Variabilità fenotipica nell'emocromatosi: studio di due potenziali modificatori genetici in PCSK7 e GNPAT.

Introduction and aim: Hereditary hemochromatosis (HH) is a genetic disease characterized by a progressive iron overload in different tissues. Homozygosity for the p.C282Y mutation is the most frequent genotype associated with the disease and it is directly responsible for an inappropriate production of hepcidin, the main regulator of iron homeostasis. Several evidences indicated that p.C282Y homozygous genotype has an incomplete penetrance due to the combined action of genetic and acquired modifier factors. Recently, the attention was focused on GNPAT rs11558492 and PCSK7 rs236918 single nucleotide polymorphisms (SNPs). The aim of my thesis was to analyse the role of these potential genetic modifiers in an Italian cohort of p.C282Y homozygotes. Materials and methods: Patients: 298 patients (205 males and 93 females) and 169 healthy controls. Exclusion criteria were: alcohol intake >50 g/day in men and >30 g/day in women, chronic hepatitis, inflammatory status. SNPs genotyping was performed by ARMS-PCR or PCR-RFLP. Random samples were confirmed by direct sequencing. Patients and controls allelic and genotypic frequencies were compared to EVS database and analysed according to serum ferritin levels (SF), liver iron concentration (LIC) measured by liver biopsy or magnetic resonance, iron removed (IR) and liver fibrosis histologically assessed by Ishak score (IS). Fisher’s exact test, chi-squared test and t-test were used to perform statistical comparisons between groups and averages of considered variables. Results: GNPAT rs11558492 analysis. Our results demonstrated that: a. allelic and genotypic frequencies were comparable among patients, controls and EVS data. No significant differences were found even considering two subgroups of males only with extreme phenotypes (SF <1000 mcg/L, IR <5 g and/or LIC <100 mcmol/g vs SF >2000 mcg/L, IR >10 g and/or LIC> 50 mcmol/g); b. according to iron indices, allelic and genotypic frequencies did not significantly differ neither among patients nor compared to controls, limited to SF; c. similarly, minor allele (G) frequency did not differ between patients with absent/mild fibrosis and patients with severe fibrosis/cirrhosis (20.5% vs 25%). PCSK7 rs236918 analysis. Our study demonstrated that: a. minor allele (C) frequency was higher in patients with severe fibrosis/cirrhosis than in patients with absent/mild fibrosis (21.9% vs 7.1%; p=0.003); b. C-allele carriers were more likely to have worse liver staging scores than wild-type patients (OR=2.77, p=0.0018; ORmale-only=2.56, p=0.0233); c. PCSK7 genotype has a direct effect on severe fibrosis/cirrhosis (OR=3.11, p=0.0157) and a mild nonsignificant indirect effect mediated through SF and IR (mediation analysis: 22% and 28%, respectively). Conclusions: Our results demonstrated that: a. GNPAT rs11558492 is not a major modifier of iron status in HH patients and controls, and is not associated with severe fibrosis/cirrhosis in HH patients. b. PCSK7 rs236918 C allele is a risk factor for cirrhosis development in Italian HH patients.