Thalassemias are inherited blood disorders that cause the body
to make fewer healthy red blood cells and less hemoglobin than
normal. Mild or severe anemia can also be present in people with
thalassemias. The two major types of thalassemia are alpha and
beta, named after defects in the hemoglobin protein chains. The
most severe form of alpha thalassemia is known as alpha
thalassemia major or hydrops fetalis. Babies with this disorder
usually die before or shortly after birth. Two genes (one from
each parent) are needed to make enough beta globin protein
chains. Beta thalassemia occurs when one or both genes are
altered. The severity of beta thalassemia depends on how badly
one or both genes are affected. If both genes are affected, the
result is moderate to severe anemia. The severe form of beta
thalassemia also is known as thalassemia major or Cooley's
anemia. Thalassemias occur most often among people of Italian,
Greek, Middle Eastern, Asian, and African descent. Severe forms
usually are diagnosed in early