ABCB11 gene mutations in Chinese children with progressive intrahepatic cholestasis and low gamma glutamyltransferase

The spectrum of novel ABCB11 gene variations in children with progressive familial intrahepatic cholestasis type 2 in Pakistani cohorts

Progressive familial intrahepatic cholestasis (PFIC) is a rare childhood manifested disease associated with impaired bile secretion with severe pruritus yellow stool, and sometimes hepatosplenomegaly. PFIC is caused by mutations in ATP8B1, ABCB11, ABCB4, TJP2, NR1H4, SLC51A, USP53, KIF12, ZFYVE19, and MYO5B genes depending on its type. ABCB11 mutations lead to PFIC2 that encodes the bile salt export pump (BSEP). Different mutations of ABCB11 have been reported in different population groups but no data available in Pakistani population being a consanguineous one. We sequenced coding exons of the ABCB11 gene along with its flanking regions in 66 unrelated Pakistani children along with parents with PFIC2 phenotype. We identified 20 variations of ABCB11: 12 in homozygous form, one compound heterozygous, and seven heterozygous. These variants include 11 missenses, two frameshifts, two nonsense mutations, and five splicing variants. Seven variants are novel candidate variants and are not detected in any of the 120 chromosomes from normal ethnically matched individuals. Insilico analysis revealed that four homozygous missense variations have high pathogenic scores. Minigene analysis of splicing variants showed exon skipping and the addition of exon. This data is a useful addition to the disease variants genomic database and would be used in the future to build a diagnostic algorithm.

Neonatal cholestasis is an early liver manifestation of children with acid sphingomyelinase deficiency

Background

Patients with acid sphingomyelinase deficiency (ASMD) may be referred to a hepatologist for liver manifestations. This study summarized the liver manifestations of patients with ASMD in the early disease course.

Methods

This study enrolled ASMD patients diagnosed by genetic tests between July 2016 and December 2020 in a national pediatric liver center. The significance of low High-density lipoprotein cholesterol (HDL-C) for aid diagnosis of ASMD in infancy was explored by reviewing 160 consecutive infants with liver manifestations, who underwent both genetic tests and lipid profile studies, between January 2020 and December 2020.

Results

A total of 7 patients were diagnosed as ASMD, and 10 known disease-causing variants were identified. Hepatosplenomegaly, elevated transaminases, and liver foam cells were observed in all the 7 patients at age ranging from 4 to 31 months. Low HDL-C was detected in 5 patients, cherry red spot in 4 patients, development delay in 3 patients, and interstitial lung diseases in 1 patient. Three ASMD patients developed cholestasis around 1 month of age, and bilirubin levels normalized at age ranging from 3 to 10 months. They had persistently elevated transaminases and hepatosplenomegaly, and died within 4 years of age. Among the 160 infants with liver manifestations, 125 (78.1%) had low HDL-C. Fifty-four had both low HDL-C and splenomegaly, including 48 cholestatic infants, but only 1 (1.9%, 1/54) infant without cholestasis was diagnosed as ASMD.

Conclusions

ASMD can manifest as neonatal cholestasis in the early disease course. Cholestasis is a pitfall when low HDL-C is used for aid diagnosis of ASMD in infants with splenomegaly.

The Presence of Vacuolated Kupffer Cells Raises a Clinical Suspicion of Niemann-Pick Disease Type C in Neonatal Cholestasis

