1 5220 74 PRIMARY BILIARY CHOLANGITIS: A TALE OF EPIGENETICALLY-INDUCED SECRETORY FAILURE? PRIMARY BILIARY CHOLANGITIS (PBC) IS A CHRONIC CHOLESTATIC LIVER DISEASE ASSOCIATED WITH AUTOIMMUNE-RELATED DESTRUCTION OF SMALL TO MEDIUM SIZE INTRAHEPATIC BILE DUCTS. THE AETIOLOGY OF PBC IS UNKNOWN AND ITS PATHOGENESIS REMAINS OBSCURE. BOTH GENETIC VARIANTS AND ENVIRONMENTAL FACTORS HAVE BEEN LINKED TO INCREASED PBC SUSCEPTIBILITY, WITH OTHER ALTERATIONS KNOWN TO COOPERATE IN DISEASE PATHOBIOLOGY. INCREASING EVIDENCE INDICATES THE PRESENCE OF EPIGENETIC ABNORMALITIES IN PBC, PARTICULARLY ALTERATIONS OF CHOLANGIOCELLULAR MICRORNAS (MIRNAS OR MIRS). THIS REVIEW HIGHLIGHTS AND DISCUSSES THE MOST RELEVANT EPIGENETIC ALTERATIONS FOUND IN PATIENTS WITH PBC, FOCUSING ON THE ROLE OF MIR-506 IN THE PROMOTION OF CHOLESTASIS AND IMMUNE ACTIVATION. 2018 2 5590 29 ROLE OF THE BICARBONATE-RESPONSIVE SOLUBLE ADENYLYL CYCLASE IN CHOLANGIOCYTE APOPTOSIS IN PRIMARY BILIARY CHOLANGITIS; A NEW HYPOTHESIS. PRIMARY BILIARY CHOLANGITIS (PBC) IS A CHRONIC FIBROSING CHOLANGIOPATHY CHARACTERIZED BY AN AUTOIMMUNE STEREOTYPE AND DEFECTIVE BILIARY BICARBONATE SECRETION DUE TO DOWN-REGULATION OF ANION EXCHANGER 2 (AE2). DESPITE THE AUTOIMMUNE FEATURES, IMMUNOSUPPRESSANTS ARE INEFFECTIVE WHILE TWO BILE ACID-BASED THERAPIES (URSODEOXYCHOLIC ACID AND OBETICHOLIC ACID) HAVE BEEN SHOWN TO IMPROVE BIOCHEMICAL AND HISTOLOGICAL FEATURES OF CHOLESTASIS AND LONG-TERM PROGNOSIS. HOWEVER, THE ETIOLOGY AND PATHOGENESIS OF PBC IS LARGELY UNKNOWN. RECENTLY, IT HAS BEEN SHOWN THAT MICRORNA-506 (MIR-506) ON CHROMOSOME X IS UP-REGULATED IN PBC CHOLANGIOCYTES AND SUPPRESSES AE2 EXPRESSION, WHICH SENSITIZES CHOLANGIOCYTES TO BILE SALT-INDUCED APOPTOSIS BY ACTIVATING SOLUBLE ADENYLYL CYCLASE (SAC), AN EVOLUTIONARILY CONSERVED BICARBONATE SENSOR. IN THIS REVIEW, WE DISCUSS THE EXPERIMENTAL EVIDENCE FOR THE EMERGING ROLE OF THE MIR-506-AE2-SAC AXIS IN PBC PATHOGENESIS. WE FURTHER HYPOTHESIZE THAT THE INITIAL DISEASE TRIGGER INDUCES AN X-LINKED EPIGENETIC CHANGE, LEADING TO A FEMALE-BIASED ACTIVATION OF THE MIR-506-AE2-SAC AXIS. THIS ARTICLE IS PART OF A SPECIAL ISSUE ENTITLED: CHOLANGIOCYTES IN HEALTH AND DISEASEEDITED BY JESUS BANALES, MARCO MARZIONI AND PETER JANSEN. 2018 3 3012 37 GENETICS AND EPIGENETICS IN THE PATHOGENESIS OF PRIMARY BILIARY CHOLANGITIS. PRIMARY BILIARY CHOLANGITIS (PBC) IS A CHRONIC, SLOWLY PROGRESSIVE CHOLESTATIC AUTOIMMUNE LIVER DISEASE PREDOMINANTLY AFFLICTING WOMEN. PBC IS CHARACTERIZED BY THE PRESENCE OF DISEASE-SPECIFIC ANTIMITOCHONDRIAL ANTIBODIES AND THE HISTOLOGICAL DESTRUCTION OF INTRAHEPATIC BILE DUCTS, WHICH EVENTUALLY LEAD TO CIRRHOSIS AND HEPATIC FAILURE. FORTUNATELY, URSODEOXYCHOLIC ACID THERAPY HAS IMPROVED THE OUTCOME OF THE VAST MAJORITY OF PBC CASES. ALTHOUGH THE ETIOLOGY OF PBC HAS NOT YET BEEN ELUCIDATED, HUMAN LEUKOCYTE ANTIGEN (HLA) CLASS II ALLELES HAVE BEEN CONSISTENTLY ASSOCIATED WITH DISEASE ONSET FOR DECADES. PBC PATIENTS MAY ALSO HAVE GENETICALLY DETERMINED RISK FACTORS IN NON-HLA REGIONS. MEANWHILE, EXPOSURE TO ENVIRONMENTAL FACTORS, SUCH AS INFECTIOUS DISEASES AND HARMFUL CHEMICALS, CAN PRODUCE EPIGENETIC ALTERATIONS IN SOME INDIVIDUALS AND SUBSEQUENT PBC ONSET. IN THIS REVIEW, WE DESCRIBE THE INFLUENCE OF HLA ALLELES AND OTHER GENE POLYMORPHISMS ON PBC ALONG WITH THE RESULTS OF GENOME-WIDE ASSOCIATION STUDIES ON THIS DISEASE AND ITS FUTURE PROSPECTS IN TERMS OF EPIGENETICS. 