Proteins involved in Congenital Muscular Dystrophy

In the mid-1990s, researchers found that a deficiency of a protein then called merosin and now more often called laminin 2 was the underlying cause of at least some cases of CMD. Merosin normally anchors muscle cells to a structure that encases them (like the skin on a hot dog) called the basal lamina.

Doctors began to classify CMD as either “merosin-deficient” or “merosin-positive.” The gene for merosin is on chromosome 6.

Then, in 1998, researchers identified mutations in the gene for integrin as another cause of CMD. Integrin, which surrounds and supports each muscle fiber, connects laminin 2 with proteins inside the cells.

As the 20th century ended, researchers began to suspect that Ullrich’s disease, now known as Ullrich CMD, was caused by a lack of collagen 6, a ropelike protein located in the area where laminin 2 is found.

Collagen 6, which helps support the muscle fiber, probably affects muscle cells via its connection to laminin 2. Laminin 2, in turn, connects to muscle cells via either of two other proteins: integrin or dystroglycan.

Dystroglycan links the outer surface of muscle cells with structures outside them via branches, made of sugar molecules that protrude from its surface and stick to laminin. The branch structure explains why mutations in diverse genes all appear to cause CMD. Each of these proteins contributes in a different way to the process of “sugar coating” (glycosylating) dystroglycan.

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