Thalassemia are forms of inherited autosomal recessive blood disorders that originated in the Mediterranean region. In thalassemia, the disease is caused by the excessive destruction or degradation of red blood cells due to formation of abnormal hemoglobin molecules, because of a defect through a genetic mutation or deletion. There are two major forms of the disease - alpha and beta (see below), which are prevalent in discrete geographical clusters around the world, where it is presumably associated with presence of malaria. The alpha form is prevalent in peoples of Western African and South Asian descent. Nowadays, it is found in populations living in Africa, the Americas and also, in Tharu in the Terai region of Nepal and India. It is believed to account for much lower malaria sicknesses and deaths, accounting for the historic ability of Tharus to survive in areas with heavy malaria infestation, where others could not.