Complete monosomy mosaic of chromosome 21: Case report and review of literature

Complete monosomy mosaic of chromosome 21 is a rare disorder. The syndromic features are highly variable. This study describes a girl of Mexican origin with complete monosomy 21 in mosaicism with novel findings, including cortical atrophy, macrostomia, pectum excavatum and immune deficiencies. Parental karyotypes were normal. FISH analysis with probes from 21q22.1–q22.2 region and centromere of X DNA probe was performed on peripheral blood lymphocytes whereas 21q22.1–q22.2 and 21q, 4p, 4q subtelomeric DNA probes were tested in fibroblasts. We propose that the monosomy 21 mosaicism is the cause of the survival of children with more than 4 months of age.

► We add new clinical findings in monosomy 21.
► The present manuscript shows a rare case of monosomy 21 in mosaicism.
► Monosomy 21 in mosaicism was confirmed through FISH analysis.
► We discard the possibility that regular monosomy 21 is compatible with life.
► We propose that survival is possible only when the patient is mosaic.