Haemoglobin O disease

**Definition:** A disease caused by the bi-parental inheritance of the gene that encodes for haemoglobin O. This disease is characterised by abnormal structure of one of the globin chains of the haemoglobin molecule. This disease may present with mild haemolytic anaemia, increased risk for gallstones, enlarged spleen, episodes of joint pain, and increased risk of infection. This disease is confirmed by identification of the haemoglobin O gene by genetic testing.