Limb–girdle muscular dystrophy (LGMD) is a genetically heterogeneous group of rare muscular dystrophies that share a set of clinical characteristics. It is characterised by progressive muscle wasting which affects predominantly hip and shoulder muscles. LGMD usually has an autosomal pattern of inheritance. It currently has no known cure or treatment.
LGMD may be triggered or worsened in genetically susceptible individuals by statins, because of their effects on HMG-CoA reductase
Signs and symptoms
By definition, all limb girdle muscular dystrophies (LGMD) cause progressive proximal weakness, meaning weakness of the muscles on or close to the torso that worsens over time. Explicitly, LGMD preferentially affects muscles of the hip girdle, thigh, shoulder girdle, and/or upper arm. The muscle weakness is generally symmetric. Usually, the hip girdle is the first area to exhibit weakness, manifesting as difficulty walking, going up and/or down stairs, rising from a chair, bending at the waist, or squatting. Because of these difficulties, falling can occur frequently. Weakness of the shoulder girdle can make lifting objects, or even elevating the arms, difficult or impossible. Rate of progression varies between patients. Eventually, the abilities to run and walk can deteriorate. The disease commonly leads to dependence on a wheelchair within years of symptom onset, although some patients maintain mobility. Eventually the disease can affect other muscles such as the ones located in the face.
By definition, LGMDs primarily affect skeletal muscles, although cardiac muscle can be affected to a lesser degree in select subtypes, which can cause palpitations
There can be significant variability in disease features and severity between LGMD subtypes, and even within any given LGMD subtype. Additional possible presentations include:
In most cases, pain is not present with LGMD, and mental function is not affected. LGMD can begin in childhood, adolescence, young adulthood or even later, the age of onset is usually between 10 and 30. Both genders are affected equally. When limb-girdle muscular dystrophy begins in childhood, the progression appears to be faster and the disease more disabling. When the disorder begins in adolescence or adulthood the disease is generally not as severe and progresses more slowly. There is no sensory neuropathy or autonomic or visceral dysfunction at presentation.
Genetics
LGMD is a genetic and heritable disorder, due to one of many genetic mutations of proteins involved in muscle function. All currently identified LGMDs have an inheritance pattern that is dominant or recessive, although the definition of LGMD allows for diseases with more complicated inheritance patterns to be classified as LGMD. Pathogenic mutations are mostly in coding regions, but non-coding causative variants were also reported. In Euroasia CAPN3 mutations are the most common cause of LGMD, however in northern Europe mutations in FKRP are also very common. HMG CoA Reductase homozygous mutation leads to a form of LGMD that may respond to treatment with the downstream metabolite mevalonolactone in the cholesterol synthesis pathway.
Diagnosis
The diagnosis of limb–girdle muscular dystrophy can be done via muscle biopsy, which will show the presence of muscular dystrophy, and genetic testing is used to determine which type of muscular dystrophy a patient has. Immunohistochemical dystrophin tests can indicate a decrease in dystrophin detected in sarcoglycanopathies. In terms of sarcoglycan deficiency there can be variance (if α-sarcoglycan and γ-sarcoglycan are not present then there's a mutation in LGMD2D).
The 2014 Evidence-based guideline summary: Diagnosis and treatment of limb–girdle and distal dystrophies indicates that individuals suspected of having the inherited disorder should have genetic testing. Other tests/analysis are: High CK levels(x10-150 times normal) MRI can indicate different types of LGMD. EMG can confirm the myopathic characteristic of the disease. Electrocardiography (cardiac arrhythmias in LGMD1B can occur)
Types
The "LGMD D" family is autosomal dominant, and the "LGMD R" family is autosomal recessive. Limb–girdle muscular dystrophy is explained in terms of gene, locus, OMIM and type as follows: