Sertoli-cell-only (SCO) syndrome, also called germ cell aplasia or Del Castillo syndrome, describes a condition of the testes in which only Sertoli cells line the seminiferous tubules.[1] 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 on the basis of 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.
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This hematoxylin and eosin section of a testis biopsy (400X) demonstrates an individual tubule lined only with Sertoli cells (Sertoli-cell-only [SCO] ....
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.[2] 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.
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Interaction between the hypothalamus and the testes. Courtesy of Wikispaces at https://malereprobio12.wikispaces.com/.
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.
A study investigating the PRPS2 protein found that PRPS2 expression was significantly greater in patients with SCO syndrome than in those with normal spermatogenesis. In SCO syndrome mouse model, PRPS2 overexpression significantly inhibited cell apoptosis and promoted cell cycle transition in TM4 Sertoli cells.[3]
Ovol1 and Ovol2, a family of zinc finger transcription factors, are expressed in spermatocytes at the pachytene stage and are suggested to be critical regulators of pachytene progression in male germ cells. Taniguchi and colleagues reported that while hOvol1 and hOvol2 were detected by reverse transcription-polymerase chain reaction (RT-PCR) in the testes of patients capable of spermatogenesis, they were not detected in those with Sertoli cell-only syndrome. The researchers concluded that further investigation of Ovol1 and Ovol2 functions in human spermatogenesis might lead to a novel therapy.[4]
Yao and colleagues found 174 microRNAs (miRNAs) were differentially expressed in human Sertoli cells in men with SCO syndrome compared with men with obstructive azoospermia, suggesting that these miRNAs may be associated with the pathogenesis of SCO syndrome.[5]
Most cases of SCO syndrome are idiopathic. A congenital absence of germ cells due to failure of migration of gonocytes is theoretically possible.
A genetic basis for SCO syndrome is under intense investigation.[6] Massive deletions in the azoospermia factor (AZF) region of the Y chromosome, specifically in AZFb/b+c, have been found in men with SCO syndrome. Five deletions arose from nonallelic homologous recombination between palindromes P5 and P1 and 2 between P4 and P1. In addition, two deletions were found at novel proximal breakpoints in the interval region between P4 and P3.[7]
Y-chromosome microdeletions are also occasionally identified as a cause of SCO syndrome.[8, 9] As research continues, more genetic and chromosomal abnormalities associated with SCO may be found.
Expression of Fas, FasL, and active caspase-3 has been detected in Sertoli cells and hyperplastic interstitial cells. This may be associated with apoptotic elimination or altered maturation of Fas-expressing germ cells through the activation of caspase-3.[10]
Exposure to chemicals and toxins may cause SCO; however, direct cause-and-effect relationships in humans have been difficult to document.
Klinefelter syndrome, 47 XXY, results in a characteristic biopsy appearance of SCO and Leydig cell hyperplasia.[11]
Attempting to distinguish between primary (congenital) and secondary (acquired) SCO syndrome is of no prognostic significance.
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 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. The most common age at presentation is 20-40 years and represents most men who are trying to initiate a pregnancy.
Sertoli-cell-only (SCO) syndrome remains a stable condition with no appreciable improvement in prognosis or sperm production. Investigations have suggested that the prevalence of testicular nodules and cancer in patients with SCO syndrome is greater than that of the baseline. Initial reports show a 26% risk of nodules and a 10.5% risk of malignancy in testicles of men with pure SCO syndrome.[12] Further studies would be helpful to support this initial report.
A number of models have been developed to predict successful sperm retrieval with testicular sperm extraction, although efficacy of these models is moderate. In general, higher patient age, higher values for serum testosterone, and lower values for serum FSH and LH were predictive for successful sperm retrieval. Idiopathic nonobstructive azoospermia and the presence of an AZFc deletion were predictive for unsuccessful sperm retrieval.[13]
Couples faced with a diagnosis of SCO syndrome should be given the options of adoption, use of donor sperm with intrauterine insemination and testicular sperm extraction with in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI). See Infertility Treatments.
