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Restriction endonuclease mapping of chromosomal DNA has been used to determine whether the alpha-globin gene deletion or non-deletion form of alpha-thalassemia is the underlying molecular defect in individuals of two unrelated German families with alpha-thalassemia syndromes. The obtained DNA pattern in all cases indicated loss of alpha-globin genes resulting in -alpha/alpha alpha, --/alpha alpha, and --/-alpha genotypes in alpha-thalassemia-2, alpha-thalassemia-1, and Hb H individuals respectively. The chromosomes showing loss of one alpha-globin gene in alpha-thalassemia-2 and Hb H disease were characterized by the so-called rightward deletion form exhibiting loss of a 3.7 kb DNA fragment in the alpha-gene cluster.

Details are given of a study of blood samples from 24 patients with Hb H disease from different Mediterranean countries and from the Far East. Four different types of alpha-thal-1 (--) were observed, namely -(alpha) (approximately 20.5-kb deletion); --MED-I (approximately 17.5-kb deletion); --MED-II (greater than 26.5-kb deletion); and --SEA (approximately 18-kb deletion, in Orientals only). The alpha-thal-2 was mainly of the deletion type (16 with the 3.7-kb deletion; 1 with the 4.2-kb deletion), while 4 of the 7 patients with a nondeletional type had the five-nucleotide deletion at the donor splice site of the first intron of the alpha 2 gene. All patients had a mild-to-moderate hemolytic anemia; no significant differences in hematology were observed between the groups. Hb A2 was decreased to about one-third of the normal level. The Hb H formation varied considerably and its quantitation was not always satisfactory. Patients with Hb H disease due to any alpha-thal-1 combined with a nondeletional alpha-thal-2 had the highest Hb H levels and a more marked anemia. The zeta chain production was small and absent in patients with the MED-II type of alpha-thal-1 because this deletion included the zeta and psi zeta genes. The highest zeta chain levels were present in the four patients with the SEA type of alpha-thal-1. The gamma chain production was increased, particularly in patients with a mutation of C----T at position -158 to the G gamma globin gene. This gamma chain was primarily present as Hb Bart's (or gamma 4) and only about 15% was recovered as Hb F or alpha 2 gamma 2. The evaluation of the rate of gamma chains produced in these patients was greatly facilitated by data from one patient who had Hb H disease and a heterozygosity for the A gamma-beta+-HPFH. The low levels of Hb A2 and of Hb F (relative to Hb Bart's) can be explained by a decreased affinity of alpha chains for delta and gamma chains as compared with beta chains in conditions of severe alpha chain deficiency.

We have determined the molecular characteristics of alpha-thalassemia in 12 HbH subjects from Taiwan by restriction endonuclease mapping with alpha- and zeta-specific probes. We have found four types of defects in the alpha-thalassemia-2 genetic determinant: -alpha 3.7 type I; -alpha 4.2; alpha CS alpha; and alpha alpha T. All HbH subjects carried the --SEA genotype in the alpha-thalassemia-1 determinant. At least two different subtypes of --SEA genotype were observed in this study.

Molecular characterization of the alpha-thalassemia mutations present in nine HbH subjects from Cuba was achieved by digestion with Bam HI, Bgl II, and Apa I and hybridization with alpha- and zeta-specific probes. The results show that the molecular basis of the genetic defect is quite homogeneous, all the subjects carrying the - alpha 3.7 type I/--SEA genotype. Variations are observed in the size of the zeta polymorphic fragments.

DNA mapping was performed in seven unrelated Hb H patients and nine carriers for alpha-thalassemia trait originating from Algeria. This study has allowed us to identify four alpha-thalassemia haplotypes: the (-alpha 3.7) haplotype, which is the most frequent (18 of 23 alpha-thalassemic chromosomes), the (-(alpha)20.5) haplotype, a (--) haplotype, and an (alpha alpha)T haplotype. Our results also show that the (-alpha 3.7) haplotypes encountered in the Algerian population are heterogeneous and differ by the site of the unequal crossover responsible for the 3.7-kb deletion and the size of the interzeta fragment. In addition, during this survey we observed that normal chromosomes bearing a polymorphic BglII site are associated with different interzeta fragments.

A close association between specific restriction fragment polymorphism patterns and specific mutations in Mediterranean people with thalassemia has been demonstrated by Kazazian et al. (1984). This finding is useful to characterize the number and types of mutations in each ethnic group for setting up prenatal diagnosis in the first trimester of pregnancy by the oligonucleotide technique. For this reason we studied 99 beta thal and 46 beta A chromosomes in the Sicilian population. We found seven different cleavage patterns, not considering two new haplotypes so far uncharacterized. Many of the patients (68.3%) were genetic compounds for different haplotypes while only 31.7% were haplotype homozygotes. They may still be thalassemia compound heterozygotes. These findings confirm the molecular basis of the heterogeneity of beta thalassemia in Sicily.

An Algerian family with a high degree of consanguinity and including two homozygotes for Hb-G Philadelphia is presented. Whether homozygotes or heterozygotes, all subjects displayed microcytosis (with various degrees of poikilocytosis) and a moderately depressed alpha-globin chain synthesis. Hb H and Heinz bodies were absent. DNA mapping revealed the presence of a 3.7 kb deletion resulting from the rightward type of recombination event between alpha 2 and alpha 1 genes on both the alpha A/ and the alpha G/ chromosomes. Such data indicate that the -alpha A/ and -alpha G/ haplotypes are involved and suggest that the -alpha G/ haplotype, which is very rare in Algeria, has an African Black origin. In subjects with genotype (-alpha A/-alpha G) or (-alpha G/-alpha G), the output of the remaining alpha genes is sufficiently high to avoid the appearance of Hb H. This situation contrasts with that reported in an Algerian patient, who had a (-alpha A/-alpha A) genotype but who was producing Hb H (Whitelaw et al. 1980). The data collected from this family suggest that the -alpha A/ haplotypes are heterogeneous in Algerians.