This variation is caused not by compound heterozygosity, but rather by the fact that several different enzyme defects can cause the disease. Clinically, most cases of hemochromatosis are found in homozygotes for the most common mutation in the HFE gene. But at each gene locus associated with the disease, there is the possibility of compound heterozygosity, often caused by inheritance of two unrelated alleles, of which one is a common or classic mutation, while the other is a rare or even novel one.
This variation arises not due to compound heterozygosity, but rather because of the presence of multiple enzyme mutations that can lead to the disease. In clinical terms, most cases of hemochromatosis are found in individuals who possess two copies of the most common mutation in the HFE gene. Nevertheless, at each location where the disease is linked to a specific gene, there is a chance of compound heterozygosity, often resulting from inheriting one common or classic allele and one rare or novel allele.