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Multiminicore disease is a disorder that primarily affects muscles used for movement (skeletal muscles). This condition causes muscle weakness and related health problems that range from mild to life-threatening.
Researchers have identified at least four forms of multiminicore disease, which can be distinguished by their characteristic signs and symptoms. The most common form, called the classic form, causes muscle weakness beginning in infancy or early childhood. This weakness is most noticeable in muscles of the trunk and neck (axial muscles) and is less severe in the arm and leg muscles. Muscle weakness causes affected infants to appear “floppy” (hypotonic) and can delay the development of motor skills such as sitting, standing, and walking. The disease causes muscles of the ribcage and spine to stiffen. When combined with weakness of the muscles needed for breathing, this stiffness leads to severe or life-threatening respiratory problems. Almost all children with multiminicore disease develop an abnormal curvature of the spine (scoliosis), which appears during childhood and steadily worsens over time.
Other forms of multiminicore disease have different patterns of signs and symptoms. They are less common than the classic form, together accounting for about 25 percent of all cases. The atypical forms of the condition tend to be milder and cause few or no problems with breathing. The moderate form with hand involvement causes muscle weakness and looseness of the joints, particularly in the arms and hands. Another form of multiminicore disease, known as the antenatal form with arthrogryposis, is characterized by stiff, rigid joints throughout the body (arthrogryposis), distinctive facial features, and other birth defects. Paralysis of the eye muscles (external ophthalmoplegia) is a primary feature of another atypical form of multiminicore disease. This form of the condition also causes general muscle weakness and feeding difficulties that appear in the first year of life.
Many people with multiminicore disease also have an increased risk of a developing a severe reaction to certain drugs used during surgery and other invasive procedures. This reaction is called malignant hyperthermia. Malignant hyperthermia occurs in response to some anesthetic gases, which are used to block the sensation of pain, and with a particular type of muscle relaxant. If given these drugs, people at risk for malignant hyperthermia may experience muscle rigidity, breakdown of muscle fibers (rhabdomyolysis), a high fever, increased acid levels in the blood and other tissues (acidosis), and a rapid heart rate. The complications of malignant hyperthermia can be life-threatening unless they are treated promptly.
Multiminicore disease gets its name from small, disorganized areas called minicores, which are found in muscle fibers of many affected individuals. These abnormal regions can only be seen under a microscope. Although the presence of minicores can help doctors diagnose multiminicore disease, it is unclear how they are related to muscle weakness and the other features of this condition.