Is there a reason incest leads to a lot of genetic disorders?

Double dose of genes: Genetic disorders are more likely to show up from incest because people who are related have many genes in common. Usually the genes that cause genetic disorders are rare but if the parents share genes the baby is likely to get a double dose of the rare gene so the disorder is more likely to be apparent. For some genes it requires the same gene come from both parents to show up in the child.