This is a very rare condition (named after the Greek god Proteus) and is usually sporadic. Possible transmission of the condition from father to son has been described once (Goodship et al. 1991), but there is considerable debate about this in view of diagnostic pitfalls (Turner 1999). Somatic mosaicism was postulated to explain some cases (Reardon et al. 1996), and this hypothesis has been supported by the identification of somatic mosaic activating mutations in AKT1 in most if not all cases of well-characterized Proteus syndrome (Lindhurst et al. 2011). Congenital lipomas occur, sometimes with hemangiomatous or lymphangiomatous elements, and progress and are associated with partial or complete hemihypertrophy, asymmetry, and disfiguration. Accelerated growth is seen in the first few years of life. Exostoses of the skull cause macrocephaly and skull asymmetry with frontal bossing. Localized deformities develop, especially of the hands and feet, and hemihypertrophy (segmental to total) is common.
Dermatological features include pigmented nevi, diffuse areas of hyperpigmented and depigmented areas of skin, and linear verrucous epidermal nevi, and massive cerebroid gyriform hyperplasia with rugosity of the soles of the feet is a characteristic feature. Bony and adipose overgrowth may lead to bizarre macrodactyly. Subcutaneous hamartomatous Tumours, pigmented areas of skin, bony abnormalities, and lung cysts have been described (Nishimura and Koslowski 1990). Intelligence is usually normal. There is a theoretical risk of malignancy in this overgrowth syndrome, and a testicular mesothelioma at the age of 4 years has been described in a severe case (Barker et al. 2001).
Mutations in PTEN have been detected in a subset of cases. The second PTEN allele has been shown to be inactivated in the abnormal tissue (Zhou et al. 2000, 2001; Smith et al. 2002).