[A new syndrome of mental retardation and chromosomic instability in 3 siblings].

We report on three brothers with mental retardation, microcephaly and prominent ears whose cytogenetic studies showed no fragile X. However, an elevated frequency of spontaneous chromosome aberrations compared with that in normal individuals was found. The chromosome aberrations included acentric fragments, rings, dicentrics and radial figures. The lymphocytes did not show an increased sensitivity to mitomycin C nor to gamma radiation. It is suggested that this is a new hereditary syndrome of mental retardation with chromosome instability, probably recessive X linked.