[Terminal partial mosaic monosomy of the short arm of chromosome 3, in discordant monozygotic twins, 46,XY/46,XY, del (3) (p25)].

A 22 months old male child, a second monozygotic twin with distal partial monosomy of the short arm of chromosome 3 in mosaicism and anomalies in dermatoglyphics is described. Patient presents retardation of intrauterine and postnatal growth, psychomotor retardation, microcephalia, mongoloid deviation of palpebral clefts, macroglossia with constant sucking, congenital cardiopathy cryptorchism, hypospadias and generalized hypertonia. Twin is a normal infant with normal karyotype. Genotypic similarity and clinical picture is discussed.