Introduction

Hypomelanosis of Ito (HI) or incontinentia pigmenti achromians was described in 1952 by Ito, a Japanese dermatologist. The importance of HI derives from its frequent association with epilepsy and mental retardation (Pascual-Castroviejo et al., 1988, 1989; Pascual-Castroviejo, 1989; Ruiz-Maldonado et al., 1992). Mosaics for chromosomal abnormalities have been reported for several years in HI patients (Flannery et al., 1985; Flannery, 1990; Koiffmann et al., 1993; Fritz et al., 1998) but are not present in every case. Some authors have argued that HI is merely a symptom or a descriptive term that occurs in many conditions, all of which are characterized by chromosomal mosaicism (Donnai et al., 1988; Thomas et al., 1989; Ritter et al., 1990; Sybert, 1994). In support of this argument, skin lesions which conform to Baschko lines represent genetic mosaicism, but are not always an indication of HI. On the contrary, some authors think that HI is a symptom of mosaicism (Donnai et al., 1988; Thomas et al., 1989; Ritter et al., 1990; Sybert et al., 1990; Happle, 1998). Given the high frequency of neurological dysfunction associated with HI, the absence of typical neonatal signs of incontinentia pigmenti (IP) in all cases of HI, and the absence of chromosomal anomalies in many patients with HI, this hypothesis is difficult to prove.