The neurofibromatosis type 1 gene is found on chromosome 17. It codes for a protein called neurofibromin, which is a tumour suppressor protein. Inheritance of mutations in this gene is autosomal dominant .

Criteria

There are clear diagnostic criteria for NF1 based on the classical features of the condition. There must be at least 2 of the 7 features to indicate a diagnosis. You can remember this with the mnemonic CRABBING.

• C – Café-au-lait spots (6 or more) measuring ≥ 5mm in children or ≥ 15mm in adults
• R – Relative with NF1
• A – Axillary or inguinal freckles
• BB – Bony dysplasia such as Bowing of a long bone or sphenoid wing dysplasia
• I – Iris hamartomas (Lisch nodules) (2 or more) are yellow brown spots on the iris
• N – Neurofibromas (2 or more) or 1 plexiform neurofibroma
• G – Glioma of the optic nerve

Investigations

Diagnosis is based on clinical criteria and no investigations are required to make a definitive diagnosis.

Genetic testing can be used where there is doubt.

Xrays can be used to investigate bone pain and bone lesions.

Imaging with CT and MRI scans can be used to investigate lesions in the brain, spinal cord and elsewhere in the body.

Management

There is no treatment of the underlying disease process or to prevent the development of neurofibromas or complications.

Management is to control symptoms, monitor the disease and treat complications.

Complications