Consider a few recent examples. First, in medical genetics there is a set of overlapping disorders known as Noonan syndrome, LEOPARD syndrome, neurofibromatosis Type 1, and neurofibromatosis–Noonan syndrome, and all tend to be characterized by facial dysmorphisms, short stature, and congenital heart defects (Sarkozy et al., 2007). However, recent molecular analysis of aspects of target genes led to the conclusion that the overlap between the former two disorders and the latter two was not paralleled by common molecular events (De Luca et al., 2005). That the two sets of disorders have distinct genetic causes has led to improved, more specific clinical recommendations (Sarkozy et al., 2007). Despite their morphological similarity, which resulted in their similar names, the two sets of disorders have different genetic etiologies. Entities once thought to be the same were recognized not to be.
