Monosomy 21: A possible stepwise evolution of the karyotype

The authors describe a female infant with manifestations of complete monosomy for chromosome 21 intrauterine growth retardation, failure to thrive, craniofacial anomalies, arthrogryposis-like features, and psychomotor retardation. Chromosome analysis demonstrated mosaicism for 3 different cell lines in the various tissues examined; 45,XX,-21/46,XX,del(21)(q11) 46,XX. The existence of these 3 lines suggests a possible explanation for the few cases of 'complete monosomy 21' which have been reported.