RARE DISEASE
Citrullinemia type II
Citrullinemia type II
Citrullinemia type II
Synonyms: Adult-onset citrin deficiency, Adult-onset citrullinemia type 2, Adult-onset citrullinemia type II, CTLN2, Citrullinemia type 2
Synonyms: Adult-onset citrin deficiency, Adult-onset citrullinemia type 2, Adult-onset citrullinemia type II, CTLN2, Citrullinemia type 2
Synonyms: Adult-onset citrin deficiency, Adult-onset citrullinemia type 2, Adult-onset citrullinemia type II, CTLN2, Citrullinemia type 2
Drug discovery
2
drugs
With orphan designations
Overview
Citrullinemia type II (CTLN2) is an autosomal recessive urea cycle disorder caused by SLC25A13 mutations, leading to citrin deficiency. It primarily manifests in adulthood with hyperammonemia, neuropsychiatric symptoms (delirium, seizures), and liver dysfunction. Neonatal presentations (NICCD) include cholestasis and failure to thrive. Triggers include high-carbohydrate diets, alcohol, or fasting. Biochemical hallmarks include elevated citrulline (20× normal) and mild-moderate hyperammonemia, with normal-to-high arginine levels [1][3][13].
Categories: rare genetic diseases, rare hepatic diseases, rare inborn errors of metabolism
Research Papers
113 drug discovery papers about Citrullinemia type II, with 1 first-in-class and 1 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
113 drug discovery papers about Citrullinemia type II, with 1 first-in-class and 1 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
gene therapies
2023-03-16 | Exogenous aralar/slc25a12 can replace citrin/slc25a13 as malate aspartate shuttle component in liver
The deficiency of CITRIN, the liver mitochondrial aspartate–glutamate carrier (AGC), is the cause of four human clinical phenotypes, neonatal intrahepatic cholestasis caused by CITRIN deficiency (NICCD), silent period, failure to thrive and dyslipidemia caused by CITRIN deficiency (FTTDCD), and citrullinemia type II (CTLN2). Clinical symptoms can be traced back to disruption of the malate-aspartate shuttle due to the lack of citrin. A potential therapy for this condition is the expression of aralar, the AGC present in brain, to replace citrin. To explore this possibility we have first verified that the NADH/NAD+ ratio increases in hepatocytes from citrin(−/−) mice, and then found that exogenous aralar expression reversed the increase in NADH/NAD+ observed in these cells. Liver mitochondria from citrin (−/−) mice expressing liver specific transgenic aralar had a small (~ 4–6 nmoles x mg prot−1 x min−1) but consistent increase in malate aspartate shuttle (MAS) activity over that of citrin(−/−) mice. These results support the functional replacement between AGCs in the liver. To explore the significance of AGC replacement in human therapy we studied the relative levels of citrin and aralar in mouse and human liver through absolute quantification proteomics. We report that mouse liver has relatively high aralar levels (citrin/aralar molar ratio of 7.8), whereas human liver is virtually devoid of aralar (CITRIN/ARALAR ratio of 397). This large difference in endogenous aralar levels partly explains the high residual MAS activity in liver of citrin(−/−) mice and why they fail to recapitulate the human disease, but supports the benefit of increasing aralar expression to improve the redox balance capacity of human liver, as an effective therapy for CITRIN deficiency.
