Rs34139813

rs34139813 is a SNP for the Hemoglobin beta HBB gene, which is responsible for the protein beta-globin, a component of hemoglobin inside red blood cells. Usually, hemoglobin contains two subunits of beta-globin and two subunits of alpha-globin. Variations in the HBB gene can be unnoticeable, while others may affect a persons health, resulting in various hemoglobin disorders such as beta thalassemia, sickle cell disease, and hemoglobin C.

In 1979, a new mutant hemoglobin with high oxygen affinity was discovered in a Greek family and called Hemoglobin Crete, but the patients were heterozygous only for Hb Crete and often also had mutations for beta-thalassemia which affects the same gene. This mutant Hb was identified as resulting from a Ala129Pro missense mutation in HBB and identified by sequencing as rs34139813 (G->C). In 2005, a homozygous Hb Crete individual without any additional beta-thalassemia mutations was identified.

The Hb Crete phenotype (both homozygous and heterozygous) is associated with erythrocytosis and microcytosis. Hb Crete patients may have functional anemia, with a thalassemic-like phenotype as a result of a deficit of beta-globin chains. Patients may also have elevated cardiac output ultimately leading to cardiac insufficiency.