Interstitial microdeletion of the short arm of chromosome 16 is responsible for clinical features of the Rubinstein-Taybi syndrome. In most cases there is a very short microdeletion, with the character of point mutation and therefore sequencing of CBP gene is necessary for the detection of the mutation. Author reports a case of an infant patient with familial occurrence of mental retardation.

        Key words: interstitial microdeletion of 16p, point mutation of CBP gene, Rubinstein-Taybi syndrome, familial occurrence of mental retardation