2001-01-01 | Long-term correction of urea cycle disorders
Long-term correction of urea cycle disorders is achieved by correction of the enzymatic defect in hepatocytes. Currently, orthotopic liver transplantation is the primary means of achieving this correction. In the United States most liver transplantations for urea cycle disorders have been restricted to patients with ornithine transcarbamylase deficiency and argininosuccinic aciduria. However, patients with citrullinemia have also received transplants, but more so in Europe and Japan. Recent advances in organ procurement, surgical technique, and immunosuppression have significantly decreased morbidity and mortality. However, unique short-term complications associated with surgery and long-term complications associated with chronic immunosuppression have spurred continued efforts to develop gene replacement therapies for management of acute metabolic decompensations as intercurrent therapy until liver transplantation, and ultimately, for long-term correction. The pathophysiology of urea cycle disorders requires gene vector delivery systems that are highly efficient for liver transduction and transgene expression. To date, adenoviral vectors are unique in fulfilling these criteria, and significant data have been gained in both animal and human studies with early versions of adenoviral vectors. Ultimately, the development of helper-dependent adenoviral vectors may offer the long-term expression and increased margin of safety necessary for adjunctive therapies. (J Pediatr 2001;138:S62-S71)
2000-10-01 | Correction of argininosuccinate synthetase (AS) deficiency in a murine model of citrullinemia with recombinant adenovirus carrying human AS cDNA
Citrullinemia is an autosomal recessive disorder caused by the deficiency of argininosuccinate synthetase (AS). It is characterized by elevated levels of blood citrulline and ammonia, which often results in hyperammonemic coma and early neonatal death in affected children. We have explored the use of adenoviral vectors as a treatment modality in a murine model of citrullinemia, the Ass mouse. The Ass mouse has no endogenous AS activity due to a targeted interruption of the AS gene. Homozygous mutant animals develop high levels of blood citrulline, become hyperammonemic, and die within 24–48 h after birth. We demonstrated that the neonatal crisis in Ass mice can be ameliorated by the injection of a recombinant adenovirus carrying human AS cDNA (Ad.CMVhAS) within hours after birth. The average life span of the virus-treated animals was extended from 30 ± 9.5 h to 16.1 ± 1.6 days. A second viral infusion 14 days after the first dose further prolonged the life span to an average of 36.2 ± 7.0 days, and to 40.7 ± 3.3 days with a concurrent daily injection of arginine and sodium benzoate. Significantly increased liver AS activity (47.3 ± 7.9% of normal) was detected 24 h after viral infusion, which reached peak levels (80–90% of normal) at day 7 and decreased to about 20% of normal within 2–3 weeks after viral infusion. Southern blot analysis of liver DNA revealed a transduction efficiency of about one viral genome per hepatocyte 7 days after viral infusion and a gradual decrease of viral genome per cell parallel to the loss of liver AS activity. Plasma glutamine levels were partially normalized in virus-treated animals and were completely normalized in animals receiving Ad.CMVhAS concurrently with alternative pathway therapy. Plasma arginine levels were also partially normalized. Together, these results demonstrated that the recombinant adenovirus was capable of conferring AS activity in the liver of the recipient animals within 24 h, and the neonatal crisis of hyperammonemia could be averted by acute treatment with the AS containing adenovirus.
1999-03-30 | Hepatocyte gene therapy in a large animal: A neonatal bovine model of citrullinemia
The development of gene-replacement therapy for inborn errors of metabolism has been hindered by the limited number of suitable large-animal models of these diseases and by inadequate methods of assessing the efficacy of treatment. Such methods should provide sensitive detection of expression in vivo and should be unaffected by concurrent pharmacologic and dietary regimens. We present the results of studies in a neonatal bovine model of citrullinemia, an inborn error of urea-cycle metabolism characterized by deficiency of argininosuccinate synthetase and consequent life-threatening hyperammonemia. Measurements of the flux of nitrogen from orally administered 15 NH 4 to [ 15 N]urea were used to determine urea-cycle activity in vivo . In control animals, these isotopic measurements proved to be unaffected by pharmacologic treatments. Systemic administration of a first-generation E1 -deleted adenoviral vector expressing human argininosuccinate synthetase resulted in transduction of hepatocytes and partial correction of the enzyme defect. The isotopic method showed significant restoration of urea synthesis. Moreover, the calves showed clinical improvement and normalization of plasma glutamine levels after treatment. The results show the clinical efficacy of treating a large-animal model of an inborn error of hepatocyte metabolism in conjunction with a method for sensitively measuring correction in vivo . These studies will be applicable to human trials of the treatment of this disorder and other related urea-cycle disorders.
1998-05-01 | Metabolic engineering as therapy for inborn errors of metabolism – development of mice with phenylalanine hydroxylase expression in muscle
Treatment of many inherited liver enzyme deficiencies requires the removal of toxic intermediate metabolites from the blood of affected individuals. We propose that circulating toxins can be adequately cleared and disease phenotype influenced by enzyme expressed in tissues other than the liver. Phenylalanine hydroxylase (PAH) activity was constitutively expressed in skeletal and cardiac muscle of transgenic mice which carried the PAH cDNA under the transcriptional control of the mouse muscle creatine kinase promoter. Muscle PAH-expressing mice were bred to liver PAH-deficient, hyperphenylalaninemic mice to yield progeny that lack PAH activity in liver but express PAH in muscle. These mice exhibited hyperphenylalaninemia at baseline, but serum phenylalanine levels decreased significantly when the mice were supplemented with tetrahydrobiopterin (BH4), a required cofactor for PAH. This is the first demonstration that a liver-specific enzyme, when expressed in a heterologous tissue and supplied with necessary cofactors, can effectively clear toxic metabolites from the circulation of individuals with inherited enzyme deficiency. This result suggests that gene therapy targeted to heterologous tissues, such as muscle, will be effective in the treatment of selected inborn errors of metabolism.
small molecules
2026-04-02 | Development of a quantitative real-time PCR-based newborn screening system for citrin deficiency using dried blood spots.
