Exploring differences of sex development

Eric Vilain, M.D., Ph.D., is well versed in the “world of uncertainty” that surrounds differences of sex development. Since joining Children’s National as the director of the Center for Genetic Medicine Research in 2017, he’s shared with our research and clinical faculty and staff his expertise about the ways that genetic analysis might help address some of the complex social, cultural and medical implications of these differences.

Over the summer, he gave a keynote address entitled “Disorders/Differences of Sex Development: A World of Uncertainty” during Children’s National’s Research and Education Week, an annual celebration of research, education, innovation and scholarship at Children’s National and around the world. In January 2018, he shared a more clinically oriented version of the talk at a special Children’s National Grand Rounds session.

The educational objective of these talks is to inform researchers and providers about the mechanisms of differences of sex development (DSD), which are defined as congenital conditions in which the development of chromosomal, gonadal or anatomical sex is atypical.

The primary goal, though, is to really shine light on the complexity of this hot topic, and share how powerful genetic tools can be used to provide vital, concrete information for care providers, patients and families to assist with difficult treatment (and non-treatment) decisions.

“A minority of DSD cases are able to receive a genetic diagnosis today,” he points out. “But geneticists know how important it is to come to a diagnosis and so we seek to increase the number of patients who receive a concrete genetic diagnosis. It impacts genetic counseling and reproductive options, and provides a better ability to predict long term outcomes.”

“These differences impact physiology and medicine. We want to better understand the biology of reproduction, with an emphasis on finding ways to preserve fertility at all costs, and how these variations may lead to additional complications, including cancer risk.”

At conception, he explains, both XX and XY embryos have bipotential gonads capable of differentiating into a testis or an ovary, though embryos are virtually indistinguishable from a gender perspective up until six weeks in utero.

Whether or not a bipotential gonad forms is largely left up to the genetic makeup of the individual. For example, a gene in the Y chromosome (SRY) triggers a cascade of genes that lead to testis development. If there is no Y chromosome, it triggers a series of pro-female genes that lead to ovarian development.

Dr. Vilain notes that a variation of enzymes or transcription factors can occur at any single step of sex development and alter all the subsequent steps. Depending on the genotype, an individual may experience normal gonadal development, but abnormal development of the genitalia, for example.

He also noted that these genes are critical to determining the differences between men and women in non-gonadal tissues, including differences in gene expression within the brain. One study in the lab of investigator Matt Bramble, Ph.D., investigates if gonadal hormones impact sex differences in the brain by modifying the genome.

This work is a prime example of research informing the care provided to patients and families. Dr. Vilain is also a member of the multidisciplinary clinical team of the PROUD Clinic at Children’s National, a program completely devoted to caring for patients with a wide array of genetic and endocrine issues, including urogenital disorders and variations of sex development.