Does great-grandson deformity have anything to do with grandparents being cousins?

Great-grandchild deformity is related to grandparents and grandmothers being cousins.

Couples who are married by close relatives are likely to die young, and the death probability is more than three times that of children born to couples who are not married by close relatives. Moreover, the marriage of close relatives will greatly increase the congenital malformation rate of children born to close relatives, and children born to close relatives are prone to congenital malformation.

China's "Marriage Law" clearly stipulates that if marriage is prohibited, lineal blood relatives and collateral blood relatives within three generations are prohibited from getting married. Lineal blood relatives refer to the blood relatives of the next generation who gave birth to themselves or their own children, that is, the so-called biological flesh and blood or biological flesh and blood. Tracing back to parents, grandparents, great-grandparents, down to children, grandchildren, great-grandchildren and so on, they are all lineal blood relatives.