Need simple will give ! why can damage to a nucleic acid lead to a person not producing an enzyme?

Because the nucleic acid is damaged, so how is it going to produce anything without a miracle?

Nucleic acids are the main information-carrying molecules of the cell, and, by directing the process of protein synthesis, they determine the inherited characteristics of every living thing. 

So if that is damaged then, of course, you would be out of luck.

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later