Shahin Ramazi - Ph.D. Candidate of Genetics, Department of Biology, School of Natural Sciences, University of Tabriz, Tabriz, Iran
Ali Fasihi - Ph.D. Candidate of Genetics, Department of Genetics, School of Biology, Tarbiat Modares University, Tehran, Iran
Maryam Godarziyan - Master of Nursing, Iranian Research Center on Healthy Aging, Sabzevar University of Medical Sciences, Sabzevar, Iran
Morteza Hashemzadeh-Chaleshtori - Professor, Department of Human Genetics, School of Medicine, Cellular and Molecular Research Center, Shahrekord University of Medical Sciences, Shahrekord, Iran

Background & Aims: Nearly ۳۰ hereditary disorders in humans result from an increase in the number of copies of simple repeats in genomic DNA, including fragile X syndrome, myotonic dystrophy, Huntington’s disease, and Friedreich’s ataxia. One the most frequently occurring types of mutation is trinucleotide repeat expansion. The present study was conducted with the aim of investigating the cause and molecular mechanisms of repeat expansions DNA and their pathogenic mechanisms in diverse classes of genetic diseases. Methods: Scientific databases were searched using the keywords expandable DNA repeat fragile X, myotonic dystrophy, Huntington’s disease, and Friedreich’s ataxia. After primary screening, articles which were related to the studies topic were further considered and analyzed. Results: DNA repeats seem to be predisposed to such expansion due to their unusual structural features, which disrupt the cellular replication, repair, and recombination processes. The majority of these debilitating diseases are caused by repeat expansions in the noncoding regions of their resident genes. The pathogenic mechanism underling these disorders include loss of function in protein and gain of function in protein or ribonucleic acid (RNA). Conclusion: Although diseases caused by trinucleotide repeat expansion vary in their phenotypes, they are somewhat similar in their pathogenic mechanism and medical findings. It is likely that progress made in this field will be beneficial to patients who have other neurological diseases

Expandable DNA repeat, Fragile X syndrome, Myotonic dystrophy, Huntington’s disease, Friedreich’s ataxia