SHOX Gene Offers Clue to Why Men Are Taller Than Women, Study Finds

A new study has shed light on a long-standing biological question: Why are men, on average, taller than women?

Published in the Proceedings of the National Academy of Sciences (PNAS), the study identifies a partial explanation in the form of a gene known as SHOX, which plays a key role in regulating human height. While both men and women carry the SHOX gene—located near the tips of the sex chromosomes X and Y—the gene appears to exert a greater influence in males.

SHOX Present in Both Sexes, but More Active in Males

Females have two X chromosomes, while males possess one X and one Y chromosome. Interestingly, SHOX is found on both chromosomes, raising the question: if both sexes have the gene, why does it seem to favor male height?

The answer lies in gene activity. In females, one of the X chromosomes is largely inactivated, a natural process known as X-inactivation. However, certain genes near the tips of the X chromosome—including SHOX—may escape this silencing to some extent, though not completely. In contrast, males have one active SHOX gene on the X chromosome and another fully active copy on the Y chromosome, effectively giving them a slightly higher dosage of the gene.

Evidence from Rare Genetic Variants

To test whether SHOX truly contributes to the height difference, researchers analyzed data from nearly one million individuals across three major biobanks in the United States and the United Kingdom. They focused on people with rare chromosomal variations, such as an extra X or Y chromosome, or a missing sex chromosome entirely.

The study found that individuals with an extra Y chromosome tended to be taller than those with an extra X. This supported the hypothesis that the Y-linked version of the SHOX gene has a stronger effect on growth. Moreover, individuals with a single X and no Y—a condition known as Turner syndrome—were often significantly shorter.

According to senior author Dr. Matthew Oetjens, a genetics researcher at Geisinger College of Health Sciences in Pennsylvania, this heightened SHOX activity in males accounts for nearly 25% of the average 5-inch height gap between men and women.

A Piece of the Puzzle

While SHOX doesn't fully explain the male-female height disparity, it is a significant contributor. The rest, experts say, is likely due to hormonal influences—especially testosterone—as well as other genetic and environmental factors.

“This is definitely cool,” said Dr. Eric Schadt, a professor of genetics and genomic sciences at Mount Sinai School of Medicine in New York City. “Even though the effect is modest, it does explain 20% or so of the height difference. It's a great use of biobank data to help solve a lingering biological mystery.”

In sum, while SHOX is not the sole reason men are taller than women, this newly uncovered insight provides a valuable glimpse into the complex interplay of genetics, sex chromosomes, and human growth.