Comparing rare variants versus common in the pathogenesis of nonalcoholic fatty liver disease: a whole exome sequencing approach.

BACKGROUND/PURPOSE: Genome-wide association studies have reported the association of common variants with nonalcoholic fatty liver disease in genes, namely, PNPLA3/TM6SF2/MBOAT7/HSD17B13, across ethnicities. However, the approach does not identify rarer variants with a higher effect size. We therefore sequenced the complete exonic regions of patients with nonalcoholic steatohepatitis and controls to compare rare and common variants with a role in the pathogenesis. METHODS: This is a prospective study that recruited 54 individuals with/without fatty infiltration. Patients with biopsy-proven nonalcoholic steatohepatitis and persistently elevated liver enzymes were included. Controls were with normal CT/MR fat fraction. DNA was isolated from whole blood, amplified (SureSelectXT Human All Exon V5 + UTR kit) and sequenced (Illumina). Data were filtered for quality, aligned (hg19), and annotated (OpenCRAVAT). Pathogenic (Polyphen-2/SIFT/ClinVar) variants and variants reported to be associated with NAFLD based on published literature were extracted from our data and compared between patients and controls. RESULTS: The mean age of controls (N = 17) and patients (N = 37) was 46.88 ± 6.94 and 37.46 ± 13.34 years, respectively. A total of 251 missense variants out of 89 286 were classified as pathogenic. Of these, 106 (42.23%) were unique to the patients and remaining (n = 145; 57.77%) were found in both patients and controls. Majority (25/37; 67.57%) patients had a minimum of one or more rare pathogenic variant(s) related to liver pathology that was not seen in the controls. CONCLUSION: Elucidating the contribution of rare pathogenic variants would enhance our understanding of the pathogenesis. Including the rarer genes in the polygenic risk scores would enhance prediction power.

NUDT15 C415T variant compared with TPMT genotyping in predicting azathioprine-induced leucopenia: prospective analysis of 1014 inflammatory bowel disease patients in India.

BACKGROUND: Recent studies reported that Nudix Hydrolase 15(NUDT 15) gene variant (C415T) can better predict thiopurine induced leucopenia in Asian patients with inflammatory bowel disease (IBD) than thiopurine S-methyl transferase (TPMT). AIM: To evaluate the role of the NUDT variant compared with TPMT in predicting azathioprine induced leucopenia in Indian IBD patients. METHODS: Prospectively collected data of consecutive patients treated with azathioprine from a large IBD registry were analysed for side effects, discontinuation time, and initial and maximum dose tolerated. Genotyping of NUDT15 C415T (rs116855232; p.R139C) was carried out retrieving blood samples from bio-repository employing real time polymerase chain reaction with age and sex-matched healthy volunteers. The association of NUDT15 C415T with leucopenia (<3 × 109 /L) and neutropenia (<1.5 × 109 /L) was evaluated. TPMT genotyping was done in patients who developed leucopenia. RESULTS: Among 1014 patients (mean age 35.84 ± 12.74 years; 61% males; 54% ulcerative colitis, 44% Crohn's disease and 2% IBD-unclassified), 79 were excluded due to inadequate blood samples. Of the remaining 935, 81 (9%) developed leucopenia and 70 (7.5%) developed neutropenia. The variant "T" allele [heterozygous (CT) and homozygous (TT) versus wild type (CC)] was associated with a 19-fold higher odds (OR19.35, 95% CI11.55-32.42; P < 0.0001) of leucopenia and 21-fold higher odds of neutropenia (OR21.41, 95% CI12.25-37.41). There was significant difference in median dose tolerated between CC, CT and TT (1.35, 1.38 and 0.92 mg/kg body weight, respectively) (P = 0.037) and median duration of therapy (18, 15 and 10 months for CC/CT/TT) (P = 0.003). NUDT15 genotype was an independent risk factor for leucopenia (hazard ratio (HR): CT 11.31, 95% CI6.85-18.03, P < 0.0001 and TT 31.283, 95% CI14.76-66.30 compared to CC) and neutropenia (HR: CT 13.04, 95% CI7.65-22.22, P < 0.0001 and TT 43.39, 95% CI20.21-92.68 compared to CC). The sensitivities for predicting leucopenia and neutropenia by number of mutant NUDT 15 alleles based on additive predictive model were 66.67% and 70% with a receptor operator characteristic curve area under curve value of 0.791 and 0.807, respectively. Among patients with leucopenia, only 6.2% were heterozygous and none were homozygous for TPMT variants. CONCLUSION: NUDT15 variant genotyping appears to be a better predictor for azathioprine-induced leucopenia in an Indian population than TPMT with high accuracy and can be useful in optimizing azathioprine dosage.

