Shagreen patch on the skin of a 22 year old African American male patient with tuberous sclerosis. Shagreen patches are a type of collagenous connective tissue naevi (birth mark). Tuberous sclerosis is a rare genetic disorder that causes benign (non-cancerous) tumours to grow in the brain and other organs, including the kidneys, heart, eyes, lungs and skin. It can cause seizures, intellectual disabilities and delayed development, as well as lung and kidney diseases.