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Q&A with Australian Health Practitioners
What causes facioscapulohumeral muscular dystrophy?
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Dr Ryan Hislop
Chiropractor
Ryan Hislop is the Clinical Director at the Orange Chiropractic Health and Wellness Centre. As an experienced and evidence-based diagnostician, Ryan works largely by medical … View Profile
The cause remains unknown, however there is a strong genetic and heriditary link.FSHD has been classified into two types: FSHD1A and FSHD1B. Whilst the symptoms are the same; the difference between the types is in their genetic locus.
The following has been taken from the FSH society.
Facioscapulohumeral muscular dystrophy 1A (FSHD1A), also known as chromosome 4 linked facioscapulohumeral muscular dystrophy, is by far the most common. FSHD1A is associated by genetic testing with the deletion of 3.3-kb repeats from a chromosomal tandem repeat called D4Z4 located near the end of chromosome 4 at the 4q35-qter location. The D4Z4 region is a polymorphic variable number tandem repeat (VNTR) array consisting of 3.3 kb units. Unaffected individuals have a chromosome 4 D4Z4 array that has a span of 11 to 150 contiguous units. In individuals with FSHD1A, the chromosome 4 D4Z4 repeat array is contracted to a range between 1 to 10 contiguous units. There is a rough and inverse relationship between clinical severity and the number of repeats; patients with the fewest repeats typically have the most severe symptoms.
Facioscapulohumeral muscular dystrophy 1B (FSHD1B), also known as non-chromosome 4 linked facioscapulohumeral muscular dystrophy, is much less prevalent than FSHD1A. It may be caused by different genes from FSHD1A, located on the same (despite its title) or different chromosomes.
Infantile FSHD or IFSHD is a more severe form of FSHD1A and FSHD1B that has recently been categorized as a subtype of FSHD1A and FSHD1B. What makes the disease more severe has not yet been determined. Hearing loss (high frequency bilateral sensorineural), vision problems (Coats’ Disease and retinal telangiectasias), and seizures have been documented in IFSHD. Hearing loss is often more severe in IFSHD; if not detected and treated early it can interfere with learning and cognitive development.Report this post
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Dr Simon Easterbrook-Smith
Health Professional
My research interests include immunology and the mechanisms of amyloid formation. The latter has implications for people who are dealing with Alzheimer's Disease, Parkinson's Disease … View Profile
Adding to the previous response:
Facioscapulohumeral muscular dystrophy is an example of what is called an “autosomal dominant” genetic disease. That means that only one copy of the gene linked to it (the one, say, on maternal chromosome 4) needs to be mutated for the disease to occur. The contrast is with “autosomal recessive” genetic diseases - cystic fibrosis is an example - both the maternal and paternal forms of the gene in question (which is on chromosome 7 in this case) need to be mutated for the disease to develop.
The causal effects of the mutations which lead to facioscapulohumeral muscular dystrophy are very complicated so, in the interests of a lay readership, I have simplified things a bit.
They involve differences in the number of repeated base sequences in the DNA in a region of chromosome 4 called D4Z4. The effect of these repeats (which are called “macrosatellites”) is to switch off a gene called DUX4, which is usually only switched on in the testis. People with facioscapulohumeral muscular dystrophy have an abnormally low number of those D4Z4 repeats, which means that DUX4 is switched on in muscle tissue (where it shouldn’t be switched on).
The protein coded for by the DUX4 gene is what is called a “transcription factor” which means that it switches on other specific genes (good in the testis, not good in muscle tissue). It is the abnormal activity of these other specific genes (their encoded proteins are good in the testis but not good in muscle tissue) which is thought to be responsible for facioscapulohumeral muscular dystrophy.
There is a very technical free-access review of this here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4060068/pdf/2044-5040-4-12.pdfReport this post
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