Citrin deficiency is an autosomal recessive metabolic disorder caused by pathogenic variants in SLC25A13, which manifests as an age-dependent spectrum ranging from neonatal intrahepatic cholestasis (NICCD) to adolescent and adult citrin deficiency (AACD, formerly CTLN2). Early detection through newborn screening (NBS) would be a prerequisite for early treatment, but conventional NBS based on citrulline and other metabolite levels has only limited sensitivity. This study aimed to develop a simple and accurate quantitative real-time PCR (qPCR)-based newborn screening (NBS) method using dried blood spots (DBSs) as a first-tier screening test to detect the six most common SLC25A13 variants in Japan. DBS samples from 1055 healthy newborns and 19 patients with confirmed variants were analyzed. Four variants (c.674C > A, c.852_855delTATG, c.1177 + 1G > A, and c.1311 + 1G > A) were screened using the TaqMan™ SNP genotyping system, and two large insertion/deletion variants (c.1638_1660dup and c.1750_1751[insNM_138459.3:2672_24;1750 + 72_1751-4dup]) were screened using a SYBR™ Green-based qPCR system with variant-specific primers. Results of qPCR were confirmed by Sanger sequencing. In all 19 known patients with citrin deficiency, the assay correctly identified the pathogenic alleles. Among 1055 newborns, heterozygous variants were detected in 19 cases (five c.852_855delTATG, thirteen c.1177 + 1G > A, and one c.1311 + 1G > A). The overall allele frequency (0.0090) was consistent with that reported in the Japanese genome database (jMorp, 0.0102), corresponding to an estimated carrier frequency of approximately 1 in 56 individuals. The assay reliably distinguished wild-type, heterozygous, and homozygous genotypes using a single DBS punch. We established a cost-effective, rapid, and reliable qPCR-based NBS system that detects the six most prevalent SLC25A13 variants using DBSs. This method is compatible with current NBS workflows and could improve early detection and intervention for citrin deficiency in Japan and, with adaptation of the target variants, in any other (not only) East Asian population.
2024-07-18 | The therapeutic landscape of citrin deficiency.
Citrin deficiency (CD) is a recessive, liver disease caused by sequence variants in the SLC25A13 gene encoding a mitochondrial aspartate-glutamate transporter. CD manifests as different age-dependent phenotypes and affects crucial hepatic metabolic pathways including malate-aspartate-shuttle, glycolysis, gluconeogenesis, de novo lipogenesis and the tricarboxylic acid and urea cycles. Although the exact pathophysiology of CD remains unclear, impaired use of glucose and fatty acids as energy sources due to NADH shuttle defects and PPARα downregulation, respectively, indicates evident energy deficit in CD hepatocytes. The present review summarizes current trends on available and potential treatments for CD. Baseline recommendation for CD patients is dietary management, often already present as a self-selected food preference, that includes protein and fat-rich food, and avoidance of excess carbohydrates. At present, liver transplantation remains the sole curative option for severe CD cases. Our extensive literature review indicated medium-chain triglycerides (MCT) as the most widely used CD treatment in all age groups. MCT can effectively improve symptoms across disease phenotypes by rapidly supplying energy to the liver, restoring redox balance and inducing lipogenesis. In contrast, sodium pyruvate restored glycolysis and displayed initial preclinical promise, with however limited efficacy in adult CD patients. Ursodeoxycholic acid, nitrogen scavengers and L-arginine treatments effectively address specific pathophysiological aspects such as cholestasis and hyperammonemia and are commonly administered in combination with other drugs. Finally, future possibilities including restoring redox balance, amino acid supplementation, enhancing bioenergetics, improving ureagenesis and mRNA/DNA-based gene therapy are also discussed.
2024-07-16 | Pathogenesis and Management of Citrin Deficiency.
Citrin deficiency (CD) is a hereditary disorder caused by SLC25A13 mutations that manifests as neonatal intrahepatic cholestasis caused by CD (NICCD), failure to thrive and dyslipidemia caused by CD (FTTDCD), and adult-onset type 2 citrullinemia (CTLN2). Citrin, an aspartate-glutamate carrier primarily expressed in the liver, is a component of the malate-aspartate shuttle, which is essential for glycolysis. Citrin-deficient hepatocytes have primary defects in glycolysis and de novo lipogenesis and exhibit secondarily downregulated PPARα, leading to impaired β-oxidation. They are unable to utilize glucose and free fatty acids as energy sources, resulting in energy deficiencies. Medium-chain triglyceride (MCT) supplements are effective for treating CD by providing energy to hepatocytes, increasing lipogenesis, and activating the malate-citrate shuttle. However, patients with CD often exhibit growth impairment and irreversible brain and/or liver damage. To improve the quality of life and prevent irreversible damage, MCT supplementation with a diet containing minimal carbohydrates is recommended promptly after the diagnosis.
