HSD3B1 is a human gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

 that encodes for a 3beta-hydroxysteroid dehydrogenase/delta(5)-delta(4)isomerase

3-beta-HSD

3-β-HSD is an enzyme that catalyses the synthesis of progesterone from pregnenolone, 17-hydroxyprogesterone from 17-hydroxypregnenolone, and androstenedione from dehydroepiandrosterone in the adrenal gland...

 type I or hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1. While it can carry out the same function as HSD3B2

HSD3B2

HSD3B2 is a human gene that encodes for 3beta-hydroxysteroid dehydrogenase/delta-deltaisomerase type II or hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 2. It is principally expressed in steroidogenic tissues and is essential for steroid hormone production...

, it primarily localizes to different tissues, such as the placenta

Placenta

The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

 and nonsteroidogenic tissues. Its requirement for the production of progesterone

Progesterone

Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...

by the placenta, which has a vital role in pregnancy, may be one reason why no disease based on mutations in this gene has been identified to date.

Further reading