Familial erythrocytosis-7 (ECYT7) is characterized by an increased oxygen affinity of hemoglobin (Hb), which results in decreased delivery of oxygen into the peripheral tissues and compensatory polycythemia. Patients are generally asymptomatic, as compensatory polycythemia assures normal oxygen tissue delivery. Patients have normal red cell morphology (summary by Kralovics and Prchal, 2000). Wajcman and Galacteros (2005) noted that although high oxygen affinity hemoglobins are usually well tolerated in young patients, they can lead to thrombotic complications in older patients or when they are associated with another cause that increases thrombotic risk. Wajcman and Galacteros (2005) also noted that the effect of increased oxygen affinity of Hb caused by an alpha chain variant is usually milder than that caused by a beta chain variant (see 617980). [from
OMIM]