2023-05-22 | Nicotinamide riboside rescues dysregulated glycolysis and fatty acid β-oxidation in a human hepatic cell model of citrin deficiency.
Citrin deficiency (CD) is an inborn error of metabolism caused by loss-of-function of the mitochondrial aspartate/glutamate transporter, CITRIN, which is involved in both the urea cycle and malate-aspartate shuttle. Patients with CD develop hepatosteatosis and hyperammonemia but there is no effective therapy for CD. Currently, there are no animal models that faithfully recapitulate the human CD phenotype. Accordingly, we generated a CITRIN knockout HepG2 cell line using Clustered Regularly Interspaced Short Palindromic Repeats/Cas 9 genome editing technology to study metabolic and cell signaling defects in CD. CITRIN KO cells showed increased ammonia accumulation, higher cytosolic ratio of reduced versus oxidized form of nicotinamide adenine dinucleotide (NAD) and reduced glycolysis. Surprisingly, these cells showed impaired fatty acid metabolism and mitochondrial activity. CITRIN KO cells also displayed increased cholesterol and bile acid metabolism resembling those observed in CD patients. Remarkably, normalizing cytosolic NADH:NAD+ ratio by nicotinamide riboside increased glycolysis and fatty acid oxidation but had no effect on the hyperammonemia suggesting the urea cycle defect was independent of the aspartate/malate shuttle defect of CD. The correction of glycolysis and fatty acid metabolism defects in CITRIN KO cells by reducing cytoplasmic NADH:NAD+ levels suggests this may be a novel strategy to treat some of the metabolic defects of CD and other mitochondrial diseases.
2022-09-12 | Ketogenic Diet Treatment of Defects in the Mitochondrial Malate Aspartate Shuttle and Pyruvate Carrier.
The mitochondrial malate aspartate shuttle system (MAS) maintains the cytosolic NAD+/NADH redox balance, thereby sustaining cytosolic redox-dependent pathways, such as glycolysis and serine biosynthesis. Human disease has been associated with defects in four MAS-proteins (encoded by MDH1, MDH2, GOT2, SLC25A12) sharing a neurological/epileptic phenotype, as well as citrin deficiency (SLC25A13) with a complex hepatopathic-neuropsychiatric phenotype. Ketogenic diets (KD) are high-fat/low-carbohydrate diets, which decrease glycolysis thus bypassing the mentioned defects. The same holds for mitochondrial pyruvate carrier (MPC) 1 deficiency, which also presents neurological deficits. We here describe 40 (18 previously unreported) subjects with MAS-/MPC1-defects (32 neurological phenotypes, eight citrin deficiency), describe and discuss their phenotypes and genotypes (presenting 12 novel variants), and the efficacy of KD. Of 13 MAS/MPC1-individuals with a neurological phenotype treated with KD, 11 experienced benefits-mainly a striking effect against seizures. Two individuals with citrin deficiency deceased before the correct diagnosis was established, presumably due to high-carbohydrate treatment. Six citrin-deficient individuals received a carbohydrate-restricted/fat-enriched diet and showed normalisation of laboratory values/hepatopathy as well as age-adequate thriving. We conclude that patients with MAS-/MPC1-defects are amenable to dietary intervention and that early (genetic) diagnosis is key for initiation of proper treatment and can even be lifesaving.
cell therapies
2023-04-20 | A hybrid procedure of living donor liver transplantation for a pediatric patient with citrin deficiency.
