Abstract
BackgroundPartial monosomy 21 is a rare finding with variable sizes and deletion breakpoints, presenting with a broad spectrum of phenotypes.Case presentationWe report a 10-month-old boy with short stature, minor anomalies and mild motor delay. The patient had a monosomy 21 and duplication of the 21q22.11q22.3 region on the remaining derivative chromosome 21 which represents a partial 21q uniparental disomy of paternal origin, upd(21q22.11q22.3)pat. The abnormalities were characterized by karyotyping, FISH, chromosomal microarray, and genotyping.ConclusionsThis is the first case showing a monosomy 21 compensated by upd(21q22.11q22.3) as a mechanism of genomic rescue. Because there is no strong evidence showing imprinting on chromosome 21, the uniparental disomy itself is not associated with abnormal phenotype but has reduced phenotype severity of monosomy 21. We reviewed the previously published cases with isolated 21q deletions and identified a common deletion of 5.7 Mb associated with low birth weight, length and head circumference in the 21q21.2 region.
Highlights
Partial monosomy 21 is a rare finding with variable sizes and deletion breakpoints, presenting with a broad spectrum of phenotypes.Case presentation: We report a 10-month-old boy with short stature, minor anomalies and mild motor delay
This is the first case showing a monosomy 21 compensated by upd(21q22.11q22.3) as a mechanism of genomic rescue
Because there is no strong evidence showing imprinting on chromosome 21, the uniparental disomy itself is not associated with abnormal phenotype but has reduced phenotype severity of monosomy 21
Summary
Partial monosomy 21 is a rare finding with variable sizes and deletion breakpoints, presenting with a broad spectrum of phenotypes.Case presentation: We report a 10-month-old boy with short stature, minor anomalies and mild motor delay. Partial monosomy 21 is a rare finding with variable sizes and deletion breakpoints, presenting with a broad spectrum of phenotypes. Full monosomy 21 has been rarely reported and is likely to be lethal in utero [1]. It was suggested that full monosomy 21 may not exist in live born and those reported cases of monosomy 21 are likely to be either mosaicism or partial monosomy 21 resulting from a cryptic unbalanced translocation [1, 3]. Among the more than 30 cases previously reported with a partial monosomy 21, about half were isolated chromosome 21 segmental monosomy without other abnormalities identified [7, 8]. Each partial monosomy 21 case represents a rare and unique finding with variable deletion breakpoints, and the cases with partial monosomy 21 have a broad spectrum of phenotypes
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