Hereditary palmoplantar keratodermas.

Hereditary palmoplantar keratodermas (PPK) comprise a clinically and genetically heterogeneous group of genodermatoses, which share impaired epidermal differentiation resulting in prominent palmoplantar hyperkeratosis. Classically, keratodermas have been separated according to their clinical appearance into diffuse, focal, and as a feature of ectodermal dysplasias and many other syndromes. Since molecular genetic analyses have helped characterize the underlying genetic defects in an increasing number of hereditary PPK over the last two decades, a pathophysiological separation seems more reasonable. Today PPK can be classified based on defects in keratins, loricrin, desmosomes, connexins, and cathepsins. Although these proteins have different structures and functions, all of them influence epidermal differentiation and cornified envelope assembly. Depending on tissue distribution and location of mutation with a certain gene, the clinical spectrum of PPK range from a pure palmoplantar restricted skin abnormality to a complex combination of symptoms with dental anomalies, deafness, progressive cardiomyopathy and even cancer. Solely for those reasons, a correct diagnosis based on molecular genetic analyses is mandatory, although a causal therapy is still not available. Instead, several therapeutic modalities including topical ointments, surgical interventions and systemic retinoids help to reduce the patients' symptoms.