2018 4 5506 33 RHEUMATOID ARTHRITIS AND PRIMARY BILIARY CIRRHOSIS: CAUSE, CONSEQUENCE, OR COINCIDENCE? PRIMARY BILIARY CIRRHOSIS (PBC) IS A PROGRESSIVE CHOLESTATIC LIVER DISEASE CHARACTERIZED SEROLOGICALLY BY CHOLESTASIS AND THE PRESENCE OF HIGH-TITRE ANTIMITOCHONDRIAL ANTIBODIES AND HISTOLOGICALLY BY CHRONIC NONSUPPURATIVE CHOLANGITIS AND GRANULOMATA. PBC PATIENTS OFTEN HAVE CONCOMITANT AUTOIMMUNE DISEASES, INCLUDING ARTHROPATHIES. THIS RAISES THE QUESTION AS TO WHETHER THERE ARE SHARED FEATURES IN THE PATHOGENESIS OF THOSE DISEASES WITH THE PATHOGENESIS OF PBC. EPIDEMIOLOGICAL AND LARGE CASE STUDIES HAVE INDICATED THAT ALTHOUGH THE INCIDENCE OF RHEUMATOID ARTHRITIS (RA) IS NOT SIGNIFICANTLY RAISED IN PBC PATIENTS, THERE APPEARS TO BE A HIGHER RATE OF RA IN PBC PATIENTS AND THEIR RELATIVES. GENETIC STUDIES HAVE DEMONSTRATED THAT SEVERAL GENES IMPLICATED IN PBC HAVE ALSO BEEN IMPLICATED IN RA. EPIGENETIC STUDIES PROVIDED A WEALTH OF DATA REGARDING RA, BUT THE FINDINGS ON EPIGENETIC CHANGES IN PBC ARE VERY LIMITED. AS WELL, CERTAIN INFECTIOUS AGENTS IDENTIFIED IN THE PATHOGENESIS OF PBC MAY ALSO PLAY A ROLE IN THE PATHOGENESIS OF RA. THESE DATA SUGGEST THAT ALTHOUGH RA IS NOT SIGNIFICANTLY PRESENT IN PBC, SOME INDIVIDUALS WITH CERTAIN GENETIC TRAITS AND ENVIRONMENTAL EXPOSURES MAY DEVELOP BOTH CONDITIONS. THIS CONCEPT MAY ALSO APPLY TO OTHER CONCOMITANT DISEASES FOUND IN PBC PATIENTS. 2012 5 5222 28 PRIMARY BILIARY CIRRHOSIS: FAMILY STORIES. PRIMARY BILIARY CIRRHOSIS (PBC) IS A CHRONIC IMMUNE-MEDIATED CHOLESTATIC LIVER DISEASE OF UNKNOWN AETIOLOGY WHICH AFFECTS MOSTLY WOMEN IN MIDDLE AGE. FAMILIAL PBC IS WHEN PBC AFFECTS MORE THAN ONE MEMBER OF THE SAME FAMILY, AND DATA SUGGEST THAT FIRST-DEGREE RELATIVES OF PBC PATIENTS HAVE AN INCREASED RISK OF DEVELOPING THE DISEASE. MOST OFTEN, THESE FAMILIAL CLUSTERS INVOLVE MOTHER-DAUGHTER PAIRS, WHICH IS CONSISTENT WITH THE FEMALE PREPONDERANCE OF THE DISEASE. THESE CLUSTERS PROVIDE EVIDENCE TOWARDS A GENETIC BASIS UNDERLYING PBC. HOWEVER, CLUSTERS OF NONRELATED INDIVIDUALS HAVE ALSO BEEN REPORTED, GIVING STRENGTH TO AN ENVIRONMENTAL COMPONENT. TWIN STUDIES HAVE DEMONSTRATED A HIGH CONCORDANCE FOR PBC IN MONOZYGOTIC TWINS AND A LOW CONCORDANCE AMONG DIZYGOTIC TWINS. IN CONCLUSION, STUDIES OF PBC IN FAMILIES CLEARLY DEMONSTRATE THAT GENETIC, EPIGENETIC, AND ENVIRONMENTAL FACTORS PLAY A ROLE IN THE DEVELOPMENT OF THE DISEASE. 2011 6 2588 33 EPIGENETICS OF PRIMARY BILIARY CHOLANGITIS. PRIMARY BILIARY CHOLANGITIS (PBC) IS A CHRONIC CHOLESTATIC LIVER DISEASE WITH NON-SUPPURATIVE DESTRUCTION OF THE INTRAHEPATIC BILE DUCTS. THE INTERPLAY OF GENETICS AND ENVIRONMENTAL TRIGGERS CONTRIBUTES TO THE ONSET OF THE DISEASE AND SUBSEQUENTLY RESULTS IN CHOLESTASIS AND PROGRESSIVE FIBROSIS. RECENTLY, GENOME-WIDE ASSOCIATION STUDIES (GWAS) HAVE IDENTIFIED MULTIPLE GENES INFLUENCING THE SUSCEPTIBILITY TO PBC IN HLA AND NON-HLA LOCI. HOWEVER, IT IS ESTIMATED THAT THE KNOWN RISK VARIANTS MERELY ACCOUNT FOR NO MORE THAN 20% OF THE HERITABILITY OF PBC AND CAUSES OF THE REMAINING HERITABILITY REMAIN UNCERTAIN. INCREASING EVIDENCE SUGGESTS THAT THE PRESENCE OF EPIGENETIC ABNORMALITIES MAY EXPLAIN THE "MISSING HERITABILITY" THAT CANNOT BE CAPTURED BY GWAS. AMONG THESE EPIGENETIC MECHANISMS, DNA METHYLATION, HISTONE MODIFICATION, AND NONCODING RNAS (I.E. MIRNA AND LNCRNA) ARE INVOLVED IN THE PATHOGENESIS OF PBC. ADDITIONALLY, TELOMERE DYSREGULATION IN BILIARY EPITHELIAL CELLS (BECS) MAY PLAY A ROLE IN DISEASE ONSET, WHEREAS A DEFICIENCY IN SEX CHROMOSOME AND SKEWED GENE EXPRESSION IN THE X CHROMOSOME MAY TO SOME EXTENT EXPLAIN THE FEMALE DOMINANCE IN PBC. 2020 7 5272 25 PROMOTER HYPERMETHYLATION OF THE AE2/SLC4A2 GENE IN PBC. BACKGROUND & AIMS: PATIENTS WITH PRIMARY BILIARY CHOLANGITIS (PBC) EXHIBIT REDUCED AE2/SLC4A2 GENE EXPRESSION IN THE LIVER AND PERIPHERAL BLOOD MONONUCLEAR CELLS (PBMCS). AE2 ENCODES A CL(-)/HCO(3) (-) EXCHANGER INVOLVED IN BILIARY BICARBONATE SECRETION AND INTRACELLULAR PH REGULATION. REDUCED AE2 EXPRESSION IN PBC MAY BE PATHOGENIC, AS AE2-KNOCKOUT MICE REPRODUCE CHARACTERISTIC PBC FEATURES. HEREIN, WE AIMED TO IDENTIFY CPG-METHYLATION ABNORMALITIES IN AE2 PROMOTER REGIONS THAT MIGHT CONTRIBUTE TO THE REDUCED GENE TRANSCRIPTION IN PBC LIVERS AND PBMCS. METHODS: CPG-CYTOSINE METHYLATION RATES WERE INTERROGATED AT 1-BASE PAIR RESOLUTION IN UPSTREAM AND ALTERNATE AE2 PROMOTER REGIONS THROUGH PYROSEQUENCING OF BISULPHITE-MODIFIED GENOMIC DNA FROM LIVER SPECIMENS AND PBMCS. AE2A AND ALTERNATIVE AE2B1 AND AE2B2 MRNA LEVELS WERE MEASURED BY REAL-TIME PCR. HUMAN