SLC25A13 Mutations Research Articles

Rapid detection of solute carrier family 4 , member 1 ( SLC4A1) mutations and polymorphisms by high-resolution melting analysis

Objective The objective of this study is to develop and evaluate a high-resolution melting (HRM) method for detection of SLC4A1 mutations and polymorphisms. Design and methods The HRM method was optimized for detection of 18 known SLC4A1 variants. It was then used for analysis of 16 blind DNA samples highly enriched with two common mutations, Southeast Asian ovalocytosis (SAO) and band 3 Bangkok 1 (G701D), to compare the results with that of the conventional procedures. Results The HRM method was able to detect all 18 SLC4A1 variants. In the samples in which homozygous wild-type and homozygous variant could not be distinguished by difference plots, they were spiked with a sample carrying known homozygous genotype, resulting in their clear differentiation. The HRM method had 100% efficiency for detection of mutations in the blind DNA samples, when compared with that of the conventional techniques. Conclusions The developed HRM method is efficient and reproducible for detection of SLC4A1 mutations and polymorphisms.

Neonatal intrahepatic cholestasis caused by citrin deficiency: Clinical and laboratory investigation of 13 subjects in mainland of China

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is a novel inborn error of metabolism due to dysfunction of citrin protein, and much more information about this new disease is still needed for its clinical management. To investigate in detail the clinical and laboratory features of NICCD. 13 NICCD subjects in mainland of China diagnosed in our department since 2006. The anthropometric parameters of the patients at birth were compared with controls, representative biochemical changes and metabolome findings were investigated cross-sectionally, and mutations in the causative gene SLC25A13 were analyzed by protocols established previously. The patients showed reduced birth weight, length and ponderal index. Main clinical manifestations consisted of jaundice, hepato/hepatosplenomegaly and steatohepatosis on ultrasonography. Biochemical analysis revealed intrahepatic cholestasis, delayed switch of AFP to albumin, and elevated triglyceride, total cholesterol and LDL-cholesterol together with reduced HDL-cholesterol. Metabolome findings included co-existence of markers for galactosemia and tyrosinemia in urine, and elevated Cit, Met, Thr, Tyr, Lys, Arg and Orn in blood. Mutations of 851-854del, IVS6+5G>A, 1638-1660dup, A541D, IVS16ins3kb, R319X and G333D were detected in the gene SLC25A13. The diagnosis of NICCD cannot be established based just on the numerous but non-specific clinical manifestations and biochemical changes. The relatively specific metabolome features provide valuable tools for its screening and diagnosis, while SLC25A13 mutation analysis should be taken as one of the reliable tools for the definitive diagnosis. The body proportionality at birth, steatohepatosis on ultrasonography, delayed switch of AFP to albumin, dyslipidemia pattern, urinary metabolome features and the novel mutation G333D expanded the clinical spectrum of NICCD.

Chubby Face and the Biochemical Parameters for the Early Diagnosis of Neonatal Intrahepatic Cholestasis Caused by Citrin Deficiency

To identify facial and biochemical characteristics as early clinical features of neonatal intrahepatic cholestasis due to citrin deficiency (NICCD). Ten patients with diagnoses of NICCD by SLC25A13 mutation analysis in Taiwan were recruited. A "Chubby Index" was developed for objective measurement of their facial characteristics. Liver function profiles were analyzed and compared with data on neonatal hepatitis and biliary atresia. Chubby face was observed in early infancy in all 5 patients whose serial photographs were taken. A significant difference in the Chubby Index was seen between NICCD infants and healthy infants (1.331 +/- 0.07 vs 1.068 +/- 0.059; P < 0.05). NICCD is characterized by an aspartate aminotransferase-to-alanine aminotransferase ratio of 2 or greater, a direct bilirubin-to-total bilirubin ratio under 0.67, and a standard deviation score for alpha-fetoprotein of 4 or greater, with respect to neonatal hepatitis and biliary atresia. Although chubby face, abnormal liver function profiles, and multiple amino acidemia gradually disappeared after age 1 year, an increase in hepatic echogenicity was observed in most patients in long-term follow-up. Our Chubby Index is an informative measurement of the facial characteristics of infants with NICCD. The chubby face features, along with an aspartate aminotransferase-to-alanine aminotransferase ratio of 2 or greater, a direct bilirubin-to-total bilirubin ratio under 0.67, and a standard deviation score for alpha-fetoprotein of 4 or greater, may serve as useful clinical indicators for diagnosing NICCD early in infancy.

