I agree with PM. It should be left to the couple's discretion. Remember a case in my neighbourhood where the girl had 'sickle cell anemia'. This can be transferred to the kids but the boy still decided to marry. They don't have kids though. IMHO, those who have some diesease (even HIV) should be given a chance to lead a normal married life. The authority should not intervene or they will become, like 'social outcast.' (A few decade back, people with dieseases like leprosy and tuberclosis(curable now) were left on city outskirts.)