wikipedia dice:
Inbreeding leads to an increase in homozygosity (the same allele at the same locus on both members of a chromosome pair). This occurs because close relatives are much more likely to share the same alleles than unrelated individuals. This is especially important for recessive alleles that happen to be deleterious, which are harmless and inactive in a heterozygous pairing but, when homozygous, can cause serious developmental defects. Such offspring have a much higher chance of death before reaching the age of reproduction, leading to what biologists call inbreeding depression, a measurable decrease in fitness due to inbreeding among populations with deleterious recessives. Recessive genes, which can contain various genetic problems, appear more often in the offspring of procreative couplings whose members both have the same gene. For example, the child of persons who are both hemophiliac has a 25% chance of having hemophilia.
sì, comunque il rischio è più che altro per le malattie genetiche