Cation transport activity of anion exchanger 1 mutations found in inherited distal renal tubular acidosis

Anion exchanger 1 (AE1) is encoded by SLC4A1 and mediates electroneutral anion exchange across cell membranes. It is the most abundant protein in the red cell membrane, but it is also found in the basolateral membrane of renal alpha-intercalated cells, where it is required for normal urinary acidification. Recently, four point mutations in red cell AE1 have been described that convert the anion exchanger to a cation conductance. SLC4A1 mutations can also cause type 1 hypokalemic distal renal tubular acidosis (dRTA). We investigated the properties of four dRTA-associated AE1 mutations (R589H, G609R, S613F, and G701D) by heterologous expression in Xenopus laevis oocytes. Although these AE1 mutants are functional anion exchangers, unlike the red cell disease mutants, we found that they also demonstrated a cation leak. We found a large cation leak in the G701D mutant. This mutant normally requires coexpression with glycophorin A for surface membrane expression in red blood cells and oocytes. However, we found that coexpressing wild-type kidney AE1 with G701D in oocytes still caused a cation leak, consistent with heterodimerized G701D reaching the cell membrane and retaining its cation conductance property. These findings have potential structural and functional implications for AE1, and they indicate that while anion exchange and cation conductance properties are distinct, they can coexist.

Identification of 13 novel mutations including a retrotransposal insertion in SLC25A13 gene and frequency of 30 mutations found in patients with citrin deficiency

Deficiency of citrin, liver-type mitochondrial aspartate-glutamate carrier, is an autosomal recessive disorder caused by mutations of the SLC25A13 gene on chromosome 7q21.3 and has two phenotypes: neonatal intrahepatic cholestatic hepatitis (NICCD) and adult-onset type II citrullinemia (CTLN2). So far, we have described 19 SLC25A13 mutations. Here, we report 13 novel SLC25A13 mutations (one insertion, two deletion, three splice site, two nonsense, and five missense) in patients with citrin deficiency from Japan, Israel, UK, and Czech Republic. Only R360X was detected in both Japanese and Caucasian. IVS16ins3kb identified in a Japanese CTLN2 family seems to be a retrotransposal insertion, as the inserted sequence (2,667-nt) showed an antisense strand of processed complementary DNA (cDNA) from a gene on chromosome 6 (C6orf68), and the repetitive sequence (17-nt) derived from SLC25A13 was found at both ends of the insert. All together, 30 different mutations found in 334 Japanese, 47 Chinese, 11 Korean, four Vietnamese and seven non-East Asian families have been summarized. In Japan, IVS16ins3kb was relatively frequent in 22 families, in addition to known mutations IVS11 + 1G > A, 851del4, IVS13 + 1G > A, and S225X in 189, 173, 48 and 30 families, respectively; 851del4 and IVS16ins3kb were found in all East Asian patients tested, suggesting that these mutations may have occurred very early in some area of East Asia.

