Which of the following is an autoimmune disorder?

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:

Gout happens due to the accumulation of $...$ in joints.

Which of the following disorders is a genetic disorder?

$A$: Inflammation of a skeletal joint may immobilize the movements of the joint.
$R$: Uric acid crystals in the joint cavity and ossification of articular cartilage lead to this.

Select the correct statement regarding the specific disorder of the muscular or skeletal system.