A NEW TURKISH TYPE OF BETA-THALASSEMIA-MAJOR WITH HOMOZYGOSITY FOR 2 NON-CONSECUTIVE 7.6-KB DELETIONS OF THE PSI-BETA AND BETA-GENES AND ANINTACT DELTA-GENE

In a 2.5-month-old infant with P-thalassaemia major, DNA analysis of t he gamma-beta region revealed homozygosity for two large deletions rem oving the entire Psi beta and beta regions including their 5' promoter regions but leaving the delta gene intact. Tile downstream deletion w as predicted to be 7.6 kb in length extending from a point 1.5 kb on t he 3' side of the S-globin gene to about 1.8 kb on the 3' side of the P-globin gene. The upstream deletion, which was also about 7.6 kb, ext ended from a point 1.5 kb on the 5' side of the Psi beta-globin gene t o about 4.5 kb on the 3' of the Psi beta gene, The delta-globin gene w as intact. From the phenotypic expression of the disease it is conclud ed that removal of the Psi beta gene probably prevents derepression of the gamma gene that has previously been observed in the absence of th e promoter region of the beta gene and the switch mechanism from gamma to beta gene expression may take place earlier than expected.