TYPE Turkish Ggamma(Agammadeltabeta)°-Thal (see Fig. 16)
CAUSE This condition is characterized by a deletion extending from 3' to Ggamma to 3' to the 6.4 kb L1 repeat. The precise length of the deletion is 36,215 bp. The Agamma, delta, and beta genes, as well as the psibeta gene are removed. The 5' breakpoint is located 1,075 bp 3' to the termination codon of the Ggamma gene. The 3' breakpoint is 9,657 bp 3' to the termination codon of the beta gene, or 48 bp 3' to the L1 repetitive sequence.
DETECTION Gene mapping with different enzymes and probes; sequencing.
PHENOTYPE Homozygotes have a clinical picture of thalassemia intermedia with moderately severe anemia. A marked imbalance in the globin chain synthesis is evident (alpha/gamma = 5). Hb F is 100% and consists exclusively of alpha and Ggamma chains. Heterozygotes have thalassemia-like features with elevated Hb F (10-13%) which is heterogeneously distributed among the erythrocytes. The Ggamma content of Hb F is greater than 95%, while Hb A2 levels are normal (2.5%).
DISTRIBUTION This deletion was found in a few Turkish families.
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This material is from the book A Syllabus of Thalassemia Mutations (1997) by Titus H.J. Huisman, Marianne F.H. Carver, and Erol Baysal, published by The Sickle Cell Anemia Foundation in Augusta, GA, USA. Copyright © 1997 by Titus H.J. Huisman. All rights reserved. Neither this work nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, microfilming and recording, or by any information storage and retrieval systems, without permission in writing from the Author.