Adult-onset citrullinemia type II (CTLN2) is a rare autosomal recessive urea cycle disorder caused by mutations in the solute carrier family 25 member 13 (SLC25A13) gene, which encodes citrin-a mitochondrial transporter involved in the malate-aspartate shuttle. In adults, CTLN2 may present atypically as isolated hypertriglyceridemia, often misattributed to secondary dyslipidaemia. A 30-year-old Vietnamese male with longstanding severe hypertriglyceridemia, first identified at age 13, was referred after an episode of acute pancreatitis at age 28. At presentation, plasma triglyceride levels reached 34.61 mmol/l. Secondary causes were excluded. Genetic testing via next-generation sequencing revealed compound heterozygous SLC25A13 mutations: c.2T>C and c.1638_1660dup, resulting in p.Met1Thr and p.Ala554GlyfsTer17, confirming the diagnosis of CTLN2. Initiation of a low-carbohydrate, high-protein, low-fat diet combined with fenofibrate (145 mg/day) led to a rapid reduction in triglyceride levels, normalizing within two weeks and remaining stable over three months. The treatment was well tolerated, with no reported adverse effects. CTLN2 should be considered in young adults with persistent, unexplained, and severe hypertriglyceridemia. Dietary modification constitutes the cornerstone of management, with fibrates playing a supportive role. Persistent, unexplained, and severe hypertriglyceridemia in young adults should prompt consideration of inherited metabolic disorders, including adult-onset citrullinemia type II (CTLN2).Genetic testing to detect compound heterozygous or homozygous SLC25A13 variants is essential for definitive diagnosis of CTLN2.In CTLN2, dietary management with a low-carbohydrate, high-protein, low-fat represents the cornerstone, with fibrates serving as adjunctive lipid-lowering therapy.

Downregulation of the urea cycle enzyme argininosuccinate synthase (ASS1) in multiple tumors is associated with a poor prognosis partly because of the metabolic diversion of cytosolic aspartate for pyrimidine synthesis, supporting proliferation and mutagenesis owing to nucleotide imbalance. Here, we find that prolonged loss of ASS1 promotes DNA damage in colon cancer cells and fibroblasts from subjects with citrullinemia type I. Following acute induction of DNA damage with doxorubicin, ASS1 expression is elevated in the cytosol and the nucleus with at least a partial dependency on p53; ASS1 metabolically restrains cell cycle progression in the cytosol by restricting nucleotide synthesis. In the nucleus, ASS1 and ASL generate fumarate for the succination of SMARCC1, destabilizing the chromatin-remodeling complex SMARCC1-SNF5 to decrease gene transcription, specifically in a subset of the p53-regulated cell cycle genes. Thus, following DNA damage, ASS1 is part of the p53 network that pauses cell cycle progression, enabling genome maintenance and survival. Loss of ASS1 contributes to DNA damage and promotes cell cycle progression, likely contributing to cancer mutagenesis and, hence, adaptability potential.

Hyperammonemia is a serious metabolic condition marked by elevated ammonia levels in the blood, leading to neurological damage and systemic complications if untreated. While often associated with liver dysfunction, inborn metabolic errors such as fatty acid oxidation defects, pyruvate metabolism disorders, urea cycle disorders (UCDs), urea splitting bacterial infections, hemato-oncological disorders, and portosystemic shunts are less commonly recognized but significant causes, particularly outside neonatal populations. These metabolic errors, due to partial enzyme deficiencies, may present later in life with atypical symptoms. We report an acute presentation of a female patient in her late fifties with a background of noncirrhotic hyperammonemia of unknown etiology, controlled with oral sodium benzoate. She presented with ataxia, altered mental status, and delusion. The laboratory evaluation revealed significantly elevated ammonia levels, which did not respond to an increased dose of oral sodium benzoate, and she required intravenous ammonia scavengers to achieve acceptable levels. We further discuss several investigations done to establish a cause for her hyperammonemia and a psychiatric diagnosis of erotomania/de Clerambault's syndrome secondary to recurrent hyperammonemia. Although her biochemical workup had some features suggestive of type 2 citrulline deficiency, SLC25A13 mutation analysis for citrin deficiency and an extended R98 panel were negative. Thus, highlighting the complexity of diagnosis of inborn metabolic errors and treatment of metabolic hyperammonemia in the absence of an established diagnosis. It also emphasizes the need for heightened awareness and prompt treatment of inborn metabolic errors in adult patients, following the British Inherited Metabolic Disease Group (BIMDG) management guidelines to prevent severe neurological outcomes. Multidisciplinary management, including liaison with specialists in metabolics, gastroenterology, and dietetics, is crucial for optimizing patient care and outcomes in such complex cases.

Citrullinemia type I is a rare autosomal-recessive disorder caused by deficiency of argininosuccinate synthetase (ASS1). The clinical presentation includes the acute neonatal form, characterized by ammonia and citrulline accumulation in blood, which may lead to encephalopathy, coma, and death, and the milder late-onset form. Current treatments are unsatisfactory, and the only curative treatment is liver transplantation. We permanently modified the hepatocyte genome in lethal citrullinemia mice (Ass1fold/fold) by inserting the ASS1 cDNA into the albumin locus through the delivery of two AAV8 vectors carrying the donor DNA and the CRISPR-Cas9 platform. The neonatal treatment completely rescued mortality ensuring survival up to 5 months of age, with plasma citrulline levels significantly decreased, while plasma ammonia levels remained unchanged. In contrast, neonatal treatment with a liver-directed non-integrative AAV8-AAT-hASS1 vector failed to improve disease parameters. To model late-onset citrullinemia, we dosed postnatal day (P) 30 juvenile animals using the integrative approach, resulting in lifespan improvement and a minor reduction in disease markers. Conversely, treatment with the non-integrative vector completely rescued mortality, reducing plasma ammonia and citrulline to wild-type values. In summary, the integrative approach in neonates is effective, although further improvements are required to fully correct the phenotype. Non-integrative gene therapy application to juvenile mice ensures a stable and very efficient therapeutic effect.

To find biochemical and molecular markers can assist in identifying serious liver damage of neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) patients. 138 patients under 13 days to 1.1 year old diagnosed of NICCD in our center from 2004 to 2020. Base on the abnormal liver laboratory tests, we divided 138 patients into three groups: acute liver failure (ALF), liver dysfunction, and non-liver dysfunction groups, then compared their clinical, biochemical and, molecular data. 96 % of 138 patients had high levels of citrulline and high ratio of threonine to serine, which is the distinctive feature of plasma amino acid profile for NICCD. A total of 18.1 % of 138 patients had evidence of ALF who presented the most severity hepatic damage, 51.5 % had liver dysfunction, and the remaining 30.4 % presented mild clinical symptoms (non-liver dysfunction). In ALF group, the levels of citrulline, tyrosine, TBIL, ALP, and γ-GT was significantly elevated, and the level of ALB and Fisher ratio was pronounced low. Homozygous mutations of 1,638_1660dup, IVS6+5G.A, or IVS16ins3kb in SLC25A13 gene were only found in ALF and liver dysfunction groups. Supportive treatment including medium-chain triglyceride supplemented diet and fresh frozen plasma could be life-saving and might reverse ALF. High level of citrulline, tyrosine, TBIL, ALP, γ-GT, and ammonia, low level of albumin, and low Fisher ratio were predictors to suggest severe liver damage in NICCD patients who may go on to develop fatal metabolic disorder. Early identification and proper therapy is particularly important for these patients.