Haemoglobin (Hb) G‐Philadelphia, Hb Stanleyville‐II, Hb G‐Norfolk, Hb Matsue‐Oki and Hb Mizushi can form a panel of α‐chain variants that overlap in their phenotype: the novel use of StyI to screen for Hb G‐Philadelphia

SummaryIntroduction:  Haemoglobin (Hb) G‐Philadelphia mutation is a common alpha‐globin chain variant [α68(E17)Asn > Lys]. Combined high performance liquid chromatography (HPLC) and isoelectric focusing (IEF) can be used in a presumptive diagnosis of Hb G‐Philadelphia, but there are other α‐chain variants with a similar phenotype that cannot be excluded. Our aim was to develop a novel StyI restriction enzyme assay to diagnose the common Hb G‐Philadelphia mutation and to identify any other variants with a similar phenotype by DNA sequencing.Methods:  Thirty‐one cases given a presumptive diagnosis as Hb G‐Philadelphia by HPLC and IEF were subjected to DNA analysis by restriction enzyme digestion using StyI. Negative cases were then subjected to DNA sequencing.Results:  Twenty‐two cases (78.6%) of 28 cases amplified were tested positive for Hb G‐Philadelphia by StyI restriction digestion. Sequencing of the six negative cases revealed two cases of Hb G‐Philadelphia with C→A mutation in codon 68 in α2 globin gene, plus one case each of Hb G‐Norfolk Hb Stanleyville‐II, Hb Matsue‐Oki and Hb Mizushi.Conclusion:  A novel StyI restriction enzyme can be used to confirm the commonest type of Hb G‐Philadelphia. DNA sequencing identified four other α‐chain variants with a similar HPLC and IEF phenotype.