LYMPHOBLASTOID-T2 CELLS WERE TREATED WITH 5-AZA-2 -DEOXYCYTIDINE FOR DEMETHYLATION ASSAYS. RESULTS: AE2 PROMOTERS WERE FOUND TO BE HYPERMETHYLATED IN PBC LIVERS COMPARED TO NORMAL AND DISEASED LIVER SPECIMENS. RECEIVER OPERATING CHARACTERISTIC (ROC) CURVE ANALYSIS SHOWED THAT MINIMAL CPG-HYPERMETHYLATION CLUSTERS OF 3 AE2A-CPG SITES AND 4 ALTERNATE-AE2B2-CPG SITES SPECIFICALLY DIFFERENTIATED PBC FROM NORMAL AND DISEASED CONTROLS, WITH MEAN METHYLATION RATES INVERSELY CORRELATING WITH RESPECTIVE TRANSCRIPT LEVELS. ADDITIONALLY, IN PBMCS A MINIMAL CLUSTER OF 3 HYPERMETHYLATED AE2A-CPG SITES DISTINGUISHED PBC FROM CONTROLS, AND MEAN METHYLATION RATES CORRELATED NEGATIVELY WITH AE2A MRNA LEVELS IN THESE IMMUNE CELLS. ALTERNATE AE2B2/AE2B1 PROMOTERS IN PBMCS WERE CONSTITUTIVELY HYPERMETHYLATED, IN LINE WITH ABSENT ALTERNATIVE MRNA EXPRESSION IN DISEASED AND HEALTHY PBMCS. DEMETHYLATION ASSAYS TREATING LYMPHOBLASTOID-T2 CELLS WITH 5-AZA-2 -DEOXYCYTIDINE TRIGGERED AE2B2/AE2B1 EXPRESSION AND UPREGULATED AE2A-PROMOTER EXPRESSION. CONCLUSIONS: DISEASE-SPECIFIC HYPERMETHYLATION OF AE2 PROMOTER REGIONS AND SUBSEQUENT DOWNREGULATION OF AE2-GENE EXPRESSION IN THE LIVER AND PBMCS OF PATIENTS WITH PBC MIGHT BE CRITICALLY INVOLVED IN THE PATHOGENESIS OF THIS COMPLEX DISEASE. LAY SUMMARY: PRIMARY BILIARY CHOLANGITIS (PBC) IS A CHRONIC IMMUNE-ASSOCIATED CHOLESTATIC LIVER DISEASE WITH UNCLEAR COMPLEX/MULTIFACTORIAL ETIOPATHOGENESIS AFFECTING MOSTLY MIDDLE-AGED WOMEN. PATIENTS WITH PBC EXHIBIT REDUCED EXPRESSION OF THE AE2/SLC4A2 GENE. HEREIN, WE FOUND THAT AE2 PROMOTER REGIONS ARE HYPERMETHYLATED IN THE LIVER AND PERIPHERAL BLOOD MONONUCLEAR CELLS OF PATIENTS WITH PBC. THIS INCREASED METHYLATION IS ASSOCIATED WITH DOWNREGULATED AE2-GENE EXPRESSION, WHICH MIGHT CONTRIBUTE TO THE PATHOGENESIS OF PBC. THEREFORE, NOVEL EPIGENETIC TARGETS MAY IMPROVE TREATMENT IN PATIENTS WITH PBC WHO RESPOND POORLY TO CURRENT PHARMACOLOGICAL THERAPIES. 2019 8 3112 34 GEOEPIDEMIOLOGY AND (EPI-)GENETICS IN PRIMARY BILIARY CHOLANGITIS. PRIMARY BILIARY CHOLANGITIS (PBC) IS A RARE FEMALE PREPONDERANT CHRONIC AUTOIMMUNE CHOLESTATIC LIVER DISEASE, CHARACTERIZED BY INTRAHEPATIC DUCTOPENIA AND PROGRESSIVE FIBROSIS. DURING LAST DECADES INCIDENCE AND PREVALENCE SHOWED AN INCREASING RATE WHICH VARY WIDELY WORLDWIDE DEMONSTRATING AN IMPORTANT INTERACTION BETWEEN ENVIRONMENTAL AND GENETIC FACTORS. HERITABILITY SUGGESTED BY FAMILIAL OCCURRENCE AND MONOZYGOTIC TWINS CONCORDANCE HAVE BEEN CONFIRMED IN MORE STUDIES. EPIGENETICS MECHANISMS SUCH AS HISTONE MODIFICATION AND DNA METHYLATION CAN PARTIALLY EXPLAIN PREDISPOSITION AND INHERITANCE OF THIS DISEASE. NEVERTHELESS, AN ASSOCIATION WITH SPECIFIC CLASS II HUMAN LEUKOCYTE ANTIGEN (HLA) VARIANTS HAVE BEEN REPORTED, SHOWING AN INCREASE RISK IN SUSCEPTIBILITY. MORE RECENTLY, DATA REGARDING A STRONG PROTECTIVE ASSOCIATION BETWEEN PBC AND HLA ALLELES CONFIRMED THIS ASSOCIATION. AFTER RECENT GENOME-WIDE ASSOCIATION STUDIES (GWAS), A MORE INTRICATE INTERACTION BETWEEN PBC AND THE HLA REGION HAS BEEN SHOWN. FURTHERMORE, GWAS ALSO IDENTIFIED SEVERAL IMMUNE-RELATED-GENES IMPLICATED. MORE GENOME-WIDE ASSOCIATION STUDIES ON THIS DISEASE ARE NEEDED TO REACH A COMPLETE AND SYSTEMATIC KNOWLEDGE OF THIS DISEASE. IN THIS REVIEW WE DISCUSS MORE RECENT ISSUED DATA ON GEOEPIDEMIOLOGY OF PBC AND THE ROLE OF (EPI-)GENETIC MECHANISMS IN ITS PATHOGENESIS. 2018 9 4175 21 MELATONIN PROTECTS CHOLANGIOCYTES FROM OXIDATIVE STRESS-INDUCED PROAPOPTOTIC AND PROINFLAMMATORY STIMULI VIA MIR-132 AND MIR-34. BIOSYNTHESIS OF MELATONIN BY CHOLANGIOCYTES IS ESSENTIAL FOR MAINTAINING THE FUNCTION OF BILIARY EPITHELIUM. HOWEVER, THIS CYTOPROTECTIVE MECHANISM APPEARS TO BE IMPAIRED IN PRIMARY BILIARY CHOLANGITIS (PBC). MIR-132 HAS EMERGED AS A MEDIATOR OF INFLAMMATION IN CHRONIC LIVER DISEASES. THE EFFECT OF MELATONIN ON OXIDATIVE STRESS AND BILE ACID-INDUCED APOPTOSIS WAS ALSO EXAMINED IN CHOLANGIOCYES OVEREXPRESSING MIR506, AS A PBC-LIKE CELLULAR MODEL. IN PBC PATIENTS THE SERUM