Inherited disorders are caused by defective genes in the cells of the body. Genes, which are made up of DNA, contain the information, the body needs to develop from the egg, and to maintain itself in good working order. Human beings have about 60,000 genes, and every cell in the body except the egg and sperm cell contain two copies of each. One of these copies is inherited from each parent.
Haemochromatosis is a recessive disorder. This means that it only develops if both copies of the gene are abnormal. If only one copy is defective an individual will be perfectly well but will be a carrier, about 20% of the population are carriers. In the diagrams below the orange colour indicates the defective gene and grey the normal gene. This means:
1. If both parents are carriers
If both parents are carriers (about 1 in 25 marriages), On average a quarter of the children will develop haemochromatosis, half will be carriers and a quarter will be normal.
2. If one parent has haemochromatosis and the other is a carrier
If one parent has Haemochromatosis and the other is a carrier
(about 1 in 3,000 marriages) on average half of the children will
develop haemochromatosis and the other half will be
3. If both parents suffer from haemochromatosis
If both parents suffer from Haemochromatosis diagram (a rare event, occurring in about 1 in 10,000 marriages) all the children will inherit two defective genes and all will have haemochromatosis.
It should be emphasised that the proportions given in examples 1 and 2 are averages for the whole population. For instance, in any particular family where both parents are carriers, it would be possible for all children to be affected, all to be carriers or all to be normal.