Whole-Exome Sequencing Identifies a Variant in Phosphatidylethanolamine N-Methyltransferase Gene to be Associated With Lean-Nonalcoholic Fatty Liver Disease.

BACKGROUND AND AIM: Nonalcoholic fatty liver disease (NAFLD) is a spectrum of liver diseases with simple steatosis on one end and hepatocellular carcinoma on the other. Although obesity is a known risk factor for NAFLD, individuals with normal body mass index (BMI) also have hepatic fatty infiltration, now termed "lean-NAFLD". It represents a distinct entity with a strong underlying genetic component. The present study aimed to sequence the complete exonic regions of individuals with lean-NAFLD to identify germline causative variants associated with disrupted hepatic fatty acid metabolism, thereby conferring susceptibility to NAFLD. METHODS: Whole blood was collected from patients with lean-NAFLD (n = 6; BMI < 23.0 kg/m2) and matched lean controls (n = 2; discovery set). Liver fat was assessed using acoustic radiation force impulse (ARFI) imaging. Patients with ultrasound-detected NAFLD (n = 191) and controls (n = 105) were part of validation set. DNA was isolated, and whole-exome sequencing (WES) was performed in the discovery cohort (Ion Proton™; Ion AmpliSeq™ Exome RDY Kit). Data were analyzed (Ion Reporter software; Life Technologies), and variants identified. Validation of variants was carried out (Taqman probes; Real time-PCR). Student's t test and Fisher's exact test were used to analyze the statistical significance. RESULTS: Although WES identified ∼74,000 variants in individual samples, using various pipelines. variants in genes namely phosphatidylethanolamine N-methyltransferase (PEMT) and oxysterol-binding protein-related protein10 (OSBPL10) that have roles in dietary choline intake and regulation of cholesterol homeostasis, respectively, were identified (discovery set). Furthermore, significant differences were noted in BMI (p = 0.006), waist/hip circumference (p > 0.001), waist/hip ratio (p > 0.001), aspartate aminotransferase (p > 0.001), alanine aminotransferase (p > 0.001), and triglycerides (p = 0.002) between patients and controls. Validation of variants (rs7946-PEMT and rs2290532-OSBPL10) revealed that variant in PEMT but not OSBPL10 gene was associated (p = 0.04) with threefold increased risk of NAFLD in lean individuals. CONCLUSION: Our results demonstrate the association of rs7946 with lean-NAFLD. WES may be an effective strategy to identify causative variants underlying lean-NAFLD.

Incidence and Risk of Gallstone Disease in Gilbert's Syndrome Patients in Indian Population.

BACKGROUND/OBJECTIVES: Individuals with Gilbert's syndrome (GS) harbor mutations in the UGT1A1 gene and are known to have elevated levels of bilirubin, which enhances the risk for gall stone formation. The aim of this study is to screen Indian patients with GS for the incidence of gall stone disease. METHODS: Individuals with persistently elevated serum bilirubin levels were genotyped for two polymorphisms (rs8175347; rs4148323) in UGT1A1 gene to confirm GS in them. Flanking regions of the above polymorphisms were amplified followed by direct sequencing. Ultrasonography was done to detect gallstone disease. Clinical data, including assessment of liver function, circulating levels of total and direct bilirubin, as well as routine hematological parameters were obtained as per standard procedures (Autoanalyzer). RESULTS: Of the total 1621 individuals subjected to genotyping, 1191 (1149 males of 29.6 ± 11.3 years with mean BMI of 22.1 ± 3.7 kg/m2 and 42 females of 30.8 ± 14.8 years with mean BMI of 20.9 ± 3.7 kg/m2) were confirmed to have GS. Gall bladder abnormalities including cholelithiasis (n = 106/1191; 8.9%), polyps (n = 18/1191; 1.5%) and gallbladder wall thickening (n = 17/1191; 1.4%) were noted. Incidence of gall stone disease was observed in 103 males (out of 1149) and 3 females (out of 42) indicating the risk of the disease to be 9.0% and 7.1% respectively in males and females with GS. CONCLUSION: Early recognition of GS by genetic analysis is required before these patients with intermittent episodes of jaundice run the risk of unnecessary operations on their bile ducts from the mistaken assumption ascribing the jaundice to a stone which has been left behind.

