Up to 48 per 100,000 (1:2100) of individuals tested positive for the mutation of DM1 in New York, although not all of these individuals would have become symptomatic. Again in New York, premutations for DM1 were found in 191 per 100,000 (1:525). DM2 prevalence is not known, but genetic studies estimate it to be as high as 1:1830. DM affects males and females approximately equally. About 30,000 people in the United States are affected. In most populations, DM1 appears to be more common than DM2. However, recent studies suggest that type 2 may be as common as type 1 among people in Germany and Finland.DM1 is the most common form of myotonic muscular dystrophy diagnosed in children, with a prevalence ranging from 1 per 100,000 in Japan to 3–15 per 100,000 in Europe. The prevalence may be as high as 1 in 500 in regions such as Quebec, possibly due to the founder effect. The incidence of congenital myotonic dystrophy is thought to be about 1:20,000. History
Myotonic dystrophy was first described by a German physician, Hans Gustav Wilhelm Steinert, who first published a series of 6 cases of the condition in 1909. Isolated case reports of myotonia had been published previously, including reports by Frederick Eustace Batten and Hans Curschmann, and type 1 myotonic dystrophy is therefore sometimes known as Curschmann-Batten-Steinert syndrome. The underlying cause of type 1 myotonic dystrophy was determined in 1992.
Cataracts can be either a cortical cataract with a blue dot appearance, or a posterior subcapsular cataract. Other organs affected include the heart, lungs, gastrointestinal tract, skin, and brain. Insulin resistance can also occur. Signs and symptoms vary considerably by severity, unusual phenotype, and form (DM1/DM2). DM1 and DM2 differ in regards to the muscles they affect, age of onset, severity of disease, and extramuscular manifestations. DM1
DM1 usually begins in the muscles of the hands, feet, neck, or face. One manifestation of facial weakness is drooping of the eyelid (ptosis). It slowly progresses to involve other muscle groups, including the heart. Myotonia tends to be more prominent in DM1 compared to DM2. Other DM1 manifestations include problems with executive function (e.g., organization, concentration, word-finding) and hypersomnia. Abnormalities in the electrical activity of the heart are common in DM1, manifesting as arrhythmias or conduction blocks. Sometimes, dilated cardiomyopathy occurs. Symptoms onset any time from birth to adulthood. The earlier the disease onset, the greater the variety of possible signs and symptoms. Thus, various diagnostic classifications based on the age of onset/severity of the disease have been proposed, although DM1 manifestations likely lie on a continuum. Congenital DM1
When DM1 onsets at birth, it is called congenital DM1. Manifestations that can be present at birth include hypotonia, respiratory failure, feeding difficulty, and club foot (talipes equinovarus), any of which tend to resolve over several years. During childhood, intellectual impairment, attention deficit hyperactivity disorder (ADHD), and autism spectrum disorders (ASD) can result.