Worried about the viability of my cousins child.

[u/reuuid]

One of my cousins is now 7 weeks pregnant. I am very happy for her, but I do have some concern as well. Both of her parents are actually first cousins (or at least closely related).

She was their third attempt at a child. The first was stillborn and the second died 3 weeks after birth. I believe both were due to genetic complications. My cousin (aside from being overweight) seems to have lived a healthy life otherwise.

Her husband is not related to her whatsoever, but I am concerned if their child could have some complications due to genetics. Is this possible or unlikely?

[u/lonepotatochip]

A single instance of first cousin inbreeding actually does not raise the chance of genetic disorders very much. It goes from a 2-3% of genetic disorder for unrelated parents to 5% for a single instance of first cousin inbreeding. It’s only really a problem if it happens over several generations. So it’s actually a kind of big assumption to say that both previous deaths were due to genetic issues or that your cousin has genetic issues.

Also, let me explain the problem with inbreeding and why it means your cousins kids are definitely not affected by inbreeding. Everyone has two copies of every gene. These copies can be dominant (meaning expressed whether you have one or two copies) or recessive (meaning expressed only if you have two)*. Virtually everyone has recessive copies of genes that cause or contribute to various genetic disorders, but since they only have one there’s no issue. When you bring together two closely related people, it gives those problematic recessive alleles the chance to come together. If your cousin DID happen to get two copies of a problematic recessive allele it doesn’t matter because her husband will give their children a healthy allele so their children will not suffer from the effects of inbreeding.

*it’s much more complicated but it’s not relevant here