The benefits of being female, in outliving the male version of the human species, are also evident at the early stages of life as girls are "hardier" in fighting off infections. We now know why; infant girls have better outcomes than their male counterparts "due to an innate genetic advantage" in responding to acute infections, a Royal College of Surgeons in Ireland study has found.
While females have a recognised survival advantage throughout the entire human lifecycle, it is particularly evident during the newborn period. Newborn boys have higher rates of infection and sepsis (a potentially life-threatening condition arising when the body’s response to infection causes injury to its own tissues and organs) compared with baby girls of the same gestational age, and have poorer survival rates, the study notes.
The explanation is to be found in our chromosomes which carry our genes, in particular the difference in chromosomal make-up between females (XX) and males (XY). The X chromosome contains more of the genes involved in immunity than does the Y chromosome.
Females can have a higher expression of these immune genes than males and this gives them an advantage in dealing with acute infections, and could also be implicated in gender differences in certain diseases. The findings are published in the current edition of Pediatric Research.
This research measured the presence of a factor called IRAK1 (interleukin-1 receptor-associated kinase 1), which contributes to immunity against infection, in the umbilical cord blood of newborn babies. Higher IRAK1 gene and protein expression, indicating gene activity, was detected in the female cord blood and the authors believe this may explain in part the different outcomes in infants tackling diseases that cause inflammation.
‘Hardier’
Lead researcher Prof Catherine Greene, associate professor of clinical microbiology at RCSI, said: "The phenomenon of female neonates being hardier than their male counterparts is well recognised. This research shows this is due to a fundamental genetic advantage which may also contribute to more effective responses to infection and disease throughout the human lifecycle."
Medical intervention in the future could target baby boys with a view to enhancing their expression of the gene and ability to fight off infections, but that was some time away.
One of the researchers David O’Driscoll, who carried out the experimental work in RCSI, said: “Our findings in full-term newborn babies suggest that a similar phenomenon could be occurring in preterm infants where gender differences can be even more marked.”
This research arose from a collaboration between the RCSI researchers and Prof Eleanor Molloy, head of Department of Paediatrics in Trinity College Dublin, who works with neonatology departments of the National Maternity Hospital; the Coombe and Crumlin children's hospital; and the Paediatrics Academic Centre at Tallaght hospital.
