We have encountered a paternity case where exclusion of the putative father was only observed in the ABO blood group (mother, B; child, A1; putative father, O), among the many polymorphic markers tested, including DNA fingerprints and microsatellite markers. Cloning a part of the ABO gene, PCR-amplified from the trio's genomes, followed by sequencing the cloned fragments, showed that one allele of the child had a hybrid nature, comprising exon 6 of the B allele and exon 7 of the O1 allele. Based on the evidence that exon 7 is crucial for the sugar-nucleotide specificity of A1 and B transferases and that the O1 allele is only specified by the 261G deletion in exon 6 of the consensus sequence of the A1 allele, we concluded that the hybrid allele encodes a transferase with A1 specificity, resulting, presumably, from de novo recombination between the B and O1 alleles of the mother during meiosis. Screening of random populations demonstrated the occurrence of four other hybrid alleles. Sequencing of intron VI from the five hybrid alleles showed that the junctions of the hybrid alleles were located within intron VI, the intron VI-exon 7 boundaries, or exon 7. Recombinational events seem to be partly involved in the genesis of sequence diversities of the ABO gene.

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SummaryA key amino acid substitution specific for allotypic Gm b markers, b0, b3, b5, were determined through sequence analyses of the pFc' fragments of IgG1 (Su) 2361] that two residues, the serine and isoleucine specific for IgG3 subclass at position 422, cause the structural change responsible for b markers. The two residues are close to each other in the CH3 domain. The allocations of the epitopes are estimated to be on two bends (residue no. [382][383][384][385][386][387][388][389][390][391][392][411][412][413][414][415][416][417][418][419][420][421][422][423][424] between the beta-strands, whose amino acid residues are present in wide contact area [Novotny et al.

SUMMARY We typed coded sera from 135 healthy controls, seventy‐six patients with autoimmne goitrous and seventy‐three with atrophic thyroiditis for IgG heavy chain markers (Gm). All subjects were Caucasian from Newfoundland. An increase in the Gm phenotype ag was found in the 149 patients with thyroiditis compared to controls (X12= 5.82, P <0.01); significance was, however, not maintained after correction for the number of variables tested. The difference in ag phenotype was more pronounced among the seventy‐three patients with atrophic thyroiditis (X12= 8.80 corrected P < 0.05). Because the haplotype ag was not significantly increased in this group, we conclude that homozygotes for Gm ag are at an increased risk of developing atrophic thyroiditis.