Sex difference in leukocyte telomere length is ablated in opposite-sex co-twins.
Level 3 - non-randomized controlled study
Observational twin cohort study comparing leukocyte telomere length across zygosity and sex pairings.
PubMed 25056338 · doi:10.1093/ije/dyu146
What was done
Leukocyte telomere length (LTL) and attrition were analyzed in 720 adult twins: 268 monozygotic same-sex twins, 308 dizygotic same-sex twins, and 144 opposite-sex twins. LTL was measured using Southern blots of terminal restriction fragments to determine if sharing an intrauterine environment with a male twin alters the normal female advantage in LTL.
What was found
In same-sex twins (monozygotic and dizygotic combined), females had longer LTL than males (mean difference ± SE: 163 ± 63 bp, P < 0.01). In opposite-sex twins, the sex difference was absent, with female LTL indistinguishable from male LTL (-31 ± 52 bp, P = 0.6), while male LTL appeared unaffected. When restricting the analysis to dizygotic pairs only, females had longer LTL than males in same-sex pairs (188 ± 90 bp, P < 0.05), but not in opposite-sex pairs (-32 ± 64 bp, P = 0.6).
Why it matters
This study provides evidence that the typical female advantage in telomere length observed in singletons is modulated in utero, consistent with potential intrauterine masculinization of female fetuses gestated alongside a male co-twin.
Limits
The study evaluated adult twins rather than newborns, inferring prenatal hormonal exposure without direct intrauterine or fetal hormone measurements. The sample size of opposite-sex twins was relatively modest (n = 144), and potential confounding postnatal environmental factors were not fully detailed in the abstract.
Cited by
- supports Opposite-sex twins do not show the typical sex difference in telomere length at birth.