LEVELS OF MELATONIN WERE FOUND INCREASED IN COMPARISON TO HEALTHY CONTROLS. WHEREAS, IN CHOLANGIOCYTES WITHIN CIRRHOTIC PBC LIVERS THE MELATONIN BIOSYNTHETIC PATHWAY WAS SUBSTANTIALLY SUPPRESSED EVEN THOUGH THE EXPRESSIONS OF MELATONIN RATE-LIMITING ENZYME ARALKYLAMINE N-ACETYLTRANSFERASE (AANAT), AND CK-19 (MARKER OF CHOLANGIOCYTES) WERE ENHANCED. IN CHOLANGIOCYTES EXPOSED TO MITOCHONDRIAL OXIDATIVE STRESS MELATONIN DECREASED THE EXPRESSION OF PROAPOPTOTIC STIMULI (PTEN, BAX, MIR-34), WHICH WAS ACCOMPANIED BY THE INHIBITION OF A PIVOTAL MEDIATOR OF INFLAMMATORY RESPONSE NF-KAPPAB-P65 AND THE ACTIVATION OF ANTIAPOPTOTIC SIGNALING (MIR-132, BCL2). SIMILARLY, MELATONIN REDUCED BILE ACID-INDUCED PROAPOPTOTIC CASPASE 3 AND BIM LEVELS. IN SUMMARY, THE INSUFFICIENT HEPATIC EXPRESSION OF MELATONIN IN PBC PATIENTS MAY PREDISPOSE CHOLANGIOCYTES TO OXIDATIVE STRESS-RELATED DAMAGE. MELATONIN, VIA EPIGENETIC MODULATION, WAS ABLE TO SUPPRESS NF-KAPPAB SIGNALING ACTIVATION AND PROTECT AGAINST BILIARY CELLS APOPTOTIC SIGNALING. 2020 10 2142 26 EPIGENETIC INVESTIGATION OF VARIABLY X CHROMOSOME INACTIVATED GENES IN MONOZYGOTIC FEMALE TWINS DISCORDANT FOR PRIMARY BILIARY CIRRHOSIS. PRIMARY BILIARY CIRRHOSIS (PBC) IS AN AUTOIMMUNE CHRONIC CHOLESTATIC LIVER DISEASE WITH A STRONG GENETIC SUSCEPTIBILITY DUE TO THE HIGH CONCORDANCE IN MONOZYGOTIC (MZ) TWINS AND A STRIKING FEMALE PREDOMINANCE. WOMEN WITH PBC MANIFEST AN ENHANCED X MONOSOMY RATE IN PERIPHERAL LYMPHOCYTES AND WE THUS HYPOTHESIZED AN X CHROMOSOME EPIGENETIC COMPONENT TO EXPLAIN PBC FEMALE PREVALENCE. WHILE MOST GENES ON THE FEMALE INACTIVE X CHROMOSOME ARE SILENCED BY PROMOTER METHYLATION FOLLOWING X CHROMOSOME INACTIVATION (XCI), APPROXIMATELY 10% OF X- LINKED GENES EXHIBIT VARIABLE ESCAPE FROM XCI IN HEALTHY FEMALES. THIS STUDY WAS DESIGNED TO TEST THE HYPOTHESIS THAT SUSCEPTIBILITY TO PBC IS MODIFIED BY ONE OR MORE X-LINKED GENE WITH VARIABLE XCI STATUS. PERIPHERAL BLOOD MRNA AND DNA SAMPLES WERE OBTAINED FROM A UNIQUE COHORT OF MZ TWIN SETS DISCORDANT AND CONCORDANT FOR PBC. TRANSCRIPT LEVELS OF THE 125 VARIABLE XCI STATUS GENES WAS DETERMINED BY QUANTITATIVE RT-PCR ANALYSIS AND TWO GENES (CLIC2 AND PIN4) WERE IDENTIFIED AS CONSISTENTLY DOWNREGULATED IN THE AFFECTED TWIN OF DISCORDANT PAIRS. BOTH CLIC2 AND PIN4 DEMONSTRATED PARTIAL AND VARIABLE METHYLATION OF CPG SITES WITHIN 300 BP OF THE TRANSCRIPTION START SITE THAT DID NOT PREDICT THE XCI STATUS. PROMOTER METHYLATION OF CLIC2 MANIFESTED NO SIGNIFICANT DIFFERENCE BETWEEN SAMPLES AND NO SIGNIFICANT CORRELATION WITH TRANSCRIPT LEVELS. PIN4 METHYLATION SHOWED A POSITIVE TREND WITH TRANSCRIPTION IN ALL SAMPLES BUT NO DIFFERENTIAL METHYLATION WAS OBSERVED BETWEEN DISCORDANT TWINS. A GENETIC POLYMORPHISM AFFECTING THE NUMBER OF CPG SITES IN THE PIN4 PROMOTER DID NOT IMPACT METHYLATION OR TRANSCRIPT LEVELS IN A HETEROZYGOUS TWIN PAIR AND SHOWED A SIMILAR FREQUENCY IN INDEPENDENT SERIES OF UNRELATED PBC CASES AND CONTROLS. OUR RESULTS SUGGEST THAT EPIGENETIC FACTORS INFLUENCING PBC ONSET ARE MORE COMPLEX THAN METHYLATION DIFFERENCES AT X-LINKED PROMOTERS AND VARIABLY 3 INACTIVATED X-LINKED GENES MAY BE CHARACTERIZED BY PARTIAL PROMOTER METHYLATION AND BIALLELIC TRANSCRIPTION. 2011 11 5146 35 POTENTIAL ROLES FOR INFECTIOUS AGENTS IN THE PATHOPHYSIOLOGY OF PRIMARY BILIARY CIRRHOSIS: WHAT'S NEW? PRIMARY BILIARY CIRRHOSIS (PBC) IS A PROGRESSIVE CHOLESTATIC LIVER DISEASE SEROLOGICALLY CHARACTERIZED BY THE PRESENCE OF HIGH-TITER ANTIMITOCHONDRIAL ANTIBODIES AND, HISTOLOGICALLY BY CHRONIC NONSUPPURATIVE CHOLANGITIS AND GRANULOMATA. THE AETIOLOGY OF THE DISEASE REMAINS ELUSIVE, ALTHOUGH GENETIC, EPIGENETIC, ENVIRONMENTAL, AND INFECTIOUS FACTORS HAVE BEEN CONSIDERED IMPORTANT FOR THE INDUCTION OF THE DISEASE IN GENETICALLY PRONE INDIVIDUALS. THE DISEASE SHOWS A STRIKING FEMALE PREDOMINANCE AND BECOMES CLINICALLY OVERT AT THE FOURTH TO SIXTH DECADE. THESE CHARACTERISTICS HAVE PROMPTED INVESTIGATORS TO CONSIDER INFECTIONS THAT PREDOMINATE IN WOMEN AT THESE