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Background: The sickle (betas) mutation in the beta-globin gene (HBB) occurs on five "classical" betas haplotype backgrounds in ethnic groups of African ancestry. Strong selection in favour of the betas allele - a consequence of protection from severe malarial infection afforded by heterozygotes - has been associated with a high degree of extended haplotype similarity. The relationship between classical betas haplotypes and long-range haplotype similarity may have both anthropological and clinical implications, but to date has not been explored. Here we evaluate the haplotype similarity of classical betas haplotypes over 400 kb in population samples from Jamaica, The Gambia, and among the Yoruba of Nigeria (Hapmap YRI)., Results: The most common betas sub-haplotype among Jamaicans and the Yoruba was the Benin haplotype, while in The Gambia the Senegal haplotype was observed most commonly. Both subtypes exhibited a high degree of long-range haplotype similarity extending across approximately 400 kb in all three populations. This long-range similarity was significantly greater than that seen for other haplotypes sampled in these populations (P < 0.001), and was independent of marker choice and marker density. Among the Yoruba, Benin haplotypes were highly conserved, with very strong linkage disequilibrium (LD) extending a megabase across the betas mutation., Conclusion: Two different classical betas haplotypes, sampled from different populations, exhibit comparable and extensive long-range haplotype similarity and strong LD. This LD extends across the adjacent recombination hotspot, and is discernable at distances in excess of 400 kb. Although the multi-centric geographic distribution of betas haplotypes indicates strong subdivision among early Holocene sub-Saharan populations, we find no evidence that selective pressures imposed by falciparum malaria varied in intensity or timing between these subpopulations. Our observations also suggest that cis-acting loci, which may influence outcomes in sickle cell disease, could lie considerable distances away from beta-globin.

Sickle hemoglobin (Hb S;betaGlu 6 Val) is due to an A>T transversion in codon 6 of the beta-globin gene. Other variant hemoglobins mimic Hb A, S, or C on newborn screening and clinical laboratory diagnostic tools, thus making their correct identification potentially difficult. Sickling disorders can result in individuals who are compound heterozygous for beta-globin mutations (e.g., Hb SC, HbSO(Arab)). The authors report a second case of HbS/Québec-CHORI, a severe compound heterozygous sickling disorder and their experience managing this patient with hydroxyurea.

The polymorphism of the beta-globin gene haplotypes and frameworks are useful in the determination of the unicentric and multicentric origin of a mutational event. In order to improve our knowledge of the chromosomal background of the beta-globin gene in three beta-thalassemia (thal) mutations originally reported in Tunisia, namely codons 25/26 (+T), codon 30 (G-->C) and IVS-I-2 (T-->G), we have investigated 13 unrelated individuals. There were five non transfusion-dependent patients homozygous for the IVS-I-2 (T-->G) mutation, five others were homozygous for the codon 30 (G-->C) mutation, one was a homozygote for the codons 25/26 (+T) insertion mutation and one patient was a compound heterozygote for the codon 39 (C-->T) and codon 25/26 (+T) mutations; the last patient had a betaS/codon 25/26 (+T) compound heterozygous genotype. Haplotype analysis was carried out by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) based methods. The framework polymorphism was established by direct sequencing. beta-Globin gene analyses demonstrated that all IVS-I-2 (T-->G) cases were associated with haplotype IX; the codon 30 (G-->C) mutation was supported by haplotype I, while the codons 25/26 (+T) mutation was linked to haplotypes I and IX.

SSOs (single-stranded oligonucleotides) can mediate site-specific alteration of base-pairs in episomal and chromosomal target genes in mammalian cells. The TNE (targeted nucleotide exchange) can result in either repair or mutation of a gene sequence and is mediated through endogenous DNA repair pathway(s). Thus the approach provides a technique for the treatment of monogenic disorders associated with specific point mutations such as SCD (sickle cell disease). We studied the potential application of SSOs for SCD by introducing either an A to T substitution at the sixth codon of the human beta-globin gene (sickle locus) or a C to G mutation at -202 of the Ggamma-globin gene promoter region. The latter TNE is an alternative strategy to ameliorate the clinical manifestations of sickle cell anaemia by re-activating fetal haemoglobin gene expression in adult erythrocytes. A sensitive and valid PCR assay system was developed, which allows detection of point mutations as low as 0.01% at these sites. Using this system, TNE between 0.01 and 0.1% at the sickle locus or gamma-globin gene promoter region was detected after transfection with SSOs in cultured human cell lines. TNE in the Ggamma-globin promoter region exhibited varying degrees of strand bias that was dependent on SSO design and the cell's DNA mismatch repair activity. The results suggest that the endogenous DNA repair machinery may permit SSO correction of the sickle defect by modification of the beta- and/or gamma-globin genes.

