Mutational analysis of ABCC2 gene in two siblings with neonatal-onset Dubin Johnson syndrome

Neonatal Dubin-Johnson syndrome: biochemical parameters, characteristics, and genetic variants study

BACKGROUND

The clinical characteristics and gene mutation characteristics of children with Dubin-Johnson syndrome (DJS) need in-depth study.

METHODS

The clinical and genomic data of neonatal Dubin-Johnson syndrome (NDJS) and 155 cases with idiopathic cholestasis (IC) were analyzed from June 2016 to August 2020 RESULTS: ABCC2 gene variants were identified in eight patients, including one patient with homozygous variants and seven patients with compound heterozygous variants. A total of 13 different ABCC variants were detected in the NDJS patients, including three nonsense variants, six missense variants, three frameshift variants, and a splice site variant. The variant c.2443C > T (p.R815X), c.4237_4238insCT (p.H1414Lfs*17), c.960_961insGT (p.L322Cfs*3), c.4250delC (p.S1417Ffs*14), c.2224G > A (p.D742N), c.4020G > C (p.K1340N), and c.2439 + 5G > A were not reported in the Human Gene Variant Database. There was no significance in the sex, birth weight, and onset age between the NDJS and IC groups. Compared with the IC group, the NDJS group had significantly higher levels of total bilirubin (TB), but a significantly lower level of alanine transaminase and a ratio of direct bilirubin (DB) to TB. There is no significance in total bile acid, gamma-glutamyl-transpeptidase, albumin, or international normalized ratio between the two groups.

CONCLUSIONS

NDJS should be considered in prolonged neonatal intrahepatic cholestasis, especially in infants with normal or slightly elevated transaminase levels.

IMPACT

Explore the biochemical parameters, characteristics, and genetic profile of NDJS. By summarizing the characteristics of biochemical indicators, seven new mutation types of the ABCC2 gene were detected, which expanded the mutation spectrum of the ABCC2 gene. NDJS should be considered in prolonged neonatal intrahepatic cholestasis, especially in infants with normal or slightly elevated transaminase levels.

In silico screening and analysis of single-nucleotide polymorphic variants of the ABCC2 gene affecting Dubin-Johnson syndrome

BACKGROUND AND STUDY AIMS

Dubin-Johnson syndrome (DJS) is a benevolent genetic disorder of the liver with autosomal inheritance. It is a rare disorder characterized by an increase in conjugated bilirubin and anomaly in coproporphyrin clearance. DJS is caused by deleterious mutations in the ABCC2 gene. A polymorphism in the ABCC2 gene causes malfunctions in its ability to regulate the efflux of different organic anions, such as bilirubin, from hepatocytes to the canaliculi. Multidrug resistance protein 2 (MRP2) encoded by the ABCC2 gene is one of the main regulators of the export of bilirubin to respective sites. ABCC2 gene mutations have widely drawn attention in the pathology of DJS in various populations.

PATIENTS AND METHODS

The ABCC2 gene was subjected to the National Center for Biotechnology Information (NCBI) database in 2020, and non-synonymous single-nucleotide polymorphisms (nsSNPs) and variants in untranslated regions were studied using different computational servers. SIFT, Protein variation effect analyzer, and PolyPhen-2 were used to retrieve the damaging Single-nucleotide polymorphisms (SNPs); PhD-SNP, SNPs&GO, and Protein Analysis Through Evolutionary Relationships were used to predict the association of nsSNPs with DJS; Mutation3D illustrated the location of variants in the protein; SNAP2, MutPred2, ELASPIC, and HOPE were used to predict the structural and functional effects of these mutations on MRP2; and I-mutant 3.0 and MuPro were used to determine the effects of polymorphism on the function of MRP2.

RESULTS

In this study, 18,947 SNPs were screened from the NCBI database, followed by a series of refinement of variants using online available servers. We concluded that 41 ABCC2 gene variants are vital etiological candidates for DJS in humans. These 41 variants had highly damaging effects on the MRP2 protein, which may lead to deficient transportation capacity, thereby affecting the efflux of bilirubin across the canalicular membrane.

