Review Note

Haemoglobin is the protein in red blood cells that transports oxygen. During fetal development, at around 32-36 weeks gestation, {{c1::fetal haemoglobin (HbF)}} production decreases, and {{c1::adult haemoglobin (HbA)}} increases.

There is a gradual transition from HbF to HbA. At birth, around half the haemoglobin is HbF, and half is HbA. By six months of age, very little HbF is produced, and red blood cells contain almost entirely HbA.

Patients with sickle-cell disease have an abnormal variant called {{c1::haemoglobin S (HbS)}}. This variant results in sickle-shaped red blood cells.

Sickle cell anaemia is an autosomal recessive condition affecting the gene for {{c1::beta-globin}} on chromosome 11. 

One abnormal copy of the gene results in sickle-cell {{c1::trait}}. Patients with sickle-cell trait are usually asymptomatic. They are {{c1::carriers}} of the condition. Two abnormal copies result in sickle-cell {{c1::disease}}