Finger Length Ratio (2D:4D) and Aging

Abstract

This study aimed to evaluate the association between the index to ring (2D:4D) finger length ratio and aging-related
traits (hand osteoarthritis (OA), the osseographic score (OSS), and reproductive period), as well as to assess the heritability
of finger length. A Chuvashian population-based sample included 802 males (mean age 46.98±17.10 years) and 738
females (mean age 48.65±16.62 years). Age, sex, basic demographics, anthropometric data, reproductive indices (age at
menarche, menopausal age, and length of the reproductive period), and x-rays of both hands were collected. Finger length
ratio was measured on x-ray and each hand was visually classified as either type 1 – 2D>4D; type 2 ― 2D=4D; or type 3
― 2D<4D. Hand OA was defined by the number of affected joints (Kellgren-Lawrence score ≥2) and the total of Kellgren-
Lawrence scores (total OA score). OSS is a skeletal biomarker that comprises osteoporotic and OA changes observable on
a hands x-ray. We calculated the familial correlations and performed a heritability analysis of 2D:4D ratio traits in a
studied sample. After comparing the OA variables of individuals with different finger length ratio types (after adjustment
for age and BMI) significant differences were found only in females between finger ratio types of the right hand in a number
of affected joints (F=3.153, p=0. 043) and finger ratio types of the left (F=3.330, p=0. 036) and right (F=2.397, p=0. 047)
hands of the total OA score. Females with type 3 ratio had the highest adjusted values of hand OA parameters. Results of
one-way ANCOVA for finger length ratio types of the right hand showed a significant difference in OSS (df =2, F=7.569,
P=0.001), after adjustment for age, sex, and BMI. The posthoc comparison showed that individuals with type 3 (2D<4D)
ratio showed significantly higher OSS scores than ones with type 1 (p=0.012) and type 2 (p=0.003). In an analysis of finger
length ratio types of left hand also a significant difference in OSS was found (df=2, F=3.290, P=0.038). The posthoc comparison
showed that individuals with type 3 ratio showed significantly higher OSS scores than ones with type 2 (p=0.33)
ratio. We found that a low finger length ratio, a masculine visually evaluated finger length ratio type, was associated with
later menarche and a shorter reproductive period. No association was found with menopausal age. Familial correlations
of finger length ratio traits showed no significant correlation for spouses, however, parent-offspring (0.15―0.28, p<0.001)
and sibling correlations (0.13―0.38, p<0.009) were found significant. Heritability (H2) of visual classification of finger
length ratio was 0.36 for the left and 0.28 for the right hand; finger ratio was 0.55 and 0.66, respectively; the ray ratio was
0.49 and 0.59, respectively, thus indicating the existence of a clear familial aggregation of finger length ratio variation in
the Chuvashian pedigrees, which cannot be explained by pure common environmental effects