What Is Emery-Dreifuss Muscular Dystrophy? 

Introduction

Muscular dystrophies (MDs) are a group of genetic disorders characterised by progressive weakening and deterioration of the muscles. There are over 30 different types of muscular dystrophies, all of which vary in their severity, age of onset, and affected muscles. A common ground between all, however, is that the disease progresses over time, with a patient’s condition worsening gradually. It is important to note that muscular dystrophies are genetic, meaning they develop due to inheriting specific changes in genes, and thus are not contagious or caused by injury.¹

Emery-Dreifuss muscular dystrophy (EDMD) is characterised by early childhood joint contractures, increasing muscle weakness over time and issues with the heart muscle.² A contracture is defined as the tightening and shortening of a muscle in a particular area, causing a deformity and pain in that area. Additionally, the joint or muscle affected may no longer be able to function normally.³  

Emery-dreifuss muscular dystrophy: definition and types

Definition of EDMD as a specific subtype of muscular dystrophy

EDMD is a muscular dystrophy condition characterised by gradual weakness and degeneration in the upper arm and lower leg muscles. Additionally, contractures usually occur in the spine, ankles, knees, elbows, or back of the neck. This can cause several complications, including difficulties walking or running, and problems lifting arms or heavy objects above an individual’s head.⁴ 

Two primary types: EDMD1 and EDMD2

EDMD is a genetic disorder, meaning it can be passed on from parent to child due to mutations in specific genes. A gene is what instructs and guides your cells into making proteins, which are vital for a healthy and functioning body.⁵ In the case of EDMD, mutations in either the EMD gene or the LMNA are most common. These genes provide instructions for making proteins called emerin and lamin, both important for a structure inside of cells called a nuclear envelope. It acts as a membrane which separates the nucleus with genetic information from the rest of the cell.

Although both gene mutations cause the very same condition, they do show clear clinical differences. Because of this, two subtypes of EDMD have been identified, as described in the table below. ⁴

Inheritance patterns: autosomal dominant, X-linked and autosomal recessive

As mentioned, EDMD can be passed down through generations due to mutations in the genetic material. However, there are different patterns through which this can occur. 

• X-Linked recessive: Two types of chromosomes carry genetic information to make up a gene, the X and the Y chromosome. People who were assigned females at birth (AFAB) have two X chromosomes, whereas people assigned males at birth (AMAB) have one X and one Y.⁶ The X-linked recessive inheritance pattern is one of the most common ways of passing down EDMD, and can only occur in AMABs. The disease is caused by a mutation in the EDM gene, which is located on X chromosomes. In AFABs, mutations on both X chromosomes are necessary to develop symptoms of EDMD. If only one is affected, they will be carriers of the disease but won’t be affected. They can, however, pass it down to their children. In AMABs, inheriting EMD mutation with their X chromosome is enough to develop EDMD.⁷
• Autosomal dominant: This is caused by LMNA gene mutations. As mentioned above, this form of EDMD is more severe, complex and unpredictable.⁷ A parent with an autosomal dominant form of EDMD has about a 50% chance of passing it on to their child, regardless of gender.⁴ This type of mutation is not linked to chromosomes. Inheriting only one copy of a mutated gene is enough to develop the EDMD condition. 
• Autosomal recessive:  The least common way of inheriting EDMD. This inheritance pattern is also caused by the mutation of the LMNA gene, but both parents have to be carriers of the gene mutation for the disease to be inherited.⁸ 

Clinical features of EDMD

General symptoms of EDMD, which include muscle weakness, joint contractions and cardiac problems. Created with BioRender.com by Antonina Swierkowska. 

Muscle weakening and wasting

A common early symptom of EDMD is the weakening and wasting of muscles. This usually starts in the upper arm, like the triceps or biceps, and lower leg muscles. Additionally, it is very common in EDMD patients to progress to having weak neck muscles, as well as scapular winging. This is a symptom where the muscles of the scapula, also known as the shoulder blade, are too weak, causing an unstable scapula. Consequently, the affected shoulder blade sticks out from the back instead of laying flat and can affect the ability to lift, pull or push things.⁹ 

Joint contractures and limitations in movement

Joint contractures (joint shortenings) are usually the first sign of EDMD, commonly beginning in early childhood. They usually occur in the elbows, ankles and at the back of the neck, causing problems with moving the head towards the chest. Eventually, this can lead to limited movement from the entire spine. In addition, contractures in the ankles lead to difficulties walking and running, and elbow contractures can limit arm movements.⁴ The location, severity and progression of contractures can depend on several factors, including age, disease stage and the type of EDMD. 

Cardiac involvement

Problems with the heart usually don’t appear until the later stages of EDMD. The complications include:

• Heart palpitations (unusual heartbeat)
• Poor tolerance of physical activity
• Heart failure 
• Arrhythmias (problems with the rhythm/rate of heartbeat)
• Cardiomyopathy (thickening, stiffening or stretching of the heart muscle). 

