[Molecular analysis of an African family with sickle cell disease and alpha-thalassemia-2].

An etiological examination was performed on the DNA of a 13-year-old Zairean girl, who had some abnormalities in hematological and red cell morphological examinations and was homozygote for an abnormal Hb like HbS. DNA was amplified by the PCR method to obtain 1.7 kb size DNA containing the 5' region of the beta globin gene. The amplified DNA was digested with Eco 81 I and electrophoresis of the digest revealed the absence of its active site, which is on codons beta 5-7 (CCTGAGGAG) of the normal DNA. Sequencing of the cloned DNA by the dideoxy method confirmed that the codon beta 6 (GAG, Glu) mutated to a new codon GTG (Val) which is the beta S globin gene producing abnormal HbS. The haplotype of the chromosome having beta S gene was --+---++, which is the most common type in Zaire area. On the other hand, when the genomic DNA was digested with Bgl II or Bam HI and hybridized to an alpha probe, a fragment (16 kb/Bgl II or 10.5 kb/Bam HI) in addition to the normal ones (12.5 and 7.5 kb/Bgl II or 14 kb/Bam HI) was observed. This resulted from the deletion of 3.7 kb from the alpha gene arrangement, which led to alpha-thalassemia-2 (genotype: alpha 3.7-/alpha alpha). A family study demonstrated that her parents were heterozygote for HbS and her father had alpha-thalassemia-2.