KRTAP26-1 (keratin-associated protein 26-1) is a structural protein specifically expressed in hair follicles, localized to the differentiated hair cuticle 1. As a member of the keratin-associated protein family, KRTAP26-1 functions in the hair cortex where it embeds hair keratin intermediate filaments within an interfilamentous matrix through extensive disulfide bond cross-linking with cysteine-rich hair keratins, contributing to hair shaft rigidity and resistance. In wool-bearing animals, KRTAP26-1 variants associate with fiber traits; the C variant correlates with improved wool quality, including increased staple length and decreased fiber diameter 2. KRTAP26-1 is located on chromosome 21 and has been identified as a placental-specific gene 3, though attempts to use it as a noninvasive prenatal biomarker for trisomy 21 diagnosis proved unsuccessful due to low quantities of cell-free mRNA. Recent research identified KRTAP26-1 as a candidate bladder cancer-specific biomarker in urine-derived small extracellular vesicles 4, suggesting potential clinical applications in liquid biopsy approaches. The protein demonstrates protein-binding capacity and cytosolic localization 1.