Comparison of the protein and DNA approaches for the characterization of a β-globin chain variant, hemoglobin Cocody [β₂₁ (B3) Asp- → Asn], in a Caucasian patient

Summary

Over the past few years, the methodologies used for the identification of hemoglobin A variants have been greatly improved. Both the protein- and DNA-based strategies have their own advantages and limitations. In this report we illustrate the use of both assays for the characterization of a hemoglobin Cocody variant in a woman of Spanish descent. After evaluating the mobility value matrix of the abnormal hemoglobin, the amino acid transition was determined by HPLC and microsequencing of the protein. Theβ ₂₁ Asp was shown to be substituted by an Asn. At the DNA level, the only nucleotide replacement responsible for this amino acid substitution is GAT- → AAT at codon 21. The analysis of theβ-globin gene by denaturing gradient gel electrophoresis (DGGE) method showed that the mutation was situated in a fragment including exon 1. The hemoglobin variant was then identified to be hemoglobin Cocody by DNA sequencing of this fragment.