Diabetic nephropathy inherited?

　　Diabetes IS inheritable, but kidney disease is not generally thought of as an "inherited" disease.
　　Actually, diabetes, itself is not ALWAYS inherited. What is inherited is the TENDENCY to develop the disease, IF other environmental factors are there. This is why some people who are 10 pounds overweight get diabetes, but other people who are 100 pounds overweight do not. Being overweight is the environmental factor, the tendency towards diabetes is inherited.
　　So, no one in your family may actually have diabetes, but they (and you) might be "carriers". The diabetes didn't show up until some other factor "kicked it into gear".
　　Now, the kidney disease is a very common side effect of diabetes. Uncontrolled diabetes damages the capillaries, which are very important to kidney function. So many diabetics have severe kidney disease (like me), but almost all diabetics have SOME kidney damage.
　　But these two problems did not "damage your DNA". The tendency towards diabetes was already there -- just dormant in your parents, probably (how about your grandparents, great gransparents, or aunts and uncles?). The kidney disease is a side effect of diabetes, and is probably not inherited.

　　There is also a possibility to you developed diabetes completely on your own, and that you have no genetic tendency at all. This would be rare, but is not unheard of.