A Novel APOB Mutation Identified by Exome Sequencing Cosegregates With Steatosis, Liver Cancer, and Hypocholesterolemia.

From the Dipartimento Biomedico di Medicina Interna e Specialistica, Universit&agrave.
Arteriosclerosis Thrombosis and Vascular Biology (Impact Factor: 6.34). 05/2013; DOI: 10.1161/ATVBAHA.112.301101
Source: PubMed

ABSTRACT OBJECTIVE: In familial hypobetalipoproteinemia, fatty liver is a characteristic feature, and there are several reports of associated cirrhosis and hepatocarcinoma. We investigated a large kindred in which low-density lipoprotein cholesterol, fatty liver, and hepatocarcinoma displayed an autosomal dominant pattern of inheritance. APPROACH AND RESULTS: The proband was a 25-year-old female with low plasma cholesterol and hepatic steatosis. Low plasma levels of total cholesterol and fatty liver were observed in 10 more family members; 1 member was affected by liver cirrhosis, and 4 more subjects died of either hepatocarcinoma or carcinoma on cirrhosis. To identify the causal mutation in this family, we performed exome sequencing in 2 participants with hypocholesterolemia and fatty liver. Approximately 22 400 single nucleotide variants were identified in each sample. After variant filtering, 300 novel shared variants remained. A nonsense variant, p.K2240X, attributable to an A>T mutation in exon 26 of APOB (c.6718A>T) was identified, and this variant was confirmed by Sanger sequencing. The gentotypic analysis of 16 family members in total showed that this mutation segregated with the low cholesterol trait. In addition, genotyping of the PNPLA3 p.I148M did not show significant frequency differences between carriers and noncarriers of the c.6718A>T APOB gene mutation. CONCLUSIONS: We used exome sequencing to discover a novel nonsense mutation in exon 26 of APOB (p.K2240X) responsible for low cholesterol and fatty liver in a large kindred. This mutation may also be responsible for cirrhosis and liver cancer in this family.

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    ABSTRACT: Unclassified renal cell carcinoma (URCC) is a rare variant of RCC, accounting for only 3-5% of all cases. Studies on the molecular genetics of URCC are limited, and hence, we report on 2 cases of URCC analyzed using comparative genome hybridization (CGH) and the genome-wide human exon GeneChip technique to identify the genomic alterations of URCC. Both URCC patients (mean age, 72 years) presented at an advanced stage and died within 30 months post-surgery. Histologically, the URCCs were composed of undifferentiated, multinucleated, giant cells with eosinophilic cytoplasm. Immunostaining revealed that both URCC cases had strong p53 protein expression and partial expression of cluster of differentiation-10 and cytokeratin. The CGH profiles showed chromosomal imbalances in both URCC cases: gains were observed in chromosomes 1p11-12, 1q12-13, 2q20-23, 3q22-23, 8p12, and 16q11-15, whereas losses were detected on chromosomes 1q22-23, 3p12-22, 5p30-ter, 6p, 11q, 16q18-22, 17p12-14, and 20p. Compared with 18 normal renal tissues, 40 mutated genes were detected in the URCC tissues, including 32 missense and 8 silent mutations. Functional enrichment analysis revealed that the missense mutation genes were involved in 11 different biological processes and pathways, including cell cycle regulation, lipid localization and transport, neuropeptide signaling, organic ether metabolism, and ATP-binding cassette transporter signaling. Our findings indicate that URCC may be a highly aggressive cancer, and the genetic alterations identified herein may provide clues regarding the tumorigenesis of URCC and serve as a basis for the development of targeted therapies against URCC in the future.
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    ABSTRACT: Hepatocellular carcinoma (HCC) is the fourth cause of cancer related mortality, and its incidence is rapidly increasing. Viral hepatitis, alcohol abuse, and exposure to hepatotoxins are major risk factors, but nonalcoholic fatty liver disease (NAFLD) associated with obesity, insulin resistance, and type 2 diabetes, is an increasingly recognized trigger, especially in developed countries. Older age, severity of insulin resistance and diabetes, and iron overload have been reported to predispose to HCC in this context. Remarkably, HCCs have been reported in non-cirrhotic livers in a higher proportion of cases in NAFLD patients than in other etiologies. Inherited factors have also been implicated to explain the different individual susceptibility to develop HCC, and their role seems magnified in fatty liver, where only a minority of affected subjects progresses to cancer. In particular, the common I148M variant of the PNPLA3 gene influencing hepatic lipid metabolism influences HCC risk independently of its effect on the progression of liver fibrosis. Recently, rare loss-of-function mutations in Apolipoprotein B resulting in very low density lipoproteins hepatic retention and in Telomerase reverse transcriptase influencing cellular senescence have also been linked to HCC in NAFLD. Indeed, hepatic stellate cells senescence has been suggested to bridge tissue aging with alterations of the intestinal microbiota in the pathogenesis of obesity-related HCC. A deeper understanding of the mechanisms mediating hepatic carcinogenesis during insulin resistance, and the identification of its genetic determinants will hopefully provide new diagnostic and therapeutic tools.
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    ABSTRACT: Excess hepatic storage of triglycerides is considered a benign condition, but nonalcoholic steatohepatitis may progress to fibrosis and may promote atherosclerosis. Carriers of the TM6SF2 E167K variant have fatty liver due to reduced secretion of very low density lipoproteins. As a result, they have lower circulating lipids and reduced risk of myocardial infarction. In this study, we aimed to assess whether TM6SF2 E167K affects liver damage and cardiovascular outcomes in subjects at risk of nonalcoholic steatohepatitis. Liver damage was evaluated in 1201 patients who underwent liver biopsy for suspected nonalcoholic steatohepatitis; 427 were evaluated for carotid atherosclerosis. Cardiovascular outcomes were assessed in 1819 controls from the Swedish Obese Subjects cohort.Presence of the inherited TM6SF2 E167K variant was determined by Taqman assays. In the liver biopsy cohort, 188 subjects (13%) were carriers of the E167K variant. They had lower serum lipid levels than noncarriers (P<0.05), had more severe steatosis, necroinflammation, ballooning, and fibrosis (P<0.05), and were more likely to have nonalcoholic steatohepatitis (OR 1.84, 95% CI 1.23-2.79) and advanced fibrosis (OR 2.08, 95% CI 1.20-3.55), after adjustment for age, sex, body mass index, fasting hyperglycemia, and the I148M PNPLA3 risk variant. However, E167K carriers had lower risk of developing carotid plaques (OR 0.49, 95% CI 0.25-0.94). In the Swedish Obese Subjects cohort, E167K carriers had higher ALT and lower lipid levels (P<0.05), and a lower incidence of cardiovascular events (HR 0.61, 95% CI 0.39-0.95). Conclusions: Carriers of the TM6SF2 E167K variant are more susceptible to progressive nonalcoholic steatohepatitis, but are protected against cardiovascular disease. Our findings suggest that reduced ability to export very low density lipoproteins is deleterious for the liver. (Hepatology 2014;)
    Hepatology 09/2014; DOI:10.1002/hep.27490 · 11.19 Impact Factor


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May 23, 2014