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

Serum procalcitonin as a marker of neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD)

BACKGROUND

Neonatal Intrahepatic Cholestasis (NICCD), as the early-age stage of Citrin deficiency involving liver dysfunction, lacks efficient diagnostic markers. Procalcitonin (PCT) has been identified as a biomarker for infection as well as various organ damage. This study aimed to explore the potential of PCT as a biomarker for NICCD.

METHODS

In a single-center retrospective case-control study. Serum PCT concentrations before and after treatment of 120 NICCD patients, as the study group, were compared to the same number of cholestatic hepatitis patients, as the control group. The potential value of PCT to discriminate NICCD from control disease was further explored using Receiver Operating Characteristic (ROC) curve analysis and compared to those of other inflammatory markers.

RESULTS

There was a significantly higher level of PCT in NICCD patients than in the control group. PCT concentrations were only weakly correlated with neutrophil counts and CRP levels (p ˂ 0.05). At a cut-off value of 0.495 ng/mL, PCT exhibited a significantly higher diagnostic value compared to other inflammatory markers for discriminating NICCD from the control, with a sensitivity of 90.8 % and specificity of 98.3 %.

CONCLUSION

PCT might be used as an initial biomarker to discriminate children with NICCD from another hepatitis disease.

Update on the diagnosis and management of neonatal intrahepatic cholestasis caused by citrin deficiency: Expert review on behalf of the Asian Pan-Pacific Society for Pediatric Gastroenterology, Hepatology, and Nutrition

Citrin deficiency is an autosomal recessive metabolic liver disease caused by mutations in the SLC25A13 gene. The disease typically presents with cholestasis, elevated liver enzymes, hyperammonemia, hypercitrullinemia, and fatty liver in young infants, resulting in a phenotype known as "neonatal intrahepatic cholestasis caused by citrin deficiency" (NICCD). The diagnosis relies on clinical manifestation, biochemical evidence of hypercitrullinemia, and identifying mutations in the SLC25A13 gene. Several common mutations have been found in patients of East Asian background. The mainstay treatment is nutritional therapy in early infancy utilizing a lactose-free and medium-chain triglyceride formula. This approach leads to the majority of patients recovering liver function by 1 year of age. Some patients may remain asymptomatic or undiagnosed, but a small proportion of cases can progress to cirrhosis and liver failure, necessitating liver transplantation. Recently, advancements in newborn screening methods have improved the age of diagnosis. Early diagnosis and timely management improve patient outcomes. Further studies are needed to elucidate the long-term follow-up of NICCD patients into adolescence and adulthood.

Clinical and genetic analysis of 26 Chinese patients with neonatal intrahepatic cholestasis due to citrin deficiency

BACKGROUND

Neonatal intrahepatic cholestasis due to citrin deficiency (NICCD) is an autosomal recessive disorder caused by SLC25A13 genetic mutations. We retrospectively analyzed 26 Chinese infants with NICCD (years 2014-2022) in Quanzhou City.

METHODS

The plasma citrulline (CIT) concentration analyzed by tandem mass spectrometry (MS/MS), biochemical parameters and molecular analysis results are presented.

RESULTS

Twelve genotypes were discovered. The relationship between the CIT concentration and genotype is uncertain. In total, 8 mutations were detected, with 4 variations, c.851_854delGTAT, c.615 + 5G > A, c.1638_1660dup and IVS16ins3kb, constituting the high-frequency mutations. Specifically, we demonstrated 2 patients with NICCD combined with another inborn errors of metabolism (IEM). Patient No. 22 possessed compound heterozygous mutations of c.615 + 5G > A and c.790G > A in the SLC25A13 gene accompanied by compound heterozygous variations of c.C259T and c.A155G in the PTS gene. Additionally, Patient No. 26 carried c.51C > G and c.760C > T in the SLC22A5 gene as well as c.615 + 5G > A and IVS16ins3kb in the SLC25A13 gene.

CONCLUSIONS

We report a case of the simultaneous occurrence of primary carnitine deficiency (PCD) and NICCD.

Complete genomic profiles of 1496 Taiwanese reveal curated medical insights

INTRODUCTION

The population of Taiwan has a long history of ethno-cultural evolution. The Taiwanese population was isolated from other large populations such as the European, Han Chinese, and Japanese population. The Taiwan Biobank (TWB) project has built a nationwide database, particularly for personal whole-genome sequence (WGS) to facilitate basic and clinical collaboration nationally and internationally, making it one of the most valuable public datasets of the East Asian population.

OBJECTIVES

This study provides comprehensive medical genomic findings from TWB WGS data, for better characterization of disease susceptibility and the choice of ideal treatment regimens in Taiwanese population.

METHODS

We reanalyzed 1496 WGS using a PrecisionFDA Truth challenge winner method Sentieon DNAscope. Single nucleotide variants (SNV) and small insertions/deletions (INDEL) were benchmarked. We also analyzed pharmacogenomic (PGx) drug-associated alleles, and copy number variants (CNV). Multiple practicing clinicians reviewed and curated the clinically significant variants. Variant annotations can be browsed at TaiwanGenomes (https://genomes.tw).

RESULTS

We found that each participant had an average of 6,870.7 globally novel variants and 75.3% (831/1103) of the participants harbored at least one PharmGKB-selected high evidence level human leukocyte antigen (HLA) risk allele. 54 PharmGKB-reported high-level instances of evidence of Cytochrome P450 variant-drug pairs, with a population frequency of over 13.2%. We also identified 23 variants in the ACMG secondary finding V3 gene list from 25 participants, suggesting that 1.67% (25/1496) of the population is harboring at least one medical actionable variant. Our carrier status analyses suggest that one in 25 couples (3.94%) would risk having offspring with at least one pathogenic variant, which is in line with rates found in Japan and Singapore. For pathogenic CNV, we detected 6.88% and 2.02% carrier rates for alpha thalassemia and spinal muscular atrophy, respectively.

CONCLUSION

Our study highlights the overall medical insights of a complete Taiwanese genomic profile.

Citrin Deficiency: Clinical and Nutritional Features

SLC25A13 gene mutations are responsible for diseases related to citrin deficiency (CD), such as neonatal intrahepatic cholestasis caused by citrin deficiency and adult-onset type II citrullinemia (CTLN2). From childhood to adulthood, CD patients are apparently healthy due to metabolic compensation with peculiar dietary habits-disliking high-carbohydrate foods and liking fat and protein-rich foods. Carbohydrate overload and alcohol consumption may trigger the sudden onset of CTLN2, inducing hyperammonemia and consciousness disturbance. Well-compensated asymptomatic CD patients are sometimes diagnosed as having non-obese (lean) non-alcoholic fatty liver disease and steatohepatitis, which have the risk of developing into liver cirrhosis and hepatocellular carcinoma. CD-induced fatty liver demonstrates significant suppression of peroxisome proliferator-activated receptor α and its downstream enzymes/proteins involved in fatty acid transport and oxidation and triglyceride secretion as a very low-density lipoprotein. Nutritional therapy is an essential and important treatment of CD, and medium-chain triglycerides oil and sodium pyruvate are useful for preventing hyperammonemia. We need to avoid the use of glycerol for treating brain edema by hyperammonemia. This review summarizes the clinical and nutritional features of CD-associated fatty liver disease and promising nutritional interventions.

The mutation spectrum of SLC25A13 gene in citrin deficiency: identification of novel mutations in Vietnamese pediatric cohort with neonatal intrahepatic cholestasis

BACKGROUND

Citrin deficiency (CD), a disorder caused by mutations in the SLC25A13 gene, may result in neonatal intrahepatic cholestasis. This study was purposely to explore the mutation spectrum of SLC25A13 gene in Vietnamese CD patients.

METHODS

The 292 unrelated CD patients were first screened for four high-frequency mutations by PCR/PCR-RFLP. Then, Sanger sequencing was performed directly for heterozygous or undetected patients. Novel mutations identified would need to be confirmed by their parents.

RESULTS

12 pathogenic SLC25A13 mutations were identified in all probands, including three deletions c.851_854del (p.R284Rfs*3), c.70-63_133del (p.Y24_72Ifs*10), and c.[1956C>A;1962del] (p.[N652K;F654Lfs*45]), two splice-site mutations (IVS6+5G>A and IVS11+1G>A), one nonsense mutations c.1399C>T (p.R467*), one duplication mutation c.1638_1660dup (p.A554fs*570), one insertion IVSl6ins3kb (p.A584fs*585), and four missense mutation c.2T>C (p.M1T), c.1231G>A (p.V411M), c.1763G>A (p.R588Q), and c.135G>C (p.L45F). Among them, c.851_854del (mut I) was the most identified mutant allele (91.78%) with a total of 247 homozygous and 42 heterozygous genotypes of carriers. Interestingly, two novel mutations were identified: c.70-63_133del (p.Y24_72Ifs*10) and c.[1956C>A;1962del] (p.[N652K;F654Lfs*45]).

