Atypical Down syndrome phenotype with severe developmental delay, hypertonia, and seizures in a child with translocation trisomy 21.

An infant is reported who presented with a de novo 21;21 translocation trisomy 21 and an atypical phenotype for Down syndrome (DS). Findings included microcephaly, small stature, downslanting palpebral fissures, absent Brushfield spots, moderate micrognathia, left ptosis, left torticollis, severe developmental delay, seizures, and hypertonia. Further clinical evaluation using both the diagnostic criteria for DS and the Jackson checklist of 25 signs was inconsistent with the diagnosis for DS.