Mosaic trisomy 12 is a rare genetic condition with a highly variable phenotype.Clinical features associated with this condition include developmental delay,intellectual disabil-ity,dysmorphic facial features,short stature,pigmentary dysplasia,complex congenital heart defects and hypotonia(Table 1).To date,20 patients have been described in which mosaic trisomy 12 was observed in both extraembryonic and neonatal/infant tissues.Chen et al.reported two cases without phenotypic abnormalities [1].Of the 20 previously reported cases,4 resulted in neonatal or infant death.Those findings support the hypothesis that mosaic trisomy 12 man-ifests across a wide spectrum of phenotypes and that predict-ing the degree of abnormalities is quite difficult [2-4].In several cases,trisomy 12 mosaicism was detected prenatally in amnion fluid,but not postnatally [5-8].Even if the mosai-cism is not confirmed in one tissue,it may still be present in other tissues of the child.