The electrical stimulus travels from the pacemaker (sinoatrial or SA node) to the ventricles along a very specific path consisting of conducting tissue and known as the AV (atrioventricular) node. Within the right atrium of a normal heart is a natural pacemaker that initiates and controls the heartbeat. The two upper chambers are the atria and the two lower chambers are the ventricles. This means that there are problems with the transfer of electrical impulses (conduction) that regulate the normal, rhythmic pumping action of the heart. Many people with DM1 have conduction defects of the heart. Some individuals may have slurred speech because of weakness of muscles required to speak. Because of weakness of the muscle that elevates the upper eyelids, the eyelids may droop and hang partially in front of the eyes (ptosis). Two common examples of myotonia are being unable to release a doorknob after opening or shutting a door, or taking a moment to be able to release a person’s hand after shaking hands.īecause of weakness of facial muscles, affected individuals may not have facial expressions or have a mask-like facial appearance. Myotonia is usually mild or moderate in severity. This is often described as the muscles stiffening. Muscle pain and fatigue are common.įor some people, it may take longer for their muscles to relax after using them (myotonia). Muscle weakness and wasting is progressive. Less often, muscles around the eyes (extraocular), a group of muscles located on the front of the thighs (quadriceps) and various muscles of the respiratory tract are affected. Individuals with a more severe form of DM1 (commonly referred to as the classic form) have muscle weakness that most often affects certain muscles including a muscle that elevates the upper eyelid, a muscle that helps people to chew (masticate), a muscle that helps to move the neck, the muscles of the forearm closest to the hands, certain muscles in the hands, and muscles of the lower legs that help to move the ankles. Affected individuals may have fully active lives with little impact on the lifespan or quality of life. Men with the mild form have an increased likelihood of going bald. Mild DM1 may be associated with cataract, mild myotonia and sometimes diabetes. People may have mild disease or severe complications. This is the most common form of myotonic dystrophy. Generally, the signs and symptoms of these disorders progress slowly. The adult form is the most common form and usually begins in a person’s 30s. In addition, DM1 and DM2 have many symptoms that overlap, but there are also symptoms unique to each disorder, clearly marking them distinct disorders.ĭM1 can develop at birth (congenital form), during childhood (juvenile form) and during adulthood (adult form). Every person is unique and how these disorders affect a person can be very different. Many people will not develop all of the symptoms discussed below. This is true even among members of the same family.
The signs and symptoms of DM1 or DM2 can vary greatly among affected individuals. DM2 is also known as Ricker syndrome or proximal myotonic dystrophy or PROMM. Steinert who, along with colleagues, first described the classic form in the medical literature in 1909. DM1 is also known as Steinert disease, named after Dr. variation of muscle fiber size, muscle fiber necrosis, scar tissue formation and inflammation) in muscle biopsy from patients. Each disorder is characterized by specific abnormalities (e.g. The muscular dystrophies are characterized by weakness and degeneration of various voluntary muscles of the body. These alterations are inherited in an autosomal dominant manner.ĭM is a type of muscular dystrophy. DM2 is caused by an alteration in the CNBP gene. DM1 is caused by an alteration in the DMPK gene. DM type 2 (DM2) causes similar symptoms to DM1, but is generally a less severe disorder and does not cause congenital disease. Congenital DM1 is characterized by muscle weakness (hypotonia), difficulty breathing, intellectual disability and early death. before the age of 50), and abnormalities in the heart’s conduction of electrical impulses. Classic DM1 is characterized by muscle weakness and wasting (atrophy), myotonia, early-onset cataracts (i.e. Mild DM1 is characterized by clouding of the lenses of the eyes (cataracts) and sustained muscle contractions (myotonia), in which the muscles do not relax after use. DM type 1 (DM1) can be further classified as mild DM1, classic DM1 and congenital DM1. The disorder is abbreviated DM, which is for dystrophia myotonia. Myotonic dystrophy refers to two rare genetic disorders of muscle that actually affect multiple systems of the body.
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