Congenital Myopathies

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Original Editor - Niha Mulla

Top Contributors - Niha Mulla and Mila Andreew  

Introduction

Congenital myopathies are a very broad term of rare disorders present at birth. The term Congenital myopathy is reserved for a group of rare, heterogenous, inherited, primary muscle disorders that cause Gross motor delay, poor coordination, and fascial weakness; various orthopedic considerations include foot deformities, joint contractures, hip dysplasia and scoliosis. Congenital myopathy also causes hypotonia and weakness at birth or during the neonatal period and, in some cases, delayed motor development later in childhood.

Description:

As described above, Congenital myopathies are rare conditions representing a wide range of disorders in muscle development and function that cause muscle hypotonia and developmental delay. Over twenty genes have been associated with congenital myopathy subtypes.  Facial and respiratory muscle weaknesses are common too.

Congenital myopathy differs in severity, and onset of symptoms. Symptoms can be present from birth, or they can slowly progress throughout the infancy and childhood.  

Pathophysiology

There are twenty different genes that can be affected in congenital myopathy and the symptoms, of the disease depends on which gene is affected.

As per Matthew Harmelink, MD and team from medspace, “there are variations among each gene and Occasionally, these result in phenotypic overlap between genes as well as genes causing congenital myopathy to occasionally have phenotypes more consistent with congenital muscular dystrophies, limb-girdle muscular dystrophies, or even possible neuropathic or neuromuscular junction diseases”.

Epidemiology

Congenital myopathies are rare and tend to be less severe than congenital muscular dystrophies. Each type of congenital myopathy is distinguished by an underlying genetic mutation with these disorders have been shown to be inherited in x-linked, autosomal recessive and autosomal dominant forms.

Frequency: The frequency of onset of symptom is found to be 76% during the neonatal period.

Mortality/Morbidity: The largest cause of morbidity and mortality is known to be due to be happening from respiratory and/or feeding failure as a result of muscle function loss.

According to the study by Colombo et al., and as mentioned by  Matthew Harmelink, MD and collogues;  at birth, neonates with congenital myopathy required respiratory support and nasogastric feeding in 30.4% and 25.2% of cases, respectively. And 12% of patients died within the first year, whereas 74.1% achieved independent ambulation with 62.9% being late walkers.

Sex: Congenital myopathy is an extremely rare disorder that generally affects males and females in equal numbers.

Types of Congenital Myopathy

There are many types of myopathies that are congenital, some of them seen more commonly than others are listed below:

1. Nemaline myopathy
2. Central core myopathy
3. Centronuclear Myopathy
4. Congenital Fiber-Type Disproportion
5. Myosin Storage Myopathy
6. Multi-mini-core myopathy
7. Congenital fiber type disproportion myopathy
8. Myotubular myopathy
9. Sarco-tubular myopathy
10. Cylindrical spirals myopathy

Signs & Symptoms

Symptoms of congenital myopathy vary depending on the type of congenital myopathy. Also, they can be present at birth or develop throughout infancy and childhood. The most common symptoms of congenital myopathy as follows:

• Slow, progressive loss of muscle tone characterized by floppiness (hypotonia).
• Toddlers with congenital myopathies usually have muscle weakness and is more prone to falling or stumbling.
• Early motor skills like turning around and sitting up are not met as expected. Also, other critical developmental milestones may be delayed.
• Most affected muscles are that of pelvis, neck, and shoulder.
• Difficulty breathing or feeling short of breath is common due to weakness of respiratory muscles.
• Some babies with congenital myopathy have feeding issues as sucking from breast or bottle and eating with a spoon, chewing and drinking can all be abnormal and difficult.
• As the symptoms of congenital myopathies are not progressive during adulthood, most people with congenital myopathy walk normally as adults. However, some physical activities may be slightly impaired.

Causes of congenital myopathy

Some of the known causes of congenital myopathy are as follows:

• Changes/mutations in specific genes cause congenital myopathies.
• There is still emerging research on the causes of congenital myopathy as mutations have been found in more than twenty genes, that can potentially cause congenital myopathy.
• Congenital myopathy follows an autosomal recessive pattern of inheritance. Recessive genetic disorders occurs when an individual inherits a non-working gene from each parent.
• If an individual receives one working gene and one non-working gene for the disease, the person will be a carrier for the disease, but usually will not show any symptoms.
• Autosomal recessive forms of congenital myopathy have a typical onset in infancy or childhood and autosomal dominant forms have the mildest symptoms and may present in adulthood.

Evaluation and diagnosis

There are barely any specific tests to directly diagnose congenital myopathy other than muscle biopsy. Though following tests are vital for diagnosis.