Endocrine Abstracts

Understanding the molecular factors that regulate human muscle mass is acquiring increasing scientific interest. Hitherto, known (+ve) endocrine regulators of lean body mass included the GH-IGF-1 system, anabolic steroids, and (−ve) myostatin. In order to elucidate this process further, we have investigated a clinical case at a genetic and phenotypic level. A 46-year-old man with idiopathic muscle hypertrophy requiring multiple therapeutic fasciotomies underwent clinical and biochemical (endocrine) assessment followed by molecular diagnostics of his muscle tissue including Affymetrix™ microarray expression profiling, using statistical modelling to identify high probability candidate genes.

Method: Using 2 different vastus lateralis biopsies, total RNA was extracted from flash frozen muscle tissue using standard techniques. Following one round amplification, labelled cRNA was hybridised to U133A array chips run in duplicate; having passed all the quality control steps according to MIAME (minimum information about a microarray experiment) guidelines. The expression profiling data (n=4) was further analysed using an unsupervised in silico model comparing the results with a database of >120 human skeletal muscle samples processed in an identical manner. Diagnostic categorisation was performed using a tree and nodal system.

Results: Clinical examination revealed a hypermuscular individual, of Ht 1.87 m Wt 141.8 kg and BMI of 41. Baseline biochemistry, CK, 09.00 testosterone, LH/FSH, multiple GH sampling, and IGF-1 estimation were normal, as was the GH response to an oral glucose challenge. Electromyography, immunohistochemistry and western blot analysis for dystrophic conditions were also normal. Statistical modelling revealed a unique gene expression signature, in a distinct category. Our data failed to demonstate over-expression of anabolic factors e.g. IGF-1 or underexpression of myostatin. However, the microarray data suggested significant downregulation of SOCS-2 (P<0.00001), suggesting a novel, physiologically plausible, candidate gene for detailed onward investigation.