A baby girl presented with symptomatic sickle cell disease exacerbated by mild hypoxemia, despite a newborn-screening diagnosis of sickle cell trait. DNA sequencing of the beta globin gene revealed that her maternal beta globin allele was normal. Her paternal allele had not only the expected sickle-trait mutation, betaGlu6Val, but also a second, charge-neutral mutation, betaLeu68Phe. Analysis of the patient's hemoglobin revealed that the double-mutant protein, which we called "hemoglobin Jamaica Plain," had severely reduced oxygen affinity. Structural modeling suggested destabilization of the oxy conformation as a molecular mechanism for sickling in a heterozygote at an ambient partial pressure of oxygen., (Copyright 2004 Massachusetts Medical Society.)

Sickle cell anemia in Iran is accompanied by a high level of HbF and mild clinical presentation. Here we report haplotypes of the beta gene cluster found in 81 randomly selected sickle cell patients, including 47 sickle cell anemia (SS), 17 sickle cell trait (AS), and 17 sickle/thalassemia (S/thal) from southwest Iran. We found all five common typical haplotypes as well as five atypical haplotypes in our patients. Except for four patients with homozygous Benin haplotype, none of the other African typical haplotypes were found in a homozygous state. Arab-Indian was found to be the most prevalent haplotype in the study population. This haplotype accounted for 51.1% as the homozygous form in SS patients, where 69.1% of chromosomes in these patients had the Arab-Indian haplotype. Bantu A2 was the second most prevalent haplotype among all patients. The mean %HbF in SS patients was 27.83 and in the homozygous Arab-Indian haplotype it was still higher (30.40%), while in AS patients the %HbF was only 1.20. The high %Ggamma chain (71.81) in the Arab-Indian homozygous haplotype was concomitant with the presence of an Xmn I site in both chromosomes. The presence of the Arab-Indian haplotype as the predominant haplotype might be suggestive of a gene flow to/from Saudi Arabia or India. More haplotype investigations of a normal population can clarify the high incidence of Bantu A2 haplotype in our population., (Copyright 2003 Wiley-Liss, Inc.)

Hb O-Tibesti, carries in the same chain the substitution of Hb O-Arab [beta121(GH4)Glu-->Lys] and that of Hb Hamilton [beta11(A8)Val-->Ile]. Hb O-Tibesti may be distinguished from Hb O-Arab by polyacrylamide gel electrophoresis in the presence of urea and Triton-X100, and by reversed phase high performance liquid chromatography. It was found in a compound heterozygous condition with Hb S [beta6(A3)Glu-->Val] in a child of Chad-Sudanese descent, suffering from a sickle cell syndrome. Compared to the classical description of the Hb S/Hb O-Arab association, the additional Hb Hamilton mutation does not seem to modify the clinical presentation.

We have analysed, at the hematological and molecular level, 51 Hb lepore heterozygotes and three compound heterozygotes for Hb Lepore and HbS (HbLep/HbS) in 26 unselected Portuguese families. The Lepore Boston variant was present in one family, in association with classical haplotype V. All of the other Lepore alleles present haplotype III in association with XmnI (+)5' of (G)gamma gene, in tight linkage disequilibrium to the major mutation found in the Portuguese population, the Lepore Baltimore variant ( delta(68Leu)-beta(84Thr)). The three compound heterozygotes are the first HbLep/HbS individuals reported in the literature, with the Lepore Baltimore mutation linked to haplotype III. In agreement with other studies, these Lepore Baltimore heterozygotes have higher HbF (1.4-14.1% of total hemoglobin) than published cases of Lepore Boston (0.8-5.4%), which is associated with XmnI(-). Among the Lepore Baltimore heterozygotes, the (AT)xTy repeat region at -540 bp of the beta globin gene in trans to the Lepore chromosome, can account for much of the variability in HbF level. The allele (AT)7T7 is associated with lower HbF, and (AT)9T5 is associated with higher HbF. As we previously reported for beta thalassemic carriers, we observe in Lepore Baltimore carriers an effector in trans, linked to the (AT)xTy sequence, acting as an HPFH (Hereditary Persistence of Fetal Hemoglobin) determinant., (Copyright 2002 Wiley-Liss, Inc.)

