Defects in CYLD are the cause of familial cylindromatosis (CYLD) also known as turban tumor syndrome or dermal eccrine cylindromatosis. CYLD is an autosomal dominant and highly tumor type-specific disorder. The tumors (known as cylindromas because of their characteristic microscopic architecture) are believed to arise from or recapitulate the appearance of the eccrine or apocrine cells of the skin that secrete sweat and scent respectively. Cylindromas arise predominantly in hairy parts of the body with approximately 90% on the head and neck. The development of a confluent mass which may ulcerate or become infected has led to the designation "turban tumor syndrome". The skin tumors show differentiation in the direction of hair structures, hence the synonym trichoepithelioma. 
CYLD has deubiquitinating activity.