CONCLUSION

In silico tools are an alternative approach for predicting the target SNPs. Hence, previously unreported variants can be considered strong etiological candidates for diseases related to MRP2.

Clinical, Biochemical, and Molecular Characterization of Neonatal-Onset Dubin-Johnson Syndrome in a Large Case Series From the Arabs

Background: There are only a few case reports and small case series on neonatal-onset Dubin-Johnson syndrome (DJS), particularly from Far-East Asia, Iranian and Moroccan Jews, and Europe. Objectives: In this first study from the Arabs and the largest series reported to date, we characterized the clinical, laboratory, and molecular features and outcome of gene-confirmed neonatal-onset DJS. Methods: We reviewed our database of 533 cases of neonatal cholestasis that presented to our center during the period from 2008 to 2019. We identified neonates with a disease-causing mutation in ABCC2 gene. Results: Twenty-eight neonates with DJS were diagnosed (5.3%). All of the 28 were full-term, well looking neonates without hepatosplenomegaly, with cholestasis, and normal liver synthetic function since the 1 week of life that resolved within 3-6 months of age, followed by a benign course punctuated by recurrent episodes of jaundice in 43% during a median follow up period of 9.25 (range 2.5-14 years). Alanine aminotransferase levels were within normal range in 26 patients (92%) and mildly elevated in two patients. ALT levels were significantly lower in neonates with DJS than in other cases with neonatal cholestasis from other causes (p < 0.001). The median urinary coproporphyrin I% was 88% (IQ1-IQ3 = 84.2-92.7%). We identified four homozygous variants in the ABCC2 gene (from 22 unrelated families), one splicing variant (c.3258+1G>A; p.?), and three were missense variants; two of which were novel missense variants [c.1594G>A (p.Glu532Lys) and c.2439G>C (p.Lys813Asn)]. The p.Gly758Val mutation has occurred in 23 patients (from 19 unrelated families). Conclusions: Our study suggests that normal ALT-cholestasis in a well-looking neonate should trigger evaluation for DJS. The p.Gly758Val variant in ABCC2 is the most predominant mutation among Arabs with "founder effects." Identification of the predominant ABCC2 variant in any population is likely to facilitate rapid molecular analysis by future targeting of that specific mutation.

Genetic contribution of ABCC2 to Dubin-Johnson syndrome and inherited cholestatic disorders

BACKGROUND AND AIMS

The ABCC2 gene is implicated in Dubin-Johnson syndrome (DJS), a rare autosomal recessive liver disorder. The primary aim of this study was to determine the diagnostic value of ABCC2 genetic testing in the largest cohort of DJS reported to date. The high number of patients with cholestatic manifestations in this series prompted us to evaluate the genetic contribution of rare, potentially pathogenic ABCC2 variants to other inherited cholestatic disorders.

METHODS

The cohort study included 32 patients with clinical DJS diagnosis, and 372 patients referred for the following disorders: low phospholipid-associated cholelithiasis (LPAC) syndrome, intrahepatic cholestasis of pregnancy (ICP) and benign recurrent intrahepatic cholestasis (BRIC). ABCC2 was screened by next-generation sequencing.

RESULTS

Most patients with clinical DJS had positive genetic diagnosis (n = 30; 94%), with a great diversity of point mutations and copy number variations in ABCC2. Strikingly, eight (27%) of these patients showed transient cholestatic features at presentation: four neonatal cholestasis, two ICP, one contraceptive-induced cholestasis and one sporadic cholestasis. Conversely, the frequency of rare, heterozygous, potentially pathogenic ABCC2 variants in patients with LPAC, ICP or BRIC did not differ significantly from that of the general population.

CONCLUSIONS

This large series reveals that DJS is a highly homogeneous Mendelian disorder involving a large spectrum of ABCC2 variants. Genetic testing is crucial to establish early DJS diagnosis in patients with atypical presentations, such as neonatal cholestasis. This study also provides no evidence for the contribution of rare, potentially pathogenic ABCC2 variants to other inherited cholestatic disorders.

