It is a DNA- mutation of the haemoglobin chain and is a hereditary disorder
that runs in a family.
As haemoglobin constitutes of two proteins-alpha and beta, the genetic defect
related to these proteins leads to thalassemia alpha and thalassemia beta respectively.
There are various subtypes to these defects that determine the severity of disease.
Four genes make up the alpha haemoglobin chain while two make the beta one.
Higher the number of mutated genes, the more severe will be the disease.
The severity of disease also, depends on the level of inheritance i.e. if both
the parents are carriers of thalassemia, chances of developing a serious form
of disease (thalassemia major) is high. On the contrary, if only one of the
parents is a carrier, a much milder form of disease (thalassemia minor) may develop.