CHAPTER 1

INTRODUCTION

1.1            BACKGROUND: ABOUT SICKLE CELL DISEASE

Sickle-cell disease (SCD), also known as sickle-cell anaemia (SCA) and drepanocytosis, is a hereditary blood disorder that is characterized by the blood cellassuming an abnormal, rigid and sickle shape.

Sickled red blood cells have reduced oxygen carrying capacity and usually get stuck in small blood vessels causing organ damage. They are continuously destroyed by the spleen in about 10 – 20 days as compared to 120 days for normal red blood cells. The bone marrow fails to produce new cells fast enough to replace the destroyed sickled cells which causes more complications among people having it.

Every individual has two copies of haemoglobin inherited one from the father and the other from the mother. If both copies are normal, then he/she is said to be homozygous for HbAA (AA genotype). If a child inherits the two copies of mutated gene, he/she is said to be homozygous for HbSS (SS genotype). Such individuals have sickle cell anaemia and usually die before reaching adulthood. When a single mutated gene is inherited, the individual is heterozygous for HbAS (AS genotype). Heterozygous for HbAS individuals are characterized by the sickle cell trait and are referred to as sickle cell carriers. Sickle cell carriers are less affected by sickle cell anaemia complications as the normal haemoglobin can still supply oxygen to vital body organs.

There is a 50% chance that parents with the sickle cell trait will pass on the same trait ( AS ) to their child, a 25% chance that their child will have both copies of normal haemoglobin (AA) and a 25% chance that the child will have the two mutated genes ( SS ). And if one parent has sickle-cell anaemia and the other has sickle-cell…

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