Collagen VI Congenital Muscular Dystrophy
Collagen VI CMD is characterized by muscle weakness, proximal joints contractures and distal joint hyperflexibility from birth. This disorder is a result of a genetic mutation of three strands of collagen (COL6A1, COL6A2 and COL6A3) found in extracellular matrix of the muscle cells.
Characteristics of Collagen VI Congenital Muscular Dystrophy
Proximal joint contractures
Distal joint hyper flexibility
Rigid lower spine
Kyphosis (curved upper spine)
Skin changes (hyperkeratosis pilaris, keloid formation, soft/velvety skin on palms and soles of feet)
High arched palate
Posterior protrusion of the calcaneus
Slow disease progression
Outside of the clinical characteristics in an affected individual suspected of having COLVI- CMD, a genetic test would be then used to look for any mutation in the three strands/genes involving collagen 6 (COL6A1, COL6A2 and COL6A3). A genetic test would provide a more specific diagnosis and is less invasive than a skin/muscle biopsy.
The Physiology of Collagen VI Congenital Muscular Dystrophy
The extracellular matrix forms the outside environment around the muscle cell. It performs critical functions by supporting muscle cell stability and regeneration while allowing the muscle cell to adhere to the matrix. The extracellular matrix contains collagen 6 (collagen VI) which is composed of three strands, abbreviated COL6A1, COL6A2 and COL6A3. A mutation in a gene encoding any of these strands can lead to either a deficient or abnormal strand or an absent strand. A mutation can lead to a partial deficiency or a complete deficiency. Both autosomal recessive and autosomal dominant mutations causing Ullrich CMD have been recognized. Bethlem Myopathy mostly presents with autosomal dominant inheritance. There is a variable clinical spectrum connecting Ullrich CMD and Bethlem Myopathy, a theme that is repeated through other CMD subtypes.
Collagen VI-CMD is a spectrum disorder and represents a continuum of symptoms that range from early onset/severe to late onset/mild. Research has also led to an intermediate phenotype within the clinical spectrum where the symptoms are moderate in severity.
Affected individuals on the early onset/severe end of the spectrum (also known as Ullrich CMD) typically present with muscle weakness, hip dislocation at birth, kyphoscoliosis, hyperpigmented skin lesions, prominent heel bones, elbow contractures and hyperextensible finger joints. These symptoms can be present at birth or within the first two years of life. Given that collagen is not found in the brain, affected individuals typically have normal intelligence and no brain involvement. A primary driver of mortality and quality of life is respiratory insufficiency. Problems breathing will likely lead to the need for breathing support in the first or second decade of life.
Affected individuals on the late onset/mild end of the spectrum (also known as Bethlem Myopathy, LGMDD5 is autosomal dominant or LGMDR22 is autosomal recessive), experience symptoms that are less severe and slower progression. Many will continue to retain their ability to walk into adulthood and may not need breathing support until later in life.
COLVI-CMD likely represents the second most common form of CMD after LAMA2 CMD.
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