Monosomy 18q syndrome and atypical Rett syndrome in a girl with an interstitial deletion (18)(q21.1q22.3)

We describe a 6 1/2-year-old girl with an interstitial deletion of chromoso me arm 18q (18q21,1q22.3). Her clinical manifestations are a combination of those found in monosomy 18q syndrome and those of Rett syndrome. Cytogenet ic analysis demonstrated a deletion of the long arm of chromosome 18, defin ed by molecular analysis with polymorphic markers as a de novo interstitial deletion, paternally derived. The findings typical of the 18q- syndrome in cluded mental retardation, midface hypoplasia, and hypoplasia of labia majo ra, and those typical of Rett syndrome were severe mental retardation, auti stic behavior, inappropriate hand-washing movements, epilepsy, attacks of s ighing and hyperventilation, and progressive scoliosis since the age of 5 y ears. She did not have microcephaly, and the mental delay was obvious from an early age without a period of normal development, which makes the diagno sis of Rett syndrome atypical. Previously, a girl with mosaicism for a mono somy 18q associated with Rett syndrome has been described. That girl had a terminal deletion of chromosome 18q, which seems to coincide in part with t hat in the present girl. It is possible that genes in the distal region of 18q are involved in the etiology of Rett syndrome. Am. J. Med. Genet, 82:34 8-351, 1999. (C) 1999 Wiley-Liss, Inc.