Mutations in somatic cells are at least as common as in gamets. Chromosomal unbalanced aberration and autosomal gene mutation in early postzygotic status are reason of multiple malformations as well as mental and sexual defects. If the affections are not genetic lethal, can be transmitted in next generations in more severe form due to non-mosaic form (one of etiology of anticipation). Author refers Killian-Pallister syndrome due to mosaic form of trisomy of 12p with typical phenotype. The importance of syndromologic diagnosis for effective indication of special investigation and elutiation of etiology for genetic prognosis of parental reproduction is emphasized.

        Key words: Killian-Pallister chromosomal mosaic syndrome, postzygotic mutation, multiple malformations, severe central muscular hypotonia, genetic prognosis of parental reproduction