Twin studies have been used to distinguish genetic and environmental factors for many disorders in the general population, including ectodermal dysplasia, Ellis-van Creveld, and anencephaly. This review focuses on genetic disorders affecting monozygotic, dizygotic, and conjoined twins in order to better understand them. Many studies focus on twins because they have a nearly identical genome, eliminating environmental factors. In case studies, concordance rates in monozygotic twins confirmed that some disorders were caused by genetics and not environment. Discordant values ​​in twins will also be evaluated briefly. Pairing studies have also shown links between specific disorders and the genes that cause them. Knowing the location of these genes allows patients to be treated quickly and effectively. This article will discuss the possible causes of twinning and the different methods to identify abnormalities in twins. These methods also make it possible to take preventive measures against the rise of congenital malformations during prenatal development. Epigenetics in twins is also considered in terms of its effects on them. Treatments for genetic disorders in twins are reviewed, ranging from restoring malformed teeth to separating conjoined twins. Support groups for twins in treatment and their families are also briefly reviewed. Twins are truly fascinating from embryo separation to birth; and yet, the complexity of twinning is not yet fully understood in the scientific world. Scientists have studied the human body from prenatal development to birth and are still impressed by how twins form. Research on twinning is growing in this area, leading...... middle of article ......enetic and environmental influences on symptoms of attention deficit hyperactivity disorder in adults: a large twin study based on the Swedish population. Psychological. Med, 43 pp. 197-207. McGrogan, A., Franssen, CF and De Vries, CS 2011. The incidence of primary glomerulonephritis worldwide: a systematic review of the literature. Nephrology Dialysis Transplantation, 26 (2), pp. 414-430. Puttaraju, GH and Visveswariah, PM 2013. Ectodermal dysplasia in identical twins. Journal of Pharmacy and Bioallied Sciences, 5 (Suppl 2), p. 150.Tokuhara, K., Hamada, Y., Yui, R., Tanano, A., Takada, K. and Kamiyama, Y. 2005. Congenital biliary dilatation in dizygotic twins. International Pediatric Surgery, 21 (1), pp. 17-19. Van Den Berg, SM and others. 2012. Genetic analysis of rare diseases: Bayesian estimation of twin concordance rates. Behavior Genetics, 42 (5), pp.. 857-865.