CONCLUSION

The SLC25A13 mutation spectrum related to intrahepatic cholestasis infants in Vietnam revealed a quite similar pattern to Asian countries' reports. This finding supports the use of targeted SLC25A13 mutation for CD screening in Vietnam and contributed to the SLC25A13 mutation spectra worldwide. It also helps emphasize the role of DNA analysis in treatment, genetic counseling, and prenatal diagnosis.

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.

Improved diagnosis of citrin deficiency by newborn screening using a molecular second-tier test

BACKGROUND

Citrin deficiency is an autosomal recessive disorder caused by variants of the SLC25A13 gene. Although newborn screening (NBS) provides an opportunity for its early diagnosis and treatment, citrin deficiency detection rates remain lower than those estimated.

METHODS

Before 2018, NBS for citrin deficiency was based on citrulline levels alone. In June 2018, a second-tier molecular test was implemented to detect 11 common variants of the SLC25A13 gene and improve the NBS detection rates. This study compares the incidence rates and costs before and after the second-tier implementation.

RESULTS

Prior to 2018, five subjects were diagnosed via NBS, and 12 of 555,449 newborns screened were missed. In comparison, 11 subjects were diagnosed out of 198,071 newborns screened after 2018, and there were no false-negatives. The citrin deficiency detection rate increased from 1/32,673 to 1/18,006 after the second-tier test was implemented, with only a minimal increase in the total cost. The number of false-positive in our cohort was tolerable. Subjects with citrin deficiency may present with borderline elevated citrulline levels; these can remain slightly elevated or increase considerably on retest. Four patients (80%) detected prior to second-tier testing and six patients (55%) detected after it was implemented were identified based on the citrulline levels alone. However, at the time of second blood sampling, the normal citrulline level of five subjects did not exclude a citrin deficiency diagnosis.

CONCLUSIONS

Our study shows that it is vital and cost-effective to employ second-tier molecular testing to improve the detection of citrin deficiency by NBS.

Pathogenic variants of the mitochondrial aspartate/glutamate carrier causing citrin deficiency

Citrin deficiency is a pan-ethnic and highly prevalent mitochondrial disease with three different stages: neonatal intrahepatic cholestasis (NICCD), a relatively mild adaptation stage, and type II citrullinemia in adulthood (CTLN2). The cause is the absence or dysfunction of the calcium-regulated mitochondrial aspartate/glutamate carrier 2 (AGC2/SLC25A13), also called citrin, which imports glutamate into the mitochondrial matrix and exports aspartate to the cytosol. In citrin deficiency, these missing transport steps lead to impairment of the malate-aspartate shuttle, gluconeogenesis, amino acid homeostasis, and the urea cycle. In this review, we describe the geological spread and occurrence of citrin deficiency, the metabolic consequences and use our current knowledge of the structure to predict the impact of the known pathogenic mutations on the calcium-regulatory and transport mechanism of citrin.

Desflurane and remifentanil anesthesia in a child with citrin deficiency: A case report

RATIONALE

Hyperammonemia, metabolic derangement, and/or the prolonged effects of anesthetics may lead to delayed emergence from general anesthesia as well as the onset of type 2 citrullinemia, even in compensated patients with citrin deficiency.

PATIENT CONCERN

A 5-year-old girl with citrin deficiency was scheduled for blepharoplasty under general anesthesia. She developed hyperammonemia with temporary interruption of medication for a few days before surgery.

DIAGNOSIS

The patient was genetically diagnosed as citrin deficiency with a mutation in the SLC25A13 gene via newborn screening for metabolic disorders. Her citrulline and ammonia levels were well-controlled with arginine medication and protein-rich diet. Her elevated ammonia level by temporary interruption of medication was corrected with resumption of arginine medication and protein-rich diet before surgery.

INTERVENTIONS

We used desflurane and remifentanil for general anesthesia to avoid hyperammonemia and delayed emergence. End-tidal desflurane concentration and anesthetic depth were carefully monitored to avoid excessive anesthesia.

OUTCOMES

She recovered consciousness with slightly increased ammonia level immediately after anesthesia.

LESSIONS

General anesthesia of the shortest duration with the least metabolized drugs using desflurane and remifentanil, would be beneficial for rapid emergence in surgical patients with citrin deficiency. Maintenance of nitrogen scavenging medication, a protein-rich diet, and serial measurement of ammonia levels in the perioperative period are also important for avoiding hyperammonemia-related neurological dysfunction.

Hemostatic rebalance in neonatal intrahepatic cholestasis with citrin deficiency

BACKGROUND

Neonatal intrahepatic cholestasis with citrin deficiency (NICCD) results in coagulopathy due to decreased levels of vitamin (V)K-dependent clotting factors, similar to biliary atresia (BA). However, the involvement of VK-independent coagulant and anticoagulant factor(s) remains unknown. We examined relationships between coagulant and anticoagulant potential before and after nutritional treatment in NICCD.

METHODS

Three cases (aged 12, 21, and 45 days) with NICCD-associated coagulopathy were evaluated with standard coagulation/anticoagulation tests and comprehensive coagulation assays, rotational thromboelastometry, and protein C/protein S (PC/PS) pathway function assay (ThromboPath^® ), before and after nutritional treatment.

RESULTS

In all cases, activated partial thromboplastin time and prothrombin time were significantly prolonged, which is associated with very low levels of VK-independent fibrinogen and antithrombin. The initiation of nutritional treatment of medium-chain triglycerides oil improved these levels within the normal range, although low levels of other clotting factors were modestly increased. Whole blood- rotational thromboelastometry analysis revealed near-normal coagulation potential, even before treatment, comparable to healthy adults, and supportive of their non-bleeding symptoms. The introduction of nutritional treatment had further improved comprehensive coagulation potential. The global PC/PS-pathway function assay demonstrated the absence of the features of this function associated with the pathogenesis of NICCD. Compared to BA, the plasma levels of fibrinogen and antithrombin in all cases were markedly low, whilst those after treatment improved, especially to similar level of BA.

CONCLUSIONS

Neonatal intrahepatic cholestasis with citrin deficiency has the characteristic of rebalancing hemostatic mechanisms associated with coagulant and anticoagulant potential involving low levels of fibrinogen and antithrombin, suggesting a pathophysiological coagulopathy distinct from BA.

The Genetics of Inherited Cholestatic Disorders in Neonates and Infants: Evolving Challenges

Many inherited conditions cause cholestasis in the neonate or infant. Next-generation sequencing methods can facilitate a prompt diagnosis in some of these cases; application of these methods in patients with liver diseases of unknown cause has also uncovered novel gene-disease associations and improved our understanding of physiological bile secretion and flow. By helping to define the molecular basis of certain cholestatic disorders, these methods have also identified new targets for therapy as well patient subgroups more likely to benefit from specific therapies. At the same time, sequencing methods have presented new diagnostic challenges, such as the interpretation of single heterozygous genetic variants. This article discusses those challenges in the context of neonatal and infantile cholestasis, focusing on difficulties in predicting variant pathogenicity, the possibility of other causal variants not identified by the genetic screen used, and phenotypic variability among patients with variants in the same genes. A prospective, observational study performed between 2010-2013, which sequenced six important genes (ATP8B1, ABCB11, ABCB4, NPC1, NPC2 and SLC25A13) in an international cohort of 222 patients with infantile liver disease, is given as an example of potential benefits and challenges that clinicians could face having received a complex genetic result. Further studies including large cohorts of patients with paediatric liver disease are needed to clarify the spectrum of phenotypes associated with, as well as appropriate clinical response to, single heterozygous variants in cholestasis-associated genes.

