Abstract
We recently described four delta-globin gene mutations in Greek Cypriots studied by polymerase chain reaction (PCR) amplification and automated fluorescence-based DNA sequence analysis (Blood 78:3298, 1991). Selective restriction enzyme digestion of PCR products facilitated direct mutation detection. Twenty-eight additional samples from unrelated Cypriots with Hb A2 levels ranging from 0.6% to 3.6% were studied by PCR and showed the following: twelve had the delta 27 (ala–>ser) mutation, one was heterozygous for the delta IVS-2 AG–>GG change, and none had either the delta 116 (arg–>cys) or delta 141 (leu–>pro) mutations. The remaining samples were divided into two groups: 11 with borderline normal Hb A2 values that were not pursued; and four with abnormal Hb A2 values. The delta-globin genes from these four samples were sequenced and the same four changes identified in each: a C–>T at -199, a C–>T at codon 4 (thr–>ile), a silent C–>T at codon 97, and an AT deletion at position 722 in IVS-2. The codon 4 change abolishes a Ple I site whereas the codon 97 creates an Nla III site, thus facilitating rapid identification. All four changes are in cis position, suggesting that the -199 C–>T, the C–>T at codon 97, and the AT deletion in IVS-2 are neutral polymorphisms present on the codon 4 (thr–>ile) chromosome. DNA haplotype analysis suggests all five delta-globin gene mutant alleles arose independently on different chromosomal backgrounds.
We recently described four delta-globin gene mutations in Greek Cypriots studied by polymerase chain reaction (PCR) amplification and automated fluorescence-based DNA sequence analysis (Blood 78:3298, 1991). Selective restriction enzyme digestion of PCR products facilitated direct mutation detection. Twenty-eight additional samples from unrelated Cypriots with Hb A2 levels ranging from 0.6% to 3.6% were studied by PCR and showed the following: twelve had the delta 27 (ala–>ser) mutation, one was heterozygous for the delta IVS-2 AG–>GG change, and none had either the delta 116 (arg–>cys) or delta 141 (leu–>pro) mutations. The remaining samples were divided into two groups: 11 with borderline normal Hb A2 values that were not pursued; and four with abnormal Hb A2 values. The delta-globin genes from these four samples were sequenced and the same four changes identified in each: a C–>T at -199, a C–>T at codon 4 (thr–>ile), a silent C–>T at codon 97, and an AT deletion at position 722 in IVS-2. The codon 4 change abolishes a Ple I site whereas the codon 97 creates an Nla III site, thus facilitating rapid identification. All four changes are in cis position, suggesting that the -199 C–>T, the C–>T at codon 97, and the AT deletion in IVS-2 are neutral polymorphisms present on the codon 4 (thr–>ile) chromosome. DNA haplotype analysis suggests all five delta-globin gene mutant alleles arose independently on different chromosomal backgrounds.