This proposal involves a detailed molecular analysis to include cloning, sequencing and fuctional studies in an effort to define events critical to globin gene expression in humans. Four patients expressing the following novel globin phenotypes have been chosen for study: The first patient has the """"""""silent carrier"""""""" form of beta thalassemia, in which there is no mutation within the beta globin gene or its immediate 5'- or 3'-flanking region. Specific objectives include extensive DNA haplotype analysis of this family and relatives to define linkage or non-linkage of the phenotype to alpha- or beta-like globin gene clusters. We will then attempt to define the molecular basis for this lesion. The second patient has a non-deletional form of hereditary persistence of fetal hemoglobin (HPFH) of the G gamma type, and her haplotype (and presumably mutation) is different from other patients expressing the same phenotype. Specific objectives include cloning, sequencing and functional studies of her fetal globin genes in an effort to identify the HPFH determinant. The third patient expresses an unusually high level of an alpha-chain variant which is due to the presence of 2 variant loci in cis. This rare event suggests a segmental gene-conversion event in one of the variant loci giving rise to 2 variants in cis. Specific objectives include cloning and directed sequencing of the liked alpha 2-alpha 1 globin gene region in order to characterize the 2 alpha I mutations in cis, define the 5' and 3' boundaries of the proposed segmental gene-conversion event, and gain insight into the mechanism leading to the concerted evolution of this variant alpha gene. The fourth patient has a major deletion encompassing the entire beta-like globin gene cluster, and presents with microcytosis, unbalanced beta/alpha globin synthesis ratios with normal Ho A2 and low Ho F levels. Specific objectives include defining the 5' and 3' endpoints of this deletion by mapping, clonging and sequencing analysis in order to identify regions that may play a role in the generaion of these large deletional events.
