A condition caused by an inherited faulty gene. There are two types –  neurofibromatosis 1 & 2. People with neurofibromatosis 1 have an increased risk of tumours of the optic nerve (the nerve to the eye), the auditory nerve (to the ear) and some other types of brain tumour. People with neurofibromatosis 2 may develop tumours of the auditory nerve, called acoustic neuromas.