Guanidinoacetic acid (GAA) is a naturally-occurring precursor of creatine and one of the key compounds investigated in our lab. GAA is found in human serum and urine, with circulating GAA likely reflects an equilibrium between its endogenous production and utilization/excretion. GAA deficiency (as indicated by low serum GAA) has been reported in various conditions yet this intriguing clinical entity appears to be poorly characterized as yet, either as a primary deficit or a sequel of secondary disease. In recent review article published in International Journal of Medical Sciences, we summarized the inherited and acquired disorders with apparent GAA deficiency and discussed a possible relevance of GAA shortfall in clinical medicine. Read the full text here.