ATP8B1 mutations in British cases with intrahepatic cholestasis of pregnancy

BACKGROUND: Intrahepatic cholestasis of pregnancy (ICP) affects approximately 0.7% of pregnancies in the UK and is associated with prematurity, fetal distress, and intrauterine death. Homozygous mutations in the ATP8B1 gene cause cholestasis with a normal serum gamma-glutamyl transpeptidase (gamma-GT), and have been reported in two forms of cholestasis: progressive familial intrahepatic cholestasis type 1 (PFIC1) and benign recurrent intrahepatic cholestasis (BRIC). AIMS: To establish whether mutations in ATP8B1 are associated with ICP in British cases PATIENTS: Sixteen well phenotyped women with ICP without raised gamma-GT were selected for sequence analysis. Subsequently, 182 patients and 120 controls were examined for the presence of the variants detected. METHODS: All coding exons were sequenced in 16 cases. Eight ICP cases, including two women carrying a mutation, were investigated using in vivo hepatic (31)P magnetic resonance spectroscopy (MRS) RESULTS: Two heterozygous ATP8B1 transitions (208G>A and 2599C>T) that resulted in amino acid substitutions were identified; 208G>A was identified in three cases. MRS revealed an increased phosphodiester signal (Mann-Whitney U test, p = 0.03) and a decreased phosphomonoester/phosphodiester ratio (p = 0.04) in ICP cases compared with controls. CONCLUSIONS: We were able to demonstrate ATP8B1 mutations in ICP. MRS studies suggest that susceptibility to ICP is associated with a relative rise in biliary phospholipid. These data also suggest that MRS may be used for non-invasive assessment of the liver and biliary constituents in cholestasis.     

Adult progressive intrahepatic cholestasis associated with genetic variations in ATP8B1 and ABCB11

Severe intrahepatic cholestasis with low serum γ-glutamyltranspeptidase (γ-GT) activity is exceptionally rare in adult patients, and its association with multi-genetic alterations of bile salt transporters has not been reported. We investigated a 25-year-old man presenting with a four-year history of jaundice. Laboratory and radiographic examinations revealed clinical pictures of progressive intrahepatic cholestasis with low γ-GT. Serial liver histopathology demonstrated cirrhosis resulting from progressive persistent cholestatic injury. Genetic sequencing studies for the entire coding exons of ATP8B1 and ABCB11 uncovered a heterozygous missense mutation 1798 C->T (R600W) in ATP8B1 , and a homozygous nucleotide substitution 1331 T->C (V444A) in ABCB11 . In conclusion, this is a rare case of adult onset progressive intrahepatic cholestasis with low γ-GT associated with heterozygous ATP8B1 mutation and homozygous ABCB11 polymorphism. Further studies are necessary to investigate the impact of heterozygous R600W mutation and whether other cholestatic disorders are multi-genetic.     

Novel ATP8B1 mutation in an adult male with progressive familial intrahepatic cholestasis

Progressive familial intrahepatic cholestasis type 1 is a rare disease that is characterized by low serum γ-glutamyltransferase levels due to mutation in ATP8B1. We present a 23-year-old male who experienced persistent marked pruritus for eighteen years and recurrent jaundice for thirteen years, in addition to cholestasis that eventually became fatal. Genetic sequencing studies of the entire coding (exon) sequences of ATP8B1 and ABCB11 uncovered a novel heterozygous missense 3035G>T mutation (S1012I) and a synonymous 696T>C mutation in ATP8B1. The patient’s progression was associated with not only impaired familial intrahepatic cholestasis 1 (FIC1) function but also impaired bile salt export pump expression due to the impaired FIC1 function. Our findings show that patients with intermittent cholestasis can develop progressive liver disease even after several decades and require regular follow up.     

