It is not necessary to have a grandparent with this condition (0 grandparents). But it is mandatory that the parents are heterozyogtes. (and highly probable that grandparents has the c allele) Since we require to have two recessive alleles to develop this condition, this has low chances. So, consider this:
Grandfather C- <---> Grandmother C- (C- refers to either Cc or CC)
Father C- <---> Mother C-
Child cc. ---> As long as the grandparents and parents carry a -c- allele, and most important, inherit it, the child could have real chances of developing the condition.