P1502: characterization of the mutation pattern of genes associated with iron overload in a brazilian population

Topic: 29. Iron metabolism, deficiency and overload Background: Hereditary hemochromatosis (HH) is a group of genetic disorders associated with hepcidin downregulation that results in systemic iron overload. HFE gene mutations are the most found in populations of Northern European descent, but HH can be caused by other mutations in genes encoding other proteins relevant to iron metabolism, such as hepcidin (HAMP), transferrin receptor 2 (TFR2), and hemojuvelin. Given the broad racial admixture of the Brazilian population, it is unknown whether HH phenotypes in Brazil can be explained by HFE mutations. Aims: To investigate mutations in genes encoding proteins implicated in iron homeostasis in a cohort of Brazilian patients with iron overload. Methods: Upon written informed consent, we collected clinical data and peripheral venous blood from adult patients with clinical evidence of iron overload as characterized by elevated ferritin (> 200ug/mL in females, > 300ug/mL in males), transferrin saturation >50%, and/or magnetic resonance evidence of liver iron overload. Total genomic DNA was extracted (QIAamp DNA Mini Kit) and used for exome sequencing of genes implicated in iron physiology: HFE, TFR2, HJV, HAMP, SLC40A1, FTH1, FTL, TF, CYBRD1, SLC11A2, HEPH, ACO1, IREB2, SLC11A1, HBB, AHSP, TFRC, BMP6, BMP2, and UROD. Variants were considered significant if frequency <3% in the 1000G Project and with at least 10 representative fragments passing sequencing quality filters. Results: Forty patients (36 male, 90%), median age at diagnosis 50 years were included. A mutation in the HFE gene was found in 37 patients, with 5 (13%) C282Y/C282Y genotype, 5 C282Y/H63D, 7 C282Y/wild type (WT), and 20 H63D/WT. Non-HFE HH mutations were found in five patients, including TFR2 c.2255G>A (p.Arg752His), TFR2 c.1473G>A (p.Glu491Glu), and HAMP c.-72C>T. We also found patients bearing BMP6 c.283C> T (p.Pro95Ser) and BMP6 c.770G> A (p.Arg257His), which may be implicated in iron dysregulation. Four mutations not previously described were identified in association with HFE mutations: BMP6 c.211C>G (p.Leu712Val), and SLC11A1 c.692C>T (p.Pro231Leu), c.701C>G (p.Pro234Arg), and c.730G>A (p.Ala 244Thr), in association with HFE C282Y/H63D, H63D/H63D, C282Y/H63D, and C282Y/C282Y, respectively. In addition, one patient was found to have a new TFR2 mutation c.1608G>C (p.Val536Val) along with HFE H63D. We identified a beta thalassemic allele in heterozygosis in 3 patients with iron overload and heterozygosis for HFE H63D, HFE C282Y, and BMP6 c.283C>T. Summary/Conclusion: Our study suggests that, while HFE heterozygote genotypes by themselves usually do not cause iron overload, iron overload seems to be a complex quantitative trait, in which the addition of multiple genetic variants, along with environmental factors, may contribute to the dysregulation of iron absorption. A combination of multiple genetic traits, including but not restricted to HFE mutations, can work as phenotypic modifiers, and contribute to the development of iron overload. Keywords: Hemochromatosis, Iron overload, Mutation analysis, Iron metabolism