Abnormal γ-Globin Gene Arrangements in Sardinians

Abstract

An extended survey of 8,103 Sardinian newborns has been conducted for the study of abnormal γ-globin gene arrangements. Fetal hemoglobin analysis and globin gene mapping have identified five different arrangements in 24 babies: five (21%) were carriers of the -GA_γ- hybrid (thalassemic) gene, directing the synthesis of the A_γ chain and resulting in low 641%) G_γ chain and decreased Hb F levels; two (8%) carried the -A_γ-A_γ-T_- duplication, characterized by even lower (37%) G_γ levels; five (21%) carried the -G_γ-AG_γ- A_γ- triplication; one (4%) carried the -G_γ-G_γ-A_γ- triplication, and 11 (46%) the -G_γ-G_γ- duplication, all resulting in high G_γ levels (85, 83, and 88%, respectively). Thirty-six additional babies could be phenotypically classified as carriers of the same mutations. Haplotyping and γ-chain composition showed that the crossover event generating the -GA_γ- hybrid gene and the corresponding -G_γ-AG_γ-A_γ- triplication has occurred on at least three different chromosomes. The -G_γ-G_γ- duplication was associated with the chromosome having haplotype I, and the -A_γ-A_γ-T_- with the chromosome of haplotype II. As many as 2,260 babies (28%) were heterozygous, and 254 (3%) homozygous for the A_γT mutation. The incidence and relative distribution of these anomalies in Sardinia are different when compared with those of other ethnic groups.