Early diagnosis of Niemann-Pick disease type C (NP-C) in neonatal cholestasis is still challenging because splenomegaly is non-specific and oxysterol profiling studies also have a relatively low specificity. This study explores a method for identifying infants with a high clinical suspicion of NP-C in neonatal cholestasis. We reviewed the clinical findings of 9 neonatal cholestatic infants with NP-C genetically diagnosed between January 2015 and December 2020. Seven underwent liver biopsy at ages ranging from 35 to 112 d. Foam cells were only detected in 2 (28.6%, 2/7) liver tissues obtained beyond 3 months of age. However, vacuolated Kupffer cells were detected in all 7 liver tissues. Their significance was explored by using 168 neonatal cholestatic infants, who underwent genetic tests and liver biopsy between January 2018 and December 2020. Of them, 26 detected vacuolated Kupffer cells. Six (23.1%, 6/26) were diagnosed as NP-C, comparing to none of the 142 neonatal cholestatic infants without vacuolated Kupffer cells (χ² = 33.983, p < 0.001). The ratio of positive diagnosis of NP-C was 31.6% (6/19) in neonatal cholestatic infants with both vacuolated Kupffer cells and splenomegaly. Therefore, we conclude that the presence of vacuolated Kupffer cells can raise a high clinical suspicion of NP-C in neonatal cholestatic infants, especially in those with splenomegaly.

RNA Splicing: A Versatile Regulatory Mechanism in Pediatric Liver Diseases

With the development of high-throughput sequencing technology, the posttranscriptional mechanism of alternative splicing is becoming better understood. From decades of studies, alternative splicing has been shown to occur in multiple tissues, including the brain, heart, testis, skeletal muscle, and liver. This regulatory mechanism plays an important role in physiological functions in most liver diseases. Currently, due to the absence of symptoms, chronic pediatric liver diseases have a significant impact on public health. Furthermore, the progression of the disease is accelerated in children, leading to severe damage to their liver tissue if no precautions are taken. To this end, this review article summarizes the current knowledge of alternative splicing in pediatric liver diseases, paying special attention to liver damage in the child stage. The discussion of the regulatory role of splicing in liver diseases and its potential as a new therapeutic target is also included.

Structure and Function of Hepatobiliary ATP Binding Cassette Transporters

The liver is beyond any doubt the most important metabolic organ of the human body. This function requires an intensive crosstalk within liver cellular structures, but also with other organs. Membrane transport proteins are therefore of upmost importance as they represent the sensors and mediators that shuttle signals from outside to the inside of liver cells and/or vice versa. In this review, we summarize the known literature of liver transport proteins with a clear emphasis on functional and structural information on ATP binding cassette (ABC) transporters, which are expressed in the human liver. These primary active membrane transporters form one of the largest families of membrane proteins. In the liver, they play an essential role in for example bile formation or xenobiotic export. Our review provides a state of the art and comprehensive summary of the current knowledge of hepatobiliary ABC transporters. Clearly, our knowledge has improved with a breath-taking speed over the last few years and will expand further. Thus, this review will provide the status quo and will lay the foundation for new and exciting avenues in liver membrane transporter research.

ABCB11 deficiency presenting as transient neonatal cholestasis: Correlation with genotypes and BSEP expression

BACKGROUND & AIMS

ABCB11 deficiency presenting in infancy is believed generally to manifest as persistent/progressive cholestasis. We describe a group of patients with biallelic ABCB11 variants whose disorder manifested as transient neonatal cholestasis (TNC).

METHODS

Neonatal intrahepatic cholestasis in 68 children (31 males) with biallelic predictedly pathogenic variants (PPV) in ABCB11 was classified as transient (TNC group, n = 23, 11 males), intermittent (benign recurrent intrahepatic cholestasis [BRIC] group, n = 3, 1 male) or persistent/ progressive (progressive familial intrahepatic cholestasis [PFIC] group, n = 42, 19 males). Clinical, genetic and bile salt export pump (BSEP) expression information was correlated with outcomes.

RESULTS

The median onset age of jaundice was 3 days (birth to 2 months) for the TNC group and 10.5 days (birth to 3 months) for the PFIC group (P = .034). The median length of follow-up of TNC patients was 44 months (12 months-168 months). At presentation, hepatobiliary-injury biomarker values were similar between the groups (P > .05). TNC patients (17/23) more often than PFIC patients (20/42, P = .041) harboured biallelic non-null variants (predicted not to terminate translation prematurely). TNC patient livers (7/7) more often than PFIC patient livers (5/16, P = .005) expressed immunohistochemically detectable BSEP. Kaplan-Meier analysis showed better prognosis for patients with BSEP expression (P = .009). Too few BRIC patients were available for statistical study.

