ZFX is a zinc finger transcription factor located on chromosome X.11 that encodes a DNA-binding protein with 13 zinc fingers structurally similar to its Y-chromosome X ZFY 1. ZFX functions as a transcriptional activator that binds to CpG island promoters and regulates gene expression through recruitment of histone modification complexes; reduction of ZFX increases RNA polymerase II pausing at target promoters and decreases histone H4 acetylation 2. Notably, ZFX escapes X-inactivation and modulates autosomal gene expression broadly, with its effects on approximately 21% of expressed genes in lymphoblastoid cells and fibroblasts being comparable to those of the Y chrX's ZFY 3. Pathogenic ZFX variants cause X-linked intellectual developmental disorder, syndromic 37, characterized by developmental delay, behavioral abnormalities, hypotonia, and distinctive facial features including thickened eyebrows, external eye abnormalities, and ear abnormalities 4. Missense variants in the DNA-binding domain alter transcriptional activity of target genes, while truncation variants produce more severe phenotypes 4. Additional clinical associations include hyperparathyroidism and increased tumor risk in affected families 4. ZFX variants have also been identified as potential candidates in nonobstructive azoospermia, suggesting involvement in male reproductive development 5.