What causes distal muscular dystrophy (DD)?
All the forms of muscular dystrophy are inherited — that is, they’re caused by mutations (changes) in a person’s genes. Our genes are made of DNA and reside in our chromosomes. Each gene contains the “recipe” for a different protein and its variations, and these proteins are necessary for our bodies to function correctly.
When a gene has a mutation, it may make a defective protein or none at all. Most commonly, missing or defective proteins in the muscles prevent muscle cells from working properly, leading to symptoms of muscular dystrophy, including muscle weakness and wasting over time.
The different types of DD are caused by many genetic defects, not all of which are yet known. Some of the DDs have been given different names based on various symptoms but actually may be caused by defects on the same gene.
What are the inheritance patterns in DD?
Most forms of DD are inherited in an autosomal dominant pattern, but some follow a recessive pattern of inheritance.
In brief, if a disease is recessive, two copies of the defective gene (one from each parent) are required to produce the disease. Each parent would be a carrier of the gene flaw, but wouldn’t usually have the disease.
If a disease is dominant, then only one copy of the genetic defect is needed to cause the disease. Anyone with the gene flaw will have disease symptoms and can pass the disorder to children.
Many times muscular dystrophy appears to have occurred “out of the blue,” but in reality, one or both parents may be carriers, silently harboring the genetic mutation. Often parents have no idea they’re carriers of a disease until they have a child who has the disease.
A good way to find out more about these risks is to talk to your MDA clinic physician or ask to see the genetic counselor at the MDA clinic. For more, see Facts About Genetics and Neuromuscular Diseases.
Classification of Distal Muscular Dystrophies
|Types of DD||Cause||Inheritance Pattern|
|Welander distal myopathy||abnormalities in chromosome 2 gene||dominant|
|Finnish (tibial) distal myopathy||titin abnormalities||dominant|
|Miyoshi distal myopathy||dysferlin abnormalities||recessive|
|Nonaka distal myopathy; also called hereditary inclusion-body myositis type 2 (HIBM2)||GNE abnormalities||recessive|
|Gowers-Laing distal myopathy||MYH7 abnormalities||dominant|
|Hereditary inclusion-body myositis type 1 (HIBM1)||unknown||dominant|
|Distal myopathy with vocal cord and pharyngeal weakness||abnormalities in chromosome 5 gene||dominant|
Source: Washington University Neuromuscular Home Page, May 2006