CONCLUSIONS

Neonatal cholestasis associated with biallelic PPV in ABCB11 can resolve temporarily or persistently in one third of cases. Resolution is more likely in patients with biallelic non-null PPV or with liver BSEP expression.

Molecular findings in children with inherited intrahepatic cholestasis

BACKGROUND

Genetic defects account for a substantial proportion of pediatric cholestasis. This study explored the molecular findings in a large cohort of Chinese patients with inherited cholestasis.

METHODS

Between January 2012 and June 2016, 809 Chinese pediatric patients with suspected inherited intrahepatic cholestasis were evaluated by Sanger sequencing and/or panel sequencing.

RESULTS

Of the 809 patients, 273 (33.7%) obtained a genetic diagnosis. The rate of positive genetic diagnosis in patients with disease onset at 0-3 month of age was higher than that in patients with disease onset at 4 month of age or later. There were 17 distinct genetic defects diagnosed. The top 4 resulted from mutations in SLC25A13 (44.3%), JAG1 (24.5%), ABCB11 (11.0%), and ATP8B1 (5.9%). All 17 genetic disorders were diagnosed in patients with disease onset at 0-3 months of age; but only 5 were diagnosed in patients with disease onset beyond 4 months of age. A total of 217 distinct pathogenic variants, including 41 novel variants, were identified. Ten recurrent mutations were detected in SLC25A13, ATP8B1, and CYP27A1. They accounted for 48.2% of the total 477 mutant alleles.

CONCLUSIONS

There were 17 distinct genetic disorders diagnosed in Chinese pediatric patients with inherited cholestasis.

Splicing analysis of rare/novel synonymous or intronic variants identified in ABCB11 heterozygotes presenting as progressive intrahepatic cholestasis with low γ-glutamyltransferase

AIM

The aim of this study was to analyze the pathogenicity of rare/novel synonymous or intronic variants identified in ABCB11 heterozygotes presenting as progressive intrahepatic cholestasis with low γ-glutamyltransferase.

METHODS

The enrolled variants were identified in ABCB11 between October 2009 and June 2016. The effects on pre-RNA splicing were analyzed by in silico tools and minigene splicing assay.

RESULTS

There were three intronic (c.908 + 5G > A, c.2815-8A > G, and c.612-15_-6del10bp) and two synonymous (c.1809G > A, p.K603 K and c.2418C > T, p.G806G) variants with unknown significance identified in ABCB11 of five ABCB11 heterozygotes. Parental studies were carried out for four patients, and revealed that the variants with unknown significance were compound heterozygous with other pathogenic variants. The five variants with unknown significance had minor allele frequency <0.1% or were absent from controls, and had positive prediction results by in silico tools. The effects on pre-RNA splicing were further confirmed by minigene splicing assay. c.908 + 5A caused abnormal splicing in at least 78.5 ± 3.8% of products using a cryptic splice site (ss) 22 nucleotides (nt) upstream of the wild-type (WT) 5'ss. Seven nucleotides of intron 22 upstream of the WT 3'ss was retained for all products from c.2815-8G. c.612-15_-6del caused exon 8 skipping in 24.8 ± 7.7% of products, and 55 nt of exon 8 downstream of the WT 3'ss removal in remaining products. c.1809A led to exon 15 skipping. c.2418 T removed exon 20 and 62 nt of exon 21 downstream of the WT 3'ss by using a cryptic ss.

CONCLUSIONS

We successfully identified five pathogenic synonymous or intronic variants with some common features. These features might help to choose the right variant for further functional assay.