Next generation sequencing reveals co-existence of hereditary spherocytosis and Dubin–Johnson syndrome in a Chinese gril: A case report

BACKGROUND

Hereditary spherocytosis (HS) is a hereditary disease of hemolytic anemia that occurs due to the erythrocyte membrane defects. Dubin–Johnson syndrome (DJS), which commonly results in jaundice, is a benign hereditary disorder of bilirubin clearance that occurs only rarely. The co-occurrence of HS and DJS is extremely rare. We recently diagnosed and treated a case of co-occurring HS and DJS.

CASE SUMMARY

A 21-year-old female patient presented to our department because of severe jaundice, severe splenomegaly, and mild anemia since birth. We eventually confirmed the diagnosis of co-occurring DJS and HS by next generation sequencing (NGS). The treatment of ursodeoxycholic acid in combination with phenobarbital successfully increased hemoglobin and reduced total bilirubin and direct bilirubin.

CONCLUSION

The routine application of NGS can efficiently render a definite diagnosis when inherited disorders are suspected.

[Clinical features and ABCC2 genotypic analysis of an infant with Dubin-Johnson syndrome]

Dubin-Johnson syndrome (DJS) is an autosomal recessive disorder resulting from biallelic mutations of ABCC2 gene, with long-term or intermittent conjugated hyperbilirubinemia being the main clinical manifestation. This paper aims to report the clinical features and ABCC2 genotypes of an infant with DJS. A 9.5-month-old male infant was referred to the hospital due to abnormal liver function discovered over 9 months. The major clinical presentation was prolonged jaundice since neonatal period. A series of biochemistry analysis revealed markedly elevated total bilirubin, conjugated bilirubin and total bile acids. The patient had been managed in different hospitals, but the therapeutic effects were unsatisfactory due to undetermined etiology. Physical examination revealed jaundiced skin and sclera, and a palpable liver 3 cm below the right subcostal margin with medium texture. The spleen was not enlarged. Genetic analysis revealed a splice-site variant c.3988-2A>T and a nonsense variant c.3825C>G (p.Y1275X) in the ABCC2 gene of the infant, which were inherited from his mother and father respectively. The former had not been previously reported. Then ursodeoxycholic acid and phenobarbital were given orally. Half a month later, as a result, his jaundice disappeared and the biochemistry indices improved. However, the long-term outcome needs to be observed. Literature review revealed that neonates/infants with DJS presented with cholestatic jaundice soon after birth as the major clinical feature, and the ABCC2 variants exhibited marked heterogeneity.

Clinical, Pathologic, and Genetic Features of Neonatal Dubin-Johnson Syndrome: A Multicenter Study in Japan

OBJECTIVE

To clarify the clinical, pathologic, and genetic features of neonatal Dubin-Johnson syndrome.

STUDY DESIGN

Ten patients with neonatal Dubin-Johnson syndrome were recruited from 6 pediatric centers in Japan between September 2013 and October 2016. Clinical and laboratory course, macroscopic and microscopic liver findings, and molecular genetic findings concerning ATP-binding cassette subfamily C member 2 (ABCC2) were retrospectively and prospectively examined.

RESULTS

All neonates exhibited cholestasis, evident as prolonged jaundice with or without acholic stools and elevations of serum direct bilirubin as well as γ-glutamyltransferase or total bile acids. Only 38% (3 of 8) of patients who underwent liver biopsy showed a grossly black liver or melanin-like pigment deposits in hepatocytes; their biopsies were performed in early infancy. Immunohistochemically, all liver specimens showed no expression of multidrug resistance-associated protein 2 but increased expression of the bile salt export pump protein. Homozygous or compound heterozygous pathogenic variants of ABCC2 were identified in all patients, representing 11 distinct pathogenic variants including 2 not previously reported.

