Beyond Down syndrome phenotype: Paternally derived isodicentric chromosome 21 with partial monosomy 21q22.3.

Inverted isodicentric chromosome 21 is a rare form of chromosomal rearrangement that may result in trisomy 21; sometimes this rearrangement may also lead to segmental monosomy of the terminal long arm of chromosome 21. In this report, we describe the prenatal diagnosis and neonatal follow-up of a child with a paternally derived, de novo isodicentric chromosome 21 and a concurrent ∼1.2 Mb deletion of the 21q22.3 region [46,XX,idic(21)(q22.3)]. This child presented with unusual phenotype of Down syndrome and additional defects including esophageal atresia and tethered cord syndrome. The resulting phenotype in this infant might be a coalescence of the partial trisomy and monosomy 21, as well as homozygosity for idic (21). The utilization of chromosomal microarray in this case enabled accurate characterization of a rare chromosome abnormality, potentially contributes to future phenotype-genotype correlation and produced evidence for a molecular mechanism underlying this rearrangement.