AGES AS THE LIKELY CANDIDATES FOR TRIGGERING THE DISEASE. RECURRENT URINARY TRACT INFECTIONS DUE TO ESCHERICHIA COLI WERE THE FIRST INFECTIONS TO BE CONSIDERED PATHOGENETICALLY RELEVANT. OVER THE YEARS, SEVERAL OTHER MICROORGANISMS HAVE BEEN LINKED TO THE PATHOGENESIS OF PBC OWING TO EPIDEMIOLOGICAL, IMMUNOLOGICAL, MICROBIOLOGICAL, OR EXPERIMENTAL FINDINGS IN ANIMAL MODELS. RECENT STUDIES HAVE PROVIDED DATA SUPPORTING THE PATHOGENIC ROLE OF NOVOSPHINGOBIUM AROMATICIVORANS AND BETARETROVIRUSES. SEVERAL REPORTS HAVE LINKED OTHER ORGANISMS TO THE INDUCTION OF THE DISEASE AND/OR THE MAINTENANCE OF THE AUTO-AGGRESSIVE RESPONSES THAT ARE PERPETUATED OVER THE COURSE OF THE DISEASE. THIS REVIEW HIGHLIGHTS THE FINDINGS OF THE MOST RECENT STUDIES INVESTIGATING THE LINK BETWEEN INFECTIONS AND PBC. WE ALSO DISCUSS THE CLOSE INTERPLAY OF THE INFECTIOUS AGENTS WITH OTHER ENVIRONMENTAL AND GENETIC FACTORS, WHICH MAY EXPLAIN THE MULTIFACETED NATURE OF THIS PUZZLING DISEASE. 2013 12 6650 32 UPDATE ON ETIOLOGY AND PATHOGENESIS OF BILIARY ATRESIA. BILIARY ATRESIA IS A RARE INFLAMMATORY SCLEROSING OBSTRUCTIVE CHOLANGIOPATHY THAT INITIATES IN INFANCY AS COMPLETE CHOLEDOCHAL BLOCKAGE AND PROGRESSES TO THE INVOLVEMENT OF INTRAHEPATIC BILIARY EPITHELIUM. GROWING EVIDENCE SHOWS THAT BILIARY ATRESIA IS NOT A SINGLE ENTITY WITH A SINGLE ETIOLOGY BUT A PHENOTYPE RESULTING FROM MULTIFACTORIAL EVENTS WHOSE COMMON PATH IS OBLITERATIVE CHOLANGIOPATHY. THE ETIOLOGY OF BILIARY ATRESIA HAS BEEN EXPLAINED AS RESULTING FROM GENETIC VARIANTS, TOXINS, VIRAL INFECTION, CHRONIC INFLAMMATION OR BILE DUCT LESIONS MEDIATED BY AUTOIMMUNITY, ABNORMALITIES IN THE DEVELOPMENT OF THE BILE DUCTS, AND DEFECTS IN EMBRYOGENESIS, ABNORMAL FETAL OR PRENATAL CIRCULATION AND SUSCEPTIBILITY FACTORS. IT IS INCREASINGLY EVIDENT THAT THE GENETIC AND EPIGENETIC PREDISPOSITION COMBINED WITH THE ENVIRONMENTAL FACTORS TO WHICH THE MOTHER IS EXPOSED ARE POTENTIAL TRIGGERS FOR BILIARY ATRESIA. THERE IS ALSO AN INDICATION THAT A PROGRESSIVE THICKENING OF THE ARTERIAL MIDDLE LAYER OCCURS IN THIS DISEASE, SUGGESTIVE OF VASCULAR REMODELING AND DISAPPEARANCE OF THE INTERLOBULAR BILE DUCTS. IT IS SUGGESTED THAT THE HYPOXIA/ISCHEMIA PROCESS CAN AFFECT PORTAL STRUCTURES IN BILIARY ATRESIA AND IS ASSOCIATED WITH BOTH THE EXTENT OF BILIARY PROLIFERATION AND THE THICKENING OF THE MEDIAL LAYER. 2022 13 2512 31 EPIGENETICS AND PRIMARY BILIARY CIRRHOSIS: A COMPREHENSIVE REVIEW AND IMPLICATIONS FOR AUTOIMMUNITY. PRIMARY BILIARY CIRRHOSIS (PBC) IS A CHRONIC INFLAMMATORY AUTOIMMUNE DISEASE THAT DEVELOPS BASED UPON THE INTERACTION OF GENETIC AND ENVIRONMENTAL FACTORS. RECENT GENOME-WIDE ASSOCIATION STUDIES (GWAS) HAVE IDENTIFIED DOZENS OF PREDISPOSING VARIANTS INCLUDING HLA, IL12A, AND CTLA4 BUT HAVE BEEN DISAPPOINTED IN IDENTIFYING A "SMOKING GUN." THESE DISCOVERIES HIGHLIGHT THE IMPORTANCE OF THE GENETIC BACKGROUND INVOLVED IN IMMUNOLOGICAL DYSREGULATION. ALTHOUGH CONCORDANCE RATE OF PBC IN MONOZYGOTIC (MZ) TWINS IS AMONG THE HIGHEST REPORTED IN AUTOIMMUNE DISORDERS, INCOMPLETE DISEASE CONCORDANCE IN TWINS ASSOCIATED WITH DIFFERENTIALLY EXPRESSED GENES HAS BEEN DEMONSTRATED. HOWEVER, LITTLE IS UNDERSTOOD ABOUT HOW ENVIRONMENTAL ASPECTS CONTRIBUTE TO THE DISEASE AND WHY MIDDLE-AGED WOMEN ARE MORE SUSCEPTIBLE. AS A RESULT, EPIGENETIC FACTORS, WHICH CONVERT SIGNALS INDICATING ENVIRONMENTAL CHANGES INTO DYNAMIC AND HERITABLE ALTERATIONS OF TRANSCRIPTIONAL POTENTIAL, ARE GETTING INCREASED ATTENTION BY RESEARCHERS IN BOTH BASIC AND CLINICAL STUDIES. AMONG EPIGENETIC MECHANISMS, THE INSTABILITY AND SKEWED GENE EXPRESSION IN THE X CHROMOSOME MAY ACCOUNT FOR THE FEMALE PREPONDERANCE IN PBC. IN ADDITION, TRANSCRIPTIONAL REGULATION OF HISTONE MODIFICATION AND DNA METHYLATION UNDERSCORES POTENTIAL INVOLVEMENT IN DISEASE PATHOGENESIS. HIGH-THROUGHPUT TECHNIQUES ARE BEING USED TO IDENTIFY EPIGENETIC REGULATORS. IN THIS REVIEW, WE ATTEMPT TO OUTLINE RECENT PROGRESS REGARDING EPIGENETICS IN PBC AND OTHER AUTOIMMUNE DISEASES. 