HEMOCHROMATOSIS - A MENDELIAN DISEASE WHOSE GENE REMAINS TO BE IDENTIFIED

Hereditary hemochromatosis (HH) is a very severe autosomal recessive d isorder The frequency of the HH allele is estimated to be 3 to 7% in w hite populations, with a frequency of heterozygotes between 6 and 13%. Therefore, hemochromatosis is the most frequent hereditary disorder i n white populations. The genetic abnormality leads to an excessive abs orption of iron by the duodenum and the upper jejunum mucosa. The exce ss of iron is not excreted but stored in various parenchymatous organs . The phenotypic expression of the disease is characterized, in HH hom ozygotes, by an increase of the blood levels of iron and ferritin, a d ecrease in the concentration of serum transferrin combined with an inc rease of the transferrin saturation. The hemochromatosis locus is gene tically linked to the HLA-A locus, on the short arm of chromosome 6. A strong linkage disequilibrium between the HH locus and D6S105, a micr osatellite marker telomeric to HLA-A has been found. D6S105 and D6S265 , another microsatellite marker, define a haplotype that is only seen among HH homozygotes.