17-KSR Deficiency

17-KSR deficiency or 17-beta Hydroxysteroid Dehydrogenase 3 Deficiency is an intersex trait that effects 1 in 147,000 newborn AMAB or CTM individuals in which the gene called HSD17B3 does not properly provide instructions to an enzyme (an enzyme that is active in testicle production). Because of this, one does not produce testosterone at the same level as males, and thus has more femininized traits outwardly.

Most with this condition- despite their male chromosomes (XY)- have a vagina, ambiguous genitals, or a micropenis instead of a penis. Those who do have a penis usually have an oddly placed urethra.

Upon puberty, they usually gain muscle mass, have a deepening voice, facial and body hair, and possibly breasts as well. They usually are unable to produce fertile sperm, meaning reproduction is unlikely.

17-KSR deficiency in Israel
In a population within Israel, incest and inbreeding is highly common, which causes the genetic development of many individuals to turn out in an unlikely manner. Because of this, 1 in every 100-150 individuals in this area were born with 17-KSR, which is a drastically high amount compared to the average rarity of the condition.

This does not mean that incestual relations is the reason for this condition, but rather means that it can intensify the likelihood of it in development.

Resources

 * https://medlineplus.gov/genetics/condition/17-beta-hydroxysteroid-dehydrogenase-3-deficiency/
 * https://pubmed.ncbi.nlm.nih.gov/17551466/