Scientists Find Gene Behind Equine Sex Development Disorder

Androgen receptor gene mutations can make a male fetus develop as a structurally sound filly, at least on the outside.

No account yet? Register


Researchers know that a maternally inherited sex development disorder (DSD) can cause repeated cases of infertility in a single family of horses. But they’ve recently identified the gene responsible for the condition and have begun testing for it to help breeders make better mating choices.

Androgen receptor (AR) gene mutations can make a male fetus develop as a structurally sound filly—at least on the outside. Internally, these XY-chromosome horses (the chromosome for males) lack a uterus and ovaries and sometimes have malformed testes, said Tamas Révay, PhD, of the Department of Biomedical Sciences at the University of Guelph, in Ontario, Canada.

Last year, Spanish and Polish researchers developed a test for this “XY mare chromosome abnormality” based on a deletion in the SRY gene, which is found on the Y chromosome (coming from the sire). However, this SRY-gene abnormality—which appears to be spontaneous as opposed to hereditary—is just one possible cause for this DSD.

“The AR gene mutation is causing a hormonal problem, as opposed to a transcription problem in the SRY gene mutation,” said W. Allan King, PhD, also of the University of Guelph Department of Biomedical Sciences. The SRY gene manages the structural development of the ovaries and testes, whereas the AR gene manages the use of those gonads as they release hormones and cause the rest of the reproductive structures to develop. “It’s a different process,” he told The Horse

Create a free account with to view this content. is home to thousands of free articles about horse health care. In order to access some of our exclusive free content, you must be signed into

Start your free account today!

Already have an account?
and continue reading.


Written by:

Passionate about horses and science from the time she was riding her first Shetland Pony in Texas, Christa Lesté-Lasserre writes about scientific research that contributes to a better understanding of all equids. After undergrad studies in science, journalism, and literature, she received a master’s degree in creative writing. Now based in France, she aims to present the most fascinating aspect of equine science: the story it creates. Follow Lesté-Lasserre on Twitter @christalestelas.

Related Articles

Stay on top of the most recent Horse Health news with

FREE weekly newsletters from

Sponsored Content

Weekly Poll

sponsored by:

When do you begin to prepare/stock up on products/purchase products for these skin issues?
96 votes · 96 answers

Readers’ Most Popular

Sign In

Don’t have an account? Register for a FREE account here.

Need to update your account?

You need to be logged in to fill out this form

Create a free account with!