- Sertoli‑cell‑only syndrome (SCOS) is a severe form of male infertility characterised by the complete absence of germ cells within the seminiferous tubules. Only Sertoli cells line the tubules, meaning spermatogenesis cannot occur. SCOS is one of the most advanced pathological forms of non‑obstructive azoospermia and often results in a total lack of sperm in the ejaculate.
- In SCOS, the seminiferous epithelium is structurally present but functionally inactive. Sertoli cells maintain their supportive role, but without spermatogonia, spermatocytes or spermatids, the process of sperm production cannot begin. Histologically, the tubules appear uniform, with Sertoli cells lining the basement membrane and no evidence of germ‑cell layers. This pattern distinguishes SCOS from hypospermatogenesis or maturation arrest, where germ cells are present but impaired.
- SCOS can be congenital or acquired. Congenital causes include AZFa microdeletions, which are strongly associated with complete SCOS. Mutations in genes regulating germ‑cell development — such as DMRT1, NR5A1 and KIT — can also lead to germ‑cell depletion. Acquired SCOS may result from chemotherapy, radiation, testicular torsion, viral orchitis, toxins or severe varicocele. In these cases, germ cells are lost due to injury, while Sertoli cells remain.
- Hormonal profiles in SCOS often show elevated FSH, reflecting the pituitary response to reduced inhibin B from Sertoli cells. Testosterone levels may be normal or slightly reduced depending on Leydig‑cell function. Diagnosis typically requires testicular biopsy, as semen analysis alone cannot distinguish SCOS from other forms of NOA.
- Clinically, SCOS has major implications for fertility. In complete SCOS, sperm retrieval through micro‑TESE is usually unsuccessful. However, in focal SCOS, small pockets of spermatogenesis may exist, allowing occasional sperm retrieval for ICSI. Genetic counselling is recommended, especially when Y‑chromosome microdeletions or germ‑cell developmental gene mutations are suspected.
- Sertoli‑cell‑only syndrome remains a key diagnostic category in male infertility, representing the endpoint of germ‑cell loss and testicular failure. Understanding its molecular basis continues to guide research into spermatogenic regeneration, stem‑cell therapy and targeted reproductive interventions.