2016 14 6269 23 THE NEXT CHALLENGE IN PEDIATRIC CHOLESTASIS: DECIPHERING THE PATHOGENESIS OF BILIARY ATRESIA. CHOLESTASIS IS A COMMON PRESENTING SYMPTOM OF LIVER DISEASE IN INFANTS. CHIEF AMONG DISEASES PRESENTING AS NEONATAL CHOLESTASIS IS BILIARY ATRESIA, THE MOST COMMON CAUSE OF CHRONIC LIVER DISEASE IN CHILDREN, BUT LITTLE IS KNOWN ABOUT THE PATHOGENESIS OF THIS DISEASE. IN SEARCH FOR THE MOLECULAR BASIS OF BILIARY ATRESIA, WE BEGAN TWO AREAS OF INVESTIGATION. IN THE FIRST, WE INTERROGATED THE HEPATIC TRANSCRIPTOME OF CHILDREN WITH BILIARY ATRESIA AND FOUND AN INTERFERON-GAMMA (IFNGAMMA)-RICH PROINFLAMMATORY FOOTPRINT AT THE TIME OF DIAGNOSIS. TO DIRECTLY EXPLORE IF IFNGAMMA PLAYS AN IMPORTANT ROLE IN BILIARY INJURY AND OBSTRUCTION, WE USED A MOUSE MODEL OF EXPERIMENTAL BILIARY ATRESIA AND FOUND THAT INACTIVATION OF THE MURINE IFNGAMMA GENE DECREASES THE TROPISM OF LYMPHOCYTES TO NEONATAL BILE DUCTS AND PREVENTS THE INFLAMMATORY OBSTRUCTION OF THE DUCT LUMEN. FURTHER ANALYSIS OF THE EXTRAHEPATIC BILIARY TRACT ALSO OUTLINED A BROADER NETWORK OF PROINFLAMMATORY GENES AT THE ONSET AND DURING PROGRESSION TO DUCT OBSTRUCTION, WITH THE TIME-SPECIFIC ACTIVATION OF IFNGAMMA-, APOPTOSIS-, AND COMPLEMENT-DRIVEN NETWORKS. IN THE SECOND APPROACH, WE SEARCHED FOR MOLECULAR PROFILES THAT DIFFERENTIATE CLINICAL FORMS OF BILIARY ATRESIA BY ANALYZING THE HEPATIC TRANSCRIPTOME OF AGE-MATCHED SUBJECTS AT THE TIME OF DIAGNOSIS. WE FOUND A PRELIMINARY PROFILE THAT DIFFERENTIATES THE EMBRYONIC FROM THE PERINATAL FORMS OF BILIARY ATRESIA. THE PROFILE CONTAINED THE DIFFERENTIAL ACTIVATION OF GENES INVOLVED IN EPIGENETIC MECHANISMS OF DISEASE. COLLECTIVELY, THESE STUDIES PROVIDE NEW INSIGHT INTO PATHOGENESIS OF BILIARY ATRESIA AND IDENTIFY POTENTIAL THERAPEUTIC TARGETS TO FOSTER LONG-TERM OUTCOME WITH THE NATIVE LIVER. 2006 15 5221 26 PRIMARY BILIARY CHOLANGITIS: PATHOGENESIS AND THERAPEUTIC OPPORTUNITIES. PRIMARY BILIARY CHOLANGITIS IS A CHRONIC, SEROPOSITIVE AND FEMALE-PREDOMINANT INFLAMMATORY AND CHOLESTATIC LIVER DISEASE, WHICH HAS A VARIABLE RATE OF PROGRESSION TOWARDS BILIARY CIRRHOSIS. SUBSTANTIAL PROGRESS HAS BEEN MADE IN PATIENT RISK STRATIFICATION WITH THE GOAL OF PERSONALIZED CARE, INCLUDING EARLY ADOPTION OF NEXT-GENERATION THERAPY WITH LICENSED USE OF OBETICHOLIC ACID OR OFF-LABEL FIBRATE DERIVATIVES FOR THOSE WITH INSUFFICIENT BENEFIT FROM URSODEOXYCHOLIC ACID, THE CURRENT FIRST-LINE DRUG. THE DISEASE BIOLOGY SPANS GENETIC RISK, EPIGENETIC CHANGES, DYSREGULATED MUCOSAL IMMUNITY AND ALTERED BILIARY EPITHELIAL CELL FUNCTION, ALL OF WHICH INTERACT AND ARISE IN THE CONTEXT OF ILL-DEFINED ENVIRONMENTAL TRIGGERS. A CURRENT FOCUS OF RESEARCH ON NUCLEAR RECEPTOR PATHWAY MODULATION THAT SPECIFICALLY AND POTENTLY IMPROVES BILIARY EXCRETION, REDUCES INFLAMMATION AND ATTENUATES FIBROSIS IS REDEFINING THERAPY. PATIENTS ARE BENEFITING FROM PHARMACOLOGICAL AGONISTS OF FARNESOID X RECEPTOR AND PEROXISOME PROLIFERATOR-ACTIVATED RECEPTORS. IMMUNOTHERAPY REMAINS A CHALLENGE, WITH A LACK OF TARGET DEFINITION, PLEIOTROPIC IMMUNE PATHWAYS AND AN INTERPLAY BETWEEN HEPATIC IMMUNE RESPONSES AND CHOLESTASIS, WHEREIN BILE ACID-INDUCED INFLAMMATION AND FIBROSIS ARE DOMINANT CLINICALLY. THE MANAGEMENT OF PATIENT SYMPTOMS, PARTICULARLY PRURITUS, IS A NOTABLE GOAL REFLECTED IN THE DEVELOPMENT OF RATIONAL THERAPY WITH APICAL SODIUM-DEPENDENT BILE ACID TRANSPORTER INHIBITORS. 2020 16 2936 32 GENETIC AND EPIGENETIC ABNORMALITIES IN PRIMARY SCLEROSING CHOLANGITIS-ASSOCIATED CHOLANGIOCARCINOMA. PRIMARY SCLEROSING CHOLANGITIS (PSC) IS A CHOLESTATIC LIVER DISEASE OF UNKNOWN ETIOLOGY, CHARACTERIZED BY CHRONIC INFLAMMATION OF THE BILIARY TREE WITH SUBSEQUENT FIBROSIS AND CIRRHOSIS OF THE LIVER. PATIENTS WITH PSC ARE AT INCREASED RISK FOR THE DEVELOPMENT OF CHOLANGIOCARCINOMA (CCA), A HIGHLY MALIGNANT EPITHELIAL TUMOR ARISING FROM THE INTRAHEPATIC AND EXTRAHEPATIC BILE DUCTS. CURRENTLY, ORTHOTOPIC LIVER TRANSPLANTATION IS THE ONLY CURATIVE TREATMENT. THE LACK OF EFFICIENT