Hyperammonemia in Inherited Metabolic Diseases

Ammonia is a neurotoxic compound which is detoxified through liver enzymes from urea cycle. Several inherited or acquired conditions can elevate ammonia concentrations in blood, causing severe damage to the central nervous system due to the toxic effects exerted by ammonia on the astrocytes. Therefore, hyperammonemic patients present potentially life-threatening neuropsychiatric symptoms, whose severity is related with the hyperammonemia magnitude and duration, as well as the brain maturation stage. Inherited metabolic diseases caused by enzymatic defects that compromise directly or indirectly the urea cycle activity are the main cause of hyperammonemia in the neonatal period. These diseases are mainly represented by the congenital defects of urea cycle, classical organic acidurias, and the defects of mitochondrial fatty acids oxidation, with hyperammonemia being more severe and frequent in the first two groups mentioned. An effective and rapid treatment of hyperammonemia is crucial to prevent irreversible neurological damage and it depends on the understanding of the pathophysiology of the diseases, as well as of the available therapeutic approaches. In this review, the mechanisms underlying the hyperammonemia and neurological dysfunction in urea cycle disorders, organic acidurias, and fatty acids oxidation defects, as well as the therapeutic strategies for the ammonia control will be discussed.

Neonatal Intrahepatic Cholestasis Caused by Citrin Deficiency with SLC25A13 Mutation Presenting Hepatic Steatosis and Prolonged Jaundice. A Rare Case Report

Background: Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is a rare autosomal recessive disease. The incidence of citrin deficiency is estimated between 1/10,000 and 1/20,000 in Taiwan. Case report: This report describes a case of a 42 day old female infant who suffered from prolonged jaundice, poor weight gain, and anemia. The initial total/direct bilirubin levels were 8.1/3.11 mg/dL. Liver biopsy was performed at 47 days old. The pathology revealed lobules marked with macrovesicular and microvesicular fatty metamorphosis. The serum amino acid profile showed elevated levels of threonine, methionine, citrulline, and arginine. Newborn screening disclosed normal results, but the genetic study revealed SLC25A13 mutation 851-854 del and 615 + 5G > A. The genetic study of her parents showed that the father carried the SLC25A13 mutation 851-854 del and the mother carried the SLC25A13 mutation 615 + 5G > A. Treatment with ursodeoxycholic acid decreased the bilirubin levels to a normal range at the age of 5 months. Conclusion: This report illustrates that hepatic steatosis is a feature of NICCD. For every young infant patient who develops cholestasis, the pediatrician must consider NICCD as a differential diagnosis even if newborn screening shows normal findings.

Molecular epidemiologic study of citrin deficiency by screening for four reported pathogenic SLC25A13 variants in the Shaanxi and Guangdong provinces, China

BACKGROUND

Citrin deficiency (CD) is an autosomal recessive disease resulting from biallelic mutations of the SLC25A13 gene. This study aimed to investigate the molecular epidemiological features of CD in the Guangdong and Shaanxi provinces of China.

METHODS

A total of 3,409 peripheral blood samples from Guangdong and 2,746 such samples from Shaanxi province were collected. Four prevalent SLC25A13 mutations NG_012247.2 (NM_014251.3): c.852_855del, c.1638_1660dup, c.615+5G>A, and c.1751-5_1751-4ins(2684) were screened by using the conventional polymerase chain reaction (PCR)/PCR-restriction fragment length polymorphism and newly-developed multiplex PCR methods, respectively. The mutated SLC25A13 allele frequencies, carrier frequencies, and CD morbidity rates were calculated and then compared with the Chi-square and Fisher's exact tests.

RESULTS

The mutations were detected in 68 out of 6,818 SLC25A13 alleles in Guangdong and 29 out of 5,492 alleles in the Shaanxi population. The carrier frequencies were subsequently calculated to be 1/51 and 1/95, while the CD morbidity rates were 1/10,053 and 1/35,865, in the 2 populations, respectively. When compared with the Shaanxi population, Guangdong exhibited a higher frequency of mutated SLC25A13 allele (68/6,818 vs. 29/5,492, χ²=8.570, P=0.003) in general, with higher c.852_855del (54/6,818 vs. 13/5,492, χ²=17.328, P=0.000) but lower c.1751-5_1751 -4ins(2684) (2/6,818 vs. 9/5,492, P=0.015) allele frequencies. The distribution of c.615+5G>A and c.1638_1660dup between the 2 provinces, as well as all 4 prevalent mutations among different geographic regions within the 2 provinces, did not differed significantly.

CONCLUSIONS

Our findings depicted the CD molecular epidemiological features in Guangdong and Shaanxi populations, providing preliminary but significant laboratory evidences for the subsequent CD diagnosis and management in the 2 provinces of mainland China.

Adult-onset citrullinaemia type II with liver cirrhosis: A rare cause of hyperammonaemia

Adult-onset citrullinaemia type II (CTLN2) is a rare disease in Chinese patients. As a subtype of citrin deficiency (CD), it is an autosomal recessive disease related to the SLC25A13 mutation on chromosome 7q21.3. In this study, we report a case of CTLN2 presenting with paroxysmal altered consciousness and refractory hyperammonaemia. The diagnosis was finally confirmed by gene analysis. The patient recovered after liver transplantation. It can be learned from this case that CD should be considered in patients with refractory hyperammonaemia and paroxysmal mental disorder without a history of liver disease.

Rapid Genetic Diagnosis of Citrin Deficiency by Multicolor Melting Curve Analysis

Citrin deficiency caused by SLC25A13 genetic mutations is an autosomal recessive disease, and four prevalent mutations including c.851_854del, c.1638_1660dup, IVS6+5G>A, and IVS16ins3kb make up >80% of total pathogenic mutations within the Chinese population. However, suitable assays for detection of these mutations have not yet been developed for use in routine clinical practice. In the current study, a real-time PCR-based multicolor melting curve analysis (MMCA) was developed to detect the four prevalent mutations in one closed-tube reaction. The analytical and clinical performances were evaluated using artificial templates and clinical samples. All four mutations in the test samples were accurately genotyped via their labeling fluorophores and Tm values, and the standard deviations of Tm values were indicated to be <0.2°C. The limit of detection was estimated to be 500 diploid human genomes per reaction. The MMCA assay of 5,332 healthy newborns from southern China identified a total of 107 SLC25A13-mutation carriers, indicating a carrier rate of 2%. The genotypes of 107 carriers and 112 random non-carriers were validated using direct sequencing and Long-range PCR with 100% concordance. In conclusion, the assay developed in this study may potentially serve as a rapid genetic diagnostic tool for citrin deficiency.

AGC2 (Citrin) Deficiency-From Recognition of the Disease till Construction of Therapeutic Procedures

Can you imagine a disease in which intake of an excess amount of sugars or carbohydrates causes hyperammonemia? It is hard to imagine the intake causing hyperammonemia. AGC2 or citrin deficiency shows their symptoms following sugar/carbohydrates intake excess and this disease is now known as a pan-ethnic disease. AGC2 (aspartate glutamate carrier 2) or citrin is a mitochondrial transporter which transports aspartate (Asp) from mitochondria to cytosol in exchange with glutamate (Glu) and H⁺. Asp is originally supplied from mitochondria to cytosol where it is necessary for synthesis of proteins, nucleotides, and urea. In cytosol, Asp can be synthesized from oxaloacetate and Glu by cytosolic Asp aminotransferase, but oxaloacetate formation is limited by the amount of NAD⁺. This means an increase in NADH causes suppression of Asp formation in the cytosol. Metabolism of carbohydrates and other substances which produce cytosolic NADH such as alcohol and glycerol suppress oxaloacetate formation. It is forced under citrin deficiency since citrin is a member of malate/Asp shuttle. In this review, we will describe history of identification of the SLC25A13 gene as the causative gene for adult-onset type II citrullinemia (CTLN2), a type of citrin deficiency, pathophysiology of citrin deficiency together with animal models and possible treatments for citrin deficiency newly developing.

Overexpression of the peroxin Pex34p suppresses impaired acetate utilization in yeast lacking the mitochondrial aspartate/glutamate carrier Agc1p

PEX34, encoding a peroxisomal protein implicated in regulating peroxisome numbers, was identified as a high copy suppressor, capable of bypassing impaired acetate utilization of agc1∆ yeast. However, improved growth of agc1∆ yeast on acetate is not mediated through peroxisome proliferation. Instead, stress to the endoplasmic reticulum and mitochondria from PEX34 overexpression appears to contribute to enhanced acetate utilization of agc1∆ yeast. The citrate/2-oxoglutarate carrier Yhm2p is required for PEX34 stimulated growth of agc1∆ yeast on acetate medium, suggesting that the suppressor effect is mediated through increased activity of a redox shuttle involving mitochondrial citrate export. Metabolomic analysis also revealed redirection of acetyl-coenzyme A (CoA) from synthetic reactions for amino acids in PEX34 overexpressing yeast. We propose a model in which increased formation of products from the glyoxylate shunt, together with enhanced utilization of acetyl-CoA, promotes the activity of an alternative mitochondrial redox shuttle, partially substituting for loss of yeast AGC1.

