the man , known only as donor 7042 , carries a defective gene known as neurofibromatosis 1 -lrb- nf1 -rrb- that can pass on a severe , life-limiting condition to his offspring .
donor is understood to have fathered 99 ` viking babies ' -- as they are widely dubbed that now four families are suing the sperm bank and the case has raised questions among fertility experts about denmark 's booming , and unregulated , sperm export trade .