Thursday, January 29, 2015
CF - The great family mystery
My son Ryan has cystic fibrosis. This is a picture of him in a hospital mist tent when he was diagnosed at the age of 2. They said he'd probably die before he reached school age, but next month -- by the grace of God and scientific research -- he will celebrate is 38th birthday.
CF is caused by a recessive gene which means his father and I were symptomless carriers. Every time I come across a family in our tree that lost several infants I think maybe that's the CF gene showing itself.
Normally a mutation with fatal results should work its way out of a species naturally, but this mutation grew until one in 25 Americans of European origin are carriers. In order for the mutation to have become so common, being a carrier must have a benefit, geneticists tell me.
Soon after the gene was identified in 1989, researchers decided being a carrier might prevent a person from getting cholera. The CF mutation affects an ion transfer regulator that regulates salt causing thick sticky mucus. Cholera affects the same regulator causing dehydrating diarrhea. Mutated genes might be protected from the cholera bacteria.
But not enough people died of cholera to explain the numbers of people who have the mutation. So then scientists theorized that a carrier might also be protected from typhoid which also affects this salt regulator. Who knew?
But even cholera and typhoid together is not enough to explain the high incidence of the CF mutation in European populations.
In 2006 some Harvard statisticians looked at tuberculosis. Between 1600 and 1900 one in 20 deaths in Europe was caused by TB. That is a threat significant enough to explain the incidence of the CF gene.
So as I look at my family tree for indicators of the CF gene, I look not for families that lost babies. Many families did. Instead I look for families that survived epidemics...cholera, typhoid, TB. Now that's a mystery.
Posted by Sue Merrell at 10:26 AM