Understanding NF1
Neurofibromatosis type 1 (NF1), although rare, is one of the most common inherited genetic conditions, usually diagnosed in early childhood, affecting approximately 1 in 3000 people.1,2

Although NF1 is a genetic condition, only half of patients with the variant gene inherit it from a parent, while the other half develop it at random.1 An individual with the variant has a 50% chance of passing the variant on to their children.1
INT/UNB-NF1/0006 | October 2023
The below is not intended to confirm the diagnosis of NF1, which should be performed by a healthcare professional specialised in NF1.
Usually, NF1 can be diagnosed by physical examination and a family history check.2 A set of criteria was developed by a group of experts to help recognise NF1.3 Around 97% of people with NF1 will show symptoms by the age of 8 years.2
A: Two or more of the following are needed to identify NF1 in individuals who do not have a parent diagnosed with the condition:3
  1. Six or more ‘café-au-lait’ spots – discoloured, coffee-coloured patches on the skin
  2. Freckling in the armpit or around the groin area
  3. Two or more neurofibromas of any type or one plexiform neurofibroma (PN) – types of growths on nerves
  4. Optic pathway glioma – a slow-growing brain tumour around the optic nerve
  5. Two or more dome-shaped masses on the surface of the iris (Lisch nodules), or two or more bright patches in the white part of the eye (choroidal abnormalities)2
  6. A distinctive bone lesion – an abnormal change to one or more bones
  7. A defective version of the NF1 gene that is responsible for the disease, which is present in 50% of apparently normal tissue, such as white blood cells
B: A child of a parent who meets the diagnostic criteria specified above could also receive a diagnosis of NF1 if one or more of the criteria above are present.3

1. ‘Café-au-lait’ spots

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Café-au-lait spots, discoloured, coffee-coloured patches on the skin, are present in 99% of people with NF1 and first appear from birth up to 12 years of age.4

2. Freckling

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Freckling in the armpits or around the groin is present in 85% of people with NF1 and may first appear from 3 years of age to adolescence.4

3. Neurofibromas

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Neurofibromas are benign (non-cancerous) tumours that grow along the length of nerves.4 They can bulge out of the skin (cutaneous) or stay just under the surface (subcutaneous).4 Neurofibromas are present in 99% of people with NF1 and appear after 7 years of age, typically in late adolescence.4

PN are ‘interwoven’ tumours that can grow on nerves. PN can be seen or felt in up to 30% of people with NF1; however, they may be detected in up to 50% of people using whole-body imaging.4,5 They can first appear from birth up to 18 years of age.4

4. Optic pathway glioma

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Optic pathway gliomas are tumours of the optic nerve that can be identified using magnetic resonance imaging (MRI) and are observed in 15% of people with NF1.4,5 They first appear from birth up to 7 years of age.4

5. Abnormalities of the eye

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Signs of NF1 in the eye include Lisch nodules, which are lumps that grow in the iris (the coloured part of the eye) and are present in 90–95% of people with NF1.1,4 They tend to appear after 3 years of age.4

Choroidal abnormalities are bright, patchy spots and may also be seen by eye imaging examinations.2

6. Distinctive bone lesion

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Distinctive bone lesions include defects to the skeleton, for example, scoliosis (curved spine) and sphenoid wing dysplasia.1,4

Sphenoid wing dysplasia is characterised by an undersized or absent sphenoid (a bone that forms part of the skull around the eyes) and is present in less than 1% of people with NF1.4,6 It is found at birth if present.4

Other distinctive lesions include curving (bowing) of the shin bone and long bone fractures that do not heal.3

7. NF1 gene variant

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Genetic testing can be performed to identify a disease-causing NF1 gene variant.5 This variant must be present in 50% of apparently normal tissue (e.g. white blood cells) for it to be considered indicative of NF1.1
PN are ‘interwoven’ tumours that can grow on nerves. They can be seen or felt in up to 30% of people with NF1 but can be seen on whole-body imaging in up to 50% of people with NF1.4 They can cause a range of symptoms, including pain, muscle weakness and physical deformity.2,7 You can learn more about 
of NF1 and PN on the Living with NF1 page.
Living with NF1
PN can grow along any nerve and, depending on where they grow, can affect different parts of the body.7 PN are usually benign (non-cancerous), but can become malignant (cancerous) in rare cases.5

PN aren’t always easy to notice in children with NF1. Sometimes they’re located deep inside the body, meaning they can’t be seen or felt.2 Sometimes they may be recognised by skin discolouration or a bump under the skin.2

PN can grow quickly in size and may cause other symptoms, including:4,7,8
  • Pain
  • Muscle weakness
  • Visual impairment from PN around the eye
  • Loss of bladder control
  • Bowel issues, including severe constipation
  • Airway issues, including the need for mechanical support
  • Physical deformity
Approximately 30–50% of people with NF1 develop a PN.4 Detecting PN early makes managing and treating the condition easier.5 If you spot any of the symptoms above, speak to your doctor
 Learn how NF1 is treated Tamura R. Current understanding of neurofibromatosis type 1, 2, and schwannomatosis. Int J Mol Sci 2021(11);22:5850. Bergqvist C et al. Neurofibromatosis 1 French national guidelines based on an extensive literature review since 1966. Orphanet J Rare Dis 2020;15(1):37. Legius E et al. Revised diagnostic criteria for neurofibromatosis type 1 and Legius syndrome: An international consensus recommendation. Genet Med 2021;23(8):1506–1513. Ferner RE et al. Guidelines for the diagnosis and management of individuals with neurofibromatosis 1. J Med Genet 2007;44(2):81–88. Williams VC et al. Neurofibromatosis type 1 revisited. Pediatrics 2009;123(1):124–133. Radiopaedia.org. Sphenoid wing dysplasia. Available at: https://radiopaedia.org/articles/sphenoid-wing-dysplasia?lang=us Last accessed: September 2023. Gross AM et al. Association of plexiform neurofibroma volume changes and development of clinical morbidities in neurofibromatosis 1. Neuro Oncol 2018;20(12):1643–1651. Copley-Merriman C et al. Natural history and disease burden of neurofibromatosis type 1 with plexiform neurofibromas: a systematic literature review. Adolesc Health Med Ther 2021;19:55–66.