Clinical phenotype and molecular analysis of a homozygous ABCB11 mutation responsible for progressive infantile cholestasis

The bile salt export pump (BSEP) plays an important role in biliary secretion. Mutations in ABCB11, the gene encoding BSEP, induce progressive familial intrahepatic cholestasis type 2 (PFIC2), which presents with severe jaundice and liver dysfunction. A less severe phenotype, called benign recurrent intrahepatic cholestasis type 2, is also known. About 200 missense mutations in ABCB11 have been reported. However, the phenotype-genotype correlation has not been clarified. Furthermore, the frequencies of ABCB11 mutations differ between Asian and European populations. We report a patient with PFIC2 carrying a homozygous ABCB11 mutation c.386G>A (p.C129Y) that is most frequently reported in Japan. The pathogenicity of BSEP^C129Y has not been investigated. In this study, we performed the molecular analysis of this ABCB11 mutation using cells expressing BSEP^C129Y. We found that trafficking of BSEP^C129Y to the plasma membrane was impaired and that the expression of BSEP^C129Y on the cell surface was significantly lower than that in the control. The amount of bile acids transported via BSEP^C129Y was also significantly lower than that via BSEP^WT. The transport activity of BSEP^C129Y may be conserved because the amount of membrane BSEP^C129Y corresponded to the uptake of taurocholate into membrane vesicles. In conclusion, we demonstrated that c.386G>A (p.C129Y) in ABCB11 was a causative mutation correlating with the phenotype of patients with PFIC2, impairment of biliary excretion from hepatocytes, and the absence of canalicular BSEP expression in liver histological assessments. Mutational analysis in ABCB11 could facilitate the elucidation of the molecular mechanisms underlying the development of intrahepatic cholestasis.

Defects in myosin VB are associated with a spectrum of previously undiagnosed low γ-glutamyltransferase cholestasis

Hereditary cholestasis in childhood and infancy with normal serum gamma-glutamyltransferase (GGT) activity is linked to several genes. Many patients, however, remain genetically undiagnosed. Defects in myosin VB (MYO5B; encoded by MYO5B) cause microvillus inclusion disease (MVID; MIM251850) with recurrent watery diarrhea. Cholestasis, reported as an atypical presentation in MVID, has been considered a side effect of parenteral alimentation. Here, however, we report on 10 patients who experienced cholestasis associated with biallelic, or suspected biallelic, mutations in MYO5B and who had neither recurrent diarrhea nor received parenteral alimentation. Seven of them are from two study cohorts, together comprising 31 undiagnosed low-GGT cholestasis patients; 3 are sporadic. Cholestasis in 2 patients was progressive, in 3 recurrent, in 2 transient, and in 3 uncategorized because of insufficient follow-up. Liver biopsy specimens revealed giant-cell change of hepatocytes and intralobular cholestasis with abnormal distribution of bile salt export pump (BSEP) at canaliculi, as well as coarse granular dislocation of MYO5B. Mass spectrometry of plasma demonstrated increased total bile acids, primary bile acids, and conjugated bile acids, with decreased free bile acids, similar to changes in BSEP-deficient patients. Literature review revealed that patients with biallelic mutations predicted to eliminate MYO5B expression were more frequent in typical MVID than in isolated-cholestasis patients (11 of 38 vs. 0 of 13).

CONCLUSION

MYO5B deficiency may underlie 20% of previously undiagnosed low-GGT cholestasis. MYO5B deficiency appears to impair targeting of BSEP to the canalicular membrane with hampered bile acid excretion, resulting in a spectrum of cholestasis without diarrhea. (Hepatology 2017;65:1655-1669).

Clinical and ABCB11 profiles in Korean infants with progressive familial intrahepatic cholestasis

AIM: To investigate clinical profiles and mutations of ABCB11 in Koreans with progressive familial intrahepatic cholestasis 2 and review the differences between Koreans and others.

METHODS: Of 47 patients with neonatal cholestasis, five infants had chronic intrahepatic cholestasis with normal γ-glutamyl transpeptidase. Direct sequencing analyses of ABCB11, including exons and introns, were performed from peripheral blood.

RESULTS: Living donor-liver transplantation was performed in four patients because of rapidly progressive hepatic failure and hepatocellular carcinoma. Three missense mutations were found in two patients: compound heterozygous 677C>T (S226L)/3007G>A (G1003R) and heterozygous 2296G>A (G766R). The mutations were located near and in the transmembranous space.

