The recently identified type 2A juvenile haemochromatosis gene (HJV), a second candidate modifier of the C282Y homozygous phenotype.

The most common form of hereditary haemochromatosis is an adult-onset condition usually associated with the HFE C282Y/C282Y genotype. The phenotypic expression of this genotype is heterogeneous and depends on a complex interplay of genetic and non-genetic factors. The aim of the present study was to determine if mutations in the recently identified HJV gene were associated with more severe iron overload phenotypes in C282Y homozygous patients. From a cohort of 310 C282Y homozygous patients, we found nine (six males and three females) with an additional HJV missense mutation in the heterozygous state (S105L, E302K, N372D, R335Q or the previously described L101P and G320V). The iron indices of eight patients appeared to be more severe than those observed in C282Y homozygous patients of identical sex and similar age ranges. The mean serum ferritin concentration of the six males with an HJV mutation was significantly higher than that of C282Y homozygous males without an additional mutation [2350.3 (sigma=1429.9) versus 1227.2 (sigma=1130.1) microg/l; P=0.0233, Student's t-test]. We have recently reported that mutations in the gene that encodes hepcidin (HAMP) could explain one part of the C282Y/C282Y-related phenotypic heterogeneity by accentuating the iron burden. Our new data reveal that mutations in the HJV gene could be associated with a similar effect. Taken together, these results emphasize that a search for modifier genes could enable us to more precisely distinguish those C282Y homozygous patients with a higher risk to develop a severe iron overload and, consequently, clinical complications. Copyright 2004 Oxford University Press