Myostatin-related muscle hypertrophy

Myostatin-related muscle hypertrophy is a rare genetic condition characterized by reduced body fat and substantially increased skeletal muscle size, with affected individuals developing roughly double the typical amount of muscle mass. It results from mutations in the MSTN gene, which normally produces the protein myostatin, a regulator that restrains muscle growth; when the gene is defective, this restraint is lost and muscle tissue expands well beyond typical limits. The condition follows a pattern of incomplete autosomal dominance, meaning that people who inherit two mutated copies of the gene show more pronounced muscle growth than those who inherit only one. Despite the dramatic increase in muscle size, strength gains are disproportionately smaller than the increase in muscle bulk would suggest, and the condition is not known to cause other medical problems; affected individuals have normal intellectual development, though overall prevalence in humans remains unknown. The underlying myostatin gene and its effect on muscle growth were first documented in cattle, when the British farmer H. Culley described unusually muscular animals later found to carry myostatin gene deletions, in 1807, well before the same mechanism was recognized in humans.