Posted: Nov 08, 2017 8:56 am
by aban57
I find this medical case to be fascinating. I sometimes use it when people have trouble understanding how a man can "feel" like a woman, or vice versa.

When you are conceived you normally have a pair of X chromosomes if you are to become a girl and a set of XY chromosomes if you are destined to be male.
For the first weeks of life in womb you are neither, though in both sexes nipples start to grow.
Then, around eight weeks after conception, the sex hormones kick in. If you're genetically male the Y chromosome instructs your gonads to become testicles and sends testosterone to a structure called the tubercle, where it is converted into a more potent hormone called dihydro-testosterone This in turn transforms the tubercle into a penis. If you're female and you don't make dihydro-testosterone then your tubercle becomes a clitoris.
When Imperato-McGinley investigated the Guevedoces she discovered the reason they don't have male genitalia when they are born is because they are deficient in an enzyme called 5-alpha-reductase, which normally converts testosterone into dihydro-testosterone.
This deficiency seems to be a genetic condition, quite common in this part of the Dominican Republic, but vanishingly rare elsewhere. So the boys, despite having an XY chromosome, appear female when they are born. At puberty, like other boys, they get a second surge of testosterone. This time the body does respond and they sprout muscles, testes and a penis.

From Wikipedia :
5α-Reductase deficiency (5-ARD) is an autosomal recessive intersex condition caused by a mutation of the 5α reductase type II gene.

The condition is extremely rare, with areas of greater incidence known in regions of the Dominican Republic, Papua New Guinea, and Turkey.
The cases of the condition reported in the Dominican Republic are of greatest interest due to its prevalence in the small remote village of Las Salinas, where 12 out of 13 families had one or more male family members that carried the genetic mutation, though not all the carriers of the mutation were affected. The overall incidence for the village was 1 in every 90 males were affected carriers, the remainder of the village genetic males were either non-carriers or non-affected carriers.
It is thought that either a founder effect or a bottleneck effect (the villagers are interrelated and may have inherited the mutation from the same individual), in conjunction with a lack of geneflow (genes from outsiders) in the isolated geographic location of Las Salinas allowed the mutation to become amplified in the village.

I'm wondering why " not all the carriers of the mutation were affected".