TYPE HPFH-2; Ghanaian (see Fig. 13)
CAUSE A very large deletion of ~105 kb long extending from the IVS-II of the psibeta gene to ~90 kb downstream from the 3' end of the psibeta gene. The exact 5' breakpoint is at position IVS-II-51 of the psibeta gene. The 3' breakpoint is mapped to an L1 family repeat, located outside the sequence region of the beta-globin gene cluster.
DETECTION Gene mapping and sequencing. The Ggamma-globin gene does not carry the C->T mutation resulting in lower Ggamma values.
PHENOTYPE This is similar to that of HPFH-1. Heterozygotes have a normal hematology with Hb F levels averaging 24.4±2.8% (n=56) with an average Ggamma value of 32.3±4.8%. The level of Hb A2 is decreased. Homozygotes have a mild erythrocytosis (Hb 15.5-18.0 g/dl) with 100% Hb F and Ggamma values of 45-60%.
DISTRIBUTION In Black families from Africa and the Americas. First observed among Ghanaian 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.