Successful treatment with colestimide for a bout of cholestasis in a Japanese patient with benign recurrent intrahepatic cholestasis caused by ATP8B1 mutation

Benign recurrent intrahepatic cholestasis (BRIC) is an autosomal recessive disorder characterized by bouts of cholestasis that resolve spontaneously without leaving considerable liver damage. Most of BRIC patients have mutations in ATP8B1 gene coding FIC1 protein. It has been suggested that an imbalance between the gut absorption of bile acids and the liver excretion possibly causes the development of cholestasis. We encountered a Japanese woman patient with familial intrahepatic cholestasis type 1 (FIC1) deficiency manifesting BRIC, in whom a rapid and gross elevation of serum total bile acid (TBA) level preceded that of serum total bilirubin level. Interestingly, the early administration of colestimide prevented the development of hyperbilirubinemia along with the additional elevation of serum TBA level. This case suggests that FIC1 deficiency causes an imbalance between the gut absorption of bile acids and the liver excretion leading to cholestasis, and raised the possibility that colestimide may be used as an optional treatment for BRIC.     

Distinct Wilson's disease mutations in ATP7B are associated with enhanced binding to COMMD1 and reduced stability of ATP7B

BACKGROUND & AIMS: Wilson's disease (WD) is characterized by hepatic copper overload and caused by mutations in the gene encoding the copper-transporting P-type adenosine triphosphatase (ATPase) ATP7B. ATP7B interacts with COMMD1, a protein that is deleted in Bedlington terriers with hereditary copper toxicosis. Here we characterized the implications of the interaction between COMMD1 and ATP7B in relation to the pathogenesis of WD. METHODS: Glutathione-S-transferase pull-down experiments, co-immunoprecipitations, immunofluorescence microscopy, site-directed mutagenesis, and biosynthetic labeling experiments were performed to characterize the interaction between COMMD1 and ATP7B and the effects of WD causing mutations. RESULTS: COMMD1 specifically interacted with the amino-terminal region of ATP7B. This interaction was independent of intracellular copper levels and of the expression of the copper chaperone ATOX1. Four WD patient-derived mutations in this region of ATP7B significantly increased its binding to COMMD1. Two of these mutations also resulted in mislocalization and increased degradation rate of ATP7B. Although COMMD1 did not affect copper-induced trafficking of ATP7B, it markedly decreased the stability of newly synthesized ATP7B. CONCLUSIONS: Our data implicate COMMD1 in the pathogenesis of WD and indicate that COMMD1 exerts its regulatory role in copper homeostasis through the regulation of ATP7B stability.     

Autosomal dominant hereditary hemochromatosis associated with two novel Ferroportin 1 mutations in Spain

Hereditary hemochromatosis is a common disorder of iron metabolism most frequently associated with mutations in the HFE gene. Hereditary hemochromatosis may be caused by other genetic mutations including those in the SLC40A1 gene. This report describes the clinical and laboratory findings of two Spanish families with autosomal dominant iron overload associated with previously unrecognized Ferroportin 1 mutations (p.R88T and p.I180T). The phenotype of iron overload in the patients carrying these mutations could correspond to the group of clinical mutations that lose their iron export function.     

Nonsense variant of ATP8B1 gene in heterozygosis and benign recurrent intrahepatic cholestasis: A case report and review of literature

BACKGROUND Benign recurrent intrahepatic cholestasis is a genetic disorder with recurrent cholestatic jaundice due to ATP8B1 and ABCB11 gene mutations encoding for hepato-canalicular transporters. Herein, we firstly provide the evidence that a nonsense variant of ATP8B1 gene(c.1558AT) in heterozygous form is involved in BRIC pathogenesis.CASE SUMMARY A 29-year-old male showed severe jaundice and laboratory tests consistent with intrahepatic cholestasis despite normal gamma-glutamyltranspeptidase. Acute and chronic liver diseases with viral, metabolic and autoimmune etiology were excluded. Normal intra/extra-hepatic bile ducts were demonstrated by magnetic resonance. Liver biopsy showed: Cholestasis in the centrilobular and intermediate zones with bile plugs and intra-hepatocyte pigment, Kupffer's cell activation/hyperplasia and preserved biliary ducts. Being satisfied benign recurrent intrahepatic cholestasis diagnostic criteria, ATP8B1 and ABCB11 gene analysis was performed. Surprisingly, we found a novel nonsense variant of ATP8B1 gene(c.1558AT) in heterozygosis. The variant was confirmed by Sanger sequencing following a standard protocol and tested for familial segregation,showing a maternal inheritance. Immunohistochemistry confirmed a significant reduction of mutated gene related protein(familial intrahepatic cholestasis 1).The patient was treated with ursodeoxycholic acid 15 mg/kg per day and colestyramine 8 g daily with total bilirubin decrease and normalization at the 6~(th) and 12~(th) mo.CONCLUSION A genetic abnormality, different from those already known, could be involved in familial intrahepatic cholestatic disorders and/or pro-cholestatic genetic predisposition, thus encouraging further mutation detection in this field.     

