KRTAP1-3 (keratin-associated protein 1-3) is a high-sulfur hair keratin-associated protein encoded on chromosome 17-21 that plays a structural role in hair shaft formation. KRTAP1-3 belongs to a multigene family of hair keratin-associated proteins (KAPs) that form an interfilamentary matrix within the hair cortex 1. These proteins interact closely with hair keratins and are essential for creating a rigid and resistant hair shaft through extensive disulfide bond cross-linking with cysteine-rich hair keratins 2. The KRTAP1-3 gene exhibits size polymorphisms arising from intragenic deletions and duplications of pentapeptide repeats, with both frequent and rare population-specific alleles identified in Caucasian and Japanese populations 2. In situ hybridization studies localize KRTAP1-3 mRNA to the upper cortex of the hair shaft during the anagen phase 1. Clinically, KRTAP1-3 expression is significantly decreased in alopecia areata tissues, particularly in severe subtypes (alopecia totalis and universalis), suggesting its potential role as a biomarker for predicting disease progression with predictive accuracies reaching 93.8% 3. Additionally, KRTAP1-3 was identified as a gene whose expression is promoted during dental pulp cell differentiation in response to osteopontin, though its specific function in this context requires further investigation 4.