Hematological abnormalities in patients with distal renal tubular acidosis and hemoglobinopathies

Mutations of the human SLC4A1 gene encoding erythroid and kidney isoforms of anion exchanger 1 (AE1, band 3) result in erythrocyte abnormalities or distal renal tubular acidosis (dRTA) and such mutations are observed in Southeast Asia, where hemoglobinopathies are prevalent. Genetic and hematological studies in 18 Thai patients with dRTA have shown that 12 of them (67%) carried SLC4A1 mutations (7 G701D/G701D, 3 SAO/G701D, and 2 G701D/A858D). Of these 12 patients, three had homozygous G701D/G701D and heterozygous Hb E; one compound heterozygous SAO/G701D and heterozygous alpha(+)-thalassemia; and one compound heterozygous G701D/A858D and heterozygous Hb E. Of 6 patients without SLC4A1 mutation, two each carried heterozygous or homozygous Hb E and one of the latter also had Hb H disease (--(SEA)/-alpha(4.2)). The blood smears of patients with homozygous G701D/G701D showed approximately 25% ovalocytes. Strikingly, the patients with coexistence of homozygous G701D/G701D and heterozygous Hb E had 58% ovalocytes. Similarly, the patients who had compound heterozygous SAO/G701D showed 49% ovalocytes, but the patient with coexistence of compound heterozygous SAO/G701D and heterozygous alpha(+)-thalassemia had 70% ovalocytes. Our previous study has shown that under metabolic acidosis, the patients with homozygous G701D/G701D or compound heterozygous SAO/G701D had reticulocytosis, indicating compensated hemolysis. A patient with compound heterozygous SAO/G701D and heterozygous alpha(+)-thalassemia presented with hemolytic anemia and hepatosplenomegaly which was alleviated by alkaline therapy. Taken together, the coexistence of both homozygous or compound heterozygous SLC4A1 mutations and hemoglobinopathy has a combined effect on red cell morphology and degree of hemolytic anemia, which is aggravated by acidosis.

Prevalence of SLC22A4, SLC22A5 and CARD15 gene mutations in Hungarian pediatric patients with Crohn’s disease

To investigate the frequency of the common NOD2/CARD15 susceptibility variants and two functional polymorphisms of OCTN cation transporter genes in Hungarian pediatric patients with Crohn's disease (CD). A cohort of 19 unrelated pediatric and 55 unrelated adult patients with Crohn's disease and 49 healthy controls were studied. Genotyping of the three common CD-associated CARD15 variants (Arg702Trp, Gly908Arg and 1007finsC changes) with the SLC22A4 1672C-->T, and SLC22A5 -207G-->C mutations was performed by direct sequencing of the specific regions of these genes. At least one CARD15 mutation was present in 52.6% of the children and in 34.5% of the adults compared to 14.3% in controls. Surprisingly, strongly different mutation profile was detected in the pediatric versus adult patients. While the G908R and 1007finsC variants were 18.4% and 21.1% in the pediatric group, they were 1.82% and 11.8% in the adults, and were 1.02% and 3.06% in the controls, respectively. The R702W allele was increased approximately two-fold in the adult subjects, while in the pediatric group it was only approximately 64% of the controls (9.09% in the adults, 2.63% in pediatric patients, and 4.08% in the controls). No accumulation of the OCTN variants was observed in any patient group versus the controls. The frequency of the NOD2/CARD15 susceptibility variants in the Hungarian pediatric CD population is high and the profile differs from the adult CD patients, whereas the results for SLC22A4 and SLC22A5 mutation screening do not confirm the assumption that the carriage of these genotypes means an obligatory susceptibility to CD.

Homozygous SLC25A13 Mutation in a Taiwanese Patient with Adult-onset Citrullinemia Complicated with Steatosis and Hepatocellular Carcinoma

Citrullinemia is a metabolic disorder characterized by elevated plasma concentrations of citrulline and ammonia. Adult-onset citrullinemia (type II, CTLN2) has been attributed to citrin deficiency caused by mutations in the SLC25A13 gene. CTLN2 is associated with a high incidence of hepatocellular carcinoma (HCC) in Japanese. We report a 48-year-old Taiwanese man with citrullinemia, who was in good health until the age of 34 when he had repeated episodes of consciousness disturbance. Hyperammonia (201 micromol/L) was found during an episode of coma. Liver function and electrolyte levels were normal at that time. Serologic markers of viral hepatitis B and C were negative. Analysis of genomic DNA extracted from peripheral blood leukocytes showed homozygous 851del4 mutation in exon 9 of the SLC25A13 gene on chromosome 7q21.3. Fourteen years after disease onset, at the age of 48, he was admitted due to an episode of coma. Abdominal sonography and computed tomography showed a 2.5 cm tumor in the left lobe of the liver, without evidence of liver cirrhosis. Wedge resection of the tumor was performed and grade 2 HCC was diagnosed. The nontumor part of the resected specimen showed chronic persistent hepatitis with moderate steatosis. The results in this case support that both citrin deficiency and steatohepatitis may contribute to hepatocarcinogenesis.

