Genetics and hormones in testicular descent.

Testicular descent is an essential part of normal male sexual development. Any anomaly that disrupts normal testicular descent will be clinically evident as cryptorchidism. Several factors, such as Hoxa-10, epidermal growth factor (EGF), calcitonin gene-related peptide (CGRP), and hormones, especially androgens and insulin-like factor 3 (INSL-3), have been suggested as being regulators of testicular descent. Testicular descent from the lower pole of the kidney into the extra-abdominal scrotal sac is a two-stage process of transabdominal and inguino-scrotal migration. The transabdominal phase is androgen independent, whereas the inguino-scrotal phase depends on androgen action. Disruption of androgen action eg. by environmental anti-androgens are suspected as contributing to cryptorchidism. Estrogens can down-regulate INSL-3 production and thereby disturb testicular descent. Familial occurrence in some cases suggests a possible genetic background for cryptorchidism.