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How is FSHD Diagnosed?
The diagnosis of FSHD is made by a Neurologist based on the pattern of muscle weakness that is seen on bedside examination. An EMG (electromyography) may be helpful in certain cases but it only confirms the presence of a muscular dystrophy and cannot differentiate between the different muscular dystrophies. The diagnosis can then be confirmed on blood DNA test, a test which has an accuracy of about 95 %. Genetic testing in FSHD consists of testing for the presence, in one of two copies of chromosome 4, of missing copies of set of identical DNA sequences. In healthy individuals both copies of chromosome four will have more than 15 copies of this repetitive sequence of DNA whereas in individuals with FSHD, one of the two copies of this sequence of chromosome 4 will have between 1 and 11 copies only. The readout from the genetic test gives two numbers (one from each chromosome 4) and corresponds to the size of the DNA segment, known as an allele, containing the repetitive sequences. An allele size of greater than 50 Kb represents a normal allele whereas an allele from someone with FSHD will be between 12 and 38 Kb.
If the DNA is negative for the FSHD defect, there could be one of two possibilities. The first is that the person may look like they have FSHD but, in fact, have another muscular dystrophy. This is not an uncommon for one form of dystrophy to mimic another as far as its clinical presentation. In such a case, further blood testing in addition to a muscle biopsy may be needed to arrive at the proper diagnosis. The second possibility is that the person does have FSHD but fall in the 5% of individuals with FSHD where the routine genetic test will not pick up their genetic defect. Such individuals may need further detailed genetic testing.
- What is FSHD?
- How is FSHD inherited?
- What are the Symptoms of FSHD?
- Does FSHD affect other parts of the body?
- Is infantile FSHD different from other forms of FSHD?
- What can someone with FSHD Expect as they age?
- How is FSHD Diagnosed?
- What causes FSHD?
- Are there any treatments for FSHD?
For more information, please contact the Fields Center FieldsCenter@urmc.rochester.edu