Understanding Pernicious Anaemia and Vitamin Deficiency

The question asks about the specific vitamin deficiency that leads to pernicious anaemia. Pernicious anaemia is a serious type of anaemia that affects the blood.

What is Pernicious Anaemia?

Pernicious anaemia is an autoimmune condition where the body cannot make enough healthy red blood cells because it lacks vitamin B12. It's considered "pernicious" because it was historically fatal before treatments were discovered. While often linked to a deficiency in consuming vitamin B12, it's more accurately described as a problem with absorbing vitamin B12.

The Role of Vitamin B12 in Preventing Pernicious Anaemia

Vitamin B12, also known as cobalamin, is essential for several bodily functions, including:

• Production of red blood cells.
• Maintenance of nerve cells.
• Synthesis of DNA.

A deficiency in vitamin B12 impairs these processes, leading to the formation of abnormally large, immature red blood cells (megaloblasts) that cannot function correctly. This results in megaloblastic anaemia, of which pernicious anaemia is a specific type.

Why Vitamin B12 Deficiency Causes Pernicious Anaemia

The primary cause of pernicious anaemia is the inability to absorb vitamin B12 from the diet. This is usually due to a lack of a protein called Intrinsic Factor (IF). Intrinsic Factor is produced by the parietal cells in the stomach lining. Vitamin B12 binds to Intrinsic Factor, and this complex is then absorbed in the small intestine (specifically the terminal ileum). In pernicious anaemia, the body's immune system attacks and destroys the parietal cells or the Intrinsic Factor itself. Without Intrinsic Factor, dietary vitamin B12 cannot be absorbed, leading to a severe vitamin B12 deficiency over time.

Analyzing the Options

Let's look at the vitamins listed in the options and their common deficiency-related conditions:

• Vitamin B6 (Pyridoxine): Deficiency can lead to microcytic anaemia (different from megaloblastic anaemia), neurological problems, and skin disorders. It is not the cause of pernicious anaemia.
• Vitamin B12 (Cobalamin): Deficiency, particularly due to poor absorption (often linked to lack of Intrinsic Factor), is the direct cause of pernicious anaemia.
• Vitamin B2 (Riboflavin): Deficiency (ariboflavinosis) can cause skin disorders, sore throat, and swelling of mucous membranes. It is not the cause of pernicious anaemia.
• Vitamin B1 (Thiamine): Deficiency causes Beriberi, affecting the nervous system and cardiovascular system. It is not the cause of pernicious anaemia.

Based on the function of these vitamins and the specific mechanism of pernicious anaemia, the deficiency of vitamin B12 is the cause.

Conclusion

Pernicious anaemia is specifically caused by a deficiency of vitamin B12, most commonly due to the inability to absorb vitamin B12 because of a lack of Intrinsic Factor.

The correct answer is Vitamin B12.

Revision Table: Vitamin Deficiencies and Associated Conditions

Additional Information on Pernicious Anaemia

• Pernicious anaemia is an autoimmune disease targeting gastric parietal cells or Intrinsic Factor.
• Symptoms can include fatigue, weakness, pale skin, shortness of breath, and neurological problems like numbness or tingling.
• Diagnosis involves blood tests to check vitamin B12 levels, presence of antibodies against Intrinsic Factor or parietal cells, and a test for megaloblastic anaemia.
• Treatment typically involves vitamin B12 injections for life to bypass the need for intestinal absorption.
• While diet is the usual source of vitamin B12 (found in animal products), dietary intake is rarely the sole cause of pernicious anaemia itself, unlike other types of vitamin B12 deficiency.