In the hair cortex, hair keratin intermediate filaments are embedded in an interfilamentous matrix, consisting of hair keratin-associated proteins (KRTAP), which are essential for the formation of a rigid and resistant hair shaft through their extensive disulfide bond cross-linking with abundant cysteine residues of hair keratins. The matrix proteins include the high-sulfur and high-glycine-tyrosine keratins. The most frequent variant has a stop codon instead of Cys-15, giving rise to a truncated protein and is represented on the reference genome assembly (GRCh38/hg38). The variant Cys-15 is rare, except in some populations from Africa and non-Finnish Europa. The sequence shown is rare and is not represented on the reference genome assembly (GRCh38/hg38). Human have a similar number of genes as other primates despite the relative hairlessness of humans. Belongs to the KRTAP type 28 family.