Variant clinical courses of 2 patients with neonatal intrahepatic cholestasis who have a novel mutation of SLC25A13

Deficiency of citrin due to mutations of the SLC25A13 gene causes not only adult-onset type II citrullinemia, but also neonatal intrahepatic cholestasis. Neonatal intrahepatic cholestasis is a self-limiting condition and spontaneously disappears by 12 months of age without special treatment. The natural history of patients with SLC25A13 mutations is not clear. Two patients with infantile hepatic dysfunction were found to have a novel mutation of the SLC25A13 gene. DNA analyses of SLC25A13 disclosed that the first patient was a compound heterozygote for the Ex16+74_IVS17-32del516 (del516-Ex16/IVS17) and IVS11+1G→A mutations and the second one a homozygote for the del516-Ex16/IVS17 mutation. It is predicted that the 516–base pair deletion mutation leads to a frameshift from codons 556 to 564, a premature termination at codon 565, and a truncated form of the citrin protein (normal, 675 amino acids). The first patient had disseminated intravascular coagulation associated with hepatic dysfunction in the neonatal period. The other patient had persistent cholestatic jaundice and underwent an operation to rule out bile duct atresia. Without specific treatment, both patients had a favorable clinical course. In conclusion, citrin deficiency resulting from the mutation of SLC25A13 presented variant clinical courses, followed by hypercitrullinemia and intrahepatic cholestasis in infancy. The conditions in the patients were self-limiting and spontaneously disappeared.

Frequency and distribution in East Asia of 12 mutations identified in the SLC25A13 gene of Japanese patients with citrin deficiency

Deficiency of citrin, a liver-type mitochondrial aspartate-glutamate carrier (AGC), encoded by the SLC25A13 gene on chromosome 7q21.3, causes autosomal recessive disorders: adult-onset type II citrullinemia (CTLN2) and neonatal hepatitis associated with intrahepatic cholestasis (NICCD). So far, we have described 12 SLC25A13 mutations: 11 were from Japan and one from Israel. Three mutations found in Chinese and Vietnamese patients were the same as those in Japanese patients. In the present study, we identified a novel mutation IVS6+1G>C in a Japanese CTLN2 patient and widely screened 12 SLC25A13 mutations found in Japanese patients in control individuals from East Asia to confirm our preliminary results that the carrier frequency was high in Asian populations. Mutations 851-854del and 1638-1660dup were found in all Asian countries tested, and 851-854del associated with 290-haplotype in microsatellite marker D7S1812 was especially frequent. Other mutations frequently detected were IVS11+1G>A in Japanese and Korean, S225X in Japanese, and IVS6+5G>A in Chinese populations. We found a remarkable difference in carrier rates in China (including Taiwan) between north (1/940) and south (1/48) of the Yangtze River. We detected many carriers in Chinese (64/4169 = 1/65), Japanese (20/1372 = 1/69) and Korean (22/2455 = 1/112) populations, suggesting that over 80,000 East Asians are homozygotes with two mutated SLC25A13 alleles.

