disease is caused by a genetic defect which affects the activity of enzymes?

The correct answer is Inborn errors of metabolism.

Inborn errors of metabolism are a group of genetic diseases that occur when the body is unable to properly convert food into energy. These diseases are caused by defects in enzymes, which are proteins that help speed up chemical reactions in the body. When an enzyme is defective, it can cause a buildup of harmful substances in the body or a shortage of essential nutrients. This can lead to a variety of symptoms, including physical deformities, intellectual disability, and even death.