Combining newborn metabolic and genetic screening for neonatal intrahepatic cholestasis caused by citrin deficiency

To evaluate the feasibility of incorporating genetic screening for neonatal intrahepatic cholestasis, caused by citrin deficiency (NICCD), into the current newborn screening (NBS) program. We designed a high-throughput iPLEX genotyping assay to detect 28 SLC25A13 mutations in the Chinese population. From March 2018 to June 2018, 237 630 newborns were screened by tandem mass spectrometry at six hospitals. Newborns with citrulline levels between ^1/2 cutoff and cutoff values of the upper limit were recruited for genetic screening using the newly developed assay. The sensitivity and specificity of the iPLEX genotyping assay both reached 100% in clinical practice. Overall, 29 364 (12.4%) newborns received further genetic screening. Five patients with conclusive genotypes were successfully identified. The most common SLC25A13 mutation was c.851_854del, with an allele frequency of 60%. In total, 658 individuals with one mutant allele were identified as carriers. Eighteen different mutations were observed, yielding a carrier rate of 1/45. Notably, Quanzhou in southern China had a carrier rate of up to 1/28, whereas Jining in northern China had a carrier rate higher than that of other southern and border cities. The high throughput iPLEX genotyping assay is an effective and reliable approach for NICCD genotyping. The combined genetic screening could identify an additional subgroup of patients with NICCD, undetectable by conventional NBS. Therefore, this study demonstrates the viability of incorporating genetic screening for NICCD into the current NBS program.

Successful treatment of adult-onset type II citrullinemia with a low-carbohydrate diet and L-arginine after DNA analysis produced a definitive diagnosis

A 60-year-old male, who exhibited finger tremors, obnubilation, and hyperammonemia (409 μg/dL), was admitted to our hospital. Initially, we suspected that a portosystemic shunt had caused his hyperammonemia. However, his symptoms did not improve after balloon-occluded retrograde transvenous obliteration. He was subsequently found to have some peculiar eating habits, including a fondness for bean curd and peanuts, and an aversion to alcohol and sweets. Furthermore, marked citrullinemia (454.2 nmol/mL) was revealed, which led us to suspect adult-onset type II citrullinemia (CTLN2). DNA analysis of the patient and his mother, son, and daughter confirmed that he was homozygous for the c.852_855del mutation in the SLC25A13 gene, and his relatives were heterozygous for the c.852_855del mutation, which led to a definitive diagnosis. A low-carbohydrate diet and the administration of L-arginine ameliorated his symptoms. It is important to be aware that CTLN2 can occur in elderly patients. Thus, patients who exhibit symptoms of CTLN2 should be interviewed about their dietary habits and subjected to plasma amino acid analysis.In this report, we consider the metabolic disorders seen in citrin deficiency and the associated compensatory mechanisms in relation to the clinical features and treatment of CTLN2.

Sodium Taurocholate Cotransporting Polypeptide (NTCP) Deficiency Hidden Behind Citrin Deficiency in Early Infancy: A Report of Three Cases

Sodium taurocholate cotransporting polypeptide (NTCP), a carrier protein encoded by the gene SLC10A1, is expressed in the basolateral membrane of the hepatocyte to uptake bile acids from plasma. As a new inborn error of bile acid metabolism, NTCP deficiency remains far from being well understood in terms of the clinical and molecular features. Citrin deficiency is a well-known autosomal recessive disease arising from SLC25A13 mutations, and in neonates or infants, this condition presents as transient intrahepatic cholestasis which usually resolves before 1 year of age. All the three patients in this paper exhibited cholestatic jaundice and elevated total bile acids in their early infancy, which were attributed to citrin deficiency by SLC25A13 genetic analysis. In response to feeding with lactose-free and medium-chain triglycerides-enrich formula, their clinical and laboratory presentations disappeared gradually while the hypercholanemia persisted, even beyond 1 year of age. On subsequent SLC10A1 analysis, they were all homozygous for the well-known pathogenic variant c.800C > T (p.Ser267Phe), and NTCP deficiency was thus definitely diagnosed. The findings in this paper indicated that NTCP deficiency could be covered up by citrin deficiency during early infancy; however, in citrin-deficient patients with intractable hypercholanemia following resolved cholestatic jaundice, NTCP deficiency should be taken into consideration.

The genetic landscape of the human solute carrier (SLC) transporter superfamily

The human solute carrier (SLC) superfamily of transporters is comprised of over 400 membrane-bound proteins, and plays essential roles in a multitude of physiological and pharmacological processes. In addition, perturbation of SLC transporter function underlies numerous human diseases, which renders SLC transporters attractive drug targets. Common genetic polymorphisms in SLC genes have been associated with inter-individual differences in drug efficacy and toxicity. However, despite their tremendous clinical relevance, epidemiological data of these variants are mostly derived from heterogeneous cohorts of small sample size and the genetic SLC landscape beyond these common variants has not been comprehensively assessed. In this study, we analyzed Next-Generation Sequencing data from 141,456 individuals from seven major human populations to evaluate genetic variability, its functional consequences, and ethnogeographic patterns across the entire SLC superfamily of transporters. Importantly, of the 204,287 exonic single-nucleotide variants (SNVs) which we identified, 99.8% were present in less than 1% of analyzed alleles. Comprehensive computational analyses using 13 partially orthogonal algorithms that predict the functional impact of genetic variations based on sequence information, evolutionary conservation, structural considerations, and functional genomics data revealed that each individual genome harbors 29.7 variants with putative functional effects, of which rare variants account for 18%. Inter-ethnic variability was found to be extensive, and 83% of deleterious SLC variants were only identified in a single population. Interestingly, population-specific carrier frequencies of loss-of-function variants in SLC genes associated with recessive Mendelian disease recapitulated the ethnogeographic variation of the corresponding disorders, including cystinuria in Jewish individuals, type II citrullinemia in East Asians, and lysinuric protein intolerance in Finns, thus providing a powerful resource for clinical geneticists to inform about population-specific prevalence and allelic composition of Mendelian SLC diseases. In summary, we present the most comprehensive data set of SLC variability published to date, which can provide insights into inter-individual differences in SLC transporter function and guide the optimization of population-specific genotyping strategies in the bourgeoning fields of personalized medicine and precision public health.

Expanded Newborn Screening for Inborn Errors of Metabolism by Tandem Mass Spectrometry in Suzhou, China: Disease Spectrum, Prevalence, Genetic Characteristics in a Chinese Population

Expanded newborn screening for inborn errors of metabolism (IEMs) by tandem mass spectrometry (MS/MS) could simultaneously analyze more than 40 metabolites and identify about 50 kinds of IEMs. Next generation sequencing (NGS) targeting hundreds of IMEs-associated genes as a follow-up test in expanded newborn screening has been used for genetic analysis of patients. The spectrum, prevalence, and genetic characteristic of IEMs vary dramatically in different populations. To determine the spectrum, prevalence, and gene mutations of IEMs in newborns in Suzhou, China, 401,660 newborns were screened by MS/MS and 138 patients were referred to genetic analysis by NGS. The spectrum of 22 IEMs were observed in Suzhou population of newborns, and the overall incidence (excluding short chain acyl-CoA dehydrogenase deficiency (SCADD) and 3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCD)) was 1/3,163. The prevalence of each IEM ranged from 1/401,660 to 1/19,128, while phenylketonuria (PKU) (1/19,128) and Mild hyperphenylalaninemia (M-HPA) (1/19,128) were the most common IEMs, followed by primary carnitine uptake defect (PCUD) (1/26,777), SCADD (1/28,690), hypermethioninemia (H-MET) (1/30,893), 3-MCCD (1/33,412) and methylmalonic acidemia (MMA) (1/40,166). Moreover, 89 reported mutations and 51 novel mutations in 25 IMEs-associated genes were detected in 138 patients with one of 22 IEMs. Some hotspot mutations were observed for ten IEMs, including PAH gene c.728G > A, c.611A > G, and c.721C > T for Phenylketonuria, PAH gene c.158G > A, c.1238G > C, c.728G > A, and c.1315+6T > A for M-HPA, SLC22A5 gene c.1400C > G, c.51C > G, and c.760C > T for PCUD, ACADS gene c.1031A > G, c.164C > T, and c.1130C > T for SCAD deficiency, MAT1A gene c.791G > A for H-MET, MCCC1 gene c.639+2T > A and c.863A > G for 3-MCCD, MMUT gene c.1663G > A for MMA, SLC25A13 gene c.IVS16ins3Kb and c.852_855delTATG for cittrullinemia II, PTS gene c.259C > T and c.166G > A for Tetrahydrobiopterin deficiency, and ACAD8 gene c.1000C > T and c.286C > A for Isobutyryl coa dehydrogenase deficiency. All these hotspot mutations were reported to be pathogenic or likely pathogenic, except a novel mutation of ACAD8 gene c.286C > A. These mutational hotspots could be potential candidates for gene screening and these novel mutations expanded the mutational spectrum of IEMs. Therefore, our findings could be of value for genetic counseling and genetic diagnosis of IEMs.

