Mosaic monosomy 21 syndrome

Monosomy 21 is extremely rare in live-born infants. Although monosomy 21 mosaicism may be present in living individuals, the incidence is also low. Previously, 12 cases that were at first diagnosed as monosomy were reexamined and were reclassified as unbalanced translocations resulting in partial monosomy. In this report, we present a 15-month-old boy who suffered from growth retardation, psychomotor delay, and multiple anomalies, including microcephaly, a peculiar face, abnormal ears, and arthrogryposis. Chromosomal analysis demonstrated mosaicism of monosomy 21 in peripheral blood lymphocyte: 45,XY,-21 [7]/46,XY [93].