Multi/minicore myopathy

Multi/minicore myopathy (MmD), also known as multicore myopathy and minicore myopathy, is a rare, genetically inherited neuromuscular disorder characterized by the presence of multiple small areas, or cores, of reduced oxidative activity in muscle fibers. These cores are visible under a microscope after muscle biopsy. MmD is part of a group of muscle diseases called congenital myopathies, which are present from birth and affect the skeletal muscles, responsible for movement.

Causes

Multi/minicore myopathy is caused by mutations in several genes, including RYR1, SEPN1, and TTN, among others. These genes are involved in various aspects of muscle function, including the regulation of calcium release in muscle cells, which is essential for muscle contraction. The inheritance pattern of MmD can be autosomal recessive or autosomal dominant, depending on the gene mutation involved.

Symptoms

The symptoms of multi/minicore myopathy can vary widely among affected individuals. Common symptoms include muscle weakness, particularly in the proximal muscles (those closest to the body's center), such as the hips and shoulders. Other symptoms may include hypotonia (reduced muscle tone), scoliosis (curvature of the spine), respiratory difficulties, and delays in reaching motor milestones such as sitting and walking. The severity of symptoms can range from mild to severe, and in some cases, the condition can lead to life-threatening respiratory failure.

Diagnosis

Diagnosis of multi/minicore myopathy typically involves a combination of clinical evaluation, family history, and genetic testing to identify mutations in the genes associated with the condition. Muscle biopsy is also a key diagnostic tool, as it allows for the visualization of the characteristic cores within the muscle fibers. Additional tests, such as electromyography (EMG) and magnetic resonance imaging (MRI) of the muscles, may also be used to support the diagnosis.

Treatment

There is currently no cure for multi/minicore myopathy, and treatment focuses on managing symptoms and improving quality of life. Physical therapy and occupational therapy can help maintain muscle strength and flexibility, and assistive devices may be used to support mobility. In cases where respiratory muscles are affected, respiratory support may be necessary. Regular monitoring by a multidisciplinary team of healthcare providers, including neurologists, pulmonologists, and physical therapists, is important for managing the condition effectively.

Prognosis

The prognosis for individuals with multi/minicore myopathy varies depending on the severity of symptoms and the specific gene mutations involved. While some individuals may experience only mild symptoms and have a normal life expectancy, others may face significant physical disabilities and life-threatening complications, particularly related to respiratory failure.