CONCLUSIONS

Immunohistochemical staining of the liver for multidrug resistance-associated protein 2 and molecular genetic analysis of ABCC2 are crucial for accurate diagnosis of neonatal Dubin-Johnson syndrome.

Beyond Competitive Inhibition: Regulation of ABC Transporters by Kinases and Protein-Protein Interactions as Potential Mechanisms of Drug-Drug Interactions

ATP-binding cassette (ABC) transporters are transmembrane efflux transporters mediating the extrusion of an array of substrates ranging from amino acids and lipids to xenobiotics, and many therapeutic compounds, including anticancer drugs. The ABC transporters are also recognized as important contributors to pharmacokinetics, especially in drug-drug interactions and adverse drug effects. Drugs and xenobiotics, as well as pathologic conditions, can influence the transcription of ABC transporters, or modify their activity or intracellular localization. Kinases can affect the aforementioned processes for ABC transporters as do protein interactions. In this review, we focus on the ABC transporters ABCB1, ABCB11, ABCC1, ABCC4, and ABCG2 and illustrate how kinases and protein-protein interactions affect these transporters. The clinical relevance of these factors is currently unknown; however, these examples suggest that our understanding of drug-drug interactions will benefit from further knowledge of how kinases and protein-protein interactions affect ABC transporters.

Molecular Genetic Dissection and Neonatal/Infantile Intrahepatic Cholestasis Using Targeted Next-Generation Sequencing

OBJECTIVES

To ascertain a molecular genetic diagnosis for subjects with neonatal/infantile intrahepatic cholestasis (NIIC) by the use of next-generation sequencing (NGS) and to perform a genotype-phenotype correlation.

STUDY DESIGN

We recruited Japanese subjects with NIIC who had no definitive molecular genetic diagnosis. We developed a diagnostic custom panel of 18 genes, and the amplicon library was sequenced via NGS. We then compared clinical data between the molecular genetically confirmed subjects with NIIC.

RESULTS

We analyzed 109 patients with NIIC ("genetic cholestasis," 31 subjects; "unknown with complications" such as prematurity, 46 subjects; "unknown without complications," 32 subjects), and a molecular genetic diagnosis was made for 28 subjects (26%). The rate of positive molecular genetic diagnosis in each category was 22 of 31 (71%) for the "genetic cholestasis" group, 2 of 46 (4.3%) for the "unknown with complications" group, and 4 of 32 (12.5%) for the "unknown without complications" group. The grouping of the molecular diagnoses in the group with genetic cholestasis was as follows: 12 with Alagille syndrome, 5 with neonatal Dubin-Johnson syndrome, 5 with neonatal intrahepatic cholestasis caused by citrin deficiency, and 6 with progressive familial intrahepatic cholestasis or benign recurrent intrahepatic cholestasis with low gamma-glutamyl transpeptidase levels. Several clinical datasets, including age of onset, direct bilirubin, and aminotransferases, were significantly different between the disorders confirmed using molecular genetic diagnosis.

CONCLUSION

Targeted NGS can be used for molecular genetic diagnosis in subjects with NIIC. Clinical diagnosis should be accordingly redefined in the view of molecular genetic findings.

Hereditary truncating mutations of DNA repair and other genes in BRCA1/BRCA2/PALB2-negatively tested breast cancer patients

Hereditary breast cancer comprises a minor but clinically meaningful breast cancer (BC) subgroup. Mutations in the major BC-susceptibility genes are important prognostic and predictive markers; however, their carriers represent only 25% of high-risk BC patients. To further characterize variants influencing BC risk, we performed SOLiD sequencing of 581 genes in 325 BC patients (negatively tested in previous BRCA1/BRCA2/PALB2 analyses). In 105 (32%) patients, we identified and confirmed 127 truncating variants (89 unique; nonsense, frameshift indels, and splice site), 19 patients harbored more than one truncation. Forty-six (36 unique) truncating variants in 25 DNA repair genes were found in 41 (12%) patients, including 16 variants in the Fanconi anemia (FA) genes. The most frequent variant in FA genes was c.1096_1099dupATTA in FANCL that also show a borderline association with increased BC risk in subsequent analysis of enlarged groups of BC patients and controls. Another 81 (53 unique) truncating variants were identified in 48 non-DNA repair genes in 74 patients (23%) including 16 patients carrying variants in genes coding proteins of estrogen metabolism/signaling. Our results highlight the importance of mutations in the FA genes' family, and indicate that estrogen metabolism genes may reveal a novel candidate genetic component for BC susceptibility.

