Limb-girdle muscular dystrophy (LGMD) isn’t really one disease. It’s a group of disorders affecting voluntary muscles, mainly those around the hips and shoulders. The shoulder girdle is the bony structure that surrounds the shoulder area, and the pelvic girdle is the bony structure surrounding the hips. Collectively, these are called the limb girdles, and it is the muscles connected to the limb girdles that are the most affected in LGMD.
The term proximal is also used to describe the muscles that are most affected in LGMD. The proximal muscles are those closest to the center of the body; distal muscles are farther away from the center (for example, in the hands and feet). The distal muscles are affected late in LGMD, if at all.
As of late 2012, there are more than 20 different subtypes of LGMD, and this is a complex and constantly evolving area of research. See the table below for a more complete list of the LGMD subtypes.
LGMD, like other muscular dystrophies, is primarily a disorder of voluntary muscles. These are the muscles you use to move the limbs, neck, trunk and other parts of the body that are under voluntary control. Over time, muscle weakness and atrophy can lead to limited mobility and an inability to raise the arms above the shoulders.
The involuntary muscles, except for the heart (which is a special type of involuntary muscle), aren’t affected in LGMD. Digestion, bowel, bladder and sexual function remain normal. The brain, intellect and senses also are unaffected in LGMD. Cardiopulmonary complications sometimes occur in later stages of the disease. For more, see Signs and Symptoms.
LGMD is caused by a mutation in any of at least 15 different genes that affect proteins necessary for muscle function. Some types are autosomal dominant, meaning LGMD is inherited from one parent. Other types are autosomal recessive and occur when a faulty gene is inherited from each parent. For more on inheritance patterns in LGMD, see Causes/Inheritance.
At this time, progression in each type of LGMD can’t be predicted with certainty, although knowing the underlying genetic mutation can be helpful. Some forms of the disorder progress to loss of walking ability within a few years and cause serious disability, while others progress very slowly over many years and cause minimal disability.
LGMD can begin in childhood, adolescence, young adulthood or even later. Both genders are affected equally.
When limb-girdle muscular dystrophy begins in childhood, some physicians say, the progression is usually faster and the disease more disabling. When the disorder begins in adolescence or adulthood, they say, it’s generally not as severe and progresses more slowly.
MDA-supported scientists are pursuing several exciting strategies in muscular dystrophy research that have implications for LGMD. These strategies include gene therapy, exon skipping, stop codon-read through and myostatin blocking.
Here is a list of LGMD subtypes. Type 1 LGMDs are dominantly inherited, requiring only one mutation for symptoms to result. Type 2 LGMDs are recessively inherited, requiring two mutations — one from each parent — for symptoms to appear. Sometimes, LGMDs are referred to by their names, not their numbers, and some types have not been assigned numbers.
Some LGMD subtype names:
Dominant LGMD subtype numbers:
Recessive LGMD subtype numbers: