Myotonic Dystrophy (DM1 & DM2): Symptoms, Causes and Treatment
Written by the Muscular Dystrophy Pakistan (MDP) content team. Based on information from GeneReviews, NINDS and published genetic guidelines and reviews (see sources below). Last updated: October 13, 2026.
"I cannot let go of a handshake." "My hands are stiff in cold weather." "I had cataracts at 35." "My father had a pacemaker, and my uncle was always sleepy." These may sound like unrelated problems, but in many families they are pieces of one puzzle: myotonic dystrophy. It is the most common muscular dystrophy that starts in adulthood, and it is unusual because it affects far more than muscles. It can involve the eyes, the heart, sleep, digestion, hormones and even thinking and mood. Because the signs are so varied, the condition is often missed for years. This guide explains myotonic dystrophy in simple words: what it is, the two types (DM1 and DM2), the causes, symptoms, diagnosis and treatment, and what families in Pakistan should know.
Quick facts
- Myotonic dystrophy affects about 1 in 8,000 people worldwide, and it is the most common adult-onset muscular dystrophy.
- There are two main types: DM1 (Steinert disease) and DM2. DM2 is usually milder.
- Both are inherited in an autosomal dominant pattern: each child of an affected parent has a 50% chance of inheriting it.
- In DM1, the condition can become more severe and start earlier in each generation. This is called anticipation.
- The heart needs regular checks, because rhythm problems can be serious and silent.
- There is no cure, but careful monitoring and treatment of each problem can make a big difference.
What Is Myotonic Dystrophy?
Myotonic dystrophy is a genetic condition in which the muscles slowly weaken and waste, and in which the muscles are slow to relax after use. This delayed relaxation is called myotonia. For example, a person may grip a door handle or someone's hand and then find it hard to let go. Myotonic dystrophy is called a multisystem disorder, because besides the muscles it can affect the eyes, heart, lungs, digestive system, hormone glands and brain.
It is not contagious and nobody is to blame. It is caused by a change in a gene.
What Causes Myotonic Dystrophy?
Our genes are written in a four-letter code. In myotonic dystrophy, a short piece of this code is repeated far too many times, like a stuck key on a keyboard. This is called a repeat expansion. The extra copies do not make a faulty protein. Instead, the repeated stretch of genetic message becomes "sticky" and interferes with the way many other genes in the cells are read, which explains why so many parts of the body are affected.
- DM1: a CTG repeat is expanded in the DMPK gene on chromosome 19.
- DM2: a CCTG repeat is expanded in the CNBP gene (formerly called ZNF9) on chromosome 3.
In general, in DM1, the longer the repeat, the earlier the symptoms start and the more severe they can be.
How Is It Inherited?
Both types are inherited in an autosomal dominant pattern. One changed copy of the gene is enough, so:
- A parent with myotonic dystrophy has a 50% chance of passing it to each child, whether a boy or a girl.
- Men and women are equally affected.
- It is not caused by cousin marriage.
Anticipation in DM1. The repeat in DM1 is unstable and tends to grow longer when passed to the next generation. That is why a grandparent may only have cataracts, a parent may have mild muscle weakness, and a child may be much more affected, sometimes from birth. Anticipation is a feature of DM1, while in DM2 it is minimal or absent.
Congenital DM1. When the repeat becomes very large, a baby can be born with severe congenital myotonic dystrophy. These very large expansions are almost always passed on by the mother, who may be mildly affected and unaware that she has the condition. This is a very important reason for families to learn about their genetic risk, and it is never a mother's fault.
DM1 vs DM2: What Is the Difference?
| Feature | DM1 (Steinert) | DM2 |
|---|---|---|
| Gene | DMPK (CTG repeat) | CNBP (CCTG repeat) |
| Usual weakness | Hands, forearms, feet, face and neck (distal) | Hips, thighs and shoulders (proximal) |
| Typical onset | Teens to adulthood; also congenital and childhood forms | Adulthood; no congenital form |
| Anticipation | Yes | Minimal or none |
| Severity | Mild to severe | Usually milder |
| Muscle pain and stiffness | Can occur | Common and often prominent |
| Cataracts and heart rhythm | Very common | Can occur; heart involvement varies |
Symptoms of Myotonic Dystrophy
Muscles
- Myotonia: Slow relaxation of muscles after gripping, difficulty releasing a handshake or a door handle, stiffness that may be worse in cold weather and improve with repeated movement.
