Trisomy 16 mosaicism at chorionic villus sampling and amniocentesis with a normal physical and intellectual outcome

The identification of trisomy mosaicism in the prenatal setting is often shrouded with uncertainty for the genetic counsellor, and more importantly for the parents. The outcomes for these pregnancies may well be normal, but abnormalities and even in utero death are possibilities depending on the chromosomal abnormality and the degree of mosaicism. Advice to parents following the diagnosis of trisomy 16 mosaicism at chorionic villus sampling, with confirmation at subsequent amniocentesis, and in the setting of apparently normal fetal ultrasonography, is necessarily cautious. Malformations are seen in the majority of infants born following a diagnosis of mosaic trisomy 16 at amniocentesis, and intrauterine growth retardation, with postnatal catch-up, is the rule. We report here a case with a normal outcome by age 2.5 years and in fact with above-average language ability, and in whom trisomy mosaicism was confirmed postnatally.