Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 57 8 2020 02 15 522 524 Ali Nikfar Zanjan Metabolic Diseases Research Center, Zanjan University of Medical Sciences, Zanjan, Iran. AND Department of Genetics and Molecular Medicine, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran. AND Imam Khomeini Genetic Counseling Center, Welfare Organization of Zanjan, Zanjan, Iran. Mojdeh Mansouri 2 Department of Genetics and Molecular Medicine, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran. Gita Fatemi Abhari Imam Khomeini Genetic Counseling Center, Welfare Organization of Zanjan, Zanjan, Iran. 2019 08 27 2019 09 08 Down syndrome or trisomy 21 is the most common genetic disorder with a prevalence of 1 in 700 live-born infants. It is characterized by the intellectual disability of varying range, developmental delay, distinctive facial features and various physical abnormalities. The most frequent clinical features include hypotonia, short stature, short neck, upward slanting eyes, flat nasal bridge, bulging tongue, small ears and a single palmar crease of the hands. Mainly there are three cytogenetic forms of Down syndrome including free trisomy 21, mosaicism and Robertsonian translocation. We describe the case of a 1-year-old Iranian female child who presented to our genetic counseling center with intellectual and physical disabilities. The most common features of Down syndrome were present. The cytogenetic analysis confirmed the diagnosis, with detection of the Robertsonian translocation t(21q; 21q). The patient's parents were found to be both phenotypically and cytogenetically normal, so the identified Robertsonian translocation t(21q; 21q) probably have arisen de novo. https://acta.tums.ac.ir/index.php/acta/article/view/8050 https://acta.tums.ac.ir/index.php/acta/article/download/8050/5308