In addition to histopathological features (for a review see the article of Zając et al. [13]), differential molecular pathological diagnosis for CS subtypes can take advantage of the immunohistochemical or genetic detection of isocitrate dehydrogenase (IDH)1/2 mutations found in 50–80% of central, or periosteal CS and dedifferentiated CS, or exostosin (EXT)1/2 mutations found in peripheral CS. The gene discussed is IDH3A; the disease is Cowden syndrome 1.