Myotubular and Centronuclear Myopathies
Myotubular and Centronuclear Myopathies are a group of very rare conditions characterised by the central location of the nucleus in muscle cells, in which it is normally found at the periphery. Myotubular Myopathy normally refers to the X-linked form described here, but we also provide information about other manifistantions of the condition.
X-linked Myotubular Myopathy (XLMTM)
This is the most common of the myotubular myopathies affecting 1 in 50,000 new-born males worldwide. This is usually the most severe form with profound muscle weakness (myopathy) and decreased muscle tone (hypotonia) present at birth. Primarily affecting the skeletal muscle, motor skills are predominantly affected, causing difficulties with sitting, standing and walking. In addition, there are associated breathing and swallowing difficulties as the muscles involved in taking a breath, and in swallowing are also involved. Curvature of the spine (scoliosis) and contractures of the hips and knees can also be problematic. Cognitive function is not thought to be affected.
Muscle weakness affecting breathing can often result in the need for mechanical ventilation, sometimes periodically, during sleep or continuously. Due to these severe breathing problems, individuals with X linked myotubular myopathy (XLMTM) usually survive only into early childhood, however some have lived into adulthood. It is generally not thought to be progressive condition.
Autosomal-dominant Centronuclear Myopathy (AD-CNM)
Autosomal-dominant centronuclear myopathy also predominantly affects the skeletal muscles. Individuals with this form of myopathy often do have normal early development. However, even in those with normal early development muscle weakness usually becomes evident during adolescence or early adulthood.
Presenting symptoms are usually difficulty walking and, sometimes, muscle pain during exercise. Weakness often progressively deteriorates and wheelchair assistance may be required in mid to late childhood. More severe presentations begin in childhood and these individuals walk later than their peers and typically need wheelchair assistance in childhood or adolescence.
Autosomal-recessive Centronuclear Myopathy (AR-CNM)
This condition also presents as progressive weakness, usually beginning at birth or childhood. Symptoms may include foot abnormalities, high arched palate (roof of the mouth) and abnormal side to side curvature of the spine (scoliosis). Mild to severe breathing problems may also be present. Much less commonly the heart muscle may also be weakened, although this has not been reported in any of the genetically resolved forms to date.