Introduction: Y chromosome microdeletions (YCMD) are a common cause of non-obstructive azoospermia. While men with deletions in the azoospermia factor C (AZFc) region have a high likelihood of having sperm in the ejaculate, or sperm retrievable with effective microdissection testicular sperm extraction (mTESE) procedure, those with complete deletions in the AZFa or AZFb regions have a poor prognosis for identification of sperm. Men with AZFa deletions typically do not have any germ cells, and no men, to-date, with complete AZFb deletions have had usable sperm identified. Partial deletions of AZFb appear to portend a different prognosis for fertility potential. Our objective was to evaluate semen parameters, sperm retrieval rates and fertility outcomes in men with partial deletions of the AZFb region. Methods: We retrospectively reviewed 468 men with YCMDs who underwent testing at our institution from 4/1996 to 8/2022. Of these, we identified 20 men with partial AZFb deletions, defined as a deletion of some but not all tested segments from sY1227 to sY1291. Of these, 8 had documented semen analysis and underwent mTESE by a single, high-volume surgeon (PS). Sperm retrieval rate (SRR) was defined as the presence of mature sperm identified after processing by a trained andrologist. Results: Of the 8 men with a partial AZFb deletion, 7 (87.5%) had a sY117-sY1291 deletion, and one (12.5%) had an sY1227-sY1192 deletion. All 8 men (100%) were azoospermic. Mean testosterone levels were 450.5 ± 350.5 (ng/dL), Mean FSH 6.5±2.8 (mIU/mL). After mTESE, 1 of 7 men (14%) with an sY117-sY1291 deletion was found to have sperm, and the 1 man with a sY1227-sY1192 deletion was found to have round spermatids on histology. Overall, the SRR was 12%. All pathology specimens (n=8, 100%) demonstrated maturation arrest. Conclusions: In this large series, we demonstrate that while patients with partial AZFb deletions are azoospermic, it is possible to find sperm at least for some men with mTESE. Distinguishing partial from complete AZFb deletions may have prognostic value. Further work is needed to determine which men with partial AZFb deletions are more likely to have a successful mTESE procedure. SOURCE OF Funding: Author JG is supported in part by the Frederick J. and Theresa Dow Wallace Fund of the New York Community Trust
