Oxygen is necessary even at the cellular level to maintain its functional ability. A protein known as the Haemoglobin in the red blood cell is mainly responsible for carrying oxygen to different vital organs of the body. Normal red blood cells are oval in shape, which allows them to be flexible enough to pass through large as well as small blood vessels to deliver oxygen.
Due to genetic modification, altered version of beta globin chains are being synthesized, giving rise to haemoglobin S instead of haemoglobin. This in turn can form stiff rod like structures in red blood cells changing it to the crescent or sickle shape. These sickle shaped red blood cells are non flexible, sticking to the vessel walls. This will block the flow of blood cells; thus preventing oxygen to be supplied to nearby tissues. This hypoxic condition can give rise to sudden pain without warning.
The increased frequency of the condition can cause severe organ damage such as brain, heart, lungs, liver, heart, kidney, etc. Since the damage of the red blood cells in the sickle cell condition is higher as compared to their synthesis, the condition can give rise to severe anaemia, most of the times.