Identification of a novel splicing mutation in the SLC25A13 gene from a patient with NICCD: a case report

Background

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is an autosomal recessive disorder and one of the most common inherent causes of cholestatic jaundice in Asian infants. Mutations in the SLC25A13 gene, which encodes citrin protein expressed in the liver, have been identified as the genetic cause for NICCD.

Case presentation

Here, we report a 4-month-old female with clinical features including jaundice, hyperbilirubinemia, hyperlactacidemia, and abnormal liver function. The patient was diagnosed with NICCD by differential diagnosis using genetic analysis. Mutations in 60 jaundice-related genes were tested by using amplicon sequencing, which was performed on an Ion S5XL genetic analyzer. A compound heterozygous mutation in the SLC25A13 gene was identified, consisting of a known deletion SLC25A13:c.852_855delTATG and a novel splicing mutation SLC25A13:c.1841 + 3_1841 + 4delAA. Sanger sequencing for the proband and her parents was performed to validate the result and reveal the source of mutations.

Conclusion

A compound heterozygous mutation in the SLC25A13 gene was identified in a 4-month-old female patient with NICCD. Our data suggest that amplicon sequencing is a helpful tool for the differential diagnosis of inherited diseases with similar symptoms. Further studies of the mutation spectrum of neonatal jaundice in China are warranted.

Current treatment for citrin deficiency during NICCD and adaptation/compensation stages: Strategy to prevent CTLN2

Identification of the genes responsible for adult-onset type II citrullinemia (CTLN2) and citrin protein function have enhanced our understanding of citrin deficiency. Citrin deficiency is characterized by 1) neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD); 2) adaptation/compensation stage with unique food preference from childhood to adulthood; and 3) CTLN2. The treatment of NICCD aims to prevent the progression of cholestasis, and it includes medium chain triglycerides (MCT) milk and lactose-free milk, in addition to medications (e.g., vitamin K₂, lipid-soluble vitamins and ursodeoxycholic acid). Spontaneous remission around the age of one is common in NICCD, though prolonged cholestasis can lead to irreversible liver failure and may require liver transplantation. The adaptation/compensation stage (after one year of age) is characterized by the various signs and symptoms such as hypoglycemia, fatty liver, easy fatigability, weight loss, and neuropsychiatric symptoms. Some poorly-controlled patients show failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD). Diet therapy is the key in the adaptation/compensation stage. Protein- and fat-rich diet with a protein: fat: carbohydrate ratio being 15-25%: 40-50%: 30-40% along with the appropriate energy intake is recommended. The use of MCT oil and sodium pyruvate is also effective. The toxicity of carbohydrate is well known in the progression to CTLN2 if the consumption is over a long term or intense. Alcohol can also trigger CTLN2. Continuous intravenous hyperalimentation with high glucose concentration needs to be avoided. Administration of Glyceol® (an osmotic agent containing glycerol and fructose) is contraindicated. Because the intense treatment such as liver transplantation may become necessary to cure CTLN2, the effective preventative treatment during the adaptation/compensation stage is very important. At present, there is no report of a case with patients reported having the onset of CTLN2 who are on the diet therapy and under the appropriate medical support during the adaptation/compensation stage.

Bioinformatic and functional analysis of promoter region of human SLC25A13 gene

The human SLC25A13 gene encodes the liver type aspartate/glutamate carrier isoform 2 (AGC2, commonly named as citrin), which plays a key role in the main NADH-shuttle of human hepatocyte. Biallelic SLC25A13 mutations result in Citrin deficiency (CD). In order to identify the important regulatory region of SLC25A13 gene and elucidate the way how potential promoter mutations affect the citrin expression, we performed promoter deletion analysis and established the reporter constructs of luciferase gene-carrying SLC25A13 promoter containing several mutations located in putative transcription factor-binding sites. The luciferase activities of all promoter constructs were measured using a Dual-Luciferase Reporter Assay System. Bioinformatic analysis showed that the promoter of SLC25A13 gene lacks TATA box and obviously typical initiator element, but contains a CCAAT box and two GC box. Promoter deletion analysis confirmed the region from -221 to -1 upstream ATG was essential for SLC25A13 to maintain the promoter activity. We utilized dual-luciferase reporter system as function analytical model to tentatively assess the effect of artificially constructed promoter mutations on citrin expression, and our analysis revealed that mutated putative CCAAT box and GC box could significantly affect the citrin expression. Our study confirmed the important SLC25A13 promoter regions that influenced citrin expression in HL7702 cells, and constructed a function analytical model. This work may be useful to further identify the pathogenic mutations leading to CD in the promoter region.

Risk factors associated with mortality in neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) and clinical implications

Background

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) has high prevalence in East Asia, and has been reported in other parts of the world. NICCD is also the most common form of genetic cholestasis among East Asians. There has been reports of mortalities or liver transplants associated with NICCD, but risk factors associated with poor outcome were unknown. Our objective is to report NICCD mortalities in a tertiary pediatric hepatology center, and to explore associated risk factors along with implications to clinical practice.

Method

This is a retrospective analysis of NICCD cases collected from June 2003 until January 2017 in the Children’s Hospital of Fudan University. Clinical, biochemical, and genetic data were compared between deceased cases and survivors without liver transplant.

Results

Sixty-one confirmed NICCD cases, including 52 cases in the survival group, and 9 cases in the mortality group, were included in the analysis. Mean age at referral in the mortality group was significantly higher when compared to the survival group (9.58 ± 5.03 VS 3.96 ± 3.13 months, p < 0.000). The proportion with infection in the mortality group was significantly higher than the survival group (p = 0.023). 44.4% of patients in the mortality group did not receive lactose-free and/or medium chain triglycerides enriched (LF/MCT) formula, and this percentage was significantly higher than the survival group (9.6%, p = 0.021). Mean platelet (PLT) count in the mortality group was significantly lower than the survival group (p = 0.010). Mean serum gamma-glutamyl transpeptidase (GGT), and total cholesterol (TCH) levels were significantly lower in the mortality group when compared to the survival group with p values of 0.001, and 0.019, respectively. Those who died had higher serum ammonium levels than survivors (p = 0.016). Mean level of citrulline was significantly lower in the mortality group compared to the survival group (p = 0.010). On the other hand, mean level of tyrosine was significantly higher in the mortality group than that of the survival group (p = 0.015).

Conclusion

Late referral, presence of infection, delayed treatment with LF/MCT formula, lower platelet count, lower levels of GGT, total cholesterol, blood citrulline, and higher level of blood ammonia and tyrosine, were associated with poor prognosis in NICCD.

Electronic supplementary material

The online version of this article (10.1186/s12887-018-1383-5) contains supplementary material, which is available to authorized users.

Diversity in the incidence and spectrum of organic acidemias, fatty acid oxidation disorders, and amino acid disorders in Asian countries: Selective screening vs. expanded newborn screening

Background

Expanded newborn screening (ENBS) utilizing tandem mass spectrometry (MS/MS) for inborn metabolic diseases (IMDs), such as organic acidemias (OAs), fatty acid oxidation disorders, (FAODs), and amino acid disorders (AAs), is increasingly popular but has not yet been introduced in many Asian countries. This study aimed to determine the incidence rates of OAs, FAODs, and AAs in Asian countries and Germany using selective screening and ENBS records.

Materials and methods

Selective screening for IMDs using gas chromatography–mass spectrometry and MS/MS was performed among patients suspected to be afflicted in Asian countries (including Japan, Vietnam, China, and India) between 2000 and 2015, and the results from different countries were compared. Similarly, ENBS results from Japan, South Korea, Taiwan, and Germany were compared. Additionally, the results of selective screening and ENBS in Japan were compared.

