We report a novel mutation in a case of ichthyosis bullosa of Siemens that results in a threonine --> proline substitution in a novel location, codon 485 in a highly conserved residue position of the IATYRKLLEGE consensus motif at the end of the 2B rod domain segment of the keratin 2e chain. The disease phenotype is consistent with the inappropriate substitution of a proline near the end of the rod domain, because it lies near the predicted molecular overlap region of coiled-coil molecules, which is critical for the maintenance of the structural integrity of keratin intermediate filaments.