Monosomy 21 syndrome: further delineation including clinical, neuropathological, cytogenetic and biochemical studies.

Only six cases of living newborns with apparently complete monosomy 21 have been reported. All the previous cases with the exception of the present case died between 3 weeks and 20 months. Only one of these cases had a postmortem examination. The subject of this report was previously described at the age of 6 years (Davis et al. 1976). He survived until 11 years old and is the oldest known case of complete monosomy 21. We report here the clinical presentation over 11 years, results of gene dosage studies, cytogenetic analysis, and the neuropathological postmortem examination.