Prevalence of sickle cell anaemia
Sickle cell anaemia is a recessive disorder: only people who carry two copies of the mutant allele (i.e. homozygous) have the symptoms.
People who are heterozygous (carry one mutant allele) for the sickle cell anaemia gene have some protection against malaria, yet do not have the full symptoms of sickle cell anaemia.
There is very high prevalence of sickle cell anaemia in populations from regions where malaria was historically common because the mutant allele confers an evolutionary advantage in these regions. Malaria has now spread to other areas such as South America, but the allele is not present in these populations.
Only 0.005% of babies are born with sickle cell anaemia in the UK. However, in countries such as Nigeria where malaria is endemic, this number can be as high as 2%.