Disorders of sexual development and sex hormones: Pathology review

Clay, a 17 year old male arrives at the clinic after noticing that he’s not developing like his friends. On further questioning, Clay mentions that he was born without a sense of smell. Upon physical examination, you notice that he has no facial or body hair, and that his external genitals are small and underdeveloped for his age. You decide to run a blood test, which shows low levels of the hormones GnRH, LH, FSH, and testosterone. Finally, you order a semen analysis, which reveals a low sperm count.

Next comes Jessie, a 13 year old girl, and her concerned mother, who’s noticed that Jessie has started to develop some masculine features, such as a deeper voice and excess body hair growth. A blood test shows increased testosterone levels and low dihydrotestosterone, so you decide to perform a karyotype test, which reveals 46 chromosomes, with one X and one Y chromosome.

Okay, now based on their initial presentation, both Clay and Jessie seem to have some form of disorder of sexual development and sex hormones.

But first, let’s go over some terminology! On the one hand, we all have a genotypic sex, which is determined by our karyotype or set of chromosomes. Generally, there are two sex chromosomes; those who have X and Y sex chromosomes are typically considered genetically males, while those who only have X chromosomes are typically considered genetically females. On the other hand, phenotypic sex is determined by the primary sexual characteristics, so the genitalia and gonads, as well as the secondary sexual characteristics, such as breast and muscle development, as well as body hair and fat distribution.

The development of primary and secondary sexual characteristics is generally under control of the hypothalamic-pituitary-gonadal axis. First, the hypothalamus secretes gonadotropin-releasing hormone, or GnRH for short, which goes to the anterior pituitary to stimulate the release of gonadotropic hormones, which are luteinizing hormone or LH, and follicle-stimulating hormone or FSH. LH and FSH then stimulate the gonads to produce sex hormones; in males, LH stimulates the Leydig cells of the testes to secrete testosterone, and FSH stimulates the Sertoli cells to secrete inhibin B. Testosterone and inhibin B are responsible for the development of male primary sexual characteristics, like enlargement of the penis and testes; as well as male secondary sexual characteristics, such as a deepening of the voice, a male pattern of hair growth on the face, chest, axillae, and genital areas, and increased muscle mass.