Mondo Description Cockayne syndrome type III, also known as the mild form of Cockayne syndrome, is a rare genetic disorder that causes early (premature) aging. Unlike the more severe forms of this condition, individuals with Cockayne syndrome type III can have normal growth and development. Symptoms may include sunlight sensitivity (photosensitivity), hearing loss, eye and bone abnormalities, and changes to the brain that can be seen on imaging (brain MRIs). In general, symptoms of Cockayne syndrome type III are usually not noticeable until later in childhood.