CONCLUSION: Alterations in the transmembrane of the bile salt export pump in the Korean infants were different from those previously reported in Chinese, Japanease, Taiwanese, and European patients.

The Features of GGT in Patients with ATP8B1 or ABCB11 Deficiency Improve the Diagnostic Efficiency

Background and Aims

Genetic defects in ATP8B1 or ABCB11 account for the majority of cholestasis with low GGT. But the ranges for GGT in patients with ATP8B1 or ABCB11 deficiency are unclear. This study tried to unravel the features of GGT in these patients that improve diagnostic efficiency.

Methods

This study enrolled 207 patients with chronic cholestasis who were ordered to test for ATP8B1 and/or ABCB11 from January 2012 to December 2015. Additional 17 patients with ATPB81 or ABCB11 deficiency diagnosed between January 2004 and December 2011 were also enrolled in this study. 600 population-matched children served as controls. Clinical data were obtained by retrospectively reviewing medical records.

Results

A total of 26 patients were diagnosed with ATP8B1 deficiency and 30 patients were diagnosed with ABCB11 deficiency. GGT levels were similar between the two disorders at any observed month of age, but varied with age. The peak GGT value was <70U/L in the 2nd~6th month of life, <60U/L in the 7th~12th month and <50U/L beyond one year. GGT levels in patients with a genetic diagnosis were different from that in patients without a genetic diagnosis and controls. Larger ranges for GGT were found in patients without a genetic diagnosis. Some controls had GGT≥70U/L in the 2nd~6th month. Of the 207 patients, 39 (18.8%) obtained a genetic diagnosis. 111 patients met the ranges described above, including all the 39 patients with ATP8B1 or ABCB11 deficiency. The sensitivity was 100.0%. The rate of a positive molecular diagnosis increased to 35.1% (39/111 vs. 39/207, X² = 10.363, P = 0.001). The remaining 96 patients exceeded the ranges described above and failed to receive a genetic diagnosis. These patients accounted for 43.8% of sequencing cost.

Conclusions

GGT levels in patients with ATP8B1 or ABCB11 deficiency varied with age. The peak GGT value was <70U/L in the 2nd~6th month of life, <60U/L in the 7th~12th month and <50U/L beyond one year.

Hypothyroidism Associated with ATP8B1 Deficiency

OBJECTIVE

To examine whether hypothyroidism is an extrahepatic feature of ATPase, aminophospholipid transporter, class I, type 8B, member 1 (ATP8B1) deficiency.

STUDY DESIGN

Children with normal γ-glutamyltransferase cholestasis (n = 47; 13 patients with ATP8B1 deficiency, 19 with ATP-binding cassette, subfamily B (MDR/TAP), member 11 (ABCB11) deficiency, and 15 without either ATP8B1 or ABCB11 mutations) were enrolled. Clinical information and thyroid function test results were retrospectively retrieved from clinical records and compared. Hypothyroidism was diagnosed by clinical-biochemistry criteria (thyroid function test results).

RESULTS

Three out of 13 patients with ATP8B1 deficiency were diagnosed as hypothyroid and 2 as subclinically hypothyroid. The frequency of hypothyroidism and subclinical hypothyroidism was significantly higher than in patients with ABCB11 deficiency (5/13 vs 0/19, P = .006) and in patients without ATP8B1 or ABCB11 mutations (5/13 vs 0/15, P = .013). Thyroid function test results normalized after hormone replacement in all 5 patients, with no relief of cholestasis.

CONCLUSIONS

As hypothyroidism can be another extrahepatic feature of ATP8B1 deficiency, thyroid function should be monitored in these patients.

