Genetics of Neurofibromatosis Type 1 (NF1)

What is a gene?

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.

What are Genes?
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Genes are made of long strings of nucleotides on a section of DNA. Groups of genes are packed tightly in a chromosome.

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 2 copies of each gene. A child gets (inherits) 1 copy from his mother and the other from his father.

For more information about  genes, please see the AboutKidsHealth section on  How the Body Works: Genetics.

What causes NF1?

Every person has 2 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 2 ways to get NF1

There are 2 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 he or she has NF1 until his or her 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 1 gene from each pair of genes.


Heredity of Neurofibromatosis (NF1)
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Every person has 2 copies of the NF1 gene, one on each chromosome. If a person has one mutated NF1 gene, he or she may develop the conditions of neurofibromatosis. An affected parent has a 50% chance of passing the mutated gene on to his or her child.

NF1 is inherited as a dominant condition. "Dominant" means the mutated gene is stronger than the normal gene. This means that only 1 NF1 gene needs to be mutated for the person to develop NF1.

If a person has NF1, he or she has 1 normal NF1 gene and 1 NF1 gene with a mutation. When this person has a child, he or she 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% (1 in 2) chance of passing on NF1 to his or her children.

Adults with NF1 who are planning a family may wish to seek genetic counselling so that they can understand their risks and choices.

Key points

  • A person can get NF1 in 1 of 2 ways. Half of cases happen completely by chance. The rest of the time, NF1 is inherited or passed down from parent to child.
  • In some cases, the signs or symptoms of NF1 are so mild that a parent may not find out he or she has NF1 until a child is diagnosed.
  • A person with NF1 has a 50% (1 in 2) chance to have an affected child with each pregnancy.
  • Adults may benefit from genetic counselling to understand their risks and choices regarding planning and family.

Elena Pope, MD, MSc, FRCPC

Patricia Parkin, MD, FRCPC

Stephen Meyn, MD, PhD, FRCPC, FACMG

Andrea Shugar, MS, CGC, CCGC

3/5/2010

Crawford H, Abbott R Morrison P, McKee S. The Neurofibromatosis Association. [http://www.nfauk.org/]

 





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