Sertoli-cell-only (SCO) syndrome, also called germ cell aplasia, describes a condition of the testes in which only Sertoli cells line the seminiferous tubules. Sertoli cells help to make up the blood-testis barrier and are responsible assisting with sperm production. These cells respond to follicle-stimulating hormone (FSH) released by the hypothalamus, which helps to promote spermatogenesis. Typically, men with SCO syndrome present between age 20-40 years for evaluation of infertility and are found to be azoospermic, a term describing the absence of sperm in the ejaculate.
The physical examination findings are often unremarkable, and the diagnosis is made based on testicular biopsy findings. While investigation to identify a cause of SCO syndrome is ongoing, the etiology and mechanism of this process are currently unknown. No known effective treatment exists, but these men may be able to reproduce with assisted reproductive technology.
See the image below.
Sertoli cells have in general have several functions. They provide support to the developing spermatogonia and secrete a number of substances that aid in fetal development. For example, Sertoli cells secrete anti-müllerian hormone (AMH), which helps to ensure regression of müllerian ducts as a fetus develops into a male. They also secrete inhibin and activin, which help to regulate FSH secretion by the hypothalamus.  Activin has a positive feedback on the hypothalamus, causing increased levels of FSH necessary for sperm production. Inhibin has a negative feedback on the hypothalamus and helps to maintain testicular homeostasis. See the image below.
Involvement of other organ systems is rare, but is secondary to the underlying condition causing SCO syndrome. As an example, Klinefelter syndrome is characterized by SCO and Leydig cell hyperplasia.
The prevalence of SCO syndrome in the overall population is extremely low. Approximately 10% of US couples are affected by infertility. Of these couples, approximately 30% have a pure male factor as the underlying cause, and another 20% have a combined male and female factor. Although precise figures are difficult to obtain, less than 5%-10% of these infertile men have SCO syndrome.
SCO syndrome presents during the evaluation of azoospermia in couples having difficulty in initiating a pregnancy. These men typically present with infertility as the only symptom.
SCO syndrome has no known racial predilection; however, SCO is more common in white men. In most series, most couples who present for evaluation of male infertility are white.
SCO syndrome affects only phenotypic men.
The most common age at presentation is 20-40 years. These age groups represent most men who are trying to initiate a pregnancy.
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