Clinical features: The term "sickle cell" disease describes a group of disorders of haemoglobin in the blood, caused by an inherited alteration of betaglobin. Haemoglobin is the oxygen carrying protein found in red blood cells. Sickle cell anaemia (SCA) is the commonest of the sickle cell diseases and is defined by the presence of the abnormal haemoglobin HbS, caused by having two copies of the beta globin gene containing the mutation for HbS. The other forms of sickle cell disease result from co-inheritance of one gene for HbS with a gene for another abnormal globin beta chain variant, the most common forms being sickle-haemoglobin C disease (Hb SC) (where one of the pair of beta globin genes contains the mutation HbS and the other mutation for HbC) and two types of sickle-߭thalassaemia. SCA is characterised by episodes of pain, chronic haemolytic anaemia and severe infections, usually beginning in early childhood.
Incidence: Sickle cell disease is common in people of African, Mediterranean, Middle Eastern, and Indian ancestry and in people from the Caribbean and parts of Central and South America. The highest incidence worldwide is in West Africa where 1 in 4 of the population are carriers. Sickle cell carriers are particularly common in areas of the world where malaria is common, the sickle trait offers some protection from the parasite that causes malaria, which is carried by mosquitoes.
Inheritance: Autosomal recessive.
Gene: Beta-globin gene (HBB) on chromosome 11. One particular mutation causes HbS and everyone with sickle cell anaemia has two copies of this mutation. Many different mutations in the betaglobin gene can cause thalassaemia.
Prenatal diagnosis: Yes. If a family is considering prenatal diagnosis referral should be made to the local clinical genetics service prior to a pregnancy. This ensures family members are offered appropriate advice and investigations, to confirm whether or not prenatal diagnosis is possible.
Carrier testing: Yes
UK Support Group: Sickle Cell Society 54 Station Road London NW10 4UA Tel: 020 8961 7795 Fax: 020 8961 8346 Web: www.sicklecellsociety.org
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