Editor—Proteus syndrome (MIM 176920) is a rare, congenital, hamartomatous disorder, which is a member of a group of local overgrowth diseases. Happle1 proposed that some of these disorders are the result of the action of a lethal gene that can only survive in the mosaic state, which arises from an early somatic mutation or from a half chromatid mutation. Such a mechanism has been shown to be the underlying basis of McCune-Albright syndrome (MIM 174800).2 One of the mandatory diagnostic criteria for Proteus syndrome is a mosaic distribution of lesions and sporadic occurrence, entirely consistent with Happle's hypothesis.

Currently, little is known about the molecular causes of Proteus syndrome. It is, however, likely that the overgrowth of tissue involves all germ layers. This may be because of hyperproliferation, an absence of appropriate apoptosis, or alternatively cellular hypertrophy. There have been …