V-c.   The GGamma(AGammaDeltaBeta)°-Thalassemias

These conditions are caused by deletions which include the Agamma-globin gene; they are rare and are, with the exception of a few, found in only a few families. The phenotypes are similar to those of the GgammaAgamma(deltabeta)°-thal with a mild anemia in the heterozygote and microcytosis, hypochromia, low-to-normal levels of Hb A2, 10-15% Hb F with Ggamma chains only. Homozygotes have a thalassemia intermedia. Fig. 16 compares the locations and the sizes of the 12 types that have been discovered.

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FIG. 16. The locations and sizes of the 12 known deletions causing a Ggamma(Agammadeltabeta)°-thal.

The Indian type is a combination of two small deletions and an inversion. The Black type is likely the most common one observed. The combination of this type with Hb S is often confused with sickle cell anemia (with alpha-thal); family studies and fetal Hb analyses will give some useful data for reaching a differential diagnosis. The original proband of the Thai Ggamma(Agammadeltabeta)°-thal had a most interesting combination of this deletion, a beta°-thal and a gamma-thal.

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.