- Weakness and wasting: In DM1, weakness often starts in the hands, forearms, lower legs and feet, the neck and face. In DM2, it is more often in the hips, thighs and shoulders.
- Face: A long, thin face, drooping eyelids, weak facial muscles, thin muscles at the temples.
- Pain: Muscle pain and stiffness, which is particularly common in DM2.
Eyes
Cataracts (cloudy lenses) appear at a young age and are almost always found in DM1. They can be the first clue in a family.
Heart
The heart's electrical system can be affected, causing slow or irregular heartbeats (conduction problems and arrhythmias). These can happen without symptoms and can be serious, so regular heart tests are essential. Warning signs include fainting, dizziness, palpitations and breathlessness.
Breathing, sleep and swallowing
- Excessive daytime sleepiness is very common, even after a full night of sleep.
- Weak breathing muscles can cause breathing trouble, especially during sleep.
- Swallowing difficulty can cause choking or chest infections.
- Digestive problems such as constipation, diarrhoea, abdominal pain and gallstones can occur.
Hormones and metabolism
Insulin resistance and diabetes, thyroid problems, and low testosterone in men can occur. Early balding at the front of the head is common in men.
Brain, mood and behaviour
Some people have learning difficulties, slow thinking, poor attention, lack of motivation, anxiety or depression. These are part of the condition, not laziness or bad character, and they deserve understanding and support.
Congenital and Childhood Myotonic Dystrophy
Babies with congenital DM1 can be born very floppy, with weak breathing and feeding difficulties, and may need hospital care in the first days of life. Children who survive the early period often have developmental delay and learning difficulties, and later develop the other features of DM1. Childhood-onset DM1 usually shows up as learning, attention or speech problems, and muscle signs may come later. If a mother has DM1, planning pregnancy and delivery with a specialist is important.
How Is Myotonic Dystrophy Diagnosed?
- History and examination: The doctor looks for myotonia (for example, delayed grip release), the pattern of weakness, drooping eyelids, early cataract and a family history that may include cataracts, pacemakers, early baldness and sleepiness.
- Genetic test: The key test measures the repeat in the DMPK gene (DM1) or the CNBP gene (DM2). It confirms the diagnosis and the type. This is a specific repeat test, so please ask your doctor for it by name, as standard gene panels may not detect repeat expansions.
- EMG: A nerve and muscle test can show the typical myotonic discharges.
- CPK blood test: Normal or only mildly raised.
- Heart tests: An ECG, and sometimes more tests, to look for conduction problems.
- Other checks: Eye examination for cataracts, blood sugar and thyroid tests, sleep and breathing assessment.
Treatment and Care
There is no cure for myotonic dystrophy at the moment. Care means finding and treating each problem early, with a neurologist leading and other specialists, such as a cardiologist, eye doctor, lung or sleep specialist and an endocrinologist, joining as needed.
- Heart: A regular ECG (often every year, or as advised) and, when needed, a pacemaker or defibrillator to protect against dangerous rhythms. People with DM should never ignore fainting, dizziness or palpitations.
- Myotonia: If stiffness bothers daily life, some medicines, such as mexiletine, can ease it, but they must be prescribed and monitored by a specialist, especially because of the heart.
- Sleepiness: Assessment of sleep and breathing, and treatment of the cause when found. Some medicines can help with daytime sleepiness, depending on the individual.
- Breathing: Regular breathing checks, vaccines against flu and pneumonia, and breathing support at night when needed.
- Eyes: Eye checks and cataract surgery when vision is affected.
- Swallowing and digestion: Tell the doctor about choking or digestive problems so that they can be assessed.
- Diabetes and thyroid: Regular blood tests, and treatment when needed.
- Mood and thinking: Support for learning, attention, mood and motivation, for both the patient and the family.
- Pregnancy: Women with myotonic dystrophy should plan pregnancy and delivery with a specialist team, because complications can be more frequent and the baby may be affected.