The application of laparoscopic procedures in the liver surgery has been growing. We herein present the first case of a pediatric patient who underwent living donor liver transplantation (LDLT) using a hybrid procedure with hand-assisted laparoscopic mobilization of the liver, subsequent explantation of the diseased liver, and implantation of the graft under direct vision. A 12-year-old girl with citrin deficiency was scheduled for LDLT with a left lobe graft. After making an 8-cm upper midline incision, a 5-mm trocar was placed at the umbilicus and the right upper abdomen. Mobilization of the right liver lobe was performed using a hand-assisted laparoscopic surgery (HALS) procedure. After the extension of the midline incision, short hepatic vein dissection, encircling the right hepatic vein and hepatic hilum dissection was performed. Explantation of the liver and subsequent implantation of the liver graft were conducted under direct vision. Since the operation, her normal activities of daily life have been maintained with a normal liver function. Subsequently, her secondary sexual characteristics have recovered without any wound-related complications. A hybrid LDLT procedure was feasible for a pediatric patient. This procedure's benefits are considered meaningful for pediatric patients as it does not disrupt the rectus muscles or nerves and achieves cosmesis.
gene therapies
2023-03-16 | Exogenous aralar/slc25a12 can replace citrin/slc25a13 as malate aspartate shuttle component in liver
The deficiency of CITRIN, the liver mitochondrial aspartate–glutamate carrier (AGC), is the cause of four human clinical phenotypes, neonatal intrahepatic cholestasis caused by CITRIN deficiency (NICCD), silent period, failure to thrive and dyslipidemia caused by CITRIN deficiency (FTTDCD), and citrullinemia type II (CTLN2). Clinical symptoms can be traced back to disruption of the malate-aspartate shuttle due to the lack of citrin. A potential therapy for this condition is the expression of aralar, the AGC present in brain, to replace citrin. To explore this possibility we have first verified that the NADH/NAD+ ratio increases in hepatocytes from citrin(−/−) mice, and then found that exogenous aralar expression reversed the increase in NADH/NAD+ observed in these cells. Liver mitochondria from citrin (−/−) mice expressing liver specific transgenic aralar had a small (~ 4–6 nmoles x mg prot−1 x min−1) but consistent increase in malate aspartate shuttle (MAS) activity over that of citrin(−/−) mice. These results support the functional replacement between AGCs in the liver. To explore the significance of AGC replacement in human therapy we studied the relative levels of citrin and aralar in mouse and human liver through absolute quantification proteomics. We report that mouse liver has relatively high aralar levels (citrin/aralar molar ratio of 7.8), whereas human liver is virtually devoid of aralar (CITRIN/ARALAR ratio of 397). This large difference in endogenous aralar levels partly explains the high residual MAS activity in liver of citrin(−/−) mice and why they fail to recapitulate the human disease, but supports the benefit of increasing aralar expression to improve the redox balance capacity of human liver, as an effective therapy for CITRIN deficiency.
2001-01-01 | Long-term correction of urea cycle disorders
Long-term correction of urea cycle disorders is achieved by correction of the enzymatic defect in hepatocytes. Currently, orthotopic liver transplantation is the primary means of achieving this correction. In the United States most liver transplantations for urea cycle disorders have been restricted to patients with ornithine transcarbamylase deficiency and argininosuccinic aciduria. However, patients with citrullinemia have also received transplants, but more so in Europe and Japan. Recent advances in organ procurement, surgical technique, and immunosuppression have significantly decreased morbidity and mortality. However, unique short-term complications associated with surgery and long-term complications associated with chronic immunosuppression have spurred continued efforts to develop gene replacement therapies for management of acute metabolic decompensations as intercurrent therapy until liver transplantation, and ultimately, for long-term correction. The pathophysiology of urea cycle disorders requires gene vector delivery systems that are highly efficient for liver transduction and transgene expression. To date, adenoviral vectors are unique in fulfilling these criteria, and significant data have been gained in both animal and human studies with early versions of adenoviral vectors. Ultimately, the development of helper-dependent adenoviral vectors may offer the long-term expression and increased margin of safety necessary for adjunctive therapies. (J Pediatr 2001;138:S62-S71)
2000-10-01 | Correction of argininosuccinate synthetase (AS) deficiency in a murine model of citrullinemia with recombinant adenovirus carrying human AS cDNA
Citrullinemia is an autosomal recessive disorder caused by the deficiency of argininosuccinate synthetase (AS). It is characterized by elevated levels of blood citrulline and ammonia, which often results in hyperammonemic coma and early neonatal death in affected children. We have explored the use of adenoviral vectors as a treatment modality in a murine model of citrullinemia, the Ass mouse. The Ass mouse has no endogenous AS activity due to a targeted interruption of the AS gene. Homozygous mutant animals develop high levels of blood citrulline, become hyperammonemic, and die within 24–48 h after birth. We demonstrated that the neonatal crisis in Ass mice can be ameliorated by the injection of a recombinant adenovirus carrying human AS cDNA (Ad.CMVhAS) within hours after birth. The average life span of the virus-treated animals was extended from 30 ± 9.5 h to 16.1 ± 1.6 days. A second viral infusion 14 days after the first dose further prolonged the life span to an average of 36.2 ± 7.0 days, and to 40.7 ± 3.3 days with a concurrent daily injection of arginine and sodium benzoate. Significantly increased liver AS activity (47.3 ± 7.9% of normal) was detected 24 h after viral infusion, which reached peak levels (80–90% of normal) at day 7 and decreased to about 20% of normal within 2–3 weeks after viral infusion. Southern blot analysis of liver DNA revealed a transduction efficiency of about one viral genome per hepatocyte 7 days after viral infusion and a gradual decrease of viral genome per cell parallel to the loss of liver AS activity. Plasma glutamine levels were partially normalized in virus-treated animals and were completely normalized in animals receiving Ad.CMVhAS concurrently with alternative pathway therapy. Plasma arginine levels were also partially normalized. Together, these results demonstrated that the recombinant adenovirus was capable of conferring AS activity in the liver of the recipient animals within 24 h, and the neonatal crisis of hyperammonemia could be averted by acute treatment with the AS containing adenovirus.
