The primary defect which leads to sickle cell anemia IS (AIIMS May 2011)
|A||An abnormality in porphyrin part of hemoglobin|
|B||Replacement of glutamate by valine in B-chain of HbA|
|C||A nonsense mutation in the B-chain of HbA|
|D||Substitution of valine by glutamate in the A chain of HbA|
Replacement of glutamate by valine in B-chain of HbA
It is a autosomal recessive condition.
This is a haemolytic anemia resulting from the homozygous inheritance of a gene which causes an amino acid substitution in the hemoglobin molecule (beta – 6 glutamate → valine) creating HbS due to point mutation.
HbS (Beta 6 glue → Valine)
HbC (Beta 6 glue → Lysine)
HbE (Beta 26 glue → Lysine)
Extra Edge: Sickle cell disease is caused by a mutation in the beta gene
1. Homozygote (SS) – sickle cell anemia
2. Heterozygote (AS) – sickle cell trait (protects from falciparum malaria).
Symptomatic sickling occurs in homozygotes. Heterozygotes are asymptomatic, and present with mild anemia except in situation of hypoxia, Anaesthesia, when veno-occlusive events occur.