Understanding the Sickle-Cell Anaemia Mutation

The question describes a specific genetic mutation affecting the haemoglobin molecule.

• Mutation Type: Point mutation.
• Affected Chain: Beta-globin chain of haemoglobin.
• Specific Change: Substitution of the amino acid Glutamic acid ($\text{Glu}$) with Valine ($\text{Val}$).
• Location: Sixth position of the beta-globin chain.

Consequences of the Mutation

This single amino acid substitution alters the properties of the haemoglobin molecule. Under conditions of low oxygen, the altered haemoglobin molecules tend to polymerize, causing the red blood cells to deform into a characteristic sickle shape. This sickling of red blood cells leads to various complications associated with the disorder.

Identifying the Disorder

The disorder caused by this specific Glu to Val substitution in the beta-globin chain is known as Sickle-cell anaemia. The other options are incorrect:

• Thalassemia: A group of inherited blood disorders characterized by reduced or absent synthesis of haemoglobin chains.
• Haemophilia: A group of inherited bleeding disorders where the blood does not clot properly due to missing clotting factors.
• Phenylketonuria (PKU): An inherited metabolic disorder where the body cannot break down an amino acid called phenylalanine.

Therefore, the substitution of Glutamic acid by Valine at the sixth position of the beta-globin chain specifically causes Sickle-cell anaemia.