1999-03-30 | Hepatocyte gene therapy in a large animal: A neonatal bovine model of citrullinemia
The development of gene-replacement therapy for inborn errors of metabolism has been hindered by the limited number of suitable large-animal models of these diseases and by inadequate methods of assessing the efficacy of treatment. Such methods should provide sensitive detection of expression in vivo and should be unaffected by concurrent pharmacologic and dietary regimens. We present the results of studies in a neonatal bovine model of citrullinemia, an inborn error of urea-cycle metabolism characterized by deficiency of argininosuccinate synthetase and consequent life-threatening hyperammonemia. Measurements of the flux of nitrogen from orally administered 15 NH 4 to [ 15 N]urea were used to determine urea-cycle activity in vivo . In control animals, these isotopic measurements proved to be unaffected by pharmacologic treatments. Systemic administration of a first-generation E1 -deleted adenoviral vector expressing human argininosuccinate synthetase resulted in transduction of hepatocytes and partial correction of the enzyme defect. The isotopic method showed significant restoration of urea synthesis. Moreover, the calves showed clinical improvement and normalization of plasma glutamine levels after treatment. The results show the clinical efficacy of treating a large-animal model of an inborn error of hepatocyte metabolism in conjunction with a method for sensitively measuring correction in vivo . These studies will be applicable to human trials of the treatment of this disorder and other related urea-cycle disorders.
1998-05-01 | Metabolic engineering as therapy for inborn errors of metabolism – development of mice with phenylalanine hydroxylase expression in muscle
Treatment of many inherited liver enzyme deficiencies requires the removal of toxic intermediate metabolites from the blood of affected individuals. We propose that circulating toxins can be adequately cleared and disease phenotype influenced by enzyme expressed in tissues other than the liver. Phenylalanine hydroxylase (PAH) activity was constitutively expressed in skeletal and cardiac muscle of transgenic mice which carried the PAH cDNA under the transcriptional control of the mouse muscle creatine kinase promoter. Muscle PAH-expressing mice were bred to liver PAH-deficient, hyperphenylalaninemic mice to yield progeny that lack PAH activity in liver but express PAH in muscle. These mice exhibited hyperphenylalaninemia at baseline, but serum phenylalanine levels decreased significantly when the mice were supplemented with tetrahydrobiopterin (BH4), a required cofactor for PAH. This is the first demonstration that a liver-specific enzyme, when expressed in a heterologous tissue and supplied with necessary cofactors, can effectively clear toxic metabolites from the circulation of individuals with inherited enzyme deficiency. This result suggests that gene therapy targeted to heterologous tissues, such as muscle, will be effective in the treatment of selected inborn errors of metabolism.
small molecules
2026-04-02 | Development of a quantitative real-time PCR-based newborn screening system for citrin deficiency using dried blood spots.