DIAGNOSTIC METHODS FOR EARLY DETECTION AND THE LIMITED THERAPEUTIC OPTIONS FOR CCA ARE MAJOR PROBLEMS AND ARE ASSOCIATED WITH POOR SURVIVAL. THE PATHOGENESIS OF PSC-ASSOCIATED CCA IS COMPLEX AND POORLY UNDERSTOOD. IT SEEMS THAT PRO-INFLAMMATORY CYTOKINES PLAY AN IMPORTANT ROLE IN GENETIC AND EPIGENETIC CHANGES THAT CONTRIBUTE TO THE CARCINOGENIC PROCESS. THE MAPPING OF GENETIC ALTERATIONS MAY ELUCIDATE MOLECULAR TARGETS THAT MAY BE APPLIED AS BIOMARKERS TO FACILITATE EARLY DIAGNOSIS OF MALIGNANT DEGENERATION TO IMPROVE PATIENT OUTCOME. IN THE LAST DECADE, THE INTRODUCTION OF SEVERAL NOVEL MOLECULAR TECHNIQUES AVAILABLE FOR GENOME-WIDE SCREENING HAS ADVANCED OUR KNOWLEDGE ON MANY OF THE GENETIC ABNORMALITIES THAT ARE PREVALENT IN CCA AND PSC-ASSOCIATED CCA. THIS REVIEW SUMMARIZES GENETIC AND EPIGENETIC ABNORMALITIES, WHICH HAVE IMPORTANT POTENTIAL FOR CLINICAL APPLICATION. 2013 17 4472 33 MOLECULAR PATHOGENESIS OF CHOLANGIOCARCINOMA. BACKGROUND: CHOLANGIOCARCINOMAS ARE A HETEROGENEOUS GROUP OF MALIGNANCIES ARISING FROM A NUMBER OF CELLS OF ORIGIN ALONG THE BILIARY TREE. ALTHOUGH MOST CASES IN WESTERN COUNTRIES ARE SPORADIC, LARGE POPULATION-BASED STUDIES HAVE IDENTIFIED A NUMBER OF RISK FACTORS. THIS REVIEW SUMMARISES THE EVIDENCE BEHIND REPORTED RISK FACTORS AND CURRENT UNDERSTANDING OF THE MOLECULAR PATHOGENESIS OF CHOLANGIOCARCINOMA, WITH A FOCUS ON INFLAMMATION AND CHOLESTASIS AS THE DRIVING FORCES IN CHOLANGIOCARCINOMA DEVELOPMENT. RISK FACTORS FOR CHOLANGIOCARCINOGENESIS: CHOLESTATIC LIVER DISEASES (E.G. PRIMARY SCLEROSING CHOLANGITIS AND FIBROPOLYCYSTIC LIVER DISEASES), LIVER CIRRHOSIS, AND BILIARY STONE DISEASE ALL INCREASE THE RISK OF CHOLANGIOCARCINOMA. CERTAIN BACTERIAL, VIRAL OR PARASITIC INFECTIONS SUCH AS HEPATITIS B AND C AND LIVER FLUKES ALSO INCREASE CHOLANGIOCARCINOMA RISK. OTHER RISK FACTORS INCLUDE INFLAMMATORY DISORDERS (SUCH AS INFLAMMATORY BOWEL DISEASE AND CHRONIC PANCREATITIS), TOXINS (E.G. ALCOHOL AND TOBACCO), METABOLIC CONDITIONS (DIABETES, OBESITY AND NON-ALCOHOLIC FATTY LIVER DISEASE) AND A NUMBER OF GENETIC DISORDERS. MOLECULAR PATHOGENESIS OF CHOLANGIOCARCINOMA: REGARDLESS OF AETIOLOGY, MOST RISK FACTORS CAUSE CHRONIC INFLAMMATION OR CHOLESTASIS. CHRONIC INFLAMMATION LEADS TO INCREASED EXPOSURE OF CHOLANGIOCYTES TO THE INFLAMMATORY MEDIATORS INTERLEUKIN-6, TUMOUR NECROSIS FACTOR-A, CYCLO-OXYGENASE-2 AND WNT, RESULTING IN PROGRESSIVE MUTATIONS IN TUMOUR SUPPRESSOR GENES, PROTO-ONCOGENES AND DNA MISMATCH-REPAIR GENES. ACCUMULATING BILE ACIDS FROM CHOLESTASIS LEAD TO REDUCED PH, INCREASED APOPTOSIS AND ACTIVATION OF ERK1/2, AKT AND NF-KAPPAB PATHWAYS THAT ENCOURAGE CELL PROLIFERATION, MIGRATION AND SURVIVAL. OTHER MEDIATORS UPREGULATED IN CHOLANGIOCARCINOMA INCLUDE TRANSFORMING GROWTH FACTOR-BETA, VASCULAR ENDOTHELIAL GROWTH FACTOR, HEPATOCYTE GROWTH FACTOR AND SEVERAL MICRORNAS. INCREASED EXPRESSION OF THE CELL SURFACE RECEPTOR C-MET, THE GLUCOSE TRANSPORTER GLUT-1 AND THE SODIUM IODIDE SYMPORTER LEAD TO TUMOUR GROWTH, ANGIOGENESIS AND CELL MIGRATION. STROMAL CHANGES ARE ALSO OBSERVED, RESULTING IN ALTERATIONS TO THE EXTRACELLULAR MATRIX COMPOSITION AND RECRUITMENT OF FIBROBLASTS AND MACROPHAGES THAT CREATE A MICROENVIRONMENT PROMOTING CELL SURVIVAL, INVASION AND METASTASIS. CONCLUSION: REGARDLESS OF AETIOLOGY, MOST RISK FACTORS FOR CHOLANGIOCARCINOMA CAUSE CHRONIC INFLAMMATION AND/OR CHOLESTASIS, LEADING TO THE ACTIVATION OF COMMON INTRACELLULAR PATHWAYS THAT RESULT IN REACTIVE CELL PROLIFERATION, GENETIC/EPIGENETIC MUTATIONS AND CHOLANGIOCARCINOGENESIS. AN UNDERSTANDING OF THE MOLECULAR PATHOGENESIS OF CHOLANGIOCARCINOMA IS VITAL WHEN DEVELOPING NEW DIAGNOSTIC BIOMARKERS AND TARGETED THERAPIES FOR THIS DISEASE. 