Which disease is associated with joints in humans?

Which of the following is an incorrect statement about myasthenia gravis?
$(I)$ It is not an autoimmune disorder.
$(II)$ It affects the neuromuscular junction.
$(III)$ It occurs due to low $Ca^{++}$ in body fluid.
$(IV)$ Paralysis of skeletal muscle is a symptom of myasthenia gravis.

Chronic autoimmune disorder affecting the neuromuscular junction, leading to fatigue, weakening, and paralysis of skeletal muscle, is called:

Provide information regarding disorders of the skeletal and muscular system.

Select the correct statement with respect to locomotion in humans.

Osteoporosis,an age-related disorder of the skeletal system,is characterized by: