- Dystrophia myotonica
- Myotonia atrophica
- Myotonia dystrophica
Your QuestionA doctor recommended that I undergo some genetic testing following my biopsy that revealed myotonic dystrophy. What is this condition, and what may be the underlying cause? Also, I cannot find a more affordable genetic lab than the one I was referred to? Can you help locate one?
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Questions on this page
- What is myotonic dystrophy?
- What causes myotonic dystrophy?
- What are nucleotide repeats or expansions? How does this specific type of mutation cause myotonic dystrophy?
- Where I can find information about which laboratories are offering genetic testing for myotonic dystrophy? How can I find out how much these laboratories charge for genetic testing?
- How can I find a genetics professional in my area?
- How can I find additional resources for myotonic dystrophy?
There are two types of myotonic dystrophy: myotonic dystrophy type 1 and myotonic dystrophy type 2. The symptoms in people with myotonic dystrophy type 2 tend to be milder than in those with type 1. Although both types are inherited in an autosomal dominant pattern, they are caused by mutations in different genes. Myotonic dystrophy type 1 is caused by mutations in the DMPK gene, while type 2 is caused by mutations in the CNBP gene.
The exact functions of these genes in not well understood. The DMPK gene may play a role in communication within cells, specifically in cells of the heart, brain, and skeletal muscles. The CNBP gene gives directions to make a protein found mainly in cells of the heart and skeletal muscles, where it is thought to regulate the activities of other genes.
Myotonic dystrophy type 1 is caused by the expansion of the triplet repeat CTG in the DMPK gene. The disease occurs when the CTG segment is abnormally repeated from 50 to 5,000 times. Myotonic dystrophy type 2 is caused by expansion of a string of four nucleotides: C, C, T, and G. When the CCTG string is abnormally repeated 75 to more than 11,000 times the disease occurs. In both types of myotonic dystrophy, the mutations that cause the conditions result in the production of abnormal products that are normally used in the making of proteins. The abnormal product interacts with certain proteins to form clumps within the cell. The changes that occur prevent cells in muscles and other tissues from working properly, leading to the signs and symptoms seen in myotonic dystrophy types 1 and 2.
Myotonic dystrophy type 1
Myotonic dystrophy type 2
Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.
The following online resources can help you find a genetics professional in your community:
- The National Society for Genetic Counselors provides a searchable directory of US and international genetic counseling services.
- The American College of Medical Genetics has a searchable database of US genetics clinics.
- The University of Kansas Medical Center provides a list of US and international genetic centers, clinics, and departments.
- The American Society of Human Genetics maintains a database of its members, which includes individuals who live outside of the United States. Visit the link to obtain a list of the geneticists in your country, some of whom may be researchers that do not provide medical care.
- Myotonic dystrohpy. Genetics Home Reference (GHR). November 2010; http://ghr.nlm.nih.gov/condition=myotonicdystrophy. Accessed 7/15/2011.
- Fragile X Syndrome. Centre for Genetics Education. 2007; http://www.genetics.com.au/pdf/factsheets/fs42.pdf. Accessed 6/17/2009.
- DMPK. Genetics Home Reference. November 2010; http://ghr.nlm.nih.gov/gene=dmpk. Accessed 5/11/2011.
- CNBP. Genetics Home Reference. October 2010; http://ghr.nlm.nih.gov/gene=cnbp. Accessed 5/11/2011.