Segmental overgrowth syndromes, consisting of a spectrum of disorders with vascular, cutaneous and skeletal abnormalities, are sporadic, non-hereditary disorders (Biesecker and Spinner, 2013; Lindhurst et al., 2011). It was originally postulated by Happle that such disorders arise as a result of mosaic somatic mutations and that complete heterozygosity for the causal mutation could be either lethal to the affected individual or the affected person would be incapable of germline transmission (Happle, 1987). The prototype of the mosaic postnatal overgrowth syndromes is the Proteus syndrome commonly manifesting with connective tissue nevi and bone overgrowth, but central nervous system and the eyes can also be affected. The tissue overgrowth in Proteus syndrome is non-congenital and progressive, the diagnosis is often delayed, and the cases can be difficult to manage. The Proteus syndrome is caused by heterozygous activating mutations in the AKT1 gene (Biesecker, 2006).