Novel hemoglobin α chain elongation resulting from a 15-residue insertion and tandem duplication of the F helix

Hb Ashburton [β12(A9)Thr → Pro; HBB: c.37A > C], a novel, mildly unstable variant and the first substitution identified at codon 12

We report the identification of a novel, slightly unstable hemoglobin (Hb) variant [β12(A9)Thr → Pro; HBB: c.37A > C] that came to our attention during Hb A1C ion exchange chromatography where it migrated as a trailing shoulder on the Hb A0 peak. On electrospray ionization mass spectrometry (ESI MS), this electrophoretically silent variant was detected as an unresolved β component with a 2 Da decrease in average β chain mass. Reversed phase high performance liquid chromatography (HPLC) confirmed the presence of a more hydrophilic β chain with a mass 4 Da less than normal β(A) and showed it represented 40.0% of the total β-globin. Tryptic mapping revealed the [M + 1H] ion of peptide βT-2 had shifted from 932.5 to 928.5 m/z, suggesting a point mutation of Thr → Pro at position β12(A9). This substitution was confirmed by fragmentation analysis of the [M + 2H] ion (464.8 m/z) of the new βT-2 peptide and it represents a novel mutation which we have named Hb Ashburton.

Novel α2 gene deletion (c.349_359 del GAGTTCACCCC) identified in association with the -α3.7 deletion

We report a novel α2 gene mutation identified in compound heterozygosity with the common -α(3.7) deletion. The mutation (c.349_359 del GAGTTCACCCC), causes a frameshift after codon α115 with the predicted extension of the αchain from 141 to 166 residues. The new polypeptide would be expected to have a mass of 17,463 Da, but no such product was detected in hemolysates, confirming the mutation's thalassemic phenotype. Mechanistically, the deletion is probably caused by replication slippage during DNA synthesis as the sequence is bracketed by a CC repeat. The lack of protein expression is probably caused by loss of critical binding sites to the chaperone, α Hb stabilizing protein (AHSP).

Multiple linked β and α globin genes in Atlantic cod: A PCR based strategy of genomic exploration

Allozyme variation in Atlantic cod hemoglobins shows various signs of natural selection. We report a genomic exploration of globin genes in this non-model organism. Applying a PCR based strategy with a strict criterion of phylogenetically informative sites we estimate the number of linked β and α globin genes. We estimate PCR error rate by PCR of cloned DNA and recloning and by analysis of singleton variable sites among clones. Based on the error rate we exclude variable sites so that the remaining variation meets successively stricter criteria of doubleton and triplet variable site. Applying these criteria we find ten clusters of linked β/α globin genes in the genome of Atlantic cod. Six variable amino acid changes in both genes were found in linkage disequilibrium with silent nucleotide substitutions. A phylogenetic tree, based on our strictly phylogenetically informative sites among 57 clones from 19 individuals, is split into two major branches by an amino acid change in a β gene. This change is supported by extensive linkage disequilibrium between the amino acid change and numerous other phylogenetically informative silent nucleotide sites. The different gene sets in the genome may represent different loci encoding different globins and/or allelic variation at some loci.