Congenital Myasthenic Syndrome – Symptoms and Causes
Overview
Congenital myasthenic syndromes are rare inherited disorders. These disorders cause muscle weakness, which gets worse during physical activity. Genetic mutations that affect how muscles work cause these conditions.
The syndromes typically appear at birth or during early childhood and continue throughout a person’s life.
These disorders can affect many different muscle groups in the body. These include those used for speaking, eating and swallowing, eye movements and blinking, breathing, and walking.
The specific gene mutation determines which type of congenital myasthenic syndrome a person has. These genetic differences also influence the symptoms and how severe the condition is for each person.
While there is no cure, medications often help manage the muscle weakness effectively. The right medication depends on identifying which gene is causing the condition. In rare cases, some children have such mild forms that they don’t need treatment.
Signs and Symptoms
Congenital myasthenic syndromes cause muscle weakness that gets worse with activity. People with these syndromes often show symptoms at birth. However, when symptoms are mild, doctors might not diagnose the condition until childhood or, in rare cases, early adulthood.
The main symptom in all types of congenital myasthenic syndrome is muscle weakness that gets worse with activity. This can affect any muscles used for movement, but most commonly impacts the muscles controlling the eyelids, eyes, chewing, and swallowing.
Babies and young children with this condition may experience progressive loss of muscle function with use. This weakness can cause:
- Droopy eyelids and poor eye control, sometimes with double vision
- Trouble chewing and swallowing food
- Weak facial muscles
- A weak cry
- Slurred or nasal-sounding speech
- Delays in crawling and walking
- Difficulty with fine motor skills like brushing teeth
- Problems holding the head up
- Breathing difficulties, which may worsen during illness, fever, or stress
Depending on the specific type of congenital myasthenic syndrome, other symptoms may include:
- Joint, spine, or foot deformities
- Unusual facial features
- Hearing problems
- Weakness, numbness, or pain in hands and feet
- Seizures
- Kidney issues
- Rarely, cognitive challenges
When to Contact a Doctor
If you notice any of these signs in your child, or if you have concerns about similar symptoms in yourself, make an appointment with your doctor. Early diagnosis and treatment can help manage symptoms and prevent complications.
Causes
Congenital myasthenic syndrome (CMS) stems from genetic factors involving more than 30 different genes. The classification of CMS depends on which part of the neuromuscular junction is affected. This junction serves as the communication point between nerve and muscle cells.
The disruption can occur in three main locations:
- Presynaptic area – where the nerve impulse begins.
- Synaptic space – the gap between nerve and muscle cells.
- Postsynaptic area – where muscle cells receive signals (most common location).
Some types of CMS result from problems with glycosylation. This is a complex process that helps cells communicate with each other. When glycosylation doesn’t work properly, nerve signals to muscles can become disrupted.
Most cases of CMS follow an autosomal recessive inheritance pattern. This means:
- Both parents carry one copy of the abnormal gene
- Parents typically show no symptoms
- A child must inherit two copies (one from each parent) to develop the condition
- Children with only one copy become carriers but don’t develop CMS
In rare cases, CMS can follow an autosomal dominant pattern, where only one parent needs to pass on the affected gene. Sometimes the genetic change happens randomly and isn’t inherited from either parent.
In some instances, doctors can’t identify the specific gene causing the condition.
The location of the disruption and the specific gene involved determine the type and severity of symptoms a person experiences. These genetic changes interfere with the normal signaling between nerves and muscles, leading to muscle weakness.
Risk Factors
Children face a risk of getting a congenital myasthenic syndrome when they inherit two copies of the faulty geneโone from each parent. This follows an autosomal recessive pattern of inheritance.
Parents who carry one copy of the gene typically show no symptoms themselves. When both parents are carriers, their child has a 25% chance of developing the condition.
Children who inherit just one copy of the gene usually remain symptom-free but become carriers who might pass the gene to their own children.
