Correct Option
Haemophilia is an inherited genetic disorder characterized by the impaired ability of blood to clot. This condition arises due to a deficiency or absence of specific blood clotting factors, most commonly Factor VIII or Factor IX. As an X-linked recessive trait, it predominantly affects males. Individuals with haemophilia experience prolonged bleeding even from minor injuries or spontaneous internal bleeding, which can be severe and potentially life-threatening.
Incorrect Options
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Option 1 (decrease in haemoglobin level): A decrease in haemoglobin levels is a primary characteristic of anaemia, a condition distinct from haemophilia, which affects blood clotting rather than oxygen-carrying capacity.
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Option 2 (rheumatic heart disease): Rheumatic heart disease is an inflammatory condition that can develop as a complication of untreated streptococcal infection, particularly rheumatic fever. It is not a genetic blood disorder like haemophilia.
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Option 3 (decrease in 'NBC'): Assuming 'NBC' refers to a decrease in red blood cells (RBCs) or white blood cells (WBCs), neither is the defining characteristic of haemophilia. A decrease in red blood cells is associated with anaemia, while a decrease in white blood cells can indicate various immune or bone marrow disorders. Haemophilia specifically involves a defect in the blood clotting cascade.