Novel beta-spectrin mutations in hereditary spherocytosis associated with decreased levels of mRNA

Hereditary spherocytosis (HS) is one of the most frequent and heterogeneous inherited haemolytic anaemias. It is associated with abnormalities of several erythrocyte membrane proteins. We investigated relative mRNA quantification of red blood cell membrane protein genes using real-time quantitative polymerase chain reaction (qPCR) in order to better characterize HS cases and to select genes to search for mutations in patients with spherocytosis. qPCR experiments indicated that the spectrin β gene ( SPTB ) could be involved in anaemia pathogenesis. DNA analysis of SPTB in the HS subjects with decreased SPTB mRNA levels revealed the presence of five previously undescribed mutations: R1756X, 781delT and IVS22nt-4G>A, 1502insA and IVS20nt-2A>G.     

ATP8B1 is essential for maintaining normal hearing

ATP8B1 deficiency is caused by autosomal recessive mutations in ATP8B1, which encodes the putative phospatidylserine flippase ATP8B1 (formerly called FIC1). ATP8B1 deficiency is primarily characterized by cholestasis, but extrahepatic symptoms are also found. Because patients sometimes report reduced hearing capability, we investigated the role of ATP8B1 in auditory function. Here we show that ATP8B1/Atp8b1 deficiency, both in patients and in Atp8b1^G308V/G308V mutant mice, causes hearing loss, associated with progressive degeneration of cochlear hair cells. Atp8b1 is specifically localized in the stereocilia of these hair cells. This indicates that the mechanosensory function and integrity of the cochlear hair cells is critically dependent on ATP8B1 activity, possibly through maintaining lipid asymmetry in the cellular membranes of stereocilia.     

ATP2B1 gene polymorphisms associated with resistant hypertension in the Japanese population

Single-nucleotide polymorphisms (SNP) of ATP2B1 gene are associated with essential hypertension but their association with resistant hypertension (RHT) remains unexplored. The authors examined the relationship between ATP2B1 SNPs and RHT by genotyping 12 SNPs in ATP2B1 gene of 1124 Japanese individuals with lifestyle-related diseases. Patients with RHT had inadequate blood pressure (BP) control using three antihypertensive drugs or used ≥4 antihypertensive drugs. Patients with controlled hypertension had BP controlled using ≤3 antihypertensive drugs. The association between each SNP and RHT was analyzed by logistic regression. The final cohort had 888 (79.0%) and 43 (3.8%) patients with controlled hypertension and RHT, respectively. Compared with patients homozygous for the minor allele of each SNP in ATP2B1, a significantly higher number of patients carrying the major allele at 10 SNPs exhibited RHT (most significant at rs1401982: 5.8% vs. 0.8%, p = .014; least significant at rs11105378: 5.7% vs. 0.9%, p = .035; most nonsignificant at rs12817819: 5.1% vs. 10%, p = .413). After multivariate adjustment for age, sex, systolic BP, and other confounders, the association remained significant for rs2681472 and rs1401982 (OR: 7.60, p < .05 and OR: 7.62, p = .049, respectively). Additionally, rs2681472 and rs1401982 were in linkage disequilibrium with rs11105378. This study identified two ATP2B1 SNPs associated with RHT in the Japanese population. rs1401982 was most closely associated with RHT, and major allele carriers of rs1401982 required significantly more antihypertensive medications. Analysis of ATP2B1 SNPs in patients with hypertension can help in early prediction of RHT and identification of high-risk patients who are more likely to require more antihypertensive medications.     

