Motor neurone disease (MND) is a progressive degenerative disorder of motor neurones in the spinal cord and brain. Loss of these cells results in weakness and wasting of the muscles. The disorder usually starts in middle life and the effects of MND – initial symptoms, rate and pattern of progression, and survival time after diagnosis – vary significantly.
This fact sheet has been prepared for people who have asked about the genetics of MND, genetic testing or further research into MND and for people impacted by familial MND.
About 10% of MND is ‘familial’; that is, there is or has been more than one affected person in a family. The remaining 90% of people with MND are the only affected person in their family and are said to have ‘sporadic’ MND.
People with familial MND have the disorder because of a mutation in a gene. A mutation is an error in the genetic code which causes a gene to work abnormally. People with genetic mutations can pass these onto their children. If a person has an MND-related genetic mutation each of their children has a 50/50 chance of inheriting the MND-related genetic mutation.
People who inherit an MND-related genetic mutation have a high, but as yet uncertain, chance of developing MND during their lifetime. However, not all people with an MND-related genetic mutation will develop MND.
The age at which symptoms of MND appear in people with an MND-related genetic mutation varies greatly. It can be as early as the 20s and as late as the 80s. As well, the age of onset can vary considerably within a family, even though the mutation carried by family members is the same. The average age of onset of familial MND is around 45 years.
Mutations in the genes that cause MND are also found in some people who have sporadic MND. The number of people with sporadic MND who also have an MND-related gene mutation is not known.
• In 1993 the first genetic mutation related to MND was discovered in the superoxide dismutase 1 gene (SOD1). About 20% of familial MND is caused by mutations in the SOD1 gene.
• In 2008 mutations in the TAR DNA binding protein (TDP-43) gene code were found to cause TDP–43 to become toxic, causing MND in a small percentage of MND families. Researchers are yet to find out how and why TDP-43 behaves abnormally to cause MND.
• In 2009 a gene mutation that causes a rare inherited form of MND, FUS (Fused in Sarcoma, a protein) was discovered. Researchers have found that genetic mutations of FUS are a cause of MND for a small number of familial forms of MND and account for between 3% - 5% of MND families.
• In 2011 the discovery of mutations in the C9ORF72 gene was announced and has since been found in about 40% of all families with familial MND.
Although there are still some MND families in which the faulty gene has not yet been identified, the SOD1 gene and other MND-related gene mutations discovered in recent years now account for about 65% of all people with familial MND.
Researchers continue in their quest to find the mutations in other genes that cause familial MND in the 35% of familial MND families in which the genetic cause has yet to be identified.
Researchers are carrying out further studies to:
• understand how the known genetic faults cause MND
• work out how many of those with a faulty gene will actually go on to develop MND later in life
• identify mutations in other genes which may cause familial MND
• discover ways of preventing and treating familial and sporadic MND
It is now possible to test for the presence of mutations in the SOD1, TDP43, FUS and C9ORF72 genes in a person diagnosed with familial MND. Other family members can also be tested to determine if they have the same mutation that caused MND in their relative. For example, adult children or brothers and sisters of an affected person can be tested.
Unborn children can be tested to determine if they have inherited the mutation known in the family.
Pre-implantation genetic diagnosis (PGD), an advanced screening technique, can be used in conjunction with IVF to determine whether an embryo has inherited the familial MND gene.
Some people who have an MND gene mutation may never develop symptoms. For those with an MND gene mutation who go on to develop symptoms, it is not possible to predict the age when symptoms will first appear.
Research will increase our understanding of the mechanism by which these mutations cause MND, and may lead to treatments which can prevent or delay the onset of MND in someone with an MND-related genetic mutation. It is possible that research into MND caused by genetic mutations will also contribute to our understanding of the causes of other types of MND.
Some reasons people have given for wanting to know if they have an MND-related genetic mutation:
• I am the sort of person who wants to know as much as possible about myself and my future and find it hard to live with uncertainty.
