Thalassemias are part of a group of hemoglobin synthesis disorders in which a defect exists in the rate of production of one or more of the globin chains. This defect results from either a heterozygous or homozygous deletion or inactivation of a globin chain gene.

Thalassemias are named according to the affected gene or the globin chain that is showing reduced or absent synthesis.

Globin chain loci are found on:

• chromosome 11 (beta, delta, epsilon, and gamma)
• chromosome 16 (alpha, and zeta)