From OMIM
In the evaluation of male infertility, the Sertoli cell-only (SCO) syndrome is diagnosed on testicular biopsy when either no germ cells are visible in any seminiferous tubules (SCO type I) or germ cells are present in a minority of tubules (SCO type II). It is believed that the latter variant arises from a failure to complete differentiation and maturation of spermatocytes and spermatids, leading to degeneration of germ cells within most tubules (Sargent et al., 1999). Another, possibly X-linked, form of Sertoli cell-only syndrome has also been reported (305700). Heterogeneity of Spermatogenic Failure See 415000 for a general discussion of the AZF region of the Y chromosome and Y-linked nonobstructive spermatogenic failure. For a discussion of phenotypic and genetic heterogeneity of spermatogenic failure, see SPGF1 (258150).  http://www.omim.org/entry/400042

From MedlinePlus Genetics
Some men with Y chromosome infertility who have mild to moderate oligospermia may eventually father a child naturally. Men with oligospermia may also be helped with assisted reproductive technologies; most men with Y chromosome infertility have some sperm cells in the testes that can be extracted for this purpose.

Y chromosome infertility is a condition that affects the production of sperm and causes male infertility, which means it is difficult or impossible for affected men to father children. An affected man's body may produce no mature sperm cells (azoospermia), fewer than the usual number of sperm cells (oligospermia), or sperm cells that are abnormally shaped or that do not move properly. Men with Y chromosome infertility do not have any other signs or symptoms related to the condition.  https://medlineplus.gov/genetics/condition/y-chromosome-infertility