<P> Haemolytic crises are acute accelerated drops in haemoglobin level . The red blood cells break down at a faster rate . This is particularly common in patients with coexistent G6PD deficiency . Management is supportive, sometimes with blood transfusions . </P> <P> One of the earliest clinical manifestations is dactylitis, presenting as early as six months of age, and may occur in children with sickle - cell trait . The crisis can last up to a month . Another recognised type of sickle crisis, acute chest syndrome, is characterised by fever, chest pain, difficulty breathing, and pulmonary infiltrate on a chest X-ray . Given that pneumonia and sickling in the lung can both produce these symptoms, the patient is treated for both conditions . It can be triggered by painful crisis, respiratory infection, bone - marrow embolisation, or possibly by atelectasis, opiate administration, or surgery . Hematopoietic ulcers may also occur . </P> <P> Normally, humans have haemoglobin A, which consists of two alpha and two beta chains, haemoglobin A2, which consists of two alpha and two delta chains, and haemoglobin F, consisting of two alpha and two gamma chains in their bodies . Out of these three types, haemoglobin F dominates until about 6 weeks of age . Afterwards, haemoglobin A dominates throughout life . In people diagnosed with sickle cell disease, at least one of the β - globin subunits in hemoglobin A is replaced with what's known as hemoglobin S. In sickle cell anemia, a common form of sickle cell disease, hemoglobin S replaces both β - globin subunits in the hemoglobin . </P> <P> Sickle - cell conditions have an autosomal recessive pattern of inheritance from parents . The types of haemoglobin a person makes in the red blood cells depend on what haemoglobin genes are inherited from her or his parents . If one parent has sickle - cell anaemia and the other has sickle - cell trait, then the child has a 50% chance of having sickle - cell disease and a 50% chance of having sickle - cell trait . When both parents have sickle - cell trait, a child has a 25% chance of sickle - cell disease, 25% do not carry any sickle - cell alleles, and 50% have the heterozygous condition . </P>

The mutation that results in sickle cell anemia is
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