X-linked myotubular myopathy (MTMX) is a rare disorder that is part of a group of disorders called centronuclear myopathies. This condition almost always affects males and mainly impacts the strength and tone of the muscles used for movement, known as skeletal muscles.
Most people with this condition have the severe form. Signs might show up even before birth with reduced fetal movement or too much amniotic fluid. After birth, babies usually have low muscle tone, leading to issues like trouble feeding, delayed motor development, and the need for a ventilator to help with breathing. Some can’t move by themselves and may experience weakness in the eye muscles, distinctive facial features like a large head and narrow face, and absent reflexes. Less common features include stiff joints, a curved spine, liver problems, frequent infections, and seizures. Many individuals with this form also have intellectual disabilities. In the moderate form, milestones might be less severely delayed, and individuals may breathe on their own or with minimal help from a ventilator. The mild form shows improvement in muscle weakness, near-normal motor development, the ability to walk, and reduced need for ventilator support. The characteristic facial features are less likely to develop in these milder forms. It’s important to note that predicting the form of the disease based on genetic mutations is usually not possible. Currently, there’s no cure for MTMX. Treatment aims to maximize functional abilities and minimize complications.
MTMX is caused by pathogenic variants in the MTM1 gene exhibit X-linked recessive inheritance. This means that one pathogenic variant is enough to cause the disease in both males (who have one X chromosome and one Y chromosome) and females (who have two X chromosomes) may experience symptoms depending on how many copies of the X chromosome that has the pathogenic variant are turned on in the cells.
Most female carriers do not have symptoms, however there are reports of carrier females developing mild/moderate symptoms associated with this condition.
Another name for this condition is X-linked centronuclear myopathy.
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Revised November 2023
