KRT31 encodes keratin 31, a type I intermediate filament protein that plays a crucial role in hair shaft structure and differentiation. The protein functions as a structural component of the hair follicle, with expression patterns indicating its involvement in hair fiber formation and morphology determination 1. KRT31 works in partnership with keratin 85, forming part of the cytoskeletal network essential for proper hair shaft development 2. The gene shows specific spatial and temporal expression patterns during hair follicle growth cycles, with transcription occurring in a coordinated sequence during anagen phase and ceasing during telogen 1. Mechanistically, KRT31 expression is regulated by both vitamin D receptor (VDR) and β-catenin signaling pathways, where VDR promotes β-catenin-mediated hair follicle differentiation 3. Disease relevance includes its role in monilethrix, a rare hereditary hair disorder characterized by beaded hair shafts and increased fragility, where nonsense variants in KRT31 cause autosomal dominant inheritance patterns 2. Additionally, KRT31 downregulation is observed in alopecia areata lesional scalp tissue 4. Clinical significance extends to forensic applications, where KRT31 protein can be detected and sequenced from small hair shaft samples for identification purposes 5.