Muscular Dystrophy

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What is muscular dystrophy, Duchenne and Becker types?

Muscular dystrophies are a group of genetic conditions characterized by progressive muscle weakness and wasting. The Duchenne and Becker types of muscular dystrophy primarily affect the skeletal muscles, which are used for movement, and the muscles of the heart. Duchenne muscular dystrophy is the most common form of muscular dystrophy in children.

Duchenne and Becker muscular dystrophies have similar signs and symptoms and are caused by mutations in the same gene. The two conditions differ in their severity and age of onset. In people with Duchenne muscular dystrophy, muscle weakness tends to appear in early childhood and progress rapidly. Heart problems, which can become life-threatening, typically begin in the teenage years. The signs and symptoms of Becker muscular dystrophy are usually milder and exhibit a large range of variation. In general, they become apparent later in childhood or adolescence and progress at a much slower rate.

How common is muscular dystrophy, Duchenne and Becker types?

Duchenne and Becker muscular dystrophies together affect 1 in 3,500 to 5,000 male births. Between 400 and 600 boys in the United States are born with these conditions each year. Females are rarely affected by these forms of muscular dystrophy.

What genes are related to muscular dystrophy, Duchenne and Becker types?

Mutations in the DMD gene cause muscular dystrophy, Duchenne and Becker types.

The DMD gene makes a protein called dystrophin. This protein helps stabilize and protect muscle fibers and may play a role in chemical signaling within cells. Mutations in the DMD gene alter the structure or function of dystrophin, or prevent any functional dystrophin from being produced. As a result, muscle fibers become damaged with repeated use. The damaged fibers weaken and die over time, leading to the muscle weakness and heart problems characteristic of Duchenne and Becker muscular dystrophies.

How do people inherit muscular dystrophy, Duchenne and Becker types?

This condition is inherited in an X-linked recessive pattern. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. In males (who have only one X chromosome) one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes) a mutation must be present in both copies of the gene to cause the disorder. Males are affected by X-linked recessive disorders much more frequently than females. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

In about two thirds of cases, an affected male inherits the mutation from a mother who carries one altered copy of the DMD gene. The other one third of cases probably result from new mutations in the gene.

Females who carry one copy of a DMD mutation may have some signs and symptoms related to the condition (such as muscle weakness and cramping), but these are typically milder than the signs and symptoms seen in affected males.

Source: National Institutes of Health

Researchers from University of Tokyo publish findings in life sciences

"To this day, nine polyglutamine-related diseases and nine polyalanine-related diseases have been reported, including Huntington's disease and oculopharyngeal muscular dystrophy. In this study, potential HPAA-HPAA interactions were examined by yeast two-hybrid assays using HPAAs of approximately 30 residues in length. The results indicate that hydrophobic HPAAs interact with themselves and with other hydrophobic HPAAs. Previously, we reported that hydrophobic HPAAs formed large aggregates in COS-7 cells. Here, those HPAAs were shown to have significant interactions with each other, suggesting that hydrophobicity plays an important role in aggregation. Among the observed HPAA-HPAA interactions, the Ala28-Ala29 interaction was notable because polyalanine tracts of these lengths have been established to be pathogenic in several polyalanine-related diseases. By testing several constructs of different lengths, we clarified that polyalanine self-interacts at longer lengths (>23 residues) but not at shorter lengths (six to approximately 23 residues) in a yeast two-hybrid assay and a GST pulldown assay. This self-interaction was found to be SDS sensitive in SDS-PAGE and native-PAGE assays. Moreover, the intracellular localization of these long polyalanine tracts was also observed to be disturbed. Our results suggest that long tracts of polyalanine acquire SDS-sensitive self-association properties, which may be a prerequisite event for their abnormal folding," wrote Y. Oma and colleagues, University of Tokyo.

The researchers concluded: "The misfolding of these tracts is thought to be a common molecular aspect underlying the pathogenesis of polyalanine-related diseases."

Oma and colleagues published their study in Protein Science (Interactions between homopolymeric amino acids (HPAAs). Protein Science, 2007;16(10):2195-204).

For additional information, contact Y. Oma, The University of Tokyo, Dept. of Life Sciences, Graduate School of Arts and Sciences, Meguro-ku, Tokyo, Japan.

Publisher contact information for the journal Protein Science is: Cold Spring Harbor Laboratory Press, Publications Dept., 500 Sunnyside Blvd., Woodbury, NY 11797-2924, USA.

Keywords: Japan, Tokyo, Life Sciences, Amino Acids, Pharmaceuticals, Drugs, Therapy, Treatment.

This article was prepared by Biotech Business Week editors from staff and other reports. Copyright 2007, Biotech Business Week via NewsRx.com.