Association between the ABO Type, Rh Factor and the 2D:4D Ratio: A Cross-Sectional Study in Ghana

Aims: The second-to-fourth digit ratio (2D:4D) is the putative marker of prenatal androgen exposure. The 2D:4D ratio tends to be lower in males than females; however, there are population variabilities. Previous studies have suggested a possible association between the ABO and Rhesus blood group systems with the 2D:4D ratio. This observation has not been tested in a Ghanaian population.

Study Design: The study was cross-sectional.

Place and Duration of Study: The study was conducted in Tamale between May and June 2021.

Methodology: There were 206 participants comprising males (n=94) and females (n=112), aged 18 to 32 years. The right digit ratio (2D:4DR), the left digit ratio (2D:4DL) and the right-left difference in digit ratio (Dr-l) were measured using computer-assisted analysis. The ABO blood type and the Rh factor were determined using monoclonal antibodies. The effect sizes were reported as either Hedge’s g for a t-test or partial Eta-squared (ηp2) for the one-way ANOVA test.

Results: Males’ 2D:4DL was lower than females with a small effect size (P= 0.033, g: 0.28). The differences in digit ratios by the ABO blood type had small to medium effect sizes in both males and females (P ≥ 0.050, ηp2: 0.00-.08). In females, the 2D:4DR of participants with Rh- was higher while the 2D:4DL and the Dr-l were lower than participants with the Rh+ with medium to large effect sizes (P< 0.050, g: 0.56, 0.84, 2.72 respectively). In males, the 2D:4DL and the Dr-l were higher in participants with Rh+ than the Rh- participants with large effect sizes (P< 0.050, g: 1.00, 2.52 respectively).

Conclusion: The expression of the Rhesus factor may affect the expression of the 2D:4D ratio in the study population.