Sickle cell anemia is not considered to be a significant disease in Iran, although the sickle cell trait is estimated to have a high incidence in the Southern provinces. Since 1977, when the presence of a mild sickle cell anemia was reported in this country, there have been no further investigations published giving precise data on the incidence and origins of the sickle cell mutation in Iran. We report here the finding of patients with the sickle cell trait, sickle cell anemia, and sickle-beta thalassemia in Central Iran. A survey of 300 individuals from a village in Southeast Esfahan revealed an incidence of the sickle cell trait of 8.33%. "Cascade screening" enabled 96 relatives in four surrounding villages to be tested, and the at-risk couples were offered counseling as a "sickle cell control program." The hematological indices and HbF levels of the affected patients were determined. The HbF levels were unusually high, ranging from 18% to 41.4%, and SS patients with the highest levels were asymptomatic. Linkage analysis revealed the betaS gene haplotype in this population to be the Indian-Arab haplotype.

Sickle cell anemia is a monogenic hereditary disease characterized by a mutation in the beta globin gene. Five major haplotypes associated with the beta S mutation have been defined: Benin, Bantu, Senegalian, Camerounian, and Arabo-Indian. Previous studies in northern Tunisia showed that sickle cell anemia was of Benin origin in this region. Patients from the south of Tunisia, mainly from the Kebili region, were not previously concerned. In this study, we have determined the beta S haplotype and evaluated phenotypical expression of the disease in 14 patients from this latter region. The use of four restriction endonucleases having polymorphic sites in the beta globin gene showed that all patients had the Benin haplotype, confirming the Benin origin of sickle cell anemia in Tunisia. This haplotype is associated with an heterogeneous expression of fetal hemoglobin (HbF) with extremes varying from 2.4 to 16.3% and a mean expression rate of 8.16%, which is in accordance with literature data. In spite of the haplotype homogeneity in our patients, clinical heterogeneity was noted. A unique case of alpha-thalassemia could not explain this heterogeneity. In contrast, we found a certain correlation between fetal hemoglobin expression and clinical severity.

We have systematically analyzed beta-thalassemia genes using polymerase chain reaction-related techniques, dot-blot hybridization with oligonucleotide probes, allele specific-polymerase chain reaction, and sequencing of amplified DNA fragments from 41 unrelated patients, including 37 beta-thalassemia homozygotes, three with beta-thalassemia/Hb E, and one with beta-thalassemia/Hb S. Four different beta-thalassemia mutations were detected in 78 alleles. These are the IVS-I-5 (G-->C), codon 30 (AGG-->ACG) [also indicated as IVS-I (-1)], IVS-I-1 (G-->A), and codons 41/42 (-TTCT) mutations. The distribution of the beta-thalassemia mutations in the Maldives is 58 alleles (74.3%) with the IVS-I-5 (G-->C) mutation, 12 (15.4%) with the codon 30 (AGG-->ACG) mutation, seven (9%) with the IVS-I-1 (G-->A) mutation, and one with the codons 41/42 (-TTCT) mutation. The first three mutations account for 98.7% of the total number of beta-thalassemia chromosomes studied. These mutations are clustered in the region spanning 6 bp around the junction of exon 1 and the first intervening sequence of the beta-globin gene. These observations have significant implications for setting up a thalassemia prevention and control program in the Maldives. Analysis of haplotypes and frameworks of chromosomes bearing each beta-thalassemia mutation suggested that the origin and spread of these mutations were reflected by the historical record.

In order to perform genetic counselling and prenatal diagnosis of Hb-S-beta-thalassemia disease and beta-thalassemia, we have delineated the spectrum of beta-thalassemia alleles in the Guadeloupean population. A sample of 63 unrelated families was analyzed including 70 beta-thalassemia carriers, 52 Hb-S-beta-thalassemia, and 8 patients with different beta-thalassemic hemoglobinopathies. Among the eleven mutations identified, four of them [-29 (A --> G), IVS-I-5 (G --> A), IVS-II-1 (G --> A), and IVS-I-5 (G --> C)] account for 77.6% of the beta-thalassemia chromosomes present in the studied families. The seven other variants, CD 24 (T --> A), IVS-I-2 (T --> C), Poly A (T --> C), -88 (C --> T), IVS- 11-849 (A --> G), Hb E, and Hb Lepore are less frequent. As a result, Hb S-beta+-thalassemia type 1 (low Hb A values: 5-15%) together with Hb S-beta(omicron)-thalassemia phenotypes are as frequent as Hb S-beta+-thalassemia type 2 (high Hb A values: 20-30%) in the Guadeloupean population. Patients with Hb S-beta+-thalassemia type 2 have milder hematological manifestations of the disease compared to patients with Hb S-beta(omicron)-thalassemia and Hb S-beta+-thalassemia type 1. This first report on the type and nature of beta-thalassemia mutations in Guadeloupe shows that prenatal diagnosis of Hb S-beta-thalassemia and beta-thalassemia should be feasible by direct detection of point mutation in most cases.

