Gonadal function and testicular histology in Noonan's syndrome with bilateral cryptorchidism.

Testicular histology and gonadal function were studied in 2 patients with Noonan's syndrome accompanied by bilateral cryptorchidism. Plasma FSH level was elevated above the normal range, but plasma levels of LH, prolactin, and testosterone were within normal ranges in both cases. The administration of LH-RH resulted in abnormally high response of plasma gonadotropins in both cases. The response of plasma testosterone to the administration of LH-RH was poor in case 2, but case 1 showed normal response. Testicular histology showed reduction of tubular diameter, Leydig cells per seminiferous tubules, and spermatogonia per tubule in both cases. The results indicate that bilateral cryptorchid patients with Noonan's syndrome have an abnormality in the hypothalamo-pituitary-gonadal axis.