Variants in PCSK7, PNPLA3 and TM6SF2 Are Risk Factors for the Development of Cirrhosis in Hereditary Haemochromatosis

Stephan Buch; Aneesh Sharma; Eleanor Ryan; Christian Datz; William J. H. Griffiths; Michael Way; Thomas W. M. Buckley; John D. Ryan; Stephen Stewart; Callum Wright; Paola Dongiovanni; Anna Fracanzani; Jochen Zwerina; Uta Merle; Karl Heinz Weiss; Elmar Aigner; Elisabeth Krones; Christian Dejaco; Janett Fischer; Thomas Berg; Luca Valenti; Heinz Zoller; Andrew McQuillin; Jochen Hampe; Felix Stickel; Marsha Y. Morgan

Disclosures

Aliment Pharmacol Ther. 2021;53(7):830-843. 

In This Article

Abstract and Introduction

Abstract

Background: Cirrhosis develops in <10% of individuals homozygous for the C282Y variant in the homeostatic iron regulator (HFE) gene. Carriage of PCSK7:rs236918 is associated with an increased risk of cirrhosis in this population.

Aim: To determine if genetic variants significantly associated with the risk of alcohol- and NAFLD-related cirrhosis also modulate the cirrhosis risk in C282Y homozygotes.

Methods: Variants in PCSK7, PNPLA3, TM6SF2, MBOAT7 and HSD17B13 were genotyped in 1319 C282Y homozygotes, from six European countries, of whom 171 (13.0%) had cirrhosis. Genotypic and allelic associations with the risk for developing cirrhosis were assessed, adjusting for age and sex. Fixed effects meta-analyses of the adjusted summary data for each country were performed. Post hoc association testing was undertaken in the 131 (76.6%) cases and 299 (26.0%) controls with available liver histology.

Results: Significant associations were observed between PCSK7:rs236918 (OR = 1.52 [95% CI 1.06–2.19]; P = 0.022; I2 = 0%); PNPLA3:rs738409 (OR = 1.60 [95% CI 1.22–2.11]; P = 7.37 × 10−4; I2 = 45.5%) and TM6SF2:rs58542926 (OR = 1.94 [95% CI 1.28–2.95]; P = 1.86 × 10−3; I2 = 0%) and the cirrhosis risk in C282Y homozygotes. These findings remained significant in the subpopulation with available liver histology. The population-attributable fractions were 5.6% for PCSK7:rs236918, 13.8% for PNPLA3:rs738409, 6.5% for TM6SF2:rs58542926 and 24.0% for carriage of all three variants combined.

Conclusions: The risk of cirrhosis associated with carriage of PCSK7:rs236918 was confirmed in this much larger population of C282Y homozygotes. In addition, PNPLA3:rs738409 and TM6SF2:rs58542926 were established as significant additional risk factors. More detailed genetic testing of C282Y homozygotes would allow risk stratification and help guide future management.

Introduction

Hereditary haemochromatosis (HH) is an autosomal recessive disorder of dysregulated iron metabolism characterised by elevation of serum ferritin concentrations and transferrin saturations and the accumulation of iron in the liver and other organs.[1]

HH is predominantly attributable to a cysteine to tyrosine substitution at position 282 (p.Cys282Tyr) within the homeostatic iron regulator (HFE) gene and is the most common autosomal recessive disorder in adults of northern European origin.[2,3] It has an allele frequency of 6.2% and a homozygosity frequency of 0.38% or 1:260, but there is considerable variation across Europe with a decreasing gradient from North-West to South-East. Thus, the allele frequency ranges from 10% to 12.5% in Ireland to 0% to 3% in Southern Europe; homozygosity rates range, along the same divide, from 1:150 to <1:3000.[1,3–6]

Although common, this genetic polymorphism is not always phenotypically expressed. Thus, there is considerable variability in the proportion of C282Y homozygotes who develop iron overload.[7] In a large individual patient meta-analysis of C282Y homozygotes, increased serum ferritin concentrations were found in 32% of men and 26% of women while excess liver iron concentrations were found in 42% of men and 19% of women.[3] Equally, there is considerable variability in the proportion of C282Y homozygotes, with iron overload, who develop a clinical phenotype; it is estimated that approximately 10% to 33% will eventually develop HH-associated morbidity.[7] Penetrance is generally higher in men than in women. Menstruation and pregnancy may counter excess iron absorption, at least until the menopause, but are not entirely protective.[8] Overall, the clinical expressivity of C282Y homozygosity, using strict definitions of both iron overload and iron-related organ damage, ranges from 22% to 28% in men and from 1% to 10% in women.[4,9,10]

Thus, C282Y homozygosity is a necessary but not sufficient condition for the development of HH-associated phenotypes, which strongly suggests that constitutional, environmental and genetic modifiers may play a role in gene expression.[11] Daily consumption of >60 g of alcohol, for example, increases the risk of people with HH developing cirrhosis by a factor of nine.[12,13] Likewise, the presence of obesity, diabetes and chronic viral hepatitis all augment the risk for developing cirrhosis in this population.[14–17]

The role played by additional genetic risk modulators is now attracting considerable attention. In 2012, Valenti and coworkers[18] identified a significant association between carriage of rs738409 in the patatin-like phospholipase domain containing-3 (PNPLA3) gene and the development of severe hepatic fibrosis/cirrhosis in Italian C282Y homozygotes, which was independent of the degree of iron overload. This PNPLA3 variant had previously been identified as a significant risk factor for the development of cirrhosis in individuals misusing alcohol or with non-alcoholic fatty liver disease (NAFLD).[19,20]

In 2014, Stickel and colleagues[21] reported a significant association between rs236918 in the proprotein convertase subtilisin/kexin type 7 (PCSK7) gene and the risk for developing cirrhosis in C282Y homozygotes in a German-Austrian-Swiss cohort. These findings were later confirmed by Pelucchi and coworkers in an Italian cohort.[22] No significant association was observed between PCSK7:rs236918 and the risk for developing alcohol-related cirrhosis.[21]

Several genome-wide association studies (GWAS) have been undertaken in patients with liver disease, almost exclusively European, which have identified rs58542926 in transmembrane 6 superfamily member 2 (TM6SF2) and rs641738 in membrane bound O-acyltransferase domain containing protein 7 (MBOAT7) as risk loci for alcohol-related and NAFLD-related cirrhosis.[19,23–26] Additionally, Abul-Husn and colleagues[27] have identified a splice variant rs72613567 in hydroxysteroid 17-beta dehydrogenase 13 (HSD17B13), which appears to protect against the development of alcohol- and NAFLD-related chronic liver injury in people of European ancestry, and to attenuate the risk associated with carriage of PNPLA3:rs738409. The findings in relation to alcohol-related liver disease have been confirmed by others.[28]

Thus, the aim of this study was to further evaluate the role of modifier genes in determining the risk for developing cirrhosis in homozygous carriers of C282Y in HFE.

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