Limb-girdle muscular dystrophy (LGMD) is a progressive disorder that results in weakness and wasting (atrophy) in the voluntary muscles of the shoulder and hip areas known as the limb-girdle area.
Even though the symptoms of LGMD may vary from one patient to another, some of the common ones include soreness of muscles and joints, difficulty standing from a sitting position, and difficulty in raising the arms above the head.
A genetic disease
LGMD can occur as a result of mutations in many different genes. These genes are usually the ones that provide instructions for producing proteins required for muscle maintenance and repair. These mutations result in an abnormal function of muscle proteins, which in turn lead to muscle weakness.
Inheritance of LGMD
LGMD an inherited genetic disorder. The inheritance pattern varies and depends on the form or subtype of the disease, which depends on the specific genetic mutation causing it.
The different subtypes of LGMD can be broadly categorized under two inheritance patterns, autosomal dominant and autosomal recessive. Autosomal means that the genes involved are present on the autosomes or non-sex chromosome, the X and the Y chromosome. So both males and females have the same probability of developing the disease.
When the disease is inherited in an autosomal dominant pattern, a single copy of a faulty gene, inherited from one parent, is sufficient to cause the disease. But if the disease follows an autosomal recessive pattern of inheritance, a person must inherit two mutated copies of the disease-causing gene, one from each parent, to develop the symptoms.
So for a child to develop an autosomal recessive form of LGMD, both their parents must be carriers of the defective genes. Usually, carriers do not show any symptoms and are unlikely to know that they are carriers unless someone in their family is diagnosed with LGMD, and they have been genetically tested.
Types of LGMD
There are many different types of LGMD depending on the gene affected by a mutation.
The main type of LGMD inherited in an autosomal recessive manner is called LGMD Type 2A (caused by a mutation in the CAPN3 gene) and LGMD Type 2B (caused by a mutation in the DYSF gene). LGMD Type 2A is the most common form of LGMD accounting for as many as 30 percent of all LGMD cases.
Apart from the above, there are several other forms of LGMD that are caused by mutations in other genes. Around 19 forms of LGMD have been identified, each of which occurs because of mutations in different genes involved in the production of certain muscle proteins. Even though many genes that cause LGMD have been identified, other genes that are thought to be involved in rarer forms of LGMD have yet to be identified.
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