Nature Vol. 283 14 February 1980 637 y-{J- Thalassaemia studies showing that deletion of the y- and B-genes influences {J-globin gene expression in man L. H. T. Vander Ploeg, A. Konings 11 , M. Oort*, D. Roost, L. Bernini* & R. A. Flavell§ Section for Medical Enzymology and Molecular Biology, Laboratory of Biochemistry, University of Amsterdam, Jan Swammerdam Institute, PO Box 60.000, 1005 GA Amsterdam * Scheperziekenhuis, Emmen, The Netherlands. t Centraal Laboratorium voor de Bloedtransfusiedienst, Plesmanlaan 125, Amsterdam, The Netherlands. :j: Laboratorium voor Anthropogenetica, Sylvius Laboratorium, State University Leiden, Leiden, The Netherlands In y-{3-thalassaemia, human y- and {3-globin gene expression is suppressed; this results in a severe anaemia in newborns which subsequently develops into a {3-tha/assaemia syndrome in adult life. This hereditary disease is now shown to be the result of a deletion of at least 40,000 base pairs of the y/3{3-g/obin gene locus. The y- and /3-globin genes are deleted in the affected chromosome but, surprisingly, the {3-globin gene is still present, together with a large segment of the DNA sequences flanking the gene on its 5'-side and the entire region on the 3'-side of the gene. Hence, a deletion of DNA far from the {3-g/obin gene results in the suppression of its activity. THE human non-a-globin genes are clustered in a short region of chromosome 11. During fetal life, the major haemoglobin expressed is HbF (a 2 y 2 ) where they-chains are coded for by two non-allelic y-globin genes (Gy and Ay). At about the time of birth, the expression of the y-globin genes gradually ceases and HbF is replaced by HbA (a 2 {3 2 ) and a low level of HbA 2 (a 2 8 2 ) (ref. 1). The fetal and adult genes are closely linked and gene mapping studies using Southern blotting 2 and the analysis of cloned genes have established the physical linkage of the 8- and {3-genes3.4, the two y-genes 5 and the tie up between these maps to describe the linkage between these four genes 6 - 8 • Figure 1 shows the physical map of the {3-related globin genes. Several well-defined defects in the functioning of these genes have been described. In addition to the abnormal haemoglobin proteins (such as HbS in sickle cell anaemia), inherited diseases collectively called the thalassaemias have been described in which the level of expression of these genes is altered. In the most common type, {3-thalassaemia, two forms of the disease can be distinguished. In {3+ -thalassaemia, reduced amounts of {3-globin are produced as a result of low levels of globin messenger RNA (mRNA) 1 • In the second type, {3°-thalas- saemia, no {3-globin is produced. {3°-Thalassaemia is a hetero- geneous disease and except for two forms of this disease 9 - 11 the molecular basis is unknown. The rarer disease, 8{3° -thalas- saemia, is the result of a gene deletion (see ref. 1 for references) which inactivates both the 8- and {3-globin genes. The deletion maps from the intervening sequence of the 8-globin gene 6 • 12 · 13 to a site 1,800 base pairs past the {3-globin gene 13 ; altogether, 10,000 base pairs have been deleted 13 • Finally, in the condition HPFH (hereditary persistence of fetal haemoglobin) the entire 8{3-globin gene region has been deleted (see ref. 1 for older references), spanning from sites 4 kilobase pairs in front of the 8-globin gene in two cases 6 • 7 and 7 kilobase pairs in front of the 8-globin gene in another (R. Bernards and R.A.F., unpublished) to a position well past the {3-globin gene. Several other rare forms of thalassaemia affecting the {3- related globin genes are known. In y-{3-thalassaemia, first § To whom correspondence should be addressed at the National Insti- tute for Medical Research, Laboratory of Gene Structure and Expres- sion, The Ridge Way, Mill Hill, London NW7, UK. II Present address: Erasmus University, Medical Faculty, Department of Cell Biology and Genetics, Rotterdam, The Netherlands. 0028-0836/80/070637-Q6$01.00 described by Kan et al. 14 , a severe anaemia is evident in new- borns as a result of a reduction of the y/ a synthetic ratio to about 0.5. As y-chain synthesis is switched off in the course of normal development, the disease develops into a mild {3-thalas- saemia which is unusual in that the HbA 2 (a 2 8 2 ) levels are normal, rather than elevated as in classical {3-thalassaemia. To explain this, Kan et a/. 14 postulated that the entire y8{3-region has been deleted in y-{3-thalassaemia. We show here that the Gy-, Ay- and 8-globin genes have been deleted in y-{3-thalassaemia. Surprisingly, however, the {3-globin gene is present, together with 2,500 base pairs on its immediate 5'-side and the entire 3'-extragenic region. Figure 1 compares the structure of the affected region in y-{3-thalas- saemia with the corresponding region of normal DNA. y-fJ-Thalassaemia in a Dutch family One of us (M.O.) has been involved in the treatment of a Dutch family which exhibits the same clinical symptoms as those originally described for y-{3-thalassaemia 14 • These data (includ- ing an extensive family study) will be presented in detail else- Table 1 Haematological data and {3/ a specific activity ratios for y-{3-thalassaemia Hb (gdl - 1 ) Erythrocytes (x 10 12 lx 1 ) Mean cell volume of erythrocytes (fl) Reticulocyte count (%) HbA 2 (% of total Hb) HbF (% of total Hb) {3/a synthetic chain ratio Patient 2 9.7 4.5 67 5.2 3.1 1.0 0.49 Normal females 12.0-15.0 3.5-5.5 82-94 0.5-1 1.9-3.0 0.1-1.5 0.9-1.0 Haemoglobin was determined by the cyanomethaemoglobin method, the erythrocytes counted in a Hycell counter and the mean cell volume of erythrocytes calculated from the erythrocyte count and the haemato- crit. The reticulocyte count was determined by microscopy and the HbA 2 and HbF determined as described in refs 20 and 21. The {3/a synthetic ratios were determined by the incorporation of 3 H-leucine by reticulocytes followed by the separation of the globin chains according to ref. 22. The specific activity of each chain was determined by hydrolysing the a- and {3-globins and determining the leucine content directly. The values for normal females are the average values found in the laboratories of D.R. and L.B. © 1980 Macmillan Journals Ltd