Intrahepatic cholestasis of pregnancy (ICP) is the most common pregnancy-related liver disorder. Although the etiology of ICP is not fully understood thus far, some genetic factors might contribute to the development of this condition. Sodium-taurocholate cotransporting polypeptide (NTCP), the protein encoded by the gene Solute Carrier Family 10, Member 1 (SLC10A1), is the primary transporter expressed in the basolateral membrane of the hepatocyte to uptake conjugated bile salts from the plasma. NTCP deficiency arises from biallelic SLC10A1 mutations which impair the NTCP function and cause intractably elevated levels of total bile acids (TBA) in the plasma (hypercholanemia). In this study, all the SLC10A1 exons and their flanking sequences were analyzed by Sanger sequencing to investigate the etiology for hypercholanemia in two male infants aged 2 and 20 months, respectively, from two unrelated families. As a result, both patients are homozygous for the reported pathogenic variant c.800C>T (p.Ser267Phe) that could impair the NTCP function to uptake bile acids, and the diagnosis of NTCP deficiency was thus made. Their mothers are also homozygotes of the same variant and both had been diagnosed to have ICP in the third trimester, with one of them undergoing cesarean section. The father of the first patient in this paper has the same SLC10A1 genotype c.800C>T/c.800C>T, also exhibiting slight hypercholanemia with a plasma TBA level of 21.5 μmol/L. In conclusion, we suggest that with hypercholanemia being a common laboratory change, NTCP deficiency may be a genetic factor leading to ICP and even cesarean section in clinical practice.
Sodium taurocholate cotransporting polypeptide (NTCP), a carrier protein encoded by solute carrier family 10 member 1 (SLC10A1), is expressed in the basolateral membrane of hepatocytes, where it is responsible for the uptake of bile acids from plasma into hepatocytes. The first patient with NTCP deficiency was described in 2015. A limited number of such patients have been reported in the literature and their genotypic and phenotypic features require further investigation. The current study investigated 4 patients with NTCP deficiency from two unrelated families. The patients were subjected to SLC10A1 genetic analysis and it was revealed that all patients were compound heterozygous for the c.800C>T (p.Ser267Phe) and c.595A>C (p.Ser199Arg) SLC10A1 variants. To the best of the authors' knowledge, the latter variant had not been previously reported. Further analysis in 50 healthy individuals did not identify carriers. The c.595A>C (p.Ser199Arg) variant exhibited co-segregation with hypercholanemia and exhibited a relatively conserved amino acid when compared with homologous peptides. Moreover, SWISS-MODEL prediction revealed that the mutation affected the conformation of the NTCP molecule. The 4 patients demonstrated varying degrees of hypercholanemia while a downward trend in the plasma levels of total bile acids (TBA) in 2 pediatric patients and occasionally normal TBA level in an adult case were observed. The results indicated an autosomal recessive trait for NTCP deficiency, supported the primary role of NTCP in the uptake of bile acids from plasma and suggested that hepatic uptake of bile acids may occur by means other than NTCP uptake. Moreover, the novel missense variant c.595A>C(p.Ser199Arg) enriched the SLC10A1 mutation spectrum and may serve as a new genetic marker for the molecular diagnosis and genetic counseling of NTCP deficiency.
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.
Na+-taurocholate cotransporting polypeptide deficiency (NTCPD) is an autosomal recessive disorder arising from biallelic SLC10A1 mutations. As a newly-described inborn error of bile acid metabolism, the epidemiology of this condition remains largely unclear in Chinese population so far. In this study, a total of 2,828 peripheral blood samples were collected from 12 cities in Guangdong, a province with the largest population in China, and the four prevalent SLC10A1 variants c.800C > T (p.Ser267Phe), c.263T > C (p.Ile88Thr), c.595A > C (p.Ser199Arg) and c.665T > C (p.Leu222Ser) were screened for by using polymerase chain reaction (PCR)- restriction fragment length polymorphism (RFLP). As a result, 663 mutated SLC10A1 alleles were detected, and the mutated allele frequency was calculated to be 11.72% (663/5,656), with a carrier frequency 20.69% (1/5) and a theoretical morbidity rate 1.37% (1/73) of NTCPD in Guangdong province. The variant c.800C > T (p.Ser267Phe) exhibited highest allele frequency among the four prevalent variants (χ2 = 1501.27, p < 0.0001) as well as higher allele frequency in the peripheral region than that within the Pearl River Delta (χ2 = 4.834, p < 0.05). The results suggested that NTCPD might be a disorder rather common in Guangdong province. The findings depicted the molecular epidemiologic features of NTCPD, providing preliminary but significant laboratory evidences for the subsequent NTCPD diagnosis and management in Guangdong population.
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