How do most autosomal recessive alleles that lead to lethal diseases persist in human populations?

Autosomal recessive alleles that lead to lethal diseases persist in human populations because these diseases happen after people have their children. They get inherited from both parents, one from each. The two mutated genes carry a 25 percent chance in having two normal genes in the child, a 25 percent of two recessive genes in an affected child and a 50 percent chance of an unaffected child who also is a carrier.