Anaesthesia and sedation safety: People with myotonic dystrophy can react badly to some anaesthetic and sedative medicines. Always tell every doctor, dentist and anaesthetist about your diagnosis before any procedure, and keep your genetic report with you.
Research and New Treatments
Researchers understand the cause of myotonic dystrophy well, and several experimental approaches aim to correct the effect of the repeat on the cells. They include medicines that target the faulty genetic message and gene-based strategies. Most are in early clinical trials, and none is available in Pakistan. A confirmed genetic diagnosis, including the repeat size where available, is the key requirement for joining many trials.
Myotonic Dystrophy in Pakistan
In Pakistan, myotonic dystrophy is easily missed, because each symptom is treated by a different doctor: cataracts by an eye surgeon, sleepiness by a family doctor, diabetes by a physician, and heart rhythm by a cardiologist, while nobody puts the picture together. A father with a pacemaker, a mother with cataracts at a young age, and a child with learning or breathing problems may all be part of one family condition. If this sounds familiar, ask a neurologist about myotonic dystrophy and the specific DMPK repeat test. The test is not available in every laboratory, so ask your doctor where it can be done. Genetic counselling is important, since each child of an affected parent has a 50% chance of inheriting it, and a mildly affected mother can have a severely affected baby.
MDP is collecting patient data on its registration portal, so that every family becomes visible. If you or a relative has myotonic dystrophy, please register below.
Frequently Asked Questions
What is myotonia?
Myotonia is a delay in muscle relaxation after the muscle contracts. A common example is not being able to release a grip quickly. It is often worse in the cold and gets better with repeated movement.
What is the difference between DM1 and DM2?
They are caused by repeat expansions in different genes. DM1 usually affects the hands, feet, face and neck, can start earlier and can be congenital. DM2 mostly affects the hips, thighs and shoulders, is usually milder, and has no congenital form.
Is myotonic dystrophy the same as muscular dystrophy?
It is a type of muscular dystrophy, but it is different from Duchenne or limb-girdle muscular dystrophy because it also affects many other organs and involves delayed muscle relaxation.
Can it skip a generation?
Not really. A parent with a very mild form, or one who has not been diagnosed, may seem to "skip", but the gene is passed through the parent. Mild signs such as early cataracts may be the only sign.
What is the life expectancy?
It depends on the type and severity. In classic DM1, life expectancy has been shortened, mainly due to heart and breathing complications, and past studies reported an average age at death in the late 40s to mid 50s. DM2 is usually milder. Regular heart and breathing monitoring and early treatment improve the outlook, and no figure can predict the course for one person. We do not have Pakistani data.
Which test confirms myotonic dystrophy?
A genetic test that measures the repeat size in the DMPK gene (DM1) or the CNBP gene (DM2). Please ask for it by name.
Can I have children?
Many people with myotonic dystrophy have children. Genetic counselling can explain the 50% risk, the possibility of a more severe form in the baby, and the options for pregnancy planning. Decisions are always the family's own.
Putting the Puzzle Together
Myotonic dystrophy hides in plain sight, in stiff hands, early cataracts, constant sleepiness and heart rhythm problems. Once it has a name, each piece can be checked and treated, and the whole family can be protected. If you recognise these signs in yourself or in your family, ask your doctor about myotonic dystrophy and the specific DMPK/CNBP repeat test. Follow the MDP blog for our guides on each type of muscular dystrophy, and share this article with someone who may need it.
Sources and Further Reading
- GeneReviews, Myotonic Dystrophy Type 1
- Myotonic Dystrophies: A Genetic Overview, Genes (MDPI)
- Best practice guidelines and recommendations on the molecular diagnosis of myotonic dystrophy types 1 and 2, European Journal of Human Genetics
- Myotonic dystrophy type 1 testing, 2024 revision: a technical standard of the ACMG, Genetics in Medicine
- National Institute of Neurological Disorders and Stroke (NINDS), Muscular Dystrophy information page
Medical disclaimer: This article is for awareness and education only. It is not a substitute for professional medical advice, diagnosis or treatment. Please consult a qualified doctor about any medical concern. Never start, change or stop a medicine without your doctor's advice.
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