Considering that genetic variation linked to the beta S mutation may influence the clinical manifestations of sickle cell disease, we have analyzed the beta globin cluster haplotypes in 47 patients with this condition (33 SS homozygotes, one S/beta thal (0), and 13 SC) living in London (30 West Indian, 17 West African). Of the 80 chromosomes tested, 82.5% had the Benin haplotype and of the 13 C chromosomes tested, 85% had the Bantu-A4 haplotype. A minority of patients had Bantu or Senegal haplotypes, and in 5 patients we found new haplotypes called E, H and O which may have arisen through mutation or recombination. Because of the predominance of a single haplotype (Benin) nearly all our homozygous S patients were either homozygous or heterozygous for this haplotype. We concluded that the beta globin haplotype is unlikely to be an important determinant of the clinical severity in this patient population.

An autosomally transmitted hypochromic microcytic mild anaemia with elevated haemoglobin (Hb) A2 and globin chain imbalance has been observed in a three-generation family of Portuguese origin. Extensive DNA analysis of the beta-globin gene cluster, including the complete sequencing of the beta-globin gene and flanking regions, failed to reveal any genetic alteration. The co-segregation of sickle-cell trait in this family enabled us to postulate a defective erythroid trans-acting factor was playing a role in the down-regulation of both beta A- and beta S-globin genes. Among the transcription factors that could possibly have caused the reported phenotype, NF-E2 is unlikely to be implicated, whereas Nrf1 and Nrf2 cannot be ruled out. Thus, this family carries a novel beta-thalassaemia autosomal determinant unlinked to the beta-globin gene. This observation reinforces the notion of the haemoglobinopathies as single gene disorders under polygenic regulation.

We have studied the beta-thalassemia mutations in 91 chromosomes of 43 patients with beta-thalassemia major and five with Hb S-beta-thalassemia, aged 6 months to 24 years. Many are blood transfusion-dependent and are being treated at the major hospital, the Princess Basma Hospital, in Irbid, Jordan. As many as 13 different mutations have been identified; three Mediterranean mutations [IVS-I-110 (G-->A), IVS-II-I (G-->A), and IVS-II-745 (C-->G)] were present in 54% of the chromosomes tested, while six other Mediterranean alleles were found in 24% of the chromosomes, for a total of 78% of Mediterranean origin. Sixteen chromosomes carried mutations which were observed in Arabian, Southeast Asian/Indian, and Iranian/Egyptian or Black populations; four beta-thalassemia mutations remained unidentified.

In a survey of the chromosomal backgrounds associated with the sickle cell gene in Portuguese-speaking populations from Europe and Africa, a discordance between the classical haplotype and the predicted allele at the RsaI polymorphism 5' to the beta globin gene was observed in four patients. Extensive typing of the corresponding beta s chromosomes at simple polymorphic repeat motifs revealed a novel "extended" haplotype that appeared to be a mosaic of (1) a Bantu-type DNase I hypersensitive site 2 within the beta globin gene cluster locus control region, (2) a Benin 5' subhaplotype, and (3) a Bantu 3' subhaplotype. We propose two alternative schedules for the generation of yet another chromosomal background of the sickle cell gene.

When first tested for abnormal hemoglobins, a 2-year-old boy, appeared to have Hb F, Hb S and Hb A2. Confirmatory testing revealed a beta chain variant inherited from his father and beta S from his mother. Analysis of tryptic peptides in conjunction with automated DNA sequence analysis showed that the variant hemoglobin was Hb Shelby [beta 131(H9)Gln-->Lys (CAG-->AAG)]. Heat and mechanical stabilities of various liganded Hb Shelby tetramers were compared to those of Hb A and Hb S. Oxy-Hb Shelby precipitated more readily than oxy-Hb A, but was much more stable than oxy-Hb S during mechanical agitation. In contrast, oxy-Hb Shelby was much less stable than oxy-Hb A and oxy-Hb S following heat treatment. Met-Hb Shelby was most unstable compared to other liganded forms of Hb Shelby, while deoxy- and carbonmonoxy-forms of Hb Shelby showed similar heat-induced precipitation rates. These data indicate that heat instability of Hb Shelby is accompanied by heme oxidation, and that denaturation by mechanical agitation occurs in the absence of heme oxidation. Hb Shelby, like Hb A, can form hybrids with Hb S which participate in polymer formation in vitro. However, Hb S/Hb Shelby hybrids copolymerized with Hb S less than A/S hybrids. Since the patient's MCHC value is normal, this finding coupled with the elevated Hb A2 and Hb F levels, both of which are known to inhibit polymerization of Hb S, may contribute to the patient's mild clinical presentation.