Diagnosis of ABCB11 gene mutations in children with intrahepatic cholestasis using high resolution melting analysis and direct sequencing

Intrahepatic cholestasis represents a heterogeneous group of disorders that begin during childhood, most commonly manifesting as neonatal cholestasis, and lead to ongoing liver dysfunction in children and adults. For children, inherited pathogenic factors of cholestasis have gained increasing attention owing to the rapid development of molecular biology technology. However, these methods have their advantages and disadvantages in terms of simplicity, sensitivity, specificity, time required and expense. In the present study, an effective, sensitive and economical method is recommended, termed high-resolution melting (HRM) analysis and direct sequencing, based on general polymerase chain reaction, to detect mutations in disease-causing genes. As one type of inherited intrahepatic cholestasis, progressive familial intrahepatic cholestasis type 2 (PFIC2) is caused by pathogenic mutations in the ABCB11 gene, HRM was used to detect mutations in the ABCB11 gene in the present study, and the diagnosis for PFIC2 was made by comprehensive analysis of genetic findings and clinical features. Furthermore, the characteristics of mutations and single nucleotide polymorphisms (SNPs) in the ABCB11 gene were elucidated. A total of 14 types of mutations/polymorphisms were identified in 20 patients from mainland China, including six missense mutations (p.Y337H, p.Y472C, p.R696W, p.Q931P, p.D1131V and p.H1198R), one nonsense mutation (p.R928X) and seven SNPs (p.D36D/rs3815675, p.F90F/rs4148777, p.Y269Y/rs2287616, p.I416I/rs183390670, p.V444A/rs2287622, p.A865V/rs118109635 and p.A1028A/rs497692). Five mutations were novel. The majority of the mutations were different from those detected in other population groups. A total of 4/20 patients (1/5) were diagnosed to be PFIC2 by combining genetic findings with the clinical features. Polymorphisms V444A and A1028A, with an allele frequency of 74.5 and 67.2%, respectively, were highly prevalent in the mainland Chinese subjects. No differences were found between the patients with cholestasis and the control subjects. Efficient genetic screening facilitates the clinical diagnosis of genetic disorders. The present study demonstrated that HRM analysis was efficient and effective in detecting mutations and expanded the known spectrum of ABCB11 gene mutations.

Association of variants of ABCB11 with transient neonatal cholestasis

BACKGROUND

The significance of ABCB11 variants have been studied in some cholestatic diseases, but this is not clear in transient neonatal cholestasis (TNC). The aim of the present study was to explore the association between ABCB11 variants and TNC.

METHODS

This was a case-control study. A total of 192 children with TNC referred to a tertiary referral hospital in eastern China were enrolled as subjects, and 196 healthy children were selected as controls. Part of the promoter and exons of the ABCB11 gene were sequenced directly. The single nucleotide polymorphism (SNP) site of V444A was tested using fluorescent quantitative polymerase chain reaction. Potential consequences of variants were predicted using bioinformatics software. The biochemistry indices were compared between the patients with or without possibly pathogenic variants/mutations.

RESULTS

Twenty-eight variants, including 14 novel ones, were detected. Four novel, possibly pathogenic mutations (I416I, K436N, R928Q and IVS7+5G>A) were detected in six subjects. The γ-glutamyltransferase level of these six was lower than in the others (P = 0.054). The genotype distribution of the four common SNP sites, V444A, A535A, A865V and A1082A, was not significantly different between TNC patients and controls.

CONCLUSIONS

Approximately 3% of TNC cases can be attributed to ABCB11 mutations.

Mutation detection in cholestatic patients using microarray resequencing of ATP8B1 and ABCB11

Background: Neonatal cholestasis is a common presentation of childhood liver diseases and can be a feature of various conditions including disorders of bile acid biogenesis and transport, various inborn errors of metabolism and perinatal infections. Some inherited metabolic diseases can be easily screened using biochemical assays, however many can only be accurately diagnosed by DNA sequencing. Fluorescent capillary Sanger sequencing (FS) is the gold standard method used by clinical laboratories for genetic diagnosis of many inherited conditions; however, it does have limitations. Recently microarray resequencing (MR) has been introduced into research and clinical practice as an alternative method for genetic diagnosis of heterogeneous conditions. In this report we compared the accuracy of mutation detection for MR with FS in a group of patients with ‘low-normal’ gamma glutamyl transpeptidase (gGT) cholestasis without known molecular diagnoses.

