Two of my kids are sickle cell carriers, the health visitor and my doc said this will not affect them. how do they know this?

Historical fact: The presence of trait (carrier status for sickle cell) is common.It comprises 8% of the afro-american population of the us. It is thought by many to provide some resistance to malaria among those exposed in the african continent. Over the kids lifetime there are no significant effects. Identification of carrier status is now routine in the us with state screening.