Thalassemia

Thalassemia may be associated with mental
retardation. Two different syndromes can be
distinguished: One occurs in patients with a
large (1–2 Mb) deletion on the tip of chromosome
16 including the !-globin gene cluster
(ATR-16 syndrome). The other is an X-linked
disorder with a remarkably uniform phenotype
and a mild form of HbH disease without !-globin
deletion. A trans-acting regulatory factor
appears to be encoded on the X chromosome.