Selective Breeding in Humans – A Slippery Slope? Nah.

October 26^th, 60 Minutes featured a segment on selective breeding in humans. The story focused on Genesis Genetics, a company which developed the technology for identifying those embryos within a larger set which have defective genes. Once identified, the family can choose the other “disease-free” embryos to implant via standard in-vitro fertilization techniques. When born, such children would be disease-free.

One application relates to Huntington’s chorea. Huntington’s chorea is a neurodegenerative disorder associated with cognitive decline, behavioral symptoms, and involuntary writhing movements. The disease has autosomal-dominant penetrance. The affected individual typically inherits one copy of the gene from an affected parent. In this type of inheritance model, each offspring of an affected individual has 50% risk of inheriting the mutant allele, and thus acquiring the disease.

To make matters even more challenging, symptoms become noticeable between the ages of 35 and 44 years; sometimes later. So, a potential carrier (currently asymptomatic) may be faced with making decision between rolling the dice by becoming a parent or staying child-free.

One might reasonably ask, what’s the challenge here? In families that have a relative with Huntington’s, the asymptomatic person considering becoming a parent can be checked for the defective gene. So, he/she will know whether it’s even possible to pass down the allele. If the test result says “All clear”, there’s no problem. Time for a child.

But, if the test result comes back “Carrier”, then the potential parent has learned he/she will develop a life threatening condition for which there is no substantive treatment. This 100% certainty will be more disconcerting than the prior 50% uncertainty.

Enter Genesis Genetics. Via in-vitro fertilization, the family can incubate eight (or more) embryos. Once the embryos are large enough, once of the cells can be removed and sent to Genesis for analysis. Genesis will send the clinic information as to which embryos are free of the Huntington’s chorea gene. Those embryos can be implanted with the knowledge that regardless of the parent’s genetic status, the child will be free of the disease. Presumably the family is not told whether any of the embryos even had the Huntington’s gene.

The same techniques can be used for a host of single gene diseases – BRCA1 breast cancer, cystic fibrosis, some types of colon cancer, and so on.

Being able to eradicate even the chance of a disease to one’s genetic line has tremendous appeal. Not surprisingly, such techniques have been a lightning rod for criticism. One argument for maintaining the status quo is this technique risks being a slippery slope. It will not take much to go from eradicating Huntington’s chorea to selecting embryos based on potential intelligence, sex, and eye color. Mark Hughes, the founder of Genesis Genetics, ably answered this criticism. He said he heard the same pushback 25 years ago when he first developed the methodology. To date, it’s only been used to eradicate mostly-lethal diseases. While there may be some practitioners who will abuse the technology for less noble goals, it’s hard to argue that patients would be better off passing on cystic fibrosis and Huntington’s chorea to their offspring because of the potential slippery slope. My hat’s off to Mark Hughes. His work has done so much to eliminate suffering.

The interviewer on 60 Minutes was mostly laudatory. But, she did ask about parents abusing the technology – would they select embryos based on potential intelligence, sex, and eye color? I was struck by interviewer’s appearance. Her eye color was a shade of blue found only in a Bausch and Lomb catalogue. Ironic that the person asking the tough ethical questions was wearing contact lenses, the color of which is not found in nature.