Molecular mechanisms of autosomal dominant and recessive distal renal tubular acidosis caused by SLC4A1 (AE1) mutations

Mutations of SLC4A1 (AE1) encoding the kidney anion (Cl(-)/HCO(3) (-)) exchanger 1 (kAE1 or band 3) can result in either autosomal dominant (AD) or autosomal recessive (AR) distal renal tubular acidosis (dRTA). The molecular mechanisms associated with SLC4A1 mutations resulting in these different modes of inheritance are now being unveiled using transfected cell systems. The dominant mutants kAE1 R589H, R901X and S613F, which have normal or insignificant changes in anion transport function, exhibit intracellular retention with endoplasmic reticulum (ER) localization in cultured non-polarized and polarized cells, while the dominant mutants kAE1 R901X and G609R are mis-targeted to apical membrane in addition to the basolateral membrane in cultured polarized cells. A dominant-negative effect is likely responsible for the dominant disease because heterodimers of kAE1 mutants and the wild-type protein are intracellularly retained. The recessive mutants kAE1 G701D and S773P however exhibit distinct trafficking defects. The kAE1 G701D mutant is retained in the Golgi apparatus, while the misfolded kAE1 S773P, which is impaired in ER exit and is degraded by proteosome, can only partially be delivered to the basolateral membrane of the polarized cells. In contrast to the dominant mutant kAE1, heterodimers of the recessive mutant kAE1 and wild-type kAE1 are able to traffic to the plasma membrane. The wild-type kAE1 thus exhibits a 'dominant-positive effect' relative to the recessive mutant kAE1 because it can rescue the mutant proteins from intracellular retention to be expressed at the cell surface. Consequently, homozygous or compound heterozygous recessive mutations are required for presentation of the disease phenotype. Future work using animal models of dRTA will provide additional insight into the pathophysiology of this disease.

Effects of citrin deficiency in the perinatal period: feasibility of newborn mass screening for citrin deficiency.

Deficiency of citrin due to mutations of the SLC25A13 gene causes adult-onset type II citrullinemia (CTLN2) and one type of neonatal intrahepatic cholestasis (NICCD). About half of the NICCD patients are detected based on high galactose, phenylalanine, and/or methionine concentrations on newborn mass screening (NMS). To clarify the perinatal and neonatal effects and the inconsistent results on NMS, we examined aminograms, the levels of bile acids and galactose in dried blood spots for NMS from 20 patients with NICCD. Birth weight was low for gestational age (-1.4 +/- 0.7 SD). Affected fetuses may have suffered intrauterine citrin deficiency. The first abnormality detected after birth was citrullinemia, and 19 of 20 patients had citrulline levels higher than +2 SD of controls. Tyrosine, phenylalanine, methionine, galactose, and bile acids were less affected than citrulline on d 5 after birth. Galactose and bile acids levels were increased at 1 mo in comparison with d 5 after birth due to impairment of the cytosolic NADH reducing-equivalent supply into mitochondria of hepatocytes. Patients with negative findings on NMS had low levels of total 20 amino acids. Citrulline/serine, citrulline /leucine plus isoleucine, and citrulline/total amino acids ratios, controlled for the confounding effect of low amount of total amino acids, were higher in all patients than +2 SD, +2 SD, and +3 SD of controls, respectively. NMS for citrin deficiency (frequency of homozygote with SLC25A13 mutation: 1/10,000-1/38,000 in East Asia) will be useful for clarification of the clinical course, treatment, and prevention of this disease.

Novel compound heterozygous SLC4A1 mutations in Thai patients with autosomal recessive distal renal tubular acidosis

Background: Mutations in the SLC4A1 gene have been found to cause either autosomal dominant (AD) or autosomal recessive (AR) distal renal tubular acidosis (dRTA). The SLC4A1 mutations causing AD dRTA were reported in white patients, whereas those associated with AR dRTA were often found in Southeast Asia. Here, the authors report additional novel SLC4A1 mutations in 3 patients with AR dRTA from 2 unrelated Thai families. Methods: The patients and members of their families were clinically studied. Red cell morphology and sulfate influx were examined. The SLC4A1 gene was screened, analyzed, and confirmed for mutations by molecular genetic techniques. Results: In the first family, the patient had dRTA, rickets, failure to thrive, nephrocalcinosis, and hypokalemic-hyperchloremic metabolic acidosis with a urine pH level of 7.00. He had novel compound heterozygous SLC4A1 G701D/S773P mutations, inherited from clinically normal heterozygous mother and father. In the second family, the patient and his sister had dRTA and Southeast Asian ovalocytosis (SAO) with different clinical severity. The patient had proximal muscle weakness, rickets, nephrocalcinosis, hypokalemia, normal anion gap metabolic acidosis, and urine pH level of 6.80. His sister was asymptomatic but the urine pH level could not be lowered to below 5.50 after a short acid load. Both siblings had compound heterozygous SLC4A1 SAO/R602H mutations. Conclusion: Two novel compound heterozygous SLC4A1 G701D/S773P and SAO/R602H mutations were identified in Thai patients with AR dRTA.

