F5 and alpha thalassemia spectrum: Several studies have additionally attempted to investigate associations between elevated CBFV and distinct SCD genotypes, including fetal hemoglobin levels; coinheritance of alpha thalassemia and chronic anemia; leukocyte count; and polymorphisms of methylenetetrahydrofolate reductase (MTHFR) 677C>T (rs1801133), Factor V Leiden (FV) 1691G>A (rs6025), vascular cell adhesion molecule (VCAM) 833T>C (rs1041163), and VCAM 1238G>C, although much of this data remains controversial [11–16].