Results

Among 39,270 patients who underwent selective screening, IMDs were detected in 1170. Methylmalonic acidemia was frequently identified in several countries, including Japan (81/377 diagnosed IMDs), China (94/216 IMDs), and India (72/293 IMDs). In Vietnam, however, β-ketothiolase deficiency was particularly frequent (33/250 IMDs). ENBS yielded differences in overall IMD rates by country: 1:8557 in Japan, 1:7030 in Taiwan, 1:13,205 in South Korea, and 1:2200 in Germany. Frequently discovered diseases included propionic acidemia (PPA) and phenylketonuria (PKU) in Japan, 3-methylcrotonyl-CoA carboxylase deficiency (MCCD) and PKU in Taiwan, MCCD and citrullinemia type I in South Korea, and PKU and medium-chain acyl-CoA dehydrogenase deficiency in Germany. Furthermore, in Japan, selective screening and ENBS yielded respective PPA frequencies of 14.7% and 49.4% among all organic acidemias.

Conclusion

The incidence rates of IMDs vary by country. Moreover, the disease spectra of IMDs detected via selective screening differ from those detected via ENBS.

[Clinical and genetic analysis of a pediatric patient with sodium taurocholate cotransporting polypeptide deficiency]

Sodium taurocholate cotransporting polypeptide (NTCP) deficiency is an inborn error of bile acid metabolism caused by mutations of SLC10A1 gene. This paper reports the clinical and genetic features of a patient with this disease. A 3.3-month-old male infant was referred to the hospital with the complaint of jaundiced skin and sclera over 3 months. Physical examination revealed moderate jaundice of the skin and sclera. The liver was palpable 3.5 cm below the right subcostal margin with a medium texture. Serum biochemistry analysis revealed markedly elevated bilirubin (predominantly direct bilirubin) and total bile acids (TBA), as well as decreased 25-OH-VitD level. On pathological analysis of the biopsied liver tissue, hepatocyte ballooning and cholestatic multinucleate giant cells were noted. The lobular architecture was distorted. Infiltration of inflammatory cells, predominantly lymphocytes, was seen in the portal tracts. In response to the anti-inflammatory and liver protective drugs as well as fat-soluble vitamins over 2 months, the bilirubin and transaminases levels were improved markedly while the TBA kept elevated. Because of persisting hypercholanemia on the follow-up, SLC10A1 gene analysis was performed at his age of 17.2 months. The child proved to be a homozygote of the reportedly pathogenic variant c.800C>T (p. Ser267Phe), while the parents were both carriers. NTCP deficiency was thus diagnosed. The infant was followed up until 34.3 months old. He developed well in terms of the anthropometric indices and neurobehavioral milestones. The jaundice disappeared completely. The liver size, texture and function indices all recovered. However, the hypercholanemia persisted, and the long-term outcome needs to be observed.

Early Detection and Diagnosis of Neonatal Intrahepatic Cholestasis Caused by Citrin Deficiency Missed by Newborn Screening Using Tandem Mass Spectrometry

Citrullinemia is the earliest identifiable biochemical abnormality in neonates with intrahepatic cholestasis due to a citrin deficiency (NICCD) and it has been included in newborn screening panels using tandem mass spectrometry. However, only one neonate was positive among 600,000 infants born in Sapporo city and Hokkaido, Japan between 2006 and 2017. We investigated 12 neonates with NICCD who were initially considered normal in newborn mass screening (NBS) by tandem mass spectrometry, but were later diagnosed with NICCD by DNA tests. Using their initial NBS data, we examined citrulline concentrations and ratios of citrulline to total amino acids. Although their citrulline values exceeded the mean of the normal neonates and 80% of them surpassed +3 SD (standard deviation), all were below the cutoff of 40 nmol/mL. The ratios of citrulline to total amino acids significantly elevated in patients with NICCD compared to the control. By evaluating two indicators simultaneously, we could select about 80% of patients with missed NICCD. Introducing an estimated index comprising citrulline values and citrulline to total amino acid ratios could assure NICCD detection by NBS.

Molecular diagnosis of citrin deficiency in an infant with intrahepatic cholestasis: identification of a 21.7kb gross deletion that completely silences the transcriptional and translational expression of the affected SLC25A13 allele

Neonatal Intrahepatic Cholestasis caused by Citrin Deficiency (NICCD) arises from biallelic SLC25A13 mutations, and SLC25A13 analysis provides reliable evidences for NICCD definite diagnosis. However, novel large insertions/deletions in this gene could not be detected just by conventional DNA analysis. This study aimed to explore definite diagnostic evidences for an infant highly-suspected to have NICCD. Prevalent mutation screening and Sanger sequencing of SLC25A13 gene just revealed a paternally-inherited mutation c.851_854del4. Nevertheless, neither citrin protein nor SLC25A13 transcripts of maternal origin could be detected on Western blotting and cDNA cloning analysis, respectively. On this basis, the hidden maternal mutation was precisely positioned using SNP analysis and semi-quantitative PCR, and finally identified as a novel large deletion c.-3251_c.15+18443del21709bp, which involved the SLC25A13 promoter region and the entire exon 1 where locates the translation initiation codon. Hence, NICCD was definitely diagnosed in the infant. To the best of our knowledge, the novel gross deletion, which silenced the transcriptional and translational expression of the affected SLC25A13 allele, is the hitherto largest deletion in SLC25A13 mutation spectrum. The Western blotting approach using mitochondrial protein extracted from expanded peripheral blood lymphocytes, of particular note, might be a new minimally-invasive and more-feasible molecular tool for NICCD diagnosis.

[Clinical feature and molecular diagnostic analysis of the first non-caucasian child with infantile liver failure syndrome type 1]

Infantile liver failure syndrome type 1 (ILFS1) is a Mendelian disease due to biallelic mutations in the cytoplasmic leucyl-tRNA synthetase gene (LARS). This study aimed to report the clinical and molecular features of the first non-caucasian ILFS1 patient, providing reliable evidences for the definite diagnosis of ILFS1. The 2 years and 9 months old male patient was referred to the hospital with hepatosplenomegaly over 1 year. At age 17 months, he was found to have hepatosplenomegaly and anemia. Since then, he had been managed in different hospitals. The laboratory tests showed liver dysfunction, hypoproteinemia, coagulopathy and anemia, along with histologically-confirmed cirrhosis and fatty liver; however, the etiology remained undetermined. The subsequent SLC25A13 mutation analysis by means of prevalent mutation screening and Sanger sequencing only revealed a paternally-inherited mutation c.1658G>A, and no aberrant SLC25A13 transcripts could be detected from the maternal allele on cDNA cloning analysis, ruling out the possibility of citrin deficiency. Further target exome high-throughout sequencing of genes relevant to genetic liver diseases detected a paternal c.2133_2135del (p.L712del) and a maternal c.1183G>A (p.D395N) mutation in LARS gene. This finding was then confirmed by Sanger sequencing, and ILFS1 was thus definitely diagnosed. The child has been followed up till age 4 years, and his condition became stabilized.

Blood glucose and insulin and correlation of SLC25A13 mutations with biochemical changes in NICCD patients

Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is a hereditary metabolic disease arising from biallelic mutations of SLC25A13. This study aimed to explore the characteristics of fasting blood glucose (FBG), fasting insulin (FINS) and C-peptide (C-P) levels in NICCD infants, analyze their SLC25A13 genetic mutations and further discuss the correlation between SLC25A13 genetic mutations and biochemical changes. Seventy-two cases of infants with cholestasis disease were gathered. Among them, 36 cases with NICCD diagnosis were case group. Meanwhile, 36 cases with unknown etiology but excluded NICCD were control group. FBG, FINS, C-P, ALT, AST, GGT, ALP, TG, HDL-C, LDL-C and Non-HDL-C were collected from all subjects, and DNA was extracted from venous blood for SLC25A13 mutations detection. The incidence of hypoglycemia was 3% in NICCD group. There were no significant statistical difference of FBG, FINS and C-P between NICCD and INC groups ( P > 0.05). ALT, LDL-C and Non-HDL-C levels in NICCD group were lower than the INC group, while SLC25A13 mutations were associated with the level of GGT ( P < 0.05). Ten different SLC25A13 genetic mutations were detected, among which, 851del4, IVS16ins3kb, IVS6+5 G > A and 1638ins23 mutations made up 82% of all mutations. The incidence of hypoglycemia may be higher in small gestational age infants with NICCD. Low LDL-C may be one of the characteristics of dyslipidemia in NICCD infants. There was a correlation between SLC25A13 gene mutations distribution and the GGT level, but the meaning of this finding remains to be further in-depth study. Impact statement This study aims to compare FBG, FINS, C-P, other biochemical and clinical manifestations between NICCD and non-NICCD infants, and discuss differential diagnosis of NICCD and INC beyond the genetic analysis. And investigate the correlation between SLC25A13 genetic mutations and biochemical changes. This work presented that incidence of hypoglycemia may be higher in small gestational age infants with NICCD. Low LDL-C may be one of the characteristics of dyslipidemia in NICCD infants. There was a correlation between SLC25A13 gene mutations distribution and the GGT level.

