Down Syndrome Resulting from a Rare non-Robertsonian Translocation t(11;21)(p13;q22)

Introduction: Down syndrome (DS) is a common genetic disorder, occurring in approximately 1 in 700 births. It results from an extra copy (triplication) of the whole or part of the long arm of chromosome 21 caused by different cytogenetic alterations: free trisomy, Robertsonian translocations, mosaicism, duplication of the critical region and other structural rearrangements. Non-Robertsonian chromosome translocations are very rare events with few cases reported. Case Report: We identified the non-Robertsonian translocation t(11;21)(p13;q22) and two chromosomes 21 in a female child referred with a clinical diagnosis of trisomy 21.  The infant developed the transient myeloproliferative disorder at 17 months. Cytogenetic analysis was performed in lymphocytes and bone marrow metaphases according to standard procedure - G banding and fluorescence in situ hybridization.  The karyotype study of the parents revealed that her phenotypically normal mother carries the same reciprocal translocation. Conclusion: This is the second report of the translocation t(11;21)(p13;q22),  the first one resulting in DS.  This description expands knowledge about cytogenetic variability in the etiology of DS. Future studies are needed to investigate the long-term clinical effects of the trisomy 21 associated with t(11;21)(p13;q22)