Hereditary pigmentary disorders
Pigmentation in human skin differs individually and is regulated by more than 100 genes. The discovery of an increasing number of these genes has shed light on the molecular basis and pathogenesis of genetic pigmentary disorders. They are very rare and can be caused by changes in melanocyte number or melanin synthesis as well as development, transport and transfer of melanosomes. Pigmentary disorders can be divided into hyper- and hypopigmentation, of which the distribution can be diffuse or localized. Localized hypopigmentation can be found in piebaldism, Waardenburg syndrome and Tietz syndrome, whereas diffuse forms are typical for oculocutaneous albinism, Hermansky-Pudlak syndrome, Chediak-Higashi syndrome and Griscelli syndrome. Hyperpigmentation can be divided into diffuse, reticular or localized forms. They must be distinguished from endocrinopathies which may show hyperpigmentation, and from poikilodermatous syndromes displaying internal involvement.