A Population-Based Genomic Study of Inherited Metabolic Diseases Detected Through Newborn Screening

Background

A newborn screening (NBS) program has been utilized to detect asymptomatic newborns with inherited metabolic diseases (IMDs). There have been some bottlenecks such as false-positives and imprecision in the current NBS tests. To overcome these issues, we developed a multigene panel for IMD testing and investigated the utility of our integrated screening model in a routine NBS environment. We also evaluated the genetic epidemiologic characteristics of IMDs in a Korean population.

Methods

In total, 269 dried blood spots with positive results from current NBS tests were collected from 120,700 consecutive newborns. We screened 97 genes related to NBS in Korea and detected IMDs, using an integrated screening model based on biochemical tests and next-generation sequencing (NGS) called NewbornSeq. Haplotype analysis was conducted to detect founder effects.

Results

The overall positive rate of IMDs was 20%. We identified 10 additional newborns with preventable IMDs that would not have been detected prior to the implementation of our NGS-based platform NewbornSeq. The incidence of IMDs was approximately 1 in 2,235 births. Haplotype analysis demonstrated founder effects in p.Y138X in DUOXA2, p.R885Q in DUOX2, p.Y439C in PCCB, p.R285Pfs^*2 in SLC25A13, and p.R224Q in GALT.

Conclusions

Through a population-based study in the NBS environment, we highlight the screening and epidemiological implications of NGS. The integrated screening model will effectively contribute to public health by enabling faster and more accurate IMD detection through NBS. This study suggested founder mutations as an explanation for recurrent IMD-causing mutations in the Korean population.

Idiopathic eruptive macular pigmentation in a child with citrin deficiency

Idiopathic eruptive macular pigmentation (IEMP) is a rare dermatological disorder with generally unclear etiology and pathogenesis. A 5½-year-old girl was referred to hospital with a 10 month history of brown skin rashes. In early infancy, citrin deficiency had been diagnosed with the SLC25A13 genotype c.851_854del4/c.998G > A, but all clinical and laboratory abnormalities recovered following the introduction of a lactose-free and medium-chain triglyceride-enriched formula. Physical examination at referral indicated symmetric, multiple and non-scaly brown macules on the neck, trunk, buttocks and proximal parts of the extremities. Histopathology indicated epidermal basal layer hyperpigmentation with an irregular distribution, along with a large number of melanophages in the upper dermis. The diagnosis of IEMP was thus made. Within 2 years of follow up, the rashes disappeared spontaneously and gradually. To our knowledge, this is the first description of IEMP in a patient with silent citrin deficiency.

Molecular diagnosis of pediatric patients with citrin deficiency in China: SLC25A13 mutation spectrum and the geographic distribution

Citrin deficiency (CD) is a Mendelian disease due to biallelic mutations of SLC25A13 gene. Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is the major pediatric CD phenotype, and its definite diagnosis relies on SLC25A13 genetic analysis. China is a vast country with a huge population, but the SLC25A13 genotypic features of CD patients in our country remains far from being well clarified. Via sophisticated molecular analysis, this study diagnosed 154 new CD patients in mainland China and identified 9 novel deleterious SLC25A13 mutations, i.e. c.103A > G, [c.329 - 154_c.468 + 2352del2646; c.468 + 2392_c.468 + 2393ins23], c.493C > T, c.755 - 1G > C, c.845_c.848 + 1delG, c.933_c.933 + 1insGCAG, c.1381G > T, c.1452 + 1G > A and c.1706_1707delTA. Among the 274 CD patients diagnosed by our group thus far, 41 SLC25A13 mutations/variations were detected. The 7 mutations c.775C > T, c.851_854del4, c.1078C > T, IVS11 + 1G > A, c.1364G > T, c.1399C > T and IVS16ins3kb demonstrated significantly different geographic distribution. Among the total 53 identified genotypes, only c.851_854del4/c.851_854del4 and c.851_854del4/c.1399C > T presented different geographic distribution. The northern population had a higher level of SLC25A13 allelic heterogeneity than those in the south. These findings enriched the SLC25A13 mutation spectrum and brought new insights into the geographic distribution of the variations and genotypes, providing reliable evidences for NICCD definite diagnosis and for the determination of relevant molecular targets in different Chinese areas.

Chronic hepatitis without hepatic steatosis caused by citrin deficiency in a child

Citrin deficiency manifests as both neonatal intrahepatic cholestasis (NICCD) during early infancy and adult-onset type II citrullinemia during adulthood. Hepatic steatosis is most frequently observed in patients with citrin deficiency. Thus, non-alcoholic fatty liver disease that is unrelated to being overweight is considered one of the clinical features of citrin deficiency in children and adults. However, it remains unknown whether citrin deficiency is a cause of chronic hepatitis in the absence of fatty changes to the liver that occur during childhood. We encountered an 8-year-old girl who showed no clinical features of NICCD during infancy and had persistently elevated transaminase levels for several years. Liver biopsy showed widening of the portal tracts with intense mononuclear cell infiltration and mild fibrosis but no fatty changes. However, she had peculiar dietary habits similar to those that have been observed in many patients with citrin deficiency. In addition, a slightly elevated plasma citrulline level and a high pancreatic secretory trypsin inhibitor level were detected by blood examination, and she was diagnosed with citrin deficiency. Analysis of the SLC25A13 gene revealed the presence of the compound heterozygous mutations 851del4 and IVS13 + 1G > A. Thus, citrin deficiency should be included in the differential diagnosis of chronic hepatitis in children, even in the absence of hepatic steatosis.

Novel mutations in the SLC25A13 gene in a patient with NICCD and severe manifestations

Neonatal intrahepatic cholestatic due to citrin deficiency (NICCD) is an autosomal recessive disorder caused by mutations in the SLC25A13 gene and characterized by neonatal/infantile-onset cholestatic hepatitis syndrome associated with conjugated hyperbilirubinemia and multiple aminoacidemias. We report the case of a Chinese female patient with NICCD disease who manifested prominent clinical features. The patient was diagnosed with NICCD based on cholestasis, aminoacidemia, and hypoproteinemia. She exhibited extreme aminoacidemia, coagulation disorders and untypical myocardial damage, which are rare in other NICCD patients genetically confirmed by us. This myocardial damage observed in obstructive jaundice could be caused by both hyperbilirubinemia and redundant blood bile acids. Screening the SLC25A13 gene revealed that this patient was compound heterozygous harboring two novel mutations, the c. 640C>T (p. Gln214X) in exon 7 and the c. 1709_1710insA (p. Ile570fs573X) in exon 16. Both mutations cause a premature stop codon and thereby truncated peptide or nonsense-mediated with loss of natural function accordingly. In conclusion, extremely manifested clinical features, including significant hyperbilirubinemia, multiple aminoacidemia, hypoproteinemia, coagulation disorders, and myocardial damage related to redundant blood bilirubin and bile acids, were observed in a NICCD patients with two novel mutations.

Inherited metabolic diseases in the Southern Chinese population: spectrum of diseases and estimated incidence from recurrent mutations

Inherited metabolic diseases (IMDs) are a large group of rare genetic diseases. The spectrum and incidences of IMDs differ among populations, which has been well characterised in Caucasians but much less so in Chinese. In a setting of a University Hospital Metabolic Clinic in Hong Kong, over 100 patients with IMDs have been seen during a period of 13 years (from 1997 to 2010). The data were used to define the spectrum of diseases in the Southern Chinese population. Comparison with other populations revealed a unique spectrum of common IMDs. Furthermore, the incidence of the common IMDs was estimated by using population carrier frequencies of known recurrent mutations. Locally common diseases (their estimated incidence) include (1) glutaric aciduria type 1 (∼1/60,000), (2) multiple carboxylase deficiency (∼1/60,000), (3) primary carnitine deficiency (∼1/60,000), (4) carnitine-acylcarnitine translocase deficiency (∼1/60,000), (5) glutaric aciduria type 2 (∼1/22,500), (6) citrin deficiency (∼1/17,000), (7) tetrahydrobiopterin-deficient hyperphenylalaninaemia due to 6-pyruvoyl-tetrahydropterin synthase deficiency (∼1/60,000), (8) glycogen storage disease type 1 (∼1/150,000). In addition, ornithine carbamoyltransferase deficiency and X-linked adrenoleukodystrophy are common X-linked diseases. Findings of the disease spectrum and treatment outcome are summarised here which may be useful for clinical practice. In addition, data will also be useful for policy makers in planning of newborn screening programs and resource allocation.

