Geneticists discover how sex-linked disorders arise

Researchers at the University of Melbourne have made an important discovery that explains why some babies are born with disorders of sex development.

X and Y chromosomes - by Kateryna Kon

Kateryna Kon | Shutterstock

The study suggests that a critical regulatory gene carried on the Y chromosome increases or decreases the activity of particular gene that determine whether a baby will be male or female.

First author Brittany Croft says the critical gene is called SRY. It induces another gene called SOX9 to trigger the development of testes and high concentrations of SOX9 are required for normal male development.

"However, if there is some disruption to SOX9 activity and only low levels are present, a testis will not develop resulting in a baby with a disorder of sex development."

Lead author, Professor Andrew Sinclair, says that “junk DNA” or “dark matter” forms 90% of human DNA. Rather than carrying genes, this contains regulatory segments of DNA called enhancers that increase or decrease gene activity.

“If these enhancers that control testis genes are disrupted it may lead to a baby being born with a disorder of sex development."

The purpose of the current study was to investigate how enhancers regulate SOX9 and whether their disruption would cause abnormal sex development.

Sinclair says the team found three enhancers that ensure SOX9 is activated to a high level in an XY embryo, leading to normal testis and male development.

"Importantly, we identified XX patients who would normally have ovaries and be female but carried extra copies of these enhancers, (high levels of SOX9) and instead developed testes. In addition, we found XY patients who had lost these SOX9 enhancers, (low levels of SOX9) and developed ovaries instead of testes."

Croft says this sex reversal is caused by gain or loss of the critical enhancers that regulate SOX9, which shows how vital they are for normal male development.

This study is significant because in the past researchers have only looked at genes to diagnose these patients, but we have shown you need to look outside the genes to the enhancers. The key to diagnosing many disorders may be found in these enhancers which hide in the poorly understood dark matter of our DNA.”

Professor Andrew Sinclair, Lead Author

Sally Robertson

Written by

Sally Robertson

Sally first developed an interest in medical communications when she took on the role of Journal Development Editor for BioMed Central (BMC), after having graduated with a degree in biomedical science from Greenwich University.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Robertson, Sally. (2019, June 24). Geneticists discover how sex-linked disorders arise. News-Medical. Retrieved on June 23, 2021 from

  • MLA

    Robertson, Sally. "Geneticists discover how sex-linked disorders arise". News-Medical. 23 June 2021. <>.

  • Chicago

    Robertson, Sally. "Geneticists discover how sex-linked disorders arise". News-Medical. (accessed June 23, 2021).

  • Harvard

    Robertson, Sally. 2019. Geneticists discover how sex-linked disorders arise. News-Medical, viewed 23 June 2021,


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.