Renal epithelial traffic jams and one-way streets.

The kidney contains the body’s second largest number of different cell types, modulating the great diversity of different functions that allow complex homeostasis to occur. A feature that unites all these cell types in the postglomerular nephron is that they are highly polarized; one surface being

A Novel Missense Mutation in AE1 Causing Autosomal Dominant Distal Renal Tubular Acidosis Retains Normal Transport Function but Is Mistargeted in Polarized Epithelial Cells

Mutations in SLC4A1, encoding the chloride-bicarbonate exchanger AE1, cause distal renal tubular acidosis (dRTA), a disease of defective urinary acidification by the distal nephron. In this study we report a novel missense mutation, G609R, causing dominant dRTA in affected members of a large Caucasian pedigree who all exhibited metabolic acidosis with alkaline urine, prominent nephrocalcinosis, and progressive renal impairment. To investigate the potential disease mechanism, the consequent effects of this mutation were determined. We first assessed anion transport function of G609R by expression in Xenopus oocytes. Western blotting and immunofluorescence demonstrated that the mutant protein was expressed at the oocyte cell surface. Measuring chloride and bicarbonate fluxes revealed normal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-inhibitable anion exchange, suggesting that loss-of-function of kAE1 cannot explain the severe disease phenotype in this kindred. We next expressed epitope-tagged wild-type or mutant kAE1 in Madin-Darby canine kidney cells. In monolayers grown to polarity, mutant kAE1 was detected subapically and at the apical membrane, as well as at the basolateral membrane, in contrast to the normal basolateral appearance of wild-type kAE1. These findings suggest that the seventh transmembrane domain that contains Gly-609 plays an important role in targeting kAE1 to the correct cell surface compartment. They confirm that dominant dRTA is associated with non-polarized trafficking of the protein, with no significant effect on anion transport function in vitro, which remains an unusual mechanism of human disease.

Defects in processing and trafficking of the AE1 Cl-/HCO3- exchanger associated with inherited distal renal tubular acidosis.

Distal renal tubular acidosis (dRTA) results from impaired urinary acidification by the renal collecting duct. Acquired dRTA can be secondary to diverse pathological processes, including diabetic, ischemic, fibrosing, or immunological processes; less frequently it presents as a familial disorder with either an autosomal recessive or dominant pattern of transmission. Mutations in the SLC4A1/AE1/band 3 Cl(-)/HCO(3)(-) exchanger gene have been identified as causes for both dominant and recessive forms of dRTA. These mutations comprise a group almost entirely distinct from the SLC4A1 mutations that underlie the familial hemolytic anemia of hereditary spherocytosis. Why does one group of mutations express almost exclusively an isolated erythroid phenotype, whereas the second group of mutations expresses almost exclusively a phenotype explicable entirely by defective function of renal collecting duct type A intercalated cells? This review summarizes current research addressing this central question in the pathobiology of inherited dRTA associated with mutations in the SLC4A1 gene. Studying dRTA-associated mutant AE1 polypeptides can provide novel insights into the biology of the intercalated cell and the collecting duct as well as more generally into mechanisms by which epithelial cells generate and maintain functional polarity.

