Picking traits in children

There’s discussion on blogs today about an LA Times editorial highlighting the news that an LA fertility clinic is offering selection of a few non-health related traits in embryos.

This technology was first developed for and used to screen out dangerous genetic disease traits. Couples who both carry the allele for a deadly genetic disease have a 1 in 4 chance of having a child with the disease (in some situations the child would have a 1 in 2 chance). IVF combined with embryo testing allows these couples to have a healthy child. A couple has embryos created through IVF and then a cell from the 8-cell stage embryo is removed and tested for a trait. Apparently some fertility clinics now offer gender selection and will offer selection based on “eye color, hair color and complexion”.

This technology has inherent limits–embryos are being selected from a pool of 6-10 that are created by a round of IVF. So only simple, single gene traits can be picked. If you want a boy the pool is cut in half and now the parents are picking from 3-5 embryos. If both parents have the simplest eye color situation and both carry an allele for blue eyes, 1 in 4 embryos will have it. Parents get at most two choices of simple single gene traits and few traits are determined by a single gene.

Very little is known today about normal human genetics, that is what genes to test for, but that will change and is not an inherent limit to this technology. The curious fact that we know almost nothing about the genetics of normal human traits is a story for another day.

In a few years when we have a better understanding of medical genetics parents will be able to pick the embryos with the fewest and least severe set of disease gene alleles (and even then each embryo will have many bad traits). This choice will for almost all parents trump select of any other trait. Who would pick a green-eyed baby with a 90% lifetime risk of heart disease over a one with a 10% heart disease risk and brown eyes? So concern about IVF clinics offering this is wasted breath, it is a passing notion that will last a few years at most.

This technology has no prospect of offering more detailed choices for parents. More choices would require selecting among more embryos (or among more sperm and eggs), and nothing like that is on the horizon, i.e. it won’t happen in the next thirty years.

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