2019 18 1972 31 EPIGENETIC ALTERATIONS ASSOCIATED WITH CHOLANGIOCARCINOMA (REVIEW). CHOLANGIOCARCINOMA (CCA) IS A HIGHLY LETHAL MALIGNANT TUMOR ARISING FROM THE BILIARY TRACT EPITHELIUM. CHRONIC INFLAMMATORY CONDITIONS, INCLUDING PRIMARY SCLEROSING CHOLANGITIS, LIVER FLUKE INFESTATION, AND HEPATOLITHIASIS, ARE CONSIDERED RISK FACTORS, BUT THE CAUSE IS STILL UNKNOWN IN MOST CASES. RECENT ADVANCES IN MOLECULAR PATHOGENESIS HAVE HIGHLIGHTED THE IMPORTANCE OF EPIGENETIC ALTERATIONS, INCLUDING PROMOTER HYPERMETHYLATION AND HISTONE DEACETYLATION, IN THE PROCESS OF CHOLANGIOCARCINOGENESIS. MORE RECENTLY, RESEARCH INTEREST HAS BEEN FOCUSING ON MICRORNA (MIR), A MAJOR SUBTYPE OF NON-CODING RNA. MIR IS HIGHLY CONSERVED AMONG SPECIES AND REGULATES THE EXPRESSION OF SPECIFIC TARGET GENES BY BINDING TO THE 3'-UNTRANSLATED REGIONS OF MESSENGER RNA. THE NUMBER OF STUDIES ON A POSSIBLE LINK BETWEEN MIR AND VARIOUS CANCERS IS GROWING. THIS REVIEW PROVIDES A COMPREHENSIVE OVERVIEW OF THE GENES CURRENTLY KNOWN TO BE HYPERMETHYLATED IN CCA AND THEIR PUTATIVE ROLES IN CHOLANGIOCARCINOGENESIS. THE EPIGENETIC ROLE OF MIR IN THE PATHOGENESIS OF CCA IS ALSO DISCUSSED. 2009 19 2684 22 EVALUATION OF X CHROMOSOME INACTIVATION WITH RESPECT TO HLA GENETIC SUSCEPTIBILITY IN RHEUMATOID ARTHRITIS AND SYSTEMIC SCLEROSIS. BACKGROUND: AUTOIMMUNE DISEASES, INCLUDING RHEUMATOID ARTHRITIS (RA) AND SYSTEMIC SCLEROSIS (SSC) ARE CHARACTERIZED BY A STRONG GENETIC SUSCEPTIBILITY FROM THE HUMAN LEUCOCYTE ANTIGEN (HLA) LOCUS. ADDITIONALLY, DISORDERS OF EPIGENETIC PROCESSES, IN PARTICULAR NON-RANDOM X CHROMOSOME INACTIVATION (XCI), HAVE BEEN REPORTED IN MANY FEMALE-PREDOMINANT AUTOIMMUNE DISEASES. HERE WE TEST THE HYPOTHESIS THAT WOMEN WITH RA OR SSC WHO ARE STRONGLY GENETICALLY PREDISPOSED ARE LESS SUSCEPTIBLE TO XCI BIAS. METHODS: USING METHYLATION SENSITIVE GENOTYPING OF THE ANDROGEN RECEPTOR (AR) GENE, XCI PROFILES WERE PERFORMED IN PERIPHERAL BLOOD MONONUCLEAR CELLS FROM 161 WOMEN WITH RA, 96 WOMEN WITH SSC AND 100 HEALTHY WOMEN. HLA-DRB1 AND DQB1 WERE GENOTYPED. PRESENCE OF SPECIFIC AUTOANTIBODIES WAS DOCUMENTED FOR PATIENTS. XCI SKEWING WAS DEFINED AS HAVING A RATIO >/= 80:20 OF CELLS INACTIVATING THE SAME X CHROMOSOME. RESULTS: 110 WOMEN WITH RA, 68 WOMEN WITH SSC, AND 69 CONTROLS WERE INFORMATIVE FOR THE AR POLYMORPHISM. AMONG THEM 40.9% OF RA PATIENTS AND 36.8% OF SSC PATIENTS HAD SKEWED XCI COMPARED TO 17.4% OF HEALTHY WOMEN (P = 0.002 AND 0.018, RESPECTIVELY). PRESENCE OF RA-SUSCEPTIBILITY ALLELES CODING FOR THE "SHARED EPITOPE" CORRELATED WITH HIGHER SKEWING AMONG RA PATIENTS (P = 0.002) AND SUCH CORRELATION WAS NOT OBSERVED IN OTHER WOMEN, HEALTHY OR WITH SSC. PRESENCE OF SSC-SUSCEPTIBILITY ALLELES DID NOT CORRELATE WITH XCI PATTERNS AMONG SSC PATIENTS. CONCLUSION: DATA DEMONSTRATE XCI SKEWING IN BOTH RA AND SSC COMPARED TO HEALTHY WOMEN. UNEXPECTEDLY, SKEWED XCI OCCURS MORE OFTEN IN WOMEN WITH RA CARRYING THE SHARED EPITOPE, WHICH USUALLY REFLECTS SEVERE DISEASE. THIS REINFORCES THE VIEW THAT LOSS OF MOSAICISM IN PERIPHERAL BLOOD MAY BE A CONSEQUENCE OF CHRONIC AUTOIMMUNITY. 2016 20 1169 19 CONTRIBUTION OF GENETIC, EPIGENETIC AND TRANSCRIPTOMIC DIFFERENCES TO TWIN DISCORDANCE IN MULTIPLE SCLEROSIS. EVALUATION OF: BARANZINI SE, MUDGE J, VAN VELKINBURGH JC ET AL. GENOME, EPIGENOME AND RNA SEQUENCES OF MONOZYGOTIC TWINS DISCORDANT FOR MULTIPLE SCLEROSIS. NATURE 464, 1351-1356 (2010). MULTIPLE SCLEROSIS (MS) IS A CHRONIC INFLAMMATORY DISEASE OF THE CNS. GENETICALLY IDENTICAL (MONOZYGOTIC) TWINS HAVE A CONCORDANCE RATE FOR MS OF APPROXIMATELY 30%, LENDING SUPPORT TO THE NOTION THAT THE DISEASE HAS A COMPLEX ETIOLOGY, DEVELOPING AS A RESULT OF GENETIC AND ENVIRONMENTAL FACTORS AND THEIR INTERACTIONS. HOWEVER, RECENT STUDIES HAVE HIGHLIGHTED THE FACT THAT MONOZYGOTIC TWINS MIGHT NOT ACTUALLY BE GENETICALLY IDENTICAL. IN AN EFFORT TO SEE IF THIS CAN EXPLAIN MS TWIN DISCORDANCE, BARANZINI AND COLLEAGUES SEQUENCED THE GENOME FROM A PAIR OF MONOZYGOTIC TWINS DISCORDANT FOR MS, AND ALSO EXAMINED DNA METHYLATION AND GENE EXPRESSION ACROSS THE GENOME IN THIS TWIN PAIR AND AN ADDITIONAL TWO MORE TWIN PAIRS. NO CONSISTENT DIFFERENCES IN DNA SEQUENCE, DNA METHYLATION OR GENE EXPRESSION WERE FOUND. HERE WE PUT THESE FINDINGS INTO CONTEXT AND DISCUSS THEIR SIGNIFICANCE. 2010