PRSS1 (R122H) mutation in an Indian family with low penetrance is associated with pancreatitis phenotype.

Mutations in PRSS1 gene namely R122H and N29I cause hereditary pancreatitis. They are autosomal dominant with a high penetrance (80%) reported in North American, North-east Asian, and North European ethnicities. However, the mutations are reportedly absent in Indian, African, and South American ethnicities. We report here for the first time a family from India that is positive for R122H mutation in the PRSS1 gene. The proband is symptomatic with chronic pancreatitis, however, the father although heterozygous for R122H is asymptomatic.

Regional differences in genetic susceptibility to non-alcoholic liver disease in two distinct Indian ethnicities.

AIM: To validate the association of variants in PNPLA3 (rs2281135) and TM6SF2 (rs58542926) genes with ultrasound detected non-alcoholic fatty liver disease (NAFLD). METHODS: A total of 503 individuals with and without fatty infiltration were recruited. Fatty infiltration was confirmed based on ultrasound findings. Anthropometric data and blood samples were collected from the study group. DNA was isolated from peripheral blood, quality and quantity was assessed by gel electrophoresis and spectrophotometer respectively. Genotyping of the variants in PNPLA3 and TM6SF2 genes was carried out by employing taqman probes (C_15875080_10 for PNPLA3 and C_8946351_10 for TM6SF2 SNP) on real time PCR (Stepone-Lifetechnologies). Genotype data was tested for deviations from Hardy-Weinberg equilibrium. χ2 test was used to analyze the statistical significance of the difference in genotype distribution of the studied variants in patients and controls and the strength of association was expressed as odds ratio (95%CI). A two-tailed P value of ≤ 0.05 was considered statistically significant. RESULTS: The study group comprised of 503 individuals of which 256 had fatty infiltration and 247 without fatty infiltration and thus formed the patient and control groups respectively. As the patient group could be divided in to two distinct ethnicities (ancestral South Indians-ASI and North-East Indians-NEI), further recruitment of control cohort and association analyses was carried out based on ethnicities. Of the 256 with fatty infiltration 93 were ASI and 163 were NEI and of the 247 controls 138 were ASI and 109 were NEI. As expected, there were significant differences in the anthropometric and other clinical data between the control and the patient groups. However significant differences within the ethnicities were also noted. While rs2281135 in PNPLA3 gene was significantly associated (P = 0.03) with higher risk (odds 1.9, 95%CI: 1.5-3.14, P = 0.03) of NAFLD in NEI ethnicity, rs58542926 in TM6SF2 gene was significantly associated with NAFLD with a 2.7 fold higher risk (odds 2.7, 95%CI: 1.37-5.3, P = 0.0004) of the disease. There were significantly higher proportions of individuals with variants in both the genes in the patient group in both ASI (patients - 14/93 and controls - 7/138; P = 0.009) and NEI ethnicities (patients - 17/163 and controls - 7/109; P = 0.01). CONCLUSION: Although the study identified distinct genetic susceptibility in the two ethnicities, transheterozygosity of the variants suggests higher risk of NAFLD in individuals with both the variants.

Hereditary Persistence of Alpha-Fetoprotein Is Associated with the -119G>A Polymorphism in AFP Gene.

Alpha-fetoprotein (AFP) is a glycoprotein that is produced by the liver and yolk sac during fetal development. Its levels are usually raised in malignant conditions. Hereditary persistence of AFP (HPAFP) is a rare benign condition with elevated levels of AFP. It is inherited in a dominant mode with complete penetrance and is usually not associated with any clinical disability. We report two individuals with elevated levels of AFP harboring the -119G>A polymorphism in the AFP gene. A genetic screening to rule out variants in the AFP gene is advised in cases with unexplained persistent AFP levels to avoid inappropriate treatment and surgical options.