NF1 may be due to faults (mutations) in the NF1 gene. The NF1 gene is a ‘tumour protection’ gene that helps to protect against benign and malignant tumours. Everyone has two NF1 genes (one from their mother, and one from their father). If one of the genes is not working, this is known as having a faulty NF1 gene, or having an NF1 mutation. People with a faulty NF1 gene are known to have Neurofibromatosis type 1.
Sometimes, the faulty NF1 gene is only in some of the cells of the body. This is known as being mosaic. People with mosaic NF1 may have milder features.
Sometimes, the faulty NF1 gene cannot be found using current technology, in this case NF1 can still be diagnosed using a set of criteria.