The heterozygous state of thalassemia (a+) results from deletion of one a-globin gene (a-/aa). The most
common deletions vary in length, 3.7 and 4.2 kb (-a3.7 and -a4.2). If both parents are carriers, it can be
passed to an offspring, resulting in a two-gene deletion on the two chromosomes (a-/a-). The
homozygous state of an a-thalassemia carrier occurs when both genes on the same chromosomes are
deleted, named a0 (--/aa). This is referred to as cis deletion as opposed to trans, when the deletions are
on opposite chromosomes. The a0-thalassemia is also described by the length of the deletion that removes
both a genes; the length being different in the various deletions. The more common deletions are the SEA
deletion and the Mediterranean (MED) deletion. The Philippine (FIL) and Thai (THAI) deletions are
particularly long. There are more than 35 known deletional mutations; extensive descriptions of the
various mutations have been published[11,14]. The high frequencies of the various a-thalassemias cause
a major public health burden in the region of Southeast Asia[