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• Neurofibromatosis type 1 (NF1) is a different condition from neurofibromatosis type 2 (NF2).
• NF1 is a very common genetic condition and affects about 1 in 3,000 to 5,000 people
• NF1 has a wide range of severity and many people with the condition will only be mildly affected. It is impossible to predict who will remain only mildly affected and who will be more severely affected with NF1. Even different members of the same family can be affected differently
• Most common features include having 6 or more flat, coffee-coloured 'birth marks' on the skin (cafe-au-lait patches); neurofibromas (harmless soft pink small lumps that can grow on nerves anywhere in the body; freckles in areas that are not usually exposed to sunlight; Lisch nodules (harmless small brown spots on the iris of the eye)
• People with NF1 have a change in one of their NF1 gene copies that makes the gene faulty
• The pattern of inheritance in families of the faulty gene causing NF1 is described as autosomal dominant inheritance
• When one of the parents has the faulty NF1 gene copy ie. has NF1, they have 1 chance in 2 (or 50% chance) in every pregnancy of having a child with NF1
• In about 50% of the cases, NF1 is inherited from an affected parent
• In up to 50% of the cases, the person with NF1 is the first in the family with the condition and results from a change that occurred in one copy of the NF1 gene during the formation of the egg or sperm, during or shortly after conception (a spontaneous mutation that occurred for unknown reasons)
• If spontaneous mutation occurred shortly after conception of the person, not all of the person's cells may contain the gene change: the person is said to be 'mosaic' for the faulty NF1 gene. People who have this rare form of mosaic NF1 often have symptoms that are restricted to one part of their body (see Genetics Fact Sheet 13).
  • If a child of a parent who is mosaic for NF1 inherits the faulty NF1 gene, they may be more severely affected by NF1 as the child would have the faulty gene in all the cells of their body. That child also has a 50% risk of passing on the faulty gene to his or her children
• The diagnosis of NF1 is based on clinical features and genetic testing is not required: most people with NF1 will have enough signs of the condition by age 5 years for a specialist to diagnose them with confidence
• Genetic testing for changes in the NF1 gene is not widely available and is currently expensive but can be helpful in some situations such as testing a baby in pregnancy for NF1 where one of the parents is affected (see Genetics Fact Sheet 17C). It is highly recommended that considerations for this testing be discussed in the context of genetic counselling (see Genetics Fact Sheet 3).

NF1 has a wide range of severity and many people with the condition will only be mildly affected.

For most people, with NF1 symptoms are not severe but for a few, NF1 can cause major health problems at certain stages of their lives. At present it is impossible to predict who will remain only mildly affected and who will be more severely affected with NF1. Even different members of the same family can be affected differently.

The range of features that are characteristic of NF1 are listed below in order from those that occur frequently to those that are less common:

• Flat, coffee-coloured 'birth marks' on the skin (called cafe-au-lait patches which means 'milk coffee' in French). The cafe-au-lait patches are harmless and are due to an increase in the pigment (melanin) in the cells in this area of the skin. They usually appear before two years of age. Most often, six or more are present but the number does not relate to the severity of the condition: people without NF1 can also have two or more café au lait patches
• Neurofibromas are harmless soft pink small lumps that can grow on nerves anywhere in the body. Neurofibromas are most visible in the skin and most commonly, first appear around adolescence but by age 30 years almost all people with NF1 will have several (and some have hundreds). Over time, they often slowly grow in size. They rarely cause any problems except some people may have concerns over their cosmetic impact. They are usually absent or few in childhood and generally increase in number during puberty or pregnancy
• The appearance of freckles in areas that aren't usually exposed to sunlight, particularly the armpits and groin region. Again, these are harmless.
• Lisch nodules are harmless small brown spots on the iris (the coloured part of the eye). Lisch nodules are not often visible, except to an eye specialist looking with a special eye examination microscope called a slit lamp. They do not affect vision
• Specific learning disabilities where a child of normal intellect has specific problems in certain areas of their learning eg reading, mathematics or spelling occur in around half of people with NF1. Most are usually weak in only one or two areas and can cope in a normal classroom
• Children may have short attention spans, low muscle tone, reduced co-ordination and may be slower to mature emotionally than their peers. They respond to treatments for these problems the same way as any other child
• A larger head size than usual
• Being shorter than would be expected by looking at the rest of the family
• Plexiform neurofibromas (localised areas where a tangle of extra nerve tissue sits within normal tissues) can occur anywhere in the body. They are found in around one in four people with NF1 and, in about 5% of these people, will cause a major problem with their appearance. They almost always develop before birth and most become obvious by two years of age
• Optic gliomas (non-cancerous growths of the optic nerve that connects each eye to the brain) affect a small number of children, and can slowly impair vision. They are rare over ten years of age
• Bone problems. About 15% of children with NF1 develop a noticeable curve in the spine (scoliosis) and a small number require surgery to straighten the spine. Rarely, children are born with a weakness of the shin bone so that it bows or breaks during childhood. These breaks often heal poorly and require specialist treatment
• Cancer risk. There is a slightly increased risk (10% over the person's lifetime) that a neurofibroma can become cancerous. Any rapid change in the growth or symptoms of a neurofibroma should be reported to a doctor

Ferner R. (2007). Neurofibromatosis 1. European Journal of Clinical Genetics; 15: 131-138

North K. (1998). Clinical aspects of neurofibromatosis type 1. European Journal of Paediatric Neurology;2:223-231

Neurofibromatosis Association of Australia (NFAA) Inc [online]. Available from: http://nfaa.org.au. [Accessed June 2007]

Online Mendelian Inheritance in Man, OMIM. McKusick-Nathans Institute for Genetic Medicine, Johns Hopkins University (Baltimore, MD) and National Center for Biotechnology Information, National Library of Medicine (Bethesda, MD) [online]. Available from: http://www.ncbi.nlm.nih.gov/omim/. [Accessed June 2007].