The human type I hair keratin subfamily comprises nine individual members, which can be subdivided into three groups. Group A (hHa1, hHa3-I, hHa3-II, hHa4) and B (hHa7, hHa8) each contains structurally related hair keratins, whereas group C members hHa2, hHa5, and hHa6 represent structurally rather unrelated hair keratins1.

Keratins are divided into type I (acidic) and type II (basic to neutral) members, which form the 10-nm intermediate filament cytoskeletal network of epithelial cells through the obligatory association of equimolar amounts of type I and type II keratins [2][3][4].

The various type I hair keratin antibodies proved to be highly specific in that they recognized only single protein bands when analyzed in Western blots of one-dimensionally resolved human hair keratins. One exception concerned the hHa2 antibody, which besides the prominent hHa2 protein band also reacted with a slightly larger minor band1. A LEF-1 consensus sequence is invariably located at a highly conserved position in the proximal promoter region of the members of the human type I hair keratin family but it is specifically lacking in the entire promoter of the hHa7 gene5.