(534) Concentration Matters: Genetic Disorders Prevalence in Oligozoospermic and Azoospermic Chilean Men

Introduction Genetic factors, including chromosomal abnormalities and Y-chromosome microdeletions, represent established causes of male infertility. Current International guidelines recommend genetic screening based on sperm concentration thresholds. EAU/ASRM guidelines recommend karyotype analysis for men with concentration below 5 million/mL and Y-chromosome microdeletion testing particularly in patients below 1 million/mL. However, comprehensive data comparing genetic abnormalities prevalence across distinct concentration ranges in systematically screened cohorts remain limited. Understanding real life genetic disorders prevalence, could help clinical decision-making, resource allocation and correct patient counselling. Objective The objective of the study is to determine the prevalence of genetic abnormalities (karyotype alterations and Y-chromosome microdeletions) in men presenting with azoospermia and severe oligozoospermia Methods Retrospective cohort study, analyzing 245 infertile men with severe oligozoospermia (sperm concentration ≤ 5 mill/mL) and azoospermia with palpable vas deferens, consulting at a tertiary andrological unit, between 2018 and 2025. Patients were stratified by sperm concentration: Azoospermia, ≤ 2 mill/mL and 2-5 mill/mL. All patients underwent standard G banding karyotyping and multiplex polymerase chain reaction (PCR) based Y-chromosome microdeletion analysis targeting AZFa, AZFb and AZFc regions Results Among 245 patients, 18 presented genetic abnormalities (7.3%). Distribution by concentration revealed that in the azoospermic group (n=136), 15 patients presented genetic alterations (11.2%); of which 9 were Karyotype abnormalities (6.5%) including Klinefelter syndrome variants (47,XXY and mosaics, n=3), 47,XYY mosaicism (n=1), and balanced chromosomal translocations (n=4). In this group, 7 patients presentes Y-chromosome microdeletions (5.1%) including AZFc (n=4), multiple deletions (n=2), and AZFa (n=1) In the ≤2 million/mL group (n=70): 3 patients (4.3%) presented genetic alterations. Y-chromosome microdeletionswere found in 3 patients, including AZFc (n=2) and AZFb (n=1) regions. No karyotype abnormalities were detected. Lastly, in the 2-5 million/mL group(n=39), no patients presneted genetic abnormalities. Overall, patients presenting Y-chromosome microdeletions (n=10) slightly exceeded the number of patients with karyotype abnormalities (n=9), with one patient presenting both Conclusions This study, of infertile men with seminal alterations, showed a concentration dependent gradient in genetic abnormalities prevalence. These findings validate current EAU/ASRM guidelines recommendations for genetic screening in azoospermia and severe oligozoospermia, while highlighting the diminishing diagnostic yield as sperm concentration increases. The absence of any genetic abnormalities in the 2-5 million/ml group could influence resource allocation within genetic testing protocols. Nevertheless, the 4.3% detection rate below 2 million/mL warrants extending systematic genetic evaluation in this patient group, particularly considering its implications for assisted reproductive technology planning and counselling Disclosure No