Myotonic Dystrophy Type 1 (DM1)
Description
Myotonic dystrophy type 1 (DM1), also known as Steinert‘s disease, is the most common form of muscular dystrophy in adults. It‘s a genetic disorder that primarily affects muscle function, causing progressive weakness and stiffness. DM1 can also affect other parts of the body, including the heart, eyes, and digestive system. This blog will delve into the intricacies of DM1, covering its signs and symptoms, causes, diagnosis, management, and ways to thrive with the condition.
Genes Involved
Myotonic dystrophy type 1 is caused by a mutation in the DMPK gene located on chromosome 19. The DMPK gene provides instructions for making a protein called dystrophia myotonica protein kinase (DMPK). The mutation causes an abnormal expansion of a repeated DNA sequence (CTG) within the DMPK gene, leading to an overproduction of DMPK protein. This excess protein disrupts normal cellular processes, contributing to the development of DM1.
Recognizing the Signs and Symptoms
DM1 symptoms can vary greatly from person to person and may not appear until adulthood. Common signs and symptoms include:
- Muscle Weakness: This primarily affects the muscles in the face, hands, feet, and neck, leading to difficulties with activities like buttoning clothes, combing hair, or walking.
- Muscle Stiffness: Muscles can feel tight and inflexible, particularly in the morning or after periods of inactivity.
- Myotonia: This is the hallmark symptom of DM1, characterized by delayed muscle relaxation after a contraction. This can manifest as a prolonged grip after shaking hands or difficulty releasing a door handle.
- Muscle Wasting (Atrophy): Over time, muscles can become smaller and weaker.
- Cataracts: Clouding of the lens of the eye is common in people with DM1.
- Cardiac Abnormalities: DM1 can affect the heart‘s electrical activity, leading to irregular heartbeats or other heart problems.
- Gastrointestinal Issues: Constipation, swallowing difficulties, and gastroesophageal reflux disease (GERD) are common.
- Cognitive and Behavioral Issues: Some individuals with DM1 may experience mild cognitive impairment or mood changes.
Causes
DM1 is caused by a genetic mutation. This mutation involves a specific region of DNA called the DMPK gene, which is located on chromosome 19. In individuals with DM1, the DMPK gene has an abnormal expansion of a repeated DNA sequence (CTG). This expansion disrupts the normal function of the DMPK gene, leading to the production of an abnormal protein that affects muscle function and other organs.
Inheritance/recurrence risk
DM1 is typically inherited in an autosomal dominant pattern. This means that if one parent has the mutated DMPK gene, there is a 50% chance that their child will inherit the gene and develop DM1. In some cases, the disease can arise spontaneously through a new mutation. The severity of the disease can vary greatly between individuals within the same family, with some people experiencing mild symptoms while others develop more severe complications.
