Distal Myopathies

Causes/Inheritance

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 our educational materials.

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