Report of new haplotype for ABCC2 gene: rs17222723 and rs8187718 in cis

The ATP-binding cassette, subfamily C [CFTR/MRP], member 2 (ABCC2) gene is a member of the ATP-binding cassette transporters and is involved in the transport of molecules across cellular membranes. Substrates transported by ABCC2 include antiepileptics, statins, tenofovir, cisplatin, irinotecan, and carbamazepine. Because of the pharmacogenomics implications, we developed a clinical laboratory-developed assay to test for seven variants in the ABCC2 gene: c.3563T>A (p.V1188E, rs17222723), c.1249G>A (p.V417I, rs2273697), c.3972C>T (p.I1324I, rs3740066), c.2302C>T (p.R768W, rs56199535), c.2366C>T (p.S789F, rs56220353), c.-24C>T (5'UTR, rs717620), and c.4544G>A (p.C1515Y, rs8187710). During the validation process, we noted several DNA samples, obtained from the Coriell Cell Repository, that contained both c.3563T>A, c.4544G>A, and a third variant, suggesting that c.3563T>A and c.4544G>A are in cis on the chromosome in some individuals. We obtained DNA samples from a trio (father, mother, and child), tested their ABCC2 variants, and confirmed that c.3563T>A and c.4544G>A were in cis on the same chromosome. Here, we report a new haplotype in ABCC2.

Neonatal Dubin-Johnson syndrome: novel compound heterozygous mutation in the ABCC2 gene

Dubin-Johnson syndrome (DJS) is an autosomal recessive inherited disorder characterized by conjugated hyperbilirubinemia. Neonatal-onset DJS is rare. It is caused by dysfunction of adenosine triphosphate-binding cassette, sub-family C, member 2 (ABCC2). We found a novel compound heterozygous mutation of DJS-related gene: W709R (T2145C): a missense mutation in exon 17, and R768W (C2302T), a missense mutation in exon 18. Serum diglucuronosyl bilirubin/monoglucuronosyl bilirubin ratio was high. ABCC2 may excrete diglucuronosyl bilirubin preferentially over monoglucuronosyl bilirubin.

Mutation and functional analysis of ABCC2/multidrug resistance protein 2 in a Japanese patient with Dubin-Johnson syndrome

Dubin-Johnson syndrome (DJS) is a recessive inherited disorder characterized by conjugated hyperbilirubinemia. It is caused by dysfunction of adenosine triphosphate-binding cassette, sub-family C, member 2 (ABCC2/MRP2) on the canalicular membrane of hepatocytes. We performed mutational analysis of the ABCC2/MRP2 gene in a Japanese female with DJS. Furthermore, we investigated the effects of the two identified DJS-associated mutations on MRP2 function. We found a compound heterozygous mutation in the patient: W709R (c.2124T>C), a missense mutation in exon 17, and R1310X (c.3928C>T), a nonsense mutation in exon 28. DJS-associated mutations have been shown to impair the protein maturation and transport activity of ABCC2/MRP2. We established HEK293 cell lines stably expressing one of the two identified DJS-associated mutations. Expressed W709R MRP2 was mainly core-glycosylated, predominantly retained in the endoplasmic reticulum, and exhibited no transport activity, suggesting that this mutation causes deficient maturation and impaired protein sorting. No MRP2 protein was expressed from HEK293 cells transfected with an R1310X-containing construct. This compound heterozygous mutation of the MRP2 gene causes dysfunction of the MRP2 protein and the hyperbilirubinemia seen in DJS.