The human SLC25A13 gene encodes citrin, the liver-type mitochondrial aspartate/glutamate carrier isoform 2 (AGC2), and SLC25A13 mutations cause citrin deficiency (CD), a disease entity that encompasses different age-dependant clinical phenotypes such as Adult-onset Citrullinemia Type II (CTLN2) and Neonatal Intrahepatic Cholestasis caused by Citrin Deficiency (NICCD). The analyses of SLC25A13 gene and its protein/mRNA products remain reliable tools for the definitive diagnoses of CD patients, and so far, the SLC25A13 mutation spectrum in Chinese CD patients has not been well-characterized yet. By means of direct DNA sequencing, cDNA cloning and SNP analyses, 16 novel pathogenic mutations, including 9 missense, 4 nonsense, 1 splice-site, 1 deletion and 1 large transposal insertion IVS4ins6kb (GenBank accession number KF425758), were identified in CTLN2 or NICCD patients from China, Japan and Malaysia, respectively, making the SLC25A13 variations worldwide reach the total number of 81. A large NICCD cohort of 116 Chinese cases was also established, and the 4 high-frequency mutations contributed a much larger proportion of the mutated alleles in the patients from south China than in those from the north (χ² = 14.93, P<0.01), with the latitude of 30°N as the geographic dividing line in mainland China. This paper further enriched the SLC25A13 variation spectrum worldwide, and formed a substantial contribution to the in-depth understanding of the genotypic feature of Chinese CD patients.

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.

The human solute carrier family 10 member 1 (SLC10A1) gene encodes sodium taurocholate cotransporting polypeptide (NTCP), the principal transporter of conjugated bile salts from the plasma into hepatocytes. Although the function of NTCP has been studied extensively and a number of SLC10A1 variations have been identified in humans, information regarding NTCP deficiency is limited. To date, only one patient with NTCP deficiency has been described; however, in the present study a pediatric patient who experienced intractable and striking hypercholanemia is presented. Analysis of the SLC10A1 gene in the patient revealed a homozygous p.Ser267Phe (c.800C>T) variation, which proved to be a single‑nucleotide polymorphism (SNP) in the allele frequency of 4.7% of healthy controls. This variation involved a conserved amino acid residue on the orthologous alignment that was predicted to be ̔disease‑causing̓ by functional analysis using a number of bioinformatic tools. Next generation sequencing was performed; however, no other genetic causes were identified that would affect the bile acid homeostasis in the patient. Moreover, an adult, with the same genotype as the pediatric patient, was identified for the first time as experiencing mild hypercholanemia. The molecular and clinical findings in the present study suggest, for the first time, that there is an association between p.Ser267Phe SNP and hypercholanemia, and this information may be used to clinically identify NTCP deficiency worldwide.

Sodium taurocholate cotransporting polypeptide (NTCP) deficiency: Identification of a novel SLC10A1 mutation in two unrelated infants presenting with neonatal indirect hyperbilirubinemia and remarkable hypercholanemia Sodium taurocholate cotransporting polypeptide (NTCP) deficiency: Identification of a novel SLC10A1 mutation in two unrelated infants presenting with neonatal indirect hyperbilirubinemia and remarkable hypercholanemia

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. 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. 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.

Na⁺-taurocholate cotransporting polypeptide deficiency (NTCPD) is a newly described disorder arising from biallelic mutations of the SLC10A1 gene. As a result of a lack of compelling evidence from case-control studies, its genotypic and phenotypic features remain open for in-depth investigation. This study aimed to explore the genotypic and clinical phenotypic characteristics of paediatric patients with NTCPD. The SLC10A1 genotypes of all NTCPD patients were confirmed by screening for the prevalent variant c.800C>T and Sanger sequencing when necessary. The clinical presentations and laboratory changes were collected, reviewed and analysed, and then qualitatively and quantitatively compared with the relevant controls. A total of 113 paediatric NTCPD patients were diagnosed while c.374dupG and c.682_683delCT were detected as two novel pathogenic mutations. Hypercholanemia was observed in 99.12% of the patients. Indirect hyperbilirubinemia in affected neonates exhibited higher positive rates in comparison to controls. Moreover, transient cholestatic jaundice, elevated liver enzymes and 25-hydroxyvitamin D (Vit D) deficiency during early infancy were more commonly observed in patients than in controls. All NTCPD patients exhibited favourable clinical outcomes as a result of symptomatic and supportive treatment. The findings enriched the SLC10A1 mutation spectrum and provided comprehensive insights into the phenotypic characteristics of NTCPD. NTCPD should be considered and SLC10A1 gene should be analysed in patients with above age-dependent clinical features. Furthermore, over investigation and intervention should be avoided in the management of NTCPD patients.