Although sperm may be successfully extracted from small pockets of spermatogenesis in up to 20%-40% of men with a diagnosis of SCO syndrome, the use of these sperm for IVF/ICSI is successful in only a small percentage of patients and thus should not be offered as a standard of care. Adoption is an effective option; however, couples must understand that adoption can be a lengthy and costly process. For intrauterine insemination, donor sperm may be obtained locally or nationally through sperm banks.
The most common presentation involving Sertoli-cell–only (SCO) syndrome is a young man seeking evaluation for infertility. His semen analysis will have demonstrated azoospermia (absence of sperm on semen analysis). Less commonly, these men may have severely decreased sperm densities of less than 1 million sperm per mL. In this latter situation, the testes have foci of SCO syndrome and hypospermatogenesis.
Azoospermia may be due to spermatogenic failure or obstruction. Examples of causes of spermatogenic failure include genetic factors, hormonal factors, idiopathic factors, toxin exposure, history of radiation therapy, and history of severe trauma. These conditions may be associated with SCO syndrome. Obstruction would not be associated with SCO.
In men with SCO syndrome, the testes are usually small to normal in size, with a normal shape and consistency. However, some patients may have marked atrophy of the testes. Patients with SCO syndrome exhibit normal virilization without gynecomastia.The remaining physical examination findings are typically unrevealing.
Men undergoing evaluation for infertility typically undergo hormonal evaluation with follicle-stimulating hormone (FSH) and testosterone studies. Luteinizing hormone (LH) and prolactin testing are not routinely necessary. In addition, routine testing for male infertility includes at least two semen analyses. Results are as follows:
Plasma testosterone levels are typically normal.
Azoospermia and an elevated serum FSH level (>2-3 times reference range) indicate spermatogenic failure.
Azoospermia and a serum FSH level within the reference range suggest possible spermatogenic failure or an obstruction.
The serum FSH level is typically (90%) elevated. Elevations of greater than 2.5-3 times the reference range are diagnostic for spermatogenic failure.
In its purest sense, Sertoli-cell-only (SCO) syndrome must present as azoospermia; however, a minority of men with the syndrome have foci of spermatogenesis in a testis that is predominantly SCO.
If a couple is considering intracytoplasmic sperm injection (ICSI), a micromanipulation technique in which a single sperm is injected into an oocyte, they should be offered genetic testing with a Y-chromosome microdeletion assay and karyotyping.
Azoospermia should be documented with a semen pellet analysis. The semen pellet is performed by centrifuging a grossly azoospermic semen specimen for 10 minutes at 1500-2000 rpm. This pellet is considered standard for the diagnosis of azoospermia. The pellet at the bottom of the conical tube is examined under a microscope at a magnification of 400X. If sperm are identified, then patchy spermatogenesis within the testes is present.
Men with SCO syndrome who are azoospermic are at an increased risk of testicular nodules and cancer. As such, the roles of clinical evaluation, ultrasonography, and biopsy should be emphasized.[12]
Germinal cell aplasia (SCO syndrome) is histologically characterized by seminiferous tubules that contain only Sertoli cells, with a complete absence of all germ cells. In most cases, the tunica propria and basement membranes are not thickened appreciably, and the tubules are normal or slightly decreased in diameter. The interstitium contains normal numbers of Leydig cells. One may observe a patient with an otherwise classic example of germinal cell aplasia who has an occasional tubule with some degree of spermatogenesis. Levin has classified this as germinal cell aplasia and focal spermatogenesis.
The testis biopsy is the criterion standard for diagnosis of SCO syndrome. Most urologists are familiar with the open biopsy technique. This technique may be performed with a local cord block in most men. Alternatively, a general anesthetic may be used. A small biopsy sample is taken from the surface of the testis and placed in Bouin fixative. Findings on testicular biopsy may include severe hypospermatogenesis, maturation arrest-spermatid stage, maturation arrest-spermatocyte stage, or SCO syndrome.
Men may be offered a testis biopsy to define whether an obstruction or spermatogenic failure is present. If the serum FSH level is greater than 2.5-3 times the reference range and intracytoplasmic sperm injection (ICSI) is not a consideration, the biopsy findings would not change the management plan. If the couple is considering ICSI, a diagnostic biopsy may be helpful to provide counseling regarding the possibility of finding sperm at the time of ICSI. If spermatogenic failure is predominant and rare sperm are identified, testicular extraction of sperm with ICSI may be possible at a later time. At the time of testis biopsy, a specimen may be cryopreserved for potential use of any sperm at a later time.