Methods: 29 patient DNA samples were tested for mutations in the ATP8B1 and ABCB11 genes using both FS and MR. Other known causes of “low gGT cholestasis” such as ARC syndrome and bile acid biosynthesis disorders were excluded.

Results: Mutations were identified in 13/29 samples. In 3/29 samples FS and MR gave discordant results: MR had a false positive rate of 3.4% and a false negative rate of 7%.

Conclusions: The major advantage of MR over FS is that multiple genes can be screened in one experiment, allowing rapid and cost-effective diagnoses.  However, we have demonstrated that MR technology is limited in sensitivity. We therefore recommend that MR be used as an initial evaluation, with FS deployed when genetic and clinical or histopathological findings are discordant.

The bile salt export pump (BSEP) in health and disease

The bile salt export pump (BSEP) is the major transporter for the secretion of bile acids from hepatocytes into bile in humans. Mutations of BSEP are associated with cholestatic liver diseases of varying severity including progressive familial intrahepatic cholestasis type 2 (PFIC-2), benign recurrent intrahepatic cholestasis type 2 (BRIC-2) and genetic polymorphisms are linked to intrahepatic cholestasis of pregnancy (ICP) and drug-induced liver injury (DILI). Detailed analysis of these diseases has considerably increased our knowledge about physiology and pathophysiology of bile secretion in humans. This review focuses on expression, localization, and function, short- and long-term regulation of BSEP as well as diseases association and treatment options for BSEP-associated diseases.

Chinese children with chronic intrahepatic cholestasis and high γ-glutamyl transpeptidase: clinical features and association with ABCB4 mutations

OBJECTIVE

The aims of the present study was to study the significance of ABCB4 mutations in mainland Chinese children with chronic intrahepatic cholestasis and to correlate genetic findings with clinical features and response to ursodeoxycholic acid (UDCA) therapy.

METHODS

Thirteen patients with chronic intrahepatic cholestasis and elevated serum γ-glutamyl transpeptidase activity of unknown cause were enrolled in a single pediatric center. All of the encoding exons and flanking areas of ABCB4 were sequenced. Available liver biopsy specimens were immunostained for multidrug resistance protein 3. The clinical features, biochemical parameters, and responses to therapy were compared with patients with or without ABCB4 mutation(s).

RESULTS

Six different ABCB4 mutations were identified in 3 patients; each patient was a compound heterozygote. Apart from c.139C>T (p.R47X), all were novel, including c.344+2_+3insT, c.1376A>G (p.D459G), c.1745G>A (p.R582Q), c.2077_2078delC (p.P693HfsX698), and c.3825_3826delA (p.M1276WfsX1308). Absent or reduced multidrug resistance protein 3 canalicular immunostaining was demonstrated in patients with ABCB4 mutations. Serum total bile acid levels were higher in patients with ABCB4 mutations than in patients without ABCB4 mutations (352.5 ± 97.0 vs 55.9 ± 50.4 μmol/L, P = 7.32E-05). There was no difference in other biochemical parameters between patients with and without ABCB4 mutations. After oral UDCA administration in 3 patients with ABCB4 mutations, pruritus disappeared, growth improved, spleen size decreased, and platelet counts increased. In the 10 patients without ABCB4 mutations, an inconsistent response to UDCA therapy was observed.

CONCLUSIONS

In mainland Chinese children, some cases of chronic intrahepatic cholestasis with high γ-glutamyl transpeptidase could be attributed to ABCB4 mutations. UDCA administration partially improved clinical symptoms and liver function.

Description of two new ABCB11 mutations responsible for type 2 benign recurrent intrahepatic cholestasis in a French-Canadian family

Benign recurrent intrahepatic cholestasis is a rare clinical entity that is caused by mutations in the canalicular transport genes. The present report describes two individuals from the same family whose symptoms were typical of the clinical characteristics of type 2 benign recurrent intrahepatic cholestasis. Sequencing of the ABCB11 gene revealed two previously unreported mutations that predict the absence of expression of the protein. The clinical presentation of the current cases are discussed, as are the differential diagnosis and genetic characteristics of the hereditary cholestatic disorders, overemphasizing the possibility of making a definite genetic diagnosis.

