Congenital muscular dystrophy type 1A

Alternate names

Merosin-negative congenital muscular dystrophy; Merosin-deficient congenital muscular dystrophy; Muscular dystrophy, congenital, merosin-deficient; MDC1A; Laminin alpha-2 deficiency; LAMA2-related muscular dystrophy

Definition

Congenital muscular dystrophy type 1A (MDC1A) belongs to a group of neuromuscular disorders that beings at birth or infancy and is characterized mainly by hypotonia, muscle weakness and muscle wasting.

Epidemiology

The prevalence of LAMA2-related muscular dystrophy is estimated at between 1 in 50,000 and 1 in 400,000 individuals worldwide. This condition is thought to be the most common type of congenital muscular dystrophy, accounting for between 30 and 40 percent of total cases.

Cause

• It is caused by mutations in the LAMA2 gene.
• This gene provides instructions for making a part (subunit) of certain members of a protein family called laminins.
• Laminin proteins are made of three different subunits called alpha, beta, and gamma.
• There are several forms of each subunit, and each form is produced from instructions carried by a different gene.
• The LAMA2 gene provides instructions for the alpha-2 subunit.
• This subunit is found in the laminin 2 protein, also known as merosin; it is also part of another laminin protein called laminin 4.
• Laminins are found in an intricate lattice of proteins and other molecules that forms in the spaces between cells (the extracellular matrix).
• Laminin 2 and laminin 4 play a particularly important role in the skeletal muscles.
• The laminins attach (bind) to other proteins in the extracellular matrix and in the membrane of muscle cells, which helps maintain the stability of muscle fibers.

Gene mutations

• Most LAMA2 gene mutations that cause the severe, early-onset form of LAMA2-related muscular dystrophy result in the absence of functional laminin alpha-2 subunit.
• Mutations that cause the milder, later-onset form usually result in a reduction (deficiency) of functional laminin alpha-2 subunit.
• Deficiency or absence of the laminin alpha-2 subunit results in a corresponding lack of laminin 2 and laminin 4, reducing the strength and stability of muscle tissue and leading to the signs and symptoms of LAMA2-related muscular dystrophy.

Inheritance

Autosomal recessive inheritance, a 25% chance

It is inherited in an autosomal recessive manner.

Signs and symptoms

• Infants with congenital muscular dystrophy type 1A (MDC1A) typically have poor muscle tone (hypotonia) and muscle weakness at birth.
• Within weeks after birth, some affected infants may have feeding and respiratory difficulties.
• Motor development is often delayed and limited.
• Most affected infants can sit unsupported and some can stand without assistance.
• Only a few children with MDC1A are eventually able to walk unassisted.
• Additional signs and symptoms that affected individuals may experience include joint contractures (stiff or "frozen" joints), congenital hip dislocation, scoliosis, and ophthalmoplegia (paralysis or weakness in the muscles of the eye).
• Affected children may also develop an elongated face.
• Approximately 20-30% experience seizures.
• The majority of affected individuals have normal intellectual abilities.
• Although most individuals affected with MDC1A have complete deficiency of the merosin protein, a few individuals have only a partial deficiency.
• Among individuals with a partial deficiency, the severity and age of onset varies greatly.
• One study reported that approximately 12% of individuals have later onset, slowly progressive weakness.

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

80%-99% of people have these symptoms

• Absent muscle fiber merosin
• Congenital muscular dystrophy
• Gastroesophageal reflux(Acid reflux)
• Highly elevated creatine kinase
• Hypokinesia(Decreased muscle movement)
• Inability to walk
• Increased connective tissue
• Motor delay
• Muscle fiber atrophy(Muscle fiber degeneration)
• Myositis(Muscle inflammation)
• Respiratory failure
• Weak cry

30%-79% of people have these symptoms

• Abnormal brainstem MRI signal intensity
• Abnormality of the temporomandibular joint(Abnormality of the jaw joint)
• Aspiration
• Astrocytosis
• Cerebral edema(Swelling of brain)
• EMG abnormality
• Facial palsy(Bell's palsy)
• Flexion contracture(Flexed joint that cannot be straightened)
• Impaired [[mastication](Chewing difficulties)
• Intellectual disability(Mental deficiency)
• Macroglossia(Abnormally large tongue)
• Recurrent lower respiratory tract infections(Recurrent chest infections)

5%-29% of people have these symptoms

• Abnormality of visual evoked potentials
• Arrhythmia(Abnormal heart rate)
• Atelectasis(Partial or complete collapse of part or entire lung)
• Cardiomyopathy(Disease of the heart muscle)
• Cognitive impairment(Abnormality of cognition)
• Decreased body weight(Decreased weight)
• Dysphagia(Poor swallowing)
• Focal-onset seizure(Seizure affecting one half of brain)
• Generalized non-motor (absence) seizure(Brief seizures with staring spells)
• Hyperlordosis(Prominent swayback)
• Hypoventilation(Slow breathing)
• Intercostal muscle weakness(Muscle weakness between ribs)
• Myopathic facies
• Neonatal hypotonia(Low muscle tone, in neonatal onset)
• Open mouth(Gaped jawed appearance)
• Ophthalmoplegia(Eye muscle paralysis)
• Pachygyria(Fewer and broader ridges in brain)
• Pontocerebellar atrophy
• Protruding tongue(Prominent tongue)
• Reduced ejection fraction
• Reduced tendon reflexes
• Scoliosis
• Sensorimotor neuropathy(Nerve damage causing decreased feeling and movement)

1%-4% of people have these symptoms

• Pulmonary arterial hypertension(Increased blood pressure in blood vessels of lungs)

Diagnosis

Molecular Genetics Tests may include:

• Sequence analysis of the entire coding region
• Deletion/duplication analysis

Treatment

There is currently no cure for congenital muscular dystrophy type 1A (MDC1A) and treatment generally focuses on managing the individual signs and symptoms of the condition. A multidisciplinary approach is often needed and may improve the quality and longevity of life. This may include a joint effort by orthopedic and respiratory specialists; physiotherapists; occupational therapists; and speech-language therapists. The main objective is helping each affected individual reach their full potential. Seizures or other neurological complications may require specific treatment.

Prognosis

The prognosis of this condition is poor, as many affected children do not reach adolescence.

NIH genetic and rare disease info

• NIH info on Congenital muscular dystrophy type 1A

Congenital muscular dystrophy type 1A is a rare disease.

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