Adult-onset type II citrullinemia and idiopathic neonatal hepatitis caused by citrin deficiency: involvement of the aspartate glutamate carrier for urea synthesis and maintenance of the urea cycle

Citrin is a mitochondrial aspartate glutamate carrier primarily expressed in the liver, heart, and kidney. We found that adult-onset type II citrullinemia is caused by mutations in the SLC25A13 gene that encodes for citrin. In this report, we describe the frequency of SLC25A13 mutations, the roles of citrin as a member of the urea cycle and as a member of the malate–aspartate shuttle, the relationship between its functions and symptoms of citrin deficiency, and therapeutic issues.

Screening of nine SLC25A13 mutations: their frequency in patients with citrin deficiency and high carrier rates in Asian populations

Deficiency of citrin encoded by SLC25A13 causes adult-onset type II citrullinemia (CTLN2) and idiopathic neonatal hepatitis (NICCD). So far we have diagnosed 126 (3) CTLN2 and 103 (4) NICCD patients in Japan (and other countries). From preliminary population analysis of the known nine SLC25A13 mutations, we found that the carrier frequency is high in China (1/79), Taiwan (1/98), and Korea (1/50) as well as Japan (1/69), suggesting that many patients with citrin deficiency exist in East Asia.

Effectiveness of carbohydrate-restricted diet and arginine granules therapy for adult-onset type II citrullinemia: a case report of siblings showing homozygous SLC25A13 mutation with and without the disease

Case 1 is a 37-year-old Japanese man who was admitted to this hospital with a disturbance of consciousness. A diagnosis of adult-onset type II citrullinemia was made by DNA analysis of SLC25A13 (851del4/851del4) and measurement of hepatic ASS activity (2% of control value). After regaining consciousness, Case 1 was started on a dietary therapy, revealing that hypertriglyceridemia and ketogenesis impairment deteriorated on a low-protein diet and ameliorated on a carbohydrate-restricted (high-protein) diet. Case 1 could tolerate 70 g/day of protein while using arginine granules and developed hyperammonemia only after discontinuation of the administration. Case 2 (an elder brother of Case 1) is also homozygote for the same SLC25A13 mutation. The hepatic activity of argininosuccinate synthetase was about 20% of the control value. However, Case 2 exhibited neither hyperammonemia nor lipid metabolism abnormalities. These results suggest that, although adult-onset type II citrullinemia is caused by a deficiency of citrin, which plays key roles in carbohydrates, amino acids and even lipid metabolism, some other environmental or genetic factors are required for the onset of the disease, and from the authors’ clinical experience, a carbohydrate-restricted (relatively high-protein) diet is advocated as a benefit to the patients, and that arginine granules are indispensable to this new dietary therapy.

A novel inborn error of metabolism detected by elevated methionine and/or galactose in newborn screening: neonatal intrahepatic cholestasis caused by citrin deficiency.

Adult-onset type II citrullinaemia, caused by deficiency of the citrin protein encoded by the SLC25A13 gene, is characterised by a liver-specific argininosuccinate synthetase deficiency. DNA analysis for citrin deficiency revealed that SLC25A13 mutations are the cause of a particular type of neonatal intrahepatic cholestasis. We retrospectively investigated nine infants with cholestatic jaundice of unknown origin, detected by newborn screening over a period of 17 years, to determine the role of SLC25A13 defects in children. The results of the newborn screening were varied; four neonates were positive for hypermethioninaemia, two for hyperphenylalaninaemia, one for hypergalactosaemia and two for both hypermethioninaemia and hypergalactosaemia. Clinical characteristics of the patients were severe intrahepatic cholestasis, hypercitrullinaemia, and fatty liver. The symptoms resolved in all patients by 12 months of age without special treatment other than nutritional management. Although five patients were lost to follow-up, we detected SLC25A13 mutations in the remaining four patients examined. the differential diagnosis of cholestatic jaundice of unknown origin in infants should therefore include citrin deficiency. In this paper, we stress the importance of newborn screening to detect infants with neonatal intrahepatic cholestasis caused by citrin deficiency.