Chronic auto immune disorder affecting neuro muscular junction leading to fatigue, weakening and paralysis of skeletal muscle is called as :

The correct answer is Myasthenia gravis.

Detailed Explanation:
Myasthenia gravis is a chronic autoimmune neuromuscular disease. In this disorder, the body's immune system mistakenly produces antibodies that attack, block, or destroy the acetylcholine receptors located at the neuromuscular junction (the site where nerve cells connect with muscles).
Since acetylcholine is the neurotransmitter responsible for transmitting signals from nerves to muscles to initiate contraction, the reduction in active receptors prevents effective communication. This results in the characteristic symptoms of the disease, including progressive muscle fatigue, weakness, and potentially paralysis of voluntary skeletal muscles under control, especially after periods of activity.

Analysis of other options:
• Arthritis: This refers to the inflammation of one or more joints, leading to pain, stiffness, and reduced mobility. It is not primarily a disorder of the neuromuscular junction.
• Muscular dystrophy: This is a group of genetic diseases characterized by progressive weakness and degeneration of muscle fibers due to mutations in genes responsible for the structure and function of muscles, rather than an autoimmune dysfunction.
• Gout: This is a form of inflammatory arthritis caused by the deposition of monosodium urate (uric acid) crystals in the joints, leading to sudden and severe pain and swelling.