Myotonic Dystrophy Type 1 (DM1) is a complex, genetic, and multisystemic disorder caused by the expansion of CTG trinucleotide repeats in the Dystrophia Myotonica Protein Kinase gene, leading to the formation of toxic RNA foci, which finally result in progressive muscle weakness, myotonia, and systemic complications affecting almost every organ system of the body. The gene discussed is DMPK; the disease is Myotonia.