with SLC25A20 c.199-10T>G variation is a rare condition, typically associated with severe neonatal outcomes. Recently, preimplantation genetic testing (PGT) has emerged as a screening test applicable to embryos produced through in vitro fertilization for genetic analysis before transfer. Thus, PGT allows for the identification and elimination of embryos carrying inherited genetic diseases. This case report aims to present data from PGT on intervention in the management of SLC25A20 c.199-10T>G variation, particularly in middle-income countries. A 26-year-old woman with a high-risk term pregnancy and a history of two sudden neonatal deaths underwent parental carrier testing, revealing heterozygous SLC25A20 c.199-10T>G variation in both parents. The subsequent pregnancy, identified as a homozygous for SLC25A20 c.199-10T>G mutation, was terminated at 20 weeks. The current pregnancy was successfully managed by in vitro fertilization-selective embryo transfer. Carnitine-acylcarnitine translocase deficiency owing to SLC25A20 c.199-10T>G variation can result in sudden neonatal collapse. Obstetricians should maintain a high index of suspicion in recurrent cases of unexplained early neonatal death. Parental carrier testing is crucial for prenatal management, and selective embryo transfer is a core treatment for heterozygous SLC25A20 gene carriers in this highly lethal disorder.

Disruption of acylcarnitine homeostasis results in life-threatening outcomes in humans. Carnitine-acylcarnitine translocase deficiency (CACTD) is a scarce autosomal recessive genetic disease and may result in patients' death due to heart arrest or respiratory insufficiency. However, the reasons and mechanism of CACTD inducing respiratory insufficiency have never been elucidated. Herein, we employed lipidomic techniques to create comprehensive lipidomic maps of entire lungs throughout both prenatal and postnatal developmental stages in mice. We found that the acylcarnitines manifested notable variations and coordinated the expression levels of carnitine-acylcarnitine translocase (Cact) across these lung developmental stages. Cact-null mice were all dead with a symptom of respiratory distress and exhibited failed lung development. Loss of Cact resulted in an accumulation of palmitoyl-carnitine (C16-acylcarnitine) in the lungs and promoted the proliferation of mesenchymal progenitor cells. Mesenchymal cells with elevated C16-acylcarnitine levels displayed minimal changes in energy metabolism but, upon investigation, revealed an interaction with sterile alpha motif domain and histidine-aspartate domain-containing protein 1 (Samhd1), leading to decreased protein abundance and enhanced cell proliferation. Thus, our findings present a mechanism addressing respiratory distress in CACTD, offering a valuable reference point for both the elucidation of pathogenesis and the exploration of treatment strategies for neonatal respiratory distress.

Carnitine-acylcarnitine translocase deficiency (CACTD) is a rare autosomal recessive fatty acid oxidation disorder resulting in energy deficiency due to impaired mitochondrial long-chain fatty acid transport. Hyperammonemia is a critical complication, often resistant to conventional treatment. Here, we report the case of a 7-month-old patient with CACTD, initially diagnosed at 10 days old, who presented with persistent hyperammonemia despite optimized medical nutrition therapy and conventional nitrogen scavenging with sodium benzoate. When hyperammonemia persisted, carglumic acid was introduced, leading to a sustained decrease in ammonia levels and effective long-term control. Carglumic acid, typically indicated for organic acidemias, proved beneficial in this CACTD case. The administration of carglumic acid not only provided acute resolution but also stabilized ammonia levels over prolonged follow-up. This case highlights carglumic acid as a potential therapeutic option for managing hyperammonemia in CACTD, underscoring the need for further studies to confirm its efficacy in long-term management of hyperammonemia in fatty acid oxidation disorders.

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. 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. 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. 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.

The SLC25A20 gene encodes carnitine-acylcarnitine translocase (CACT), facilitating the transport of long-chain acylcarnitine required for energy production via β-oxidation into the mitochondria. Loss-of-function mutations in this gene lead to CACT deficiency, a rare autosomal recessive disorder of fatty acid metabolism characterized by severe symptoms including cardiomyopathy, hepatic dysfunction, rhabdomyolysis, hypoketotic hypoglycemia, and hyperammonemia, often resulting in neonatal mortality. Here, we utilized CRISPR/Cas9 gene editing to isolate slc25a20 mutant zebrafish. Homozygous mutants displayed significant lethality, with the majority succumbing before reaching maturity. However, we identified a notably rare homozygous individual that survived into adulthood, prompting a histological examination. Firstly, we observed adipose tissue accumulation at various sites in the homozygous mutant. The mutant heart exhibited hypertrophy, along with degenerated myocardial and muscle cells containing numerous eosinophilic nuclei. Additionally, we found no large oil droplet vacuoles in the mutant liver; however, the hepatocytes displayed numerous small vacuoles resembling lipid droplets. Iron deposition was evident in the spleen and parts of the liver. Overall, our slc25a20 zebrafish mutant displayed tissue pathologies analogous to human CACT deficiency, suggesting its potential as a pathological model contributing to the elucidation of pathogenesis and the improvement/development of therapies for CACT deficiency.