Limited Penetrance, Variable Expression
The couple sits in the office while the doctor explains: “The decision is yours.”
A dozen blastocysts in a dish, all tested and typed.
The couple holds hands while they study the readout—a dozen genotypes, a dozen spins of genetic roulette. Antagonistic pleiotropy the new word of the day.
The wife clears her throat. “We just want our child to be smart and healthy.”
The doctor nods like he’s had this conversation before with a hundred smart, professional couples. Silicon Valley, after all, a national hotspot for children with Asperger’s.
Assortive mating, the studies explain. Engineers marrying engineers.
He turns to the wife. “In terms of IQ, you have an allele of large effect on chromosome sixteen. It has limited penetrance and variable expression, but depending on specific gene-to-gene interactions…” and here he looks closely at the wife, “it is often associated with extremely high IQ’s.”
The couple smiles.
“However, in 8% of cases, this allele produces autism spectrum disorder.”
The woman blinks.
“Most alleles of large effect are like this,” the doctor sounds almost apologetic now. “There are risks.”
“So what do we do?”
“You can choose to pass this allele on, or to eliminate it from the next generation.”
“If we eliminate it?”
“Then the risk of autism spectrum returns to baseline. However, your child will lose the likelihood for genius.”
“We just want our child to be smart and healthy,” she repeats, stalling for time, trying to imagine an answer that won’t leave her awake at night, holding a growing belly, thinking what have I done?