Second to fourth digit (2D:4D) ratio is the ratio of index to ring fingers length. It reflects prenatal androgen exposure and sensitivity. Androgens are important in the pathogenesis of acne vulgaris, This ratio may therefore be of significance in determining the expression of androgen receptors.
To investigate the relationship between second to fourth digit ratio and androgen receptor expression in female patients with acne vulgaris and to assess its association with clinical aspects of acne vulgaris.
Females patients (n = 352) with different degrees of acne vulgaris severity and 168 age-matched females were enrolled. Right, left and total second to fourth digit ratios were calculated. Biopsies from all participants were processed for androgen receptor expression by immunohistochemical method.
Right, left and total second to fourth digit ratios were significantly lower in acne vulgaris patients than controls (P < 0.001 for all), and each of them had a significant negative correlation with duration of acne vulgaris (P < 0.001; P = 0.013; P < 0.001, respectively). Androgen receptors were detected in epidermal keratinocytes, hair follicles, sebaceous glands and fibroblasts. Right second to fourth digit ratio showed a negative correlation with androgen receptor H score of keratinocytes (r = -0.28;P = 0.02), hair follicles (r = -0.22;P = 0.05) and fibroblasts (r = -0.37;P = 0.001), while left second to fourth digit ratio demonstrated negative correlation with androgen receptor H score of sebocytes (r = -0.397;P < 0.000) only.
Lack of follow-up and absence of male participants were the main limitations of this study.
A masculine second to fourth digit ratio in female patients could anticipate acne vulgaris development, its duration and severity. Moreover, this ratio is associated with an upregulation of cutaneous androgen receptors. Taken together, second to fourth digit ratio could help in designing plans for treatment of acne vulgaris.