Properly known as Myotonic Muscular Dystrophy, or MMD, the disease affects various muscles and organs in the body. "Myotonic" is an adjective for "myotonia," a term defined as the inability to relax one's muscles. MMD can take two forms, both of which derive from an abnormality in the genes of particular chromosomes.
Given the disease's root in the inability to relax muscles, MMD makes its presence known when an individual experiences difficulty performing common, muscle-related tasks. For instance, one might shake hands with someone and be unable to release the grip. Other symptoms include trouble swallowing or breathing as the respective muscles involved in those tasks weaken.
MMD's progression varies based on factors such as age, although the disease tends to develop slowly. Childhood onset causes cognitive and behavioral anomalies in addition to weakening muscles while adult-onset MMD often manifests as muscle attenuation in the face, neck, fingers, and ankles.