Human preimplantation embryos at various stages of development have been analysed using the polymerase chain reaction to amplify a 680 base pair fragment of the beta-globin gene. Successful amplification was achieved more frequently with DNA from intact embryos containing between one and 11 cells, single cumulus cells, oocytes which had failed to fertilize and polar bodies than from single blastomeres disaggregated from intact embryos and treated in an identical manner. The distribution of nuclei demonstrated using the nuclear chromophore diamino-phenyl-indole showed considerable inter-blastomere variation; however, no clear correlation between staining pattern and successful amplification was observed. The reason for the unreliable amplification of DNA from single blastomeres is unclear but this finding has important implications for preimplantation diagnosis of genetic disease.

We have determined the beta S haplotypes in 709 patients with sickle cell anemia, 30 with SC disease, 91 with S-beta-thalassemia, and in 322 Hb S heterozygotes from different countries. The methodology concerned the detection of mutations in the promoter sequences of the G gamma- and A gamma-globin genes through dot blot analysis of amplified DNA with 32P-labeled probes, and an analysis of isolated Hb F by reversed phase high performance liquid chromatography to detect the presence of the A gamma T chain [A gamma 75(E19)Ile----Thr] that is characteristic for haplotype 17 (Cameroon). The results support previously published data obtained with conventional methodology that indicates that the beta S gene arose separately in different locations. The present methodology has the advantage of being relatively inexpensive and fast, allowing the collection of a vast body of data in a short period of time. It also offers the opportunity of identifying unusual beta S haplotypes that may be associated with a milder expression of the disease. The numerous blood samples obtained from many SS patients living in different countries made it possible to compare their hematological data. Such information is included (as average values) for 395 SS patients with haplotype 19/19, for 2 with haplotype 17/17, for 50 with haplotype 20/20, for 2 with haplotype 3/3, and for 37 with haplotype 31/31. Some information on haplotype characteristics of normal beta A chromosomes is also presented.

Hb Bab-Saadoun which has a Leu----Pro substitution at position 48 of the beta chain was detected in a young Arabian boy living in Tunisia. His parents did not have the variant which suggests that it occurred as a spontaneous mutation. The substitution is located in the interhelical CD segment; leucine at beta 48 is an invariable amino acid that may be important as part of a spacer sequence between the two helices and its replacement by proline may affect the stability of the hemoglobin molecule. Hb Bab-Saadoun is unstable in heat and isopropanol stability tests and its chain was best isolated by parachloromercuribenzoate precipitation. It appears unlikely that the presence of Hb Bab-Saadoun results in a hemolytic anemia.

The silent Hb Muscat with a Leu----Val replacement at position beta 32 was discovered by reversed phase high performance liquid chromatography in two members of an Arabian family from Oman; in one person Hb Muscat occurred with Hb S and in the other with Hb A. Hb Muscat is slightly unstable but its presence has no apparent adverse effect on the health of its carriers. Additional hemoglobin abnormalities observed in this family were a common alpha-thalassemia-2 (-3.7 kb) and Hb S. The beta S haplotypes in the heterozygous carriers and the two sickle cell anemia patients were #19 (Benin) and #20 (Bantu); the latter likely originated from an East African population.

We have investigated problems encountered when using the polymerase chain reaction (PCR) to detect recombinants in gene targeting experiments in which homologous recombination occurs between incoming DNA and an endogenous target sequence. The targeting system studied was designed to correct a human sickle-cell beta-globin-encoding gene (HBBS) on human chromosome 11 by replacing the defective gene with incoming DNA carrying normal HBB sequences. Two sets of experiments were executed which led to the isolation of a clone of cells having the sickle-cell gene corrected. We found that a positive control system was essential to allow a real targeting event to be distinguished from various types of false positives that arise during the diagnostic PCR.

