RESUMEN
BACKGROUND AND AIMS: Nonalcoholic fatty liver disease is epidemiologically associated with hepatic and metabolic disorders. The aim of this study was to examine whether hepatic fat accumulation has a causal role in determining liver damage and insulin resistance. METHODS: We performed a Mendelian randomization analysis using risk alleles in PNPLA3, TM6SF2, GCKR and MBOAT7, and a polygenic risk score for hepatic fat, as instruments. We evaluated complementary cohorts of at-risk individuals and individuals from the general population: 1515 from the liver biopsy cohort (LBC), 3329 from the Swedish Obese Subjects Study (SOS) and 4570 from the population-based Dallas Heart Study (DHS). RESULTS: Hepatic fat was epidemiologically associated with liver damage, insulin resistance, dyslipidemia and hypertension. The impact of genetic variants on liver damage was proportional to their effect on hepatic fat accumulation. Genetically determined hepatic fat was associated with aminotransferases, and with inflammation, ballooning and fibrosis in the LBC. Furthermore, in the LBC, the causal association between hepatic fat and fibrosis was independent of disease activity, suggesting that a causal effect of long-term liver fat accumulation on liver disease is independent of inflammation. Genetically determined hepatic steatosis was associated with insulin resistance in the LBC and SOS. However, this association was dependent on liver damage severity. Genetically determined hepatic steatosis was associated with liver fibrosis/cirrhosis and with a small increase in risk of type 2 diabetes in publicly available databases. CONCLUSION: These data suggest that long-term hepatic fat accumulation plays a causal role in the development of chronic liver disease.
Asunto(s)
Tejido Adiposo/fisiología , Resistencia a la Insulina/fisiología , Cirrosis Hepática/etiología , Enfermedad del Hígado Graso no Alcohólico/complicaciones , Aciltransferasas/genética , Proteínas Adaptadoras Transductoras de Señales/genética , Adulto , Enfermedad Crónica , Diabetes Mellitus Tipo 2/complicaciones , Femenino , Marcadores Genéticos/genética , Humanos , Lipasa/genética , Masculino , Proteínas de la Membrana/genética , Análisis de la Aleatorización Mendeliana , Estudios ProspectivosRESUMEN
BACKGROUND AND AIMS: Type I hyperlipoproteinemia, also known as familial chylomicronemia syndrome (FCS), is a rare autosomal recessive disorder caused by variants in LPL, APOC2, APOA5, LMF1 or GPIHBP1 genes. The aim of this study was to identify novel variants in the LPL gene causing lipoprotein lipase deficiency and to understand the molecular mechanisms. METHODS AND RESULTS: A total of 3 individuals with severe hypertriglyceridemia and recurrent pancreatitis were selected from the Lipid Clinic at Sahlgrenska University Hospital and LPL was sequenced. In vitro experiments were performed in human embryonic kidney 293T/17 (HEK293T/17) cells transiently transfected with wild type or mutant LPL plasmids. Cell lysates and media were used to analyze LPL synthesis and secretion. Media were used to measure LPL activity. Patient 1 was compound heterozygous for three known variants: c.337T > C (W113R), c.644G > A (G215E) and c.1211T > G (M404R); patient 2 was heterozygous for the known variant c.658A > C (S220R) while patient 3 was homozygous for a novel variant in the exon 5 c.679G > T (V227F). All the LPL variants identified were loss-of-function variants and resulted in a substantial reduction in the secretion of LPL protein. CONCLUSION: We characterized at the molecular level three known and one novel LPL variants causing type I hyperlipoproteinemia showing that all these variants are pathogenic.
Asunto(s)
Hiperlipoproteinemia Tipo I/genética , Lipoproteína Lipasa/genética , Mutación , Adulto , Anciano , Femenino , Predisposición Genética a la Enfermedad , Células HEK293 , Heterocigoto , Homocigoto , Humanos , Hiperlipoproteinemia Tipo I/sangre , Hiperlipoproteinemia Tipo I/diagnóstico , Hiperlipoproteinemia Tipo I/enzimología , Hipertrigliceridemia/sangre , Hipertrigliceridemia/enzimología , Hipertrigliceridemia/genética , Lípidos/sangre , Lipoproteína Lipasa/metabolismo , Masculino , Persona de Mediana Edad , Pancreatitis/sangre , Pancreatitis/enzimología , Pancreatitis/genética , Fenotipo , Recurrencia , TransfecciónRESUMEN
The dbl oncogene is generated by substitution of the 5' portion of its normal counterpart with an unrelated human sequence. To analyze the genomic structure and transcriptional regulation of the dbl proto-oncogene, we have isolated human genomic clones containing the entire human proto-dbl gene, localized in Xq26. Restriction mapping of a 600kb YAC clone (yWXD311) placed proto-dbl about 50kb telomeric to the coagulation Factor IX gene. The genomic DNA fragment containing the 5' end of proto-dbl was subcloned into plasmid vectors and the nucleotide sequences of exon 1, the flanking intronic region and genomic DNA 5' of the first codon were determined. Sequence analysis of 85119bp from the region revealed the genomic structure of proto-dbl. It contains 25 exons coding for a 4.7kb transcript including large 5'- and 3'- (1218bp and 701bp, respectively) untranslated regions (UTRs). RNase protection and primer extension assays on RNA from medullary thyroid carcinoma (TT) cells, which normally express dbl, revealed a transcription start site 1218bp upstream of the ATG of the first exon. A 1.6kb genomic 5' of the translation start sites drives the expression of a CAT-reporter in transient transfections in the TT cell line, though lacking TATA or CAAT boxes.
