Abnormal regulation of HFE mRNA expression may not contribute to primary iron overload

Background and Objectives. Hereditary hemochromatosis (HHC) is a common, re cessively inherited, genetic disorder associated with an abnormality of th HFE gene. Subjects homozygous for a point mutation in the gene coding seque nce, leading to the amino acid substitution C282Y, are usually by the disea se. A second point mutation, causing the amino acid substitution H63D, has been described, and compound heterozygotes for the two or homozygotes for t he H63D mutation at risk of developing a milder form of HHC. In populations of northern European origin the C282Y substitution accounts for more than 90% of cases of HHC. In Italy, however, fewer than 70% of patients with HHC are homozygous or compound heterozygous for HFE mutations. Even in the abs ence of mutations in its coding region, the HFE gene might be involved in t he pathogenesis of HHC through inhibition of transcription of the gene or r educed stability of its mRNA. Design and Methods. Since little is known about the regulation of HFE expre ssion, we investigated 17 subjects heterozygous for one of the HFE mutation s and with biochemical evidence of iron overload and compared the levels of wild type and mutated mRNAs in their peripheral blood cells. c-DNA regions flanking the mutated codons were amplified by reverse transcriptase polyme rase chain reaction (PCR). PCR products derived from the two alleles were d ifferentiated and quantified by digestion with restriction enzymes, electro phoresis in an agarose stained with ethidium bromide and densitometric scan ning of the gel. Results. In all cases wild type and mutated mRNAs were expressed at similar levels, suggesting that reduced expression of an HFE allele coding a norma l protein is not involved in the pathogenesis of iron overload. However, we can not rule out that a tissue specific regulation of HFE expression in th e cells involved in iron absorption is altered and contributes to the patho genesis of the disease. Interpretation and Conclusions. Our results suggest that primary iron overl oad is a multigenic syndrome; this hypothesis is strongly supported by the recent demonstration that the juvenile hemochromatosis locus maps to human chromosome Iq. (C) 2000, Ferrata Storti Foundation.