Hb Iowa with a Gly----Ala mutation at position beta 119(GH2) was observed in a Black infant and her mother. The baby was also heterozygous for Hb S; Hb Iowa was confused with Hb F at birth because its electrophoretic mobility was similar to that of Hb F1. The beta chain of Hb Iowa could be readily separated from the beta A, alpha, and gamma chains by polyacrylamide gel electrophoresis and by reversed phase high performance liquid chromatography. Structural characterization was through amino acid analyses of peptides isolated from a tryptic digest of the aminoethylated beta-Iowa chain. The Gly----Ala replacement in Hb Iowa does not affect its stability and oxygen carrying properties; hematological data for mother and child were within normal ranges.

A novel deletion of at least 26 kilobase of DNA, including both alpha-globin genes, the psi alpha- and psi zeta-globin genes, but sparing the functional zeta-gene was found in a 10-year-old black boy with HbH disease and sickle cell trait. This particular deletion has not previously been described in blacks. Its existence makes it likely that the absence of Hb Barts hydrops fetalis in blacks is due to the rarity of the chromosome lacking two alpha-globin genes rather than a result of early embryonic death due to the failure to synthesize embryonic hemoglobins because of deletion of functional zeta-globin genes.

Recent advances in molecular genetics have permitted detailed study of the human alpha-globin genes and the causes of alpha-thalassemia. In this review, we examine the causes of alpha-thalassemia in the black population and the consequences of the interactions between alpha-thalassemia and structural hemoglobin variants.

We have examined the genetic polymorphism previously reported to be associated with the sickle-cell (beta s) gene. The polymorphism involves an alteration of the DNA sequence 3' to the beta-globin gene as detected with the restriction endonuclease, Hpa I. In normal individuals, the beta-globin gene is contained within a DNA fragment of 7.6 kilobases (kb), whereas 87% of individuals with sickle-cell anemia have been reported to have the beta s-gene associated with a 13.0-kb Hpa I fragment. We have studied this polymorphism in 31 New York Black individuals homozygous for sickle-cell anemia to ascertain its genetic and biochemical significance and to evaluate its potential use in the prenatal diagnosis of sickle-cell disease. Our results show only a 58% association of the beta s-gene and the 13.0-kb Hpa I fragment, as well as the presence of additional variants involving the Hpa I site. In addition, the 13.0-kb fragment is also found associated with the beta c- and beta A-genes. Thus, the Hpa I polymorphism probably represents a change in DNA not specifically associated with the beta s-gene, and appears to antedate the beta s-and beta c-mutations.

Point mutations in G gamma and A gamma globin gene promoters are associated with increased production of G gamma and A gamma globin, respectively. To determine whether an upstream promoter mutation could account for elevated A gamma in a Black adolescent with A gamma-beta+-HPFH and sickle cell trait, we cloned the 13 kb BglII fragment containing both gamma genes into phage lambda vector EMBL3. For one clone, the A gamma upstream promoter showed no hybridization to a 19 bp oligonucleotide whose sequence centered at -117. A gamma promoter sequence data for this mutant clone revealed a 13 bp deletion which eliminated the A gamma distal CCAAT box. Amplified A gamma genomic DNA of this and a similar case showed hybridization to both deletion-mutant and normal oligonucleotide probes. We propose that this 13 bp deletion removes part of the binding site for a repressor protein which is abundant in adult erythroid cells.

We describe here the screening of a small group of apparently healthy individuals belonging to the tribal communities of Koya Dora and Konda Reddi. A remarkably high incidence of deletion and nondeletion alpha + thalassemia mutants has been found with allele frequencies and distributions characteristic to each tribe. We have confirmed the strict relationship between Hb S levels and the number of alpha globin genes in double heterozygotes for the S gene and alpha thalassemia. In this population sample we did not find either heterozygous carriers of alpha 0 thalassemia (deletion of both alpha genes in "cis") or individuals showing hemolytic anemia due to inactivation of three alpha-globin genes (Hb H disease). Selection by malaria is most probably responsible for the prevalence of the various alpha + thalassemia haplotypes among the two tribal populations of Andhra Pradesh.

Restriction site polymorphisms of the beta globin gene cluster of 244 Jamaican beta S chromosomes have been studied. Various patterns of restriction site polymorphisms (haplotypes) both 5' and 3' to the beta gene have been found. These two groups of haplotypes were found to be non-randomized with respect to each other. This is in contrast to normal beta A chromosomes where the 5' and 3' haplotypes are randomized. These findings together with the large number (18) of different beta S haplotypes found indicate that the beta S mutation probably has multiple origins.