Summary Deletion of the long arm of chromosome 18 with a phenotype that may vary considerably, depending on the type of deletion and location of the breakpoint. The syndrome is marked mainly by mental retardation, midface hypoplasia, deeply set eyes, carp mouth, mild obesity, ataxia, hypotonia, malformed ears, and hyperactive and aggressive behavior. Neoplastic diseases may occur. Microcephaly, brachycephaly, dolichocephaly, high forehead, retrognathia or prognathism, and midfacial hypoplasia.
Dermatoglyphic findings consist of increased whorls on fingers and transverse palmar creases.
Polymicrogyria, brisk deep tendon reflexes and seizures. Neurofibrillary tangles have been observed in some cases. Autistic behavior and aggressiveness.