• To enable me to plan my life.
• To help with decisions about marriage and having a family.
• To provide information of importance to my children.
• If I do not have the gene, the information may help when I apply for jobs, life insurance, superannuation or when taking on long-term financial commitments.
• If I have a genetic mutation and it becomes possible to prevent MND, I can make use of the preventative measures.
Some reasons people have given for not wanting to know if they have an MND-related genetic mutation:
• I can accept living with uncertainty and will be able to plan my life without knowledge of my genetic status.
• I would not change my plans regarding marriage and having a family, whatever the test result.
• I do not think I would cope with knowing that I have the gene and will have an increased risk of developing MND.
• If I have a genetic mutation, the information may limit my life opportunities for example, in relation to career choices, life insurance, superannuation and financial matters.
• Relationships with my family, friends and workmates may change if I am shown to have the gene.
• I am always free to change my mind and can take the test in the future if, for example, a treatment becomes available that can prevent MND.
Testing is offered as part of a formal program providing the information, counselling and support a person might need when trying to decide whether to have the test and after the result has been provided. The test is usually done on genetic material (DNA) obtained from a blood sample.
Testing must be voluntary. While each person will consider the views and feelings of family and friends, the final decision must be taken by the individual concerned. It would be inappropriate for someone to take the test because of pressure to do so.
There is no Medicare rebate for testing for the presence of gene mutations that cause MND. Some genetic services may provide subsidised or free testing for several MND-related genes.
Children under 18 years of age should not be tested. Anyone having this test must be able to give informed consent. They need to understand and accept the testing process and the implications of the test result. This is a test which can give an indication of a person's future health and the results can have tremendous effects on various aspects of life. The right of parents to have information about their child does not outweigh the child's right to make a personal choice about whether or not to be tested.
DNA can be stored frozen, so blood from people with the disorder can be collected now and used in the future to help other family members when further genetic mutations are discovered.
Can I give a blood specimen for research, but without getting the result?
Researchers are keen to receive blood samples from people with a family history of MND, particularly if testing for the known mutations has proved to be negative in that family. If you would like to support research in this way, please contact your local MND Association for more information.
The result will not be released to others without the formal consent of the person tested.
Who can provide support for those taking the test?
Family, close friends or other trusted people close to the individual can provide emotional support, as can health professionals such as doctors, (clinical geneticists, neurologists, psychiatrists, general practitioners), MND Associations, counsellors (including genetic counsellors) and social workers.
Genetic counsellors can provide information and support for people who have an MND-related genetic mutation and are planning to start a family, as can health professionals such as doctors, (clinical geneticists, neurologists, psychiatrists, general practitioners) and MND Associations. Pre-implantation genetic diagnosis (PGD) involves screening IVF generated embryos for genetic conditions prior to embryo transfer with only unaffected embryos transferred to the uterus.
IVF clinics can provide information on PGD and on where this specialist screening is available. They can also provide information on the associated costs and the Medicare rebates available. Genea provides a PGD financial assistance program to those able to demonstrate financial need.
• Provide guidance and advice for people with MND, families and health professionals
• Produce and disseminate information
• Fundraise and advocate for MND research
• Advocate for the development of clinical programs which have a written protocol and provide full counselling and support for those taking the test
• Promote the sharing of knowledge and experience as research proceeds and clinical testing programs expand
• Support clinical programs which provide diagnostic testing
Genetic counselling clinics operate across Australia. The Centre for Genetics Education Ph. 02 9462 9599 maintains a national list at www.genetics.edu.au .
For information on IVF and pre-implantation genetic diagnosis (PGD) contact IVF Australia ph. 1800 111 483.
For information on the PGD assistance program contact Genea ph. 1300 361 795 or visit the website at www.genea.com.au.
For more information about familial MND contact:
• the neurologist who is treating, or treated, the person in your family with MND
• your local MND Association www.mndaust.asn.au/state-mnd-associations