ARC syndrome with high GGT cholestasis caused by VPS33B mutations

Arthrogryposis,renal dysfunction and cholestasis(ARC)syndrome(OMIM 208085)is an autosomal recessive disorder that is caused by mutations in 2 interacting genes VPS33B and VIPAS39.Mutations in VPS33B gene account for most cases of ARC.As low or normal gamma-glutamyl transpeptidase(GGT)activity has been described in all patients with ARC syndrome identified so far,ARC syndrome is a possible diagnosis for low GGT cholestasis.Here we describe a Chinese patient with neonatal cholestasis and a high GGT level in three consecutive tests.She had other typical manifestations of ARC syndrome,including arthrogryposis multiplex congenita,renal involvement and ichthyosis.Genetic study of the VPS33B gene further confirmed the diagnosis by identification of compound heterozygosity of two known disease-causing mutations,c.403+2T>A and c.1509-1510insG.The mechanism of high GGT in this patient is unclear.Nevertheless,this case indicates that ARC syndrome cannot be excluded from the differential diagnosis of neonatal cholestasis even if high GGT activity is found.     

Benign recurrent intrahepatic cholestasis associated with mutations of the bile salt export pump

A young patient with recurrent attacks of intrahepatic cholestasis is described. On the basis of clinical presentation, laboratory findings and genetic analysis, the diagnosis of benign recurrent intrahepatic cholestasis type 2 (BRIC-2) was established. By the use of BSEP-specific antibodies, almost complete absence of BSEP from the canalicular membrane of liver cells was detected in the patient. Two different BSEP mutations were found. One mutation (E186G) had been described in one BRIC-2 case; the second mutation (V444A) is more frequent and has been linked to intrahepatic cholestasis of pregnancy. It is concluded that this form of compound heterozygosity of the BSEP gene reduces the amount of BSEP protein due to protein instability or mis-targeting, which is the underlying reason for reduced bile salt excretion and cholemia.     

X-linked cholestasis in mouse due to mutations of the P4-ATPase ATP11C

Transporters at the hepatic canalicular membrane are essential for the formation of bile and the prevention of cholestatic liver disease. One such example is ATP8B1, a P4-type ATPase disrupted in three inherited forms of intrahepatic cholestasis. Mutation of the X-linked mouse gene Atp11c, which encodes a paralogous P4-type ATPase, precludes B-cell development in the adult bone marrow, but also causes hyperbilirubinemia. Here we explore this hyperbilirubinemia in two independent Atp11c mutant mouse lines, and find that it originates from an effect on nonhematopoietic cells. Liver function tests and histology revealed only minor pathology, although cholic acid was elevated in the serum of mutant mice, and became toxic to mutant mice when given as a dietary supplement. The majority of homozygous mutant females also died of dystocia in a maternal genotype-specific manner. ATP11C therefore represents a multifunctional transporter, essential for adult B-cell development, the prevention of intrahepatic cholestasis, and parturition, and is a new candidate for genetically undiagnosed cases of cholestasis and dystocia in humans.     

遗传性球形红细胞增多症合并肝内胆汁淤积致严重高胆红血症1例

<正>遗传性球形细胞增多症(Hereditary spherocytosis,HS)是一种常染色体显性遗传性疾病,临床上主要表现为溶血性贫血伴黄疸,以间接胆红素升高为主,很少合并肝内胆汁淤积和极度的高胆红素血症。我们报道1例罕见的遗传性球形细胞增多症伴有直接胆红素极度升高和肝内胆汁淤积患者,对疾病进程中一些特殊的临床表现发生的原因进行了分析。1病例摘要患者女性,49岁,会计。因反复腹痛伴尿黄皮肤黄40天于2013年10月10日入院。缘于2013年8月29日无明