Citrin deficiency is an autosomal recessive metabolic disorder caused by pathogenic variants in SLC25A13, which manifests as an age-dependent spectrum ranging from neonatal intrahepatic cholestasis (NICCD) to adolescent and adult citrin deficiency (AACD, formerly CTLN2). Early detection through newborn screening (NBS) would be a prerequisite for early treatment, but conventional NBS based on citrulline and other metabolite levels has only limited sensitivity. This study aimed to develop a simple and accurate quantitative real-time PCR (qPCR)-based newborn screening (NBS) method using dried blood spots (DBSs) as a first-tier screening test to detect the six most common SLC25A13 variants in Japan. DBS samples from 1055 healthy newborns and 19 patients with confirmed variants were analyzed. Four variants (c.674C > A, c.852_855delTATG, c.1177 + 1G > A, and c.1311 + 1G > A) were screened using the TaqMan™ SNP genotyping system, and two large insertion/deletion variants (c.1638_1660dup and c.1750_1751[insNM_138459.3:2672_24;1750 + 72_1751-4dup]) were screened using a SYBR™ Green-based qPCR system with variant-specific primers. Results of qPCR were confirmed by Sanger sequencing. In all 19 known patients with citrin deficiency, the assay correctly identified the pathogenic alleles. Among 1055 newborns, heterozygous variants were detected in 19 cases (five c.852_855delTATG, thirteen c.1177 + 1G > A, and one c.1311 + 1G > A). The overall allele frequency (0.0090) was consistent with that reported in the Japanese genome database (jMorp, 0.0102), corresponding to an estimated carrier frequency of approximately 1 in 56 individuals. The assay reliably distinguished wild-type, heterozygous, and homozygous genotypes using a single DBS punch. We established a cost-effective, rapid, and reliable qPCR-based NBS system that detects the six most prevalent SLC25A13 variants using DBSs. This method is compatible with current NBS workflows and could improve early detection and intervention for citrin deficiency in Japan and, with adaptation of the target variants, in any other (not only) East Asian population.
2024-07-18 | The therapeutic landscape of citrin deficiency.
Citrin deficiency (CD) is a recessive, liver disease caused by sequence variants in the SLC25A13 gene encoding a mitochondrial aspartate-glutamate transporter. CD manifests as different age-dependent phenotypes and affects crucial hepatic metabolic pathways including malate-aspartate-shuttle, glycolysis, gluconeogenesis, de novo lipogenesis and the tricarboxylic acid and urea cycles. Although the exact pathophysiology of CD remains unclear, impaired use of glucose and fatty acids as energy sources due to NADH shuttle defects and PPARα downregulation, respectively, indicates evident energy deficit in CD hepatocytes. The present review summarizes current trends on available and potential treatments for CD. Baseline recommendation for CD patients is dietary management, often already present as a self-selected food preference, that includes protein and fat-rich food, and avoidance of excess carbohydrates. At present, liver transplantation remains the sole curative option for severe CD cases. Our extensive literature review indicated medium-chain triglycerides (MCT) as the most widely used CD treatment in all age groups. MCT can effectively improve symptoms across disease phenotypes by rapidly supplying energy to the liver, restoring redox balance and inducing lipogenesis. In contrast, sodium pyruvate restored glycolysis and displayed initial preclinical promise, with however limited efficacy in adult CD patients. Ursodeoxycholic acid, nitrogen scavengers and L-arginine treatments effectively address specific pathophysiological aspects such as cholestasis and hyperammonemia and are commonly administered in combination with other drugs. Finally, future possibilities including restoring redox balance, amino acid supplementation, enhancing bioenergetics, improving ureagenesis and mRNA/DNA-based gene therapy are also discussed.
2024-07-16 | Pathogenesis and Management of Citrin Deficiency.
Citrin deficiency (CD) is a hereditary disorder caused by SLC25A13 mutations that manifests as neonatal intrahepatic cholestasis caused by CD (NICCD), failure to thrive and dyslipidemia caused by CD (FTTDCD), and adult-onset type 2 citrullinemia (CTLN2). Citrin, an aspartate-glutamate carrier primarily expressed in the liver, is a component of the malate-aspartate shuttle, which is essential for glycolysis. Citrin-deficient hepatocytes have primary defects in glycolysis and de novo lipogenesis and exhibit secondarily downregulated PPARα, leading to impaired β-oxidation. They are unable to utilize glucose and free fatty acids as energy sources, resulting in energy deficiencies. Medium-chain triglyceride (MCT) supplements are effective for treating CD by providing energy to hepatocytes, increasing lipogenesis, and activating the malate-citrate shuttle. However, patients with CD often exhibit growth impairment and irreversible brain and/or liver damage. To improve the quality of life and prevent irreversible damage, MCT supplementation with a diet containing minimal carbohydrates is recommended promptly after the diagnosis.
2023-05-22 | Nicotinamide riboside rescues dysregulated glycolysis and fatty acid β-oxidation in a human hepatic cell model of citrin deficiency.
