The thalassaemia is transmitted from parents to their children as dominant, Mendelian, autosomal characters (not sex-linked) and without jumping generations: if a subject is a thalassaemia carrier, at least one of his parents has to be a thalassaemia carrier; but if he is not a thalassaemia carrier, also being child of a thalassaemic parent, he cannot transmit the thalassaemia to his children.

The Mediterranean anaemia patient is, in turn, the subject that has received the thalassaemia (more exactly the β thalassaemia) from both his parents and he is homozygote for this character.

Case of History of Relatives

The expected genetic frequencies about the thalassaemia are evidenced also in the reality only if a high number of children, been born by couples at risk, is considered. If only the single families are analyzed, occasionally the percentages can be different from the attended ones: that is, it can happen that the first sick child is born after some healthy children; or that is born, following, two or three sick children. So it is worth the rule that the families with both the thalassaemic parents have the 25% of risk that a sick child could born in each pregnancy.

This is the fundamental genetic concept at the purposes of the Mediterranean anaemia prevention and that is transmitted to the whole population in fertile age during the prevention programs.

As the molecular studies have solved particular cases

Already in the 1950s subjects affected by thalassaemia intermedia, been born by a thalassaemic parent and a not thalassaemic one, had been underlined. These scientific "mysteries" have been solved by the advent of the DNA studies that have underlined the existence of mutations giving arise to β thalassaemia silent varieties. Therefore, the apparent "normal" parent in reality is carrier of a form not giving meaningful alterations of the analyses.

In turn the knowledge of α evident thalassaemias (α⁰ thalassaemias) has explained why all the children, been born in families with both the parents thalassaemia carriers, do not manifest the Mediterranean anaemia. In these cases, in reality in the families there is a β thalassaemic parent and a α thalassaemic one. The carriers of the β+α thalassaemia double heterozygosis are healthy subjects since this association does not give place to the illness.