What damages or problems in cells result from disease?

You could have rapid cell growth, rapid cell death, or maybe not enough production of cells. The cells may be too weak and serve no use.

The disease could be attacking your white blood cells but there's not enough to defend your system, or you could be anemic and loose red blood cells you can't spare.

It really depends on the type of disease. Is it an infectious disease, non-infectious? What body system is the disease attacking?