Sibs with tetrasomy 18p born to a mother with trisomy 18p.

We report a family with an 18p trisomic mother and two 18p tetrasomic daughters. The mother is phenotypically normal and healthy, but with an unusual type of trisomy 18p: 47,XX,del(18)(pter----p11.21),+i(18p) de novo. The older sister has microcephaly, mental retardation, an asymmetrical and peculiar face with low set ears, pinched up nose, high arched palate, small mouth, micrognathia, tapering fingers, asymmetrical length of legs, and an asthenic body. The younger sister was stillborn with extensive defects of the skull, congenital hydrocephalus, severe facial anomalies, and lumbosacral meningocele. Both daughters have inherited one normal chromosome 18 and an isochromosome 18p from their mother, and one normal chromosome 18 from their father. Although one quite similar family has been reported, to the best of our knowledge there have been no reports of families in which two daughters with tetrasomy 18p syndrome have been born to a mother with trisomy 18p with isochromosomes.