By analysis of the existing available data, we have found that the locations of disease-causing mutations in epidermal keratin genes are distributed in a non-random manner. Most occur in exons 1 and 7 which encode the highly conserved 1A and 2B rod domain sequence regions of the keratin chains. Recent structural studies have suggested these sequences define an important overlap between neighboring molecules in keratin intermediate filaments. In order to better map the extent of these overlap sequences and concurrently to identify those sequences likely to be sensitive to mutations, we have used a series of synthetic peptides in an established filament disassembly assay. Thus residue positions 7-16 of the 1A and positions 107-117 of the 2B rod domain segments describe the extent of the molecular overlap window wherein mutations in keratin (and perhaps other) intermediate filaments are most likely to alter filament stability and lead to abnormalities.