Something that came as a surprise to me (although it’s relatively old news): Geneticists claim to have identified the locus of genes that correlate with primary enuresis.
I knew that surveys (dating back to the 1970s) suggest that a child is very likely to wet the bed (about 75% probability) if both parents did. If one parent wet the bed, chances are about even that the child will. If neither parent wet the bed, a child generally will not; a child with no bedwetting in the family tree (parents, grandparents, uncles and aunts) is rarely a bedwetter. Those probabilities are for primary enuresis, that is, for a child over the age of 6 who has never been dry. Secondary enuresis (such as mine), which starts after being dry for some time, is not genetically correlated.
The interesting thing — to me, at any rate — is that geneticists have identified the locus of several genes that appear to be correlated between parents who were bedwetters and their children who wet the bed. Some genes appear to be dominant, some to be recessive.
Some of the genes appear to be sex-linked. That would explain why, as children get older, boys are more likely to still wet the bed than girls are. That’s reversed in my family: My sisters wet the bed to a much later age — 16 or 17 — than my brothers did, and my son was dry while his older sister was still wetting most nights.
A few caveats:
My degrees are in mathematical disciplines. I have a low regard for the rigor of medical studies based on surveys. I doubt that the surveys allow the reported precision of the correlations. I doubt that the samples are large enough or representative enough for the correlations to be very convincing. Still, if one allows a wide margin of error, even at an anecdotal level there is a basis for belief.
While I have a background in statistical methods, I’m no geneticist. My knowledge of biology is limited to 9th-grade public-school frog-chopping (for which I got the worst grade of my academic career) and (like most people with math degrees) I regarded biology as only slightly more respectable than alchemy. On the other hand, geneticists do appear to take science seriously and a pointer to an actual gene is interesting.