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An overview of Myotubular Myopathy
by: Gary and Pam Scoggin

(The authors are the founders of the Myotubular Myopathy Resource Group. This overview comes from their experiences and review of the cited references.  They are not medical professionals.)

The general description Myotubular Myopathy, also called Centronuclear Myopathy, consists of three diseases:

• Congenital X-Linked Recessive Type (MIM No. 31040)
• Congenital Autosomal Recessive Type (25520)
• Autosomal Dominant Type (16015)

The discussion below focuses on the Congenital X-Linked Recessive type (31040).

Clinical Findings

According to the Birth Defects Encyclopedia,

"Congenital X-linked recessive type has similar symptoms to the autosonomal recessive type [(e. g., respiratory distress in the newborn period; dysmorphic features such as elongated, thin facies and high-arched palate; muscular weakness diffuse but more severe in a proximal distribution. )] but is more severe with high mortality in infancy. Respiratory distress due to weakness of respiratory muscles is usually the main symptom. The affected infants are weak and hypotonic with poor cry, sucking, and coughing; weak neck muscles, and an inability to swallow. Bilateral ptosis, facial diplegia, and limitation of eye movements have been noted in some infants. Deep tendon reflexes are absent but the infant's response to painful stimuli is normal. Maternal polyhydramnios is often noted, and a history of abortions and neonatal death is frequent. Cardiomyopathy has also been reported. "

This is consistent with the clinical synopsis given in OMIM except that this source also cites seizures as another possible clinical finding.

Our observations, based on discussions with over fifty affected families, tend to verify these observations with the exception of the seizures. (One possibility is that the seizures reported in the literature may be secondary to anoxia resultant from respiratory distress.) Also, we are unaware of any confirmed cases of Cardiomyopathy among our acquaintances. An interesting observation from our experience is the frequency of blood disorders (for example, spherocytosis) and gall stones. A connection between these and the myopathy has not been positively established but has raised interest among some researchers.

Perhaps most interesting among our observations is that we are now seeing a range of expression of this disease from mild to servere. The conventional wisdom has been that X-Linked Myotubular Myopathy is almost always severe in its effects. But there are several cases where the expression has been mild. In one case, the expression was so mild that had it not been for an affected brother, X-Linked Myotubular Myopathy might not have been suspected as the cause of the child's noticible but slight floppiness. The consequences of this are profound in that this disease may be more prevalent than is suspected based on the classic clinical descriptions.

Treatment

As noted in the Birth Defects Encyclopedia, treatment is focused on the respiratory distress aspect of the disease. While the literature characterizes the results of treatment as "poor", our observations differ. In cases where aggressive interventions -- such as a tracheotomy, home ventilation, gastrostomy tube or button, fundoplication and well-trained caregivers -- have been taken affected boys have often fared well. Elsewhere in these pages is information on management techniques being used in various cases.

Prognosis

The prognosis for affected boys has historically been viewed as very poor. The Birth Defects Encyclopedia notes that "[m]ost of the boys die in infancy due to the severe weakness of the intercostals and of the diaphragm." Our observations present a more mixed picture. A number of the boys are now in the six to ten year-old range; we know of one boy who is nineteen. These boys are generally partially or totally ventilator dependent and use wheelchairs; several attend conventional public school. On the other hand, many of the boys have died in infancy. Of those surviving infancy, several have died from complications due to chickenpox, pneumonia or other respiratory diseases.

(Birth Defects Encyclopedia, Volume II; Mary Louise Buyse, MD Editor-in-Chief; Center for Birth Defects Information Services, Inc.; Dover, MA., p. 1196. )

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