In EDMD1, cardiac symptoms usually occur after other muscular issues. In contrast, EDMD2 is characterised by initial heart muscle symptoms followed by the weakening of other muscles.²

Onset and progression of symptoms 

Age of onset and disease progression varies depending on the type of EDMD, but can also vary between patients with the same type of Emery-Dreifuss MD. In general, onset occurs between the ages of 5 and 10, and the disease slowly progresses into adulthood. However, some may start showing severe symptoms earlier on in childhood. Generally, joint contractures and muscle weakness/wasting will appear within the first two decades of the disease. Cardiac involvement tends to emerge after the second decade.⁴

Underlying genetic causes

As mentioned, mutations in either the EDM or the LMNA genes are the most common cause of EDMD. To be specific, the disease results from a structural or functional problem in the proteins produced by these genes, causing “nuclear envelopathy”. This is defined as a condition featuring an impairment to the nuclear envelope. It plays a role in the protection of the mixing of contents of the nucleus and the rest of the cell, and thus the health and survival of cells. The deficiency or mutation in proteins composing this envelope can lead to a loss of the cell’s structure, especially in tissues that are often under stress such as the cardiac and skeletal muscles.² 

Diagnosis of EDMD

Three main symptoms are required for EDMD to be diagnosed in patients:

1. Early contractures: these occur in the elbow flexors (muscles responsible for bending the elbow), ankles or neck, eventually limiting the movement of the entire spine.
2. Progressive wasting and weakening of muscles: typically start in the upper arm/lower leg muscles and progress to others. 
3. Cardiac involvement: arrhythmias, conduction problems, palpitations, cardiomyopathy, etc. 

The diagnostic tools used are as follows:

• Physical examination
• Electrical tests, like electromyography (EMG), to determine the point of origin of any muscle weaknesses
• Family history and genetic testing through blood tests are not required for diagnosis, though they can help confirm it ⁴ 
• A muscle biopsy is sometimes used to determine the type of EDMD. This is a procedure where a small sample of the affected muscle tissue is removed from the body and investigated under the microscope. It is usually done under anaesthetic to reduce pain.

Management and treatment

There is currently no cure for EDMD, though patients are usually given multiple ways to manage their symptoms. Additionally, supportive care is also offered.

Physical therapy to maintain muscle function/mobility

Physical therapy, especially stretching, is recommended for managing any contractures and muscle weakness experienced. Although this will not prevent further contractures or degeneration, it may help slow down the progression of the condition and maintain a good level of muscle function.²

Cardiac monitoring and management

There are multiple treatments available for the cardiac manifestations linked to EDMD. These include antiarrhythmic drugs, pacemakers and heart transplantation. In general, EDMD patients need to keep monitoring their condition with annual cardiac assessments so that the correct treatment can be put in place before the problem becomes untreatable or fatal.⁴ 

Surgical interventions

If needed, severe contractures can be surgically removed. This is not as easy as it sounds, however, because contractures tend to reappear regularly. This means that the surgery needs to be repeated to be effective. It comes with several risks, including infection, blood clots and more. Thus, although surgical interventions have been effective in treating some contractures, it should be considered whether the benefit is worth the risks.² 

Ongoing research and future directions

Although there is currently no cure for EDMD, researchers are looking into potential treatments based on the genes involved with the disease.¹⁰ These include: 

• Gene therapy: By supplementing the defect genes with healthy ones, the progression of EDMD symptoms could be slowed down, potentially even treated completely
• Gene silencing: EDMD could be slowed down or even prevented by “turning off” the instructions made by mutant genes which create defective proteins
• Cell therapy: By replacing the weakened and dead muscle cells with donor cells/lab-produced cells, strength could be restored.

Patient outlook and quality of life

Although quality of life can be severely impaired in EDMD patients, overall life expectancy is not usually reduced. Some may completely lose the ability to walk, whereas cardiac symptoms can lead to more serious issues like heart failure. However, as mentioned above, there are several ways to manage these symptoms and improve overall quality of life. For patients who have inherited EDMD but do not show symptoms, it is important to consider the risk of passing on their disorder if they have children, using help from genetic counsellors.⁴

Summary

• EDMD is a genetic disorder causing joint contractures, progressive weakening and wasting of skeletal muscles and cardiac issues
• Symptoms usually appear in individuals between 5 to 10 years old and progress slowly into adulthood.
• Severe complications include the loss of ability to walk or run, cardiac impairment and heart failure.
• The type, severity and age of onset of symptoms depends on the type of EDMD, which is determined by the gene that was mutated. EDMD1 (caused by EDM mutation) and EDMD2 (caused by LMNA mutation) are the most common
• There is currently no cure for EDMD, but there are several ways to manage symptoms and improve quality of life. These include physical therapy, supportive care, cardiac monitoring, and interventions and surgery.
• There is ongoing research looking at potential treatments for EDMD. Gene therapy, gene silencing and cell therapy seem to be promising interventions for treating the disorder.