A failure of spermatogenesis to progress beyond the round spermatid stage. The round spermatid is the first haploid cells produced during spermatogenesis and normally further develop into mature spermatozoa. This abnormality can be visualized with testicular biopsy and is characterized seminiferous tubules with increased numbers of round spermatids with few or no mature spermatozoa. [from
HPO]