This is bullshit, my paternal grandparents were cousins and they had a pack of children and none of them suffered from any abnormal diseases.
There are many diseases which normal eye can't see forexample a mentally disorder which you cant know if the person is have it or not.
Xamud if your paternal granparents were cousin someone like you will face even The greater danger of marrying someone who come from same side of those granparents cousins. the cousin girl from same granparent and you share even more identical genes compare normal cousins who dont have granparents who were cousins. so sxb believe me your future offspring will face greater risk to all kind of deases mentally and physically. so xamud someone like you should tottaly avoid to marry close families because .