Ricketts is caused by malnutrition, lack of calcium/vitamin d, and lack of sunlight.

Therefore, if the problem is in several generations of dogs, then several generations of dogs haven't been fed/kept right (possibly in a basement/garage, fed lousy food, etc.).

The solution is easy: sunlight available to the pups, a good healthy diet with calcium/bones, and vitamin d supplementation (e.g., a little cod liver oil).

Good luck!

Jack