Some investigators discuss the use of fine-needle aspiration cytology (FNAC) prior to biopsy as a less invasive means of establishing a diagnosis. In addition, this technique can offer prognostic information regarding the likelihood of successful testicular sperm extraction (TESE).[14]
No effective medical therapy exists for Sertoli-cell-only (SCO) syndrome. If the couple is considering in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI), consultation with a reproductive endocrinologist is necessary.
Testicular sperm extraction (TESE) may be offered to couples considering IVF/ICSI. At specialty centers, as many as 20%-40% of men with SCO syndrome may be identified as having isolated foci of spermatogenesis within the testis; however, the option of using donor sperm must be discussed with the couple. At most centers, sperm recovery rates are much lower.
TESE is a testis biopsy performed with the intent of finding mature sperm within the seminiferous tubules. Multiple and extensive biopsies are typically required when SCO syndrome is present. Because spermatogenesis may be patchy within the testis, occasional pockets of isolated sperm production may be identified, even when the predominant histopathology finding is SCO syndrome.
Microsurgical TESE (mTESE) may be performed at some specialty centers, offering improved chances of successful sperm extraction with a decreased risk of morbidity.
In patients with SCO syndrome with pockets of sperm production, repair of a concurrent varicocele can increase the chances of subsequent successful surgical retrieval of sperm.
A meta-analysis of the outcomes of 37 trials enrolling a total of 1248 men with Klinefelter syndrome who underwent TESE found that sperm retrieval rates per TESE cycle of ranged from 39-48%. Similar results were observed for in both conventional TESE (35-50%) and mTESE (38-52%). Overall a total of 218 pregnancies occurred after 410 ICSI cycles for a pregnancy rate of 43%. Meta-regression analysis showed that age; testis volum;e and FSH, LH, and testosterone levels at enrollment had no effect on the final sperm retrieval or pregnancy rate.[15]
Edward David Kim, MD, FACS, Professor of Surgery, Division of Urology, University of Tennessee Graduate School of Medicine; Consulting Staff, University of Tennessee Medical Center
Disclosure: Serve(d) as a speaker or a member of a speakers bureau for: Endo.
Coauthor(s)
Adam F Stewart, MD, Resident Physician, Department of Surgery, Division of Urology, University of Tennessee Medical Center, University of Tennessee Graduate School of Medicine
Disclosure: Nothing to disclose.
Jared Moss, MD, Resident Physician, Division of Urology, University of Tennessee Graduate School of Medicine
Disclosure: Nothing to disclose.
Joe D Mobley, III, MD, MPH, Urologist, Kentucky Lake Urology Clinic
Disclosure: Nothing to disclose.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Chief Editor
Bradley Fields Schwartz, DO, FACS, Professor of Urology, Director, Center for Laparoscopy and Endourology, Department of Surgery, Southern Illinois University School of Medicine
Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: AUA Journal of Urology<br/>Serve(d) as a speaker or a member of a speakers bureau for: Cook Medical; Olympus, .
Additional Contributors
Erik T Goluboff, MD, Professor, Department of Urology, College of Physicians and Surgeons, Columbia University College of Physicians and Surgeons; Director of Urology, Allen Pavilion, New York Presbyterian Hospital
This hematoxylin and eosin section of a testis biopsy (400X) demonstrates an individual tubule lined only with Sertoli cells (Sertoli-cell-only [SCO] syndrome). The Sertoli cells line the seminiferous tubule.
Interaction between the hypothalamus and the testes. Courtesy of Wikispaces at https://malereprobio12.wikispaces.com/.
This hematoxylin and eosin section of a testis biopsy (400X) demonstrates an individual tubule lined only with Sertoli cells (Sertoli-cell-only [SCO] syndrome). The Sertoli cells line the seminiferous tubule.
Interaction between the hypothalamus and the testes. Courtesy of Wikispaces at https://malereprobio12.wikispaces.com/.
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