Can digit ratio (2D:4D) studies be helpful in explaining the aetiology of idiopathic gynecomastia?

Aetiology of idiopathic form of gynecomastia is unknown and it has not been established if it is related to factors present at the prenatal period or if it is caused by yet unidentified environmental conditions.

The aim of this study is to compare digit ratio (2D:4D) in men with idiopathic gynecomastia and unaffected male and female controls from the general population.

The study involved 250 subjects (50 men with idiopathic gynecomastia, 100 control men and 100 control women). Eight measurements were taken: body height, waist and hip circumferences, II and IV digits' lengths (right and left), and body weight, and 4 indices were calculated: BMI, WHR, and 2D:4D for the right and left hand.

2D:4D in men with gynecomastia ([median (I-III quartiles)]: 1.03 (1.01-1.04) for right hand and 1.03 (1.01-1.03) for left hand) was significantly different than the ratio in control men [0.97 (0.95-0.99)] for right and left hand) (p<0.0001) and similar to the ratio found in control women [1.02 (1-1.03)] for right and left hand) (p=1). Men with gynecomastia were characterized with higher values of the following variables: weight, waist and hip circumferences, BMI and WHR. Their body height was significantly greater than in women (p<0.0001) but similar to the values observed in control men (p=0.2687).

The findings presented in this study may influence the aetiology-related classification of gynecomastia and justify introducing the new group: "gynecomastia related to the prenatal sex hormones disturbances".