Neonatal Cholestasis - Differential Diagnoses, Current Diagnostic Procedures, and Treatment

Cholestatic jaundice in early infancy is a complex diagnostic problem. Misdiagnosis of cholestasis as physiologic jaundice delays the identification of severe liver diseases. In the majority of infants, prolonged physiologic jaundice represent benign cases of breast milk jaundice, but few among them are masked and caused by neonatal cholestasis (NC) that requires a prompt diagnosis and treatment. Therefore, a prolonged neonatal jaundice, longer than 2 weeks after birth, must always be investigated because an early diagnosis is essential for appropriate management. To rapidly identify the cases with cholestatic jaundice, the conjugated bilirubin needs to be determined in any infant presenting with prolonged jaundice at 14 days of age with or without depigmented stool. Once NC is confirmed, a systematic approach is the key to reliably achieve the diagnosis in order to promptly initiate the specific, and in many cases, life-saving therapy. This strategy is most important to promptly identify and treat infants with biliary atresia, the most common cause of NC, as this requires a hepatoportoenterostomy as soon as possible. Here, we provide a detailed work-up approach including initial treatment recommendations and a clinically oriented overview of possible differential diagnoses in order to facilitate the early recognition and a timely diagnosis of cholestasis. This approach warrants a broad spectrum of diagnostic procedures and investigations including new methods that are described in this review.

Steatogenesis in adult-onset type II citrullinemia is associated with down-regulation of PPARα

SLC25A13 (citrin or aspartate-glutamate carrier 2) is located in the mitochondrial membrane in the liver and its genetic deficiency causes adult-onset type II citrullinemia (CTLN2). CTLN2 is one of the urea cycle disorders characterized by sudden-onset hyperammonemia due to reduced argininosuccinate synthase activity. This disorder is frequently accompanied with hepatosteatosis in the absence of obesity and ethanol consumption. However, the precise mechanism of steatogenesis remains unclear. The expression of genes associated with fatty acid (FA) and triglyceride (TG) metabolism was examined using liver samples obtained from 16 CTLN2 patients and compared with 7 healthy individuals. Although expression of hepatic genes associated with lipogenesis and TG hydrolysis was not changed, the mRNAs encoding enzymes/proteins involved in FA oxidation (carnitine palmitoyl-CoA transferase 1α, medium- and very-long-chain acyl-CoA dehydrogenases, and acyl-CoA oxidase 1), very-low-density lipoprotein secretion (microsomal TG transfer protein), and FA transport (CD36 and FA-binding protein 1), were markedly suppressed in CTLN2 patients. Serum concentrations of ketone bodies were also decreased in these patients, suggesting reduced mitochondrial β-oxidation activity. Consistent with these findings, the expression of peroxisome proliferator-activated receptor α (PPARα), a master regulator of hepatic lipid metabolism, was significantly down-regulated. Hepatic PPARα expression was inversely correlated with severity of steatosis and circulating ammonia and citrulline levels. Additionally, phosphorylation of c-Jun-N-terminal kinase was enhanced in CTLN2 livers, which was likely associated with lower hepatic PPARα. Collectively, down-regulation of PPARα is associated with steatogenesis in CTLN2 patients. These findings provide a novel link between urea cycle disorder, lipid metabolism, and PPARα.

[A case of adult-onset type II citrullinemia (CTLN2) triggered by an overseas travel]

A 43-year-old male presented with abnormal behavior and consciousness disturbance on the day after traveling abroad and was admitted to our hospital. Laboratory tests showed hyperammonemia and hypercitrullinemia. The electro-encephalogram showed frontal dominant bilateral slow δ burst. He had a peculiar taste for nuts. But he didn't take nuts during the overseas travel for 3 days. The family history revealed that his younger brother died of a status epilepticus of unknown cause at the age of 29. These findings were compatible with hepatic encephalopathy due to adult-onset type II citrullinemia (CTLN2). Gene analysis provided a definite diagnosis of CTLN2. Diet and drug therapy have improved his condition. He is due to have liver transplantation which is the only established radical treatment for CTLN2 if his condition becomes worse. The present case shows that cessation of the habitual intake of nuts only for 3 days could lead to onset of CTLN2.

Inspissated bile syndrome in an infant with citrin deficiency and congenital anomalies of the biliary tract and esophagus: identification and pathogenicity analysis of a novel SLC25A13 mutation with incomplete penetrance

Biallelic mutations of the SLC25A13 gene result in citrin deficiency (CD) in humans. Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is the major CD phenotype in pediatrics; however, knowledge on its genotypic and phenotypic characteristics remains limited. The present study aimed to explore novel molecular and clinical characteristics of CD. An infant suspected to have NICCD as well as her parents were enrolled as the research subjects. SLC25A13 mutations were investigated using various methods, including cDNA cloning and sequencing. The pathogenicity of a novel mutation was analyzed bioinformatically and functionally with a yeast model. Both the infant and her father were heterozygous for c.2T>C and c.790G>A, while the mother was only a c.2T>C carrier. The novel c.790G>A mutation proved bioinformatically and functionally pathogenic. The infant had esophageal atresia and an accessory hepatic duct, along with bile plug formation confirmed by laparoscopic surgery. However, the father seemed to be healthy thus far. The findings of the present study enrich the genotypic and phenotypic characteristics of CD patients, and provided clinical and molecular evidence suggesting the possible non-penetrance of SLC25A13 mutations and the likely involvement of this gene in primitive foregut development during early embryonic life.

Three cases of adult-onset type II citrullinemia treated with different therapies: Efficacy of sodium pyruvate and low-carbohydrate diet

We report three cases of adult-onset type II citrullinemia (CTLN2) treated with different therapies including one case successfully treated with p.o. administration of sodium pyruvate and low-carbohydrate diet. Although recent advances in liver transplantation have enabled successful treatment of patients with CTLN2, several issues concerning liver transplantation remain. Further, there is still an urgent need for therapies that do not rely on liver transplantation. The first case was a 41-year-old man who developed impaired consciousness in 1992. The patient was treated with conventional therapy for hepatic encephalopathy and died of severe brain edema. The second case was a 31-year-old man who suddenly presented a syncope-like attack with hyperammonemia. He was treated with carbohydrate-restricted diet but the encephalopathy could not be controlled, and he received emergency living donor liver transplantation. The third patient was a 67-year-old man who developed abnormal behavior with hyperammonemia. He has remained well with oral sodium pyruvate and a low-carbohydrate diet without receiving liver transplantation.

Clinical, molecular and functional investigation on an infant with neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD)

BACKGROUND AND OBJECTIVE

SLC25A13 analysis has provided reliable evidences for the definitive diagnosis of citrin deficiency (CD) in the past decade. Meanwhile, these studies generated some issues yet to be resolved, including the pathogenicity of SLC25A13 missense mutations and the mRNA product from the mutation c.615+5G>A. This study aims to investigate the effect of a novel missense mutation on the aspartate/glutamate carrier (AGC) function of citrin protein, and to explore the aberrant transcript from c.615+5G>A in the same CD infant.

METHODS AND RESULTS

By means of screening for prevalent SLC25A13 mutations and exons sequencing, the patient proved a compound heterozygote of c.615+5G>A and a novel c.1064G>A (p.Arg355Gln) mutation. An aberrant transcript with retention of the entire intron 6, r.[615+1_615+1789ins; 615+5 g>a] (GenBank accession number KJ128074), which was resulted from c.615+5G>A, was detected by RT-PCR and cDNA sequencing. After bioinformatic analyses of the novel missense mutation c.1064G>A, the growth abilities of three agc1Δ yeast strains were tested, which had been transformed with recombinant or empty vectors, respectively. Besides the bioinformatically pathogenic evidences, the growth ability of the agc1Δ strains transformed with mutant recombinant was the same as with empty vector, but significantly lower than that with normal control in functional analysis.

CONCLUSIONS

A CD infant was definitely diagnosed in this paper by a genetic, transcriptional and functional analysis of SLC25A13 gene. This study provided direct laboratory evidences supporting the splice-site nature of the c.615+5G>A mutation, and the novel c.1064G>A variation, which proved a pathogenic mutation bioinformatically and functionally, enriched the SLC25A13 mutation spectrum.