en Related Fields Related Fields مقاله موردی Case Report <div style="text-align: justify;"><strong>Background:</strong> Mosaicism of a normal cell population and an unbalanced autosomal chromosome rearrangement is rarely seen. If the abnormal cell line contributes to a minor part of soma, the phenotype is expected to be normal. <strong>Case Report</strong>: We report a 29-year-old woman who had balance chromosomal translocation of 46,XX,t(5;21) with a two-year-old affected girl, characterized by mental retardation, dystrophia, hearing impartment, and dysphagia. <strong>Methods and Results:</strong> Cytogenetic investigation revealed a low mosaic unbalanced translocation of 46,XX,t(5;21)/ 46,XX, which was confirmed by fluorescence <em>in situ </em>hybridization analysis. Studying 200 metaphases and interphases of peripheral blood sample revealed 70% partial monosomy of 21q22 and partial trisomy of 5q(35.3) and 30% of normal pattern. <strong>Conclusion:</strong> In rare cases such as this study, parents with balanced translocation with no phenotypes may lead to a mosaic unbalanced translocation with abnormal phenotypes in offspring, which underscores the need for prenatal karyotyping and genetics counseling.</div> Partial monosomy 21q, Translocation t(5,21), Unbalanced autosomal chromosome translocation mosaicism 60 63 http://ibj.pasteur.ac.ir/browse.php?a_code=A-10-1-782&slc_lang=en&sid=1 Sadaf Omori Sarabi 0000-0001-8767-1154 No Paresh Pathobiology and Genetics Laboratory, Tehran, Iran Javad Karimzad Hagh 0000-0002-6940-9192 No Paresh Pathobiology and Genetics Laboratory, Tehran, Iran Claudia Behrend 0000-0001-5263-1208 No Praxisgem für Medizinische Genetik, Düsseldorf, Germany Seyed Behrooz Mohseni 0000-0002-1963-6098 No Paresh Pathobiology and Genetics Laboratory, Tehran, Iran Mitra Ansari Dezfouli 0000-0002-8496-8750 No Department of Neuroscience and Addiction Studies, School of Advanced Technologies in Medicines, Tehran University of Medical Science, Tehran, Iran Seyed Khalil Rashidi 0000-0001-8931-7087 No Biotechnology Research Center, Semnan University of Medical Science, Semnan, Iran Mir Davood Omrani 0000-0002-0673-9717 Yes Department of Medical Genetics, Faculty of Medicine, Shahid Beheshti University of Medical Science, Tehran, Iran