Why would defective collagen proteins affect an individuals joints?

Defective collagen proteins affect an individuals joints, as collagen is an important component protein in body connective tissues

Explanation:

Collagen is a crucial protein in the extracellular matrix of various connective tissues in body (tendons, ligaments, muscles). It constitutes major protein component in mammals body.

Collagen Vascular disease is a group of diseases affecting 'collagen' connecting tissue. Apart from inheritance, they can con occur due to autoimmune disease. This implies that body's immune system fights against itself & mistakenly damages its own tissues. So, these diseases have a huge bearing on body joints components. Eg : Lupus, Arthritis are common collagen vascular diseases. Arthritis mostly affects adults above 30 years of age, lupus can be diagnosed in younger people above 15 years of age also.