Select the correct statement regarding disorders of the muscular or skeletal system.

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$:
Osteoporosis is characterised by decreased bone mass and increased chances of fractures.
Reason $(R)$:
Common cause of osteoporosis is increased levels of estrogen.
In the light of the above statements,choose the most appropriate answer from the options given below:

Deposition of . . . . . . in the joints causes gout.

Select the correct statement regarding human locomotion.

Which of the following disorders affects the neuromuscular junction $(\text{NMJ})$ leading to fatigue,weakening,and paralysis of skeletal muscle?

Myasthenia gravis is due to