TYPE Laotian (deltabeta)°-Thal (see Fig. 14)
CAUSE An ~12.5 kb deletion removing DNA that extends from delta-IVS-II to the L1 repetitive sequences located 3' of the beta gene. The deletion removes the 3' end of the delta gene and the entire beta gene. The 5' breakpoint resides within an AT rich region which has been proposed as a specific recognition signal for recombination events, while the 3' breakpoint lies within a cluster of L1 repetitive sequences.
DETECTION Gene mapping defined the 5' breakpoint within delta-IVS-II between positions 775 to 781, similar to the 5' breakpoint of the Sicilian (deltabeta)°-thal. The 3' breakpoint is located between two PstI sites, 4.7 kb 3' to the beta gene, thus ending 0.7 kb upstream from the 3' breakpoint of the Sicilian (deltabeta)°-thal.
PHENOTYPE The condition is more or less asymptomatic with mild anemia, hypochromia and microcytosis (PCV 0.39 l/l; MCH 22.8 pg; MCV 71 fl), normal levels of Hb A2 (3%), and increased Hb F (11.5%). The Ggamma:Agamma ratio is 60:40 with a heterocellular distribution in F-cells (52%).
DISTRIBUTION Laotian (deltabeta)°-thal was observed in a 24-year-old Laotian male.
1. Zhang, J-W., Stamatoyannopoulos, G., and Anagnou, N.P.: Blood, 72:983, 1988.

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.