Unbiased analysis of the frequency of β-thalassemia point mutations in a population of African-American newborns

Objective. - To determine frequency of specific β-thalassemia alleles in the African-American population prospectively, using newborn screening specimens, and to evaluate the need for including these alleles in screening follow-up programs. Design. - Allele-specific oligonucleotide tests were developed and used to analyze African-American newborn screening specimens for β-thalassemia point mutations to determine their frequency. Direct sequencing of amplified DNA from the dried blood specimens was used to confirm the presence of point mutations. Population. - African-American newborns in Texas. Results. - Allele-specific oligonucleotides identified five newborn specimens carrying β-thalassemia point mutations among 471 specimens from African-American neonates. Direct sequencing of DNA from the dried blood specimens confirmed that these individuals had a normal and a mutant allele. Five newborn screening specimens in which the results of screening and DNA tests were in disagreement (four with FS by screening and AS by DNA, and one with FC by screening and AC by DNA) were analyzed for these β-thalassemia point mutations and in each case were found to be S/β- thalassemia or C/β-thalassemia compound heterozygotes, respectively. Conclusions. - Allele-specific oligonucleotides accurately identified newborn specimens carrying β-thalassemia point mutations. Direct sequencing from dried blood specimens confirmed these results. The A(-29)G allele frequency was 0.003, and the C(-88)T frequency was 0.002. These alleles also were observed among positive samples in a neonatal hemoglobinopathy screening program. Therefore, any newborn screening program with a molecular genetic follow-up component must include testing for these β-thalassemia alleles to assure timely and appropriate management for affected infants.