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.
BACKGROUND
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.


CONCLUSIONS
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.
Department of Clinical Pathology, Faculty of Medicine, Assiut University, Assiut, Egypt. mohamedkhalil1967@yahoo.com
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Khalil
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Timbs
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Henderson
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Schuh
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Hussein
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D001483:Base Sequence; D003062:Codon; D015252:Deoxyribonucleases, Type II Site-Specific; D014644:Genetic Variation / Q000235:genetics*; D006455:Hemoglobins, Abnormal / Q000235:genetics*; D006801:Humans; D009154:Mutation; D010641:Phenotype; D017422:Sequence Analysis, DNA; D055542:alpha-Globins / Q000235:genetics*
D003062:Codon; D006455:Hemoglobins, Abnormal; D055542:alpha-Globins; C031679:hemoglobin G Philadelphia; C045874:endodeoxyribonuclease StyI; D015252:Deoxyribonucleases, Type II Site-Specific