Citrin deficiency (CD) is an inborn error of metabolism caused by loss-of-function of the mitochondrial aspartate/glutamate transporter, CITRIN, which is involved in both the urea cycle and malate-aspartate shuttle. Patients with CD develop hepatosteatosis and hyperammonemia but there is no effective therapy for CD. Currently, there are no animal models that faithfully recapitulate the human CD phenotype. Accordingly, we generated a CITRIN knockout HepG2 cell line using Clustered Regularly Interspaced Short Palindromic Repeats/Cas 9 genome editing technology to study metabolic and cell signaling defects in CD. CITRIN KO cells showed increased ammonia accumulation, higher cytosolic ratio of reduced versus oxidized form of nicotinamide adenine dinucleotide (NAD) and reduced glycolysis. Surprisingly, these cells showed impaired fatty acid metabolism and mitochondrial activity. CITRIN KO cells also displayed increased cholesterol and bile acid metabolism resembling those observed in CD patients. Remarkably, normalizing cytosolic NADH:NAD+ ratio by nicotinamide riboside increased glycolysis and fatty acid oxidation but had no effect on the hyperammonemia suggesting the urea cycle defect was independent of the aspartate/malate shuttle defect of CD. The correction of glycolysis and fatty acid metabolism defects in CITRIN KO cells by reducing cytoplasmic NADH:NAD+ levels suggests this may be a novel strategy to treat some of the metabolic defects of CD and other mitochondrial diseases.
2022-09-12 | Ketogenic Diet Treatment of Defects in the Mitochondrial Malate Aspartate Shuttle and Pyruvate Carrier.
The mitochondrial malate aspartate shuttle system (MAS) maintains the cytosolic NAD+/NADH redox balance, thereby sustaining cytosolic redox-dependent pathways, such as glycolysis and serine biosynthesis. Human disease has been associated with defects in four MAS-proteins (encoded by MDH1, MDH2, GOT2, SLC25A12) sharing a neurological/epileptic phenotype, as well as citrin deficiency (SLC25A13) with a complex hepatopathic-neuropsychiatric phenotype. Ketogenic diets (KD) are high-fat/low-carbohydrate diets, which decrease glycolysis thus bypassing the mentioned defects. The same holds for mitochondrial pyruvate carrier (MPC) 1 deficiency, which also presents neurological deficits. We here describe 40 (18 previously unreported) subjects with MAS-/MPC1-defects (32 neurological phenotypes, eight citrin deficiency), describe and discuss their phenotypes and genotypes (presenting 12 novel variants), and the efficacy of KD. Of 13 MAS/MPC1-individuals with a neurological phenotype treated with KD, 11 experienced benefits-mainly a striking effect against seizures. Two individuals with citrin deficiency deceased before the correct diagnosis was established, presumably due to high-carbohydrate treatment. Six citrin-deficient individuals received a carbohydrate-restricted/fat-enriched diet and showed normalisation of laboratory values/hepatopathy as well as age-adequate thriving. We conclude that patients with MAS-/MPC1-defects are amenable to dietary intervention and that early (genetic) diagnosis is key for initiation of proper treatment and can even be lifesaving.
cell therapies
2023-04-20 | A hybrid procedure of living donor liver transplantation for a pediatric patient with citrin deficiency.
The application of laparoscopic procedures in the liver surgery has been growing. We herein present the first case of a pediatric patient who underwent living donor liver transplantation (LDLT) using a hybrid procedure with hand-assisted laparoscopic mobilization of the liver, subsequent explantation of the diseased liver, and implantation of the graft under direct vision. A 12-year-old girl with citrin deficiency was scheduled for LDLT with a left lobe graft. After making an 8-cm upper midline incision, a 5-mm trocar was placed at the umbilicus and the right upper abdomen. Mobilization of the right liver lobe was performed using a hand-assisted laparoscopic surgery (HALS) procedure. After the extension of the midline incision, short hepatic vein dissection, encircling the right hepatic vein and hepatic hilum dissection was performed. Explantation of the liver and subsequent implantation of the liver graft were conducted under direct vision. Since the operation, her normal activities of daily life have been maintained with a normal liver function. Subsequently, her secondary sexual characteristics have recovered without any wound-related complications. A hybrid LDLT procedure was feasible for a pediatric patient. This procedure's benefits are considered meaningful for pediatric patients as it does not disrupt the rectus muscles or nerves and achieves cosmesis.
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Drug Discovery Landscape
2 orphan drug designations for Citrullinemia type II.
2 orphan drug designations for Citrullinemia type II.
Drug | Therapy type | Regulator | Orphan designation | Approval | Sponsor |
|---|---|---|---|---|---|
Heterologous human adult liver-derived progenitor cells | cell therapies | EMA | 2013-07-17 | — | Cellaion |
Glyceryl tri-(4-phenylbutyrate) | small molecules | EMA | 2010-06-10 | — | Immedica Pharma AB |
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