What is a gene?
![Cell, chromosome, DNA strand, gene and DNA building blocks or nucleotides](/globalassets/assets/what_is_a_gene_med_ill_en.jpg?width=356&quality=60)
Our bodies are made up of billions of cells. The cells work together to make our bodies work. Different cells have different jobs, but they all have one thing in common: each contains genes.
Genes are the instructions that our cells use to make proteins. Genes tell our cells how to work and what to do. For example, one gene may determine the colour of your hair or your blood type.
Genes are packaged in the form of chromosomes. The information in a gene is coded in a chemical called DNA.
There are about 30,000 genes inside every cell. Each person carries two copies of each gene. A child gets (inherits) one copy from their mother and the other from their father.
For more information about genes, please see the AboutKidsHealth section on How the Body Works: Genetics.
What causes NF1?
Every person has two copies of the NF1 gene. This gene codes for a protein called neurofibromin (say: noor-oh-fie-BROH-min).
Neurofibromin's job in the body is to make sure that certain cells divide and grow in a controlled way. In particular, it stops certain cells that support the nerves from growing too much. These cells are called nerve sheath cells.
A mutation (a change in the genetic code) in the NF1 gene leads to a neurofibromin protein that does not work properly. This leads to symptoms of NF1.
There are two ways to get NF1
There are two ways a person can get NF1: as a new mutation, or by inheriting it from a parent.
A new (spontaneous) mutation
Half of all cases of NF1 occur by chance. This is called a new or spontaneous mutation. A change occurs in the NF1 gene at the time of, or shortly after, conception. Conception is the time when the father's sperm and the mother's egg join and the egg is fertilized.
In this case, neither parent of the affected child will have NF1. Spontaneous gene mutations are not inherited from either parent.
Inherited from a parent with NF1
The other half of people with NF1 inherited it from one of their parents. This means that a parent with a mutation in the NF1 gene passed the mutated gene to the child.
In some cases, the signs or symptoms of NF1 are so mild that a parent may not find out they have NF1 until their child is diagnosed.
How NF1 is inherited
Genes come in pairs, as do the chromosomes that carry them. When we have children, each parent passes half of their genetic material to their children, meaning one gene from each pair of genes.
![Chromosome distribution from an affected parent with one chromosome with NF1 gene mutation an unaffected parent](/globalassets/assets/neurofibromatosis_genetics_med_ill_en.jpg?width=356&quality=60)
NF1 is inherited as a dominant condition. Dominant means the mutated gene is stronger than the normal gene. This means that only one NF1 gene needs to be mutated for the person to develop NF1.
If a person has NF1, they have one normal NF1 gene and one NF1 gene with a mutation. When this person has a child, they can pass on either the normal NF1 gene or the NF1 gene with the mutation. In other words, a person with NF1 has a 50% (one in two) chance of passing on NF1 to their children.
Adults with NF1 who are planning a family may wish to seek genetic counselling so that they can understand their risks and choices.