CYP19A1 encodes aromatase, a cytochrome P450 monooxygenase that catalyzes the conversion of androgens (androstenedione and testosterone) to estrogens (estrone and estradiol). The enzyme performs three successive oxidation reactions, including a final aromatization step that yields a phenolic A ring. CYP19A1 also converts dihydrotestosterone to delta1,10-dehydro 19-nordihydrotestosterone and exhibits 2-hydroxylase activity toward estrone. The reaction mechanism uses molecular oxygen, with one oxygen atom inserted into substrate and the other reduced to water, powered by NADPH via cytochrome P450 reductase. CYP19A1 polymorphisms show controversial associations with endometriosis risk; the CYP19A1 rs10046 variant did not meet statistical significance in a meta-analysis of endometriosis-related polymorphisms 1. In women with stage III-IV endometriosis, intrafollicular CYP19A1 expression in granulosa cells failed to correlate with estradiol levels, contrasting with controls, though no difference in baseline CYP19A1 expression was detected between disease and control groups 2. At the population level, gnomAD v4.1 classifies this gene as loss-of-function tolerant (LOEUF=0.79); this is distinct from clinical pathogenicity, as ClinVar contains 84 pathogenic or likely pathogenic variants. Clinically, CYP19A1 inhibitors including anastrozole, letrozole, and exemestane are widely used in breast cancer therapy to suppress estrogen biosynthesis.