A West African couple present to your surgery, they are planning on having a baby, but they are both known to be sickle-cell trait. They have come to discuss the chances of their baby being affected by the disorder.
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Sickle-cell disease is caused by a point mutation in the beta-globin chain of haemoglobin, causing glutamic acid to be replaced by valine at the sixth position. The beta-globin gene is found on chromosome 11.
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Sickle-cell trait is the heterozygous, or carrier state, of sickle-cell disease, in which a person has one abnormal allele and one normal allele. The two alleles are co-dominant, and, therefore, patients that are sickle-cell trait create both normal and abnormal haemoglobin. They, therefore, do not display the same severity of disease symptoms as those patients that have sickle-cell disease.
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As with all autosomal recessive conditions, if both parents are carriers (sickle-cell trait) then there is a 50% chance of their child being an unaffected carrier (being sickle-cell trait), a 25% chance of the child being unaffected and a 25% chance of the child going on to develop the condition (sickle-cell disease).
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