Background & Aims: Hereditary hemochromatosis is associated with C282Y homo
zygosity. Some heterozygotes may also present with abnormal iron parameters
. However, the precise role of H63D and C282Y mutations in iron overload is
poorly understood, We investigated the level of expression of the mutated
and unmutated HFE alleles in these heterozygous patients. Methods: We studi
ed the expression of HFE messenger RNAs in peripheral blood mononuclear cel
ls from 34 heterozygotes using reverse-transcription polymerase chain react
ion (PCR) followed by enzymatic digestion or sequence analysis of the PCR p
roducts, which allows relative quantification of mutated and unmutated tran
scripts, HFE proteins were quantified by Western blotting in Epstein-Barr v
irus-immortalized lymphocyte extracts from 2 C282Y and H63D homozygotes and
a compound heterozygote, Results: (187C > G; H63D) mutated transcripts pre
dominated in H63D and compound heterozygotes and the normal transcripts in
C282Y heterozygotes. The amount of HFE protein was increased in the H63D ho
mozygotes and the compound heterozygote compared with the C282Y homozygotes
. In addition, we found a new mutation at codon 282 (C282S) associated with
severe iron overload, Conclusions: We demonstrate the existence of differe
ntial allelic expression of the HFE alleles, suggesting that the (187C > G;
H63D) mutation plays a role in the disease expression in H63D heterozygote
s, in particular when associated with environmental or host factors.