Morphologic findings in progressive familial intrahepatic cholestasis 2 (PFIC2): correlation with genetic and immunohistochemical studies

Progressive familial intrahepatic cholestasis, type 2 (PFIC2), characterized by cholestasis in infancy that may progress to cirrhosis, is caused by mutation in ABCB11, which encodes bile salt export pump (BSEP). We correlated histopathologic, immunohistochemical, and ultrastructural features in PFIC2 with specific mutations and clinical course. Twelve patients with clinical PFIC2 and ABCB11 mutations were identified, and 22 liver biopsy and explant specimens were assessed. All had hepatocellular cholestasis; most had canalicular bile plugs. At least 1 specimen from every patient had centrizonal/sinusoidal fibrosis, often with periportal fibrosis. Neonatal hepatitis-like features (inflammation, giant cells, necrosis) varied. In 2 of the 5 patients with paired specimens obtained >6 months apart, lobular and portal fibrosis worsened. Transmission electron microscopy (EM) in all 9 patients studied showed canalicular dilatation, microvilli loss, abnormal mitochondrial internal structure, and varying intracanalicular accumulation of finely granular bile. Canalicular staining for BSEP was absent in 10 patients and present in 2 patients, 1 of whom had intermittent symptoms. ABCB11 sequencing of all patients identified 6 novel and 10 previously described mutations, with nonsense, missense, and/or noncoding mutations in the 10 patients without immunohistochemically demonstrable BSEP. Missense and/or noncoding mutations were identified in the 2 patients with demonstrable BSEP, whose clinical course was more indolent. Mutations ending ABCB11 transcription appear linked, through hepatocellular necrosis and fibrosis, to worse outcome. In conclusion, light microscopy and electron microscopy findings in clinical PFIC2 can support diagnosis, but are variable and nonspecific. Therefore, no correlation between specific mutations and histopathology is yet possible.

The mutation spectrum of the SLC25A13 gene in Chinese infants with intrahepatic cholestasis and aminoacidemia

BACKGROUND

SLC25A13 gene mutations cause citrin deficiency, which leads to neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD). Information on the mutation spectrum of SLC25A13 in the Chinese population is limited. The aim of this study was to explore the mutation spectrum of the SLC25A13 gene in Chinese infants with intrahepatic cholestasis and various forms of aminoacidemia.

METHODS

Sequence analyses were performed on 39 infants with intrahepatic cholestasis and various forms of aminoacidemia. Novel mutations were subjected to homology and structural analyses. Western blots were performed when liver specimens available.

RESULTS

Genetic testing revealed the presence of SLC25A13 gene mutations (9 heterozygotes, 6 homozygotes and 13 compound heterozygotes) in 28 infants. Subsequent Western blot analysis revealed 22 cases of citrin deficiency, accounting for 56.4% of the 39 patients. Twelve types of mutations, including nine known mutations and three novel mutations, were found. Of the 49 mutated alleles, known ones include 851del4 (26 alleles, 53.1%), 1638ins23 (6 alleles, 12.2%), IVSl6ins3kb (3 alleles, 6.1%), IVS6+5G>A (2 alleles, 4.1%), E601K (2 alleles, 4.1%) and IVS11+1G>A, R184X, R360X and R585H (1 allele each, 2.0%). The three novel mutations were a splice site change (IVS6+1G>A), a deletion mutation (1092_1095delT) and a missense mutation (L85P), each in one allele.

CONCLUSIONS

The mutation spectrum of the SLC25A13 gene in a Chinese population of infants with intrahepatic cholestasis with various forms of aminoacidemia was found to be different from that of other population groups in East Asia. The SLC25A13 gene mutation is the most important cause of infantile intrahepatic cholestasis with various forms of aminoacidemia.