A tandem duplication of chromosome 21 in a newborn showing a phenotype inconsistent with Down syndrome

A patient with Down syndrome with a de novo derivative chromosome 21

Pure partial trisomy of chromosome 21 is a rare event. The patients with this aberration are very important for setting up precise karyotype-phenotype correlations particularly in Down syndrome phenotype. We present here a patient with Down syndrome with a de novo derivative chromosome 21. Karyotype of the patient was designated as 46,XY,der(21)(p13)dup(21)(q11.2q21.3)dup(21)(q22.2q22.3) with regard to cytogenetic, FISH and array-CGH analyses. Non-continuous monosomic, disomic and trisomic chromosomal segments through the derivative chromosome 21 were detected by array-CGH analysis. STR analyses revealed maternal origin of the de novo derivative chromosome 21. The dual-specificity tyrosine (Y)-phosphorylation regulated kinase 1A (DYRK1A) and Down Syndrome Critical Region 1 (DSCR1) genes that are located in Down syndrome critical region, are supposed to be responsible for most of the clinical findings of Down syndrome. However, our patient is the first patient with Down syndrome whose clinical findings were provided in detail, with a de novo derivative chromosome 21 resulting from multiple chromosome breaks excluding DYRK1A and DSCR1 gene regions.