1. A diagnosis of LGMD is arrived at by a process of elimination. This tool assumes that the diagnostic exclusion of other, more common types of MD (Duchenne, Becker, Myotonic, FSH, etc.) was performed. In addition the tool assumes that neurogenic causes of muscular weakness (Spinal Muscular Atrophy, Charcot-Marie-Tooth, etc.), metabolic myopathies (Pompe, McArdle, etc.), and autoimmune causes of muscle weakness have already been considered and excluded.
2. Some types of LGMD present as distal muscular dystrophies. Although, this tool considers one of the more common forms of distal muscular dystrophy, Nonaka Distal Myopathy (aka HIBM2), it does not consider all of the currently-identified types of distal MD. A listing of currently-identified types of distal MD is given at http://neuromuscular.wustl.edu/musdist/distal.html.
3. New genetic types of LGMD continue to be identified. It is estimated that with current knowledge, about 75% of LGMD patients are able to be diagnosed with a specific type.
4. Even for currently-identified types of LGMD, a number of case reports in the medical literature describe patients whose phenotypes are atypical, or outside the previously-reported spectrum of their particular form of LGMD. The tool may not be able to correctly diagnose patients whose symptoms are unusual or unreported for their type of LGMD.
5. The “gold standard” for diagnosis of a specific type of LGMD is identification of pathological mutations by genetic sequencing (on one allele for a dominant inheritance, on both alleles for a recessive inheritance). In some cases, testing at the protein level is desirable before proceeding to genetic sequencing. Thus, this tool’s output should be considered a recommendation for which genes or proteins to consider in further testing, and not a diagnosis in itself.