Centronuclear and myotubular myopathies

Overview

Centronuclear myopathies (CNM) are a group of related congenital conditions causing low muscle tone and weakness from birth or early childhood. X-linked myotubular myopathy (XLMTM) is the most severe form; other types follow an autosomal dominant or recessive pattern and tend to be milder.

Symptoms

XLMTM is usually the earliest and most serious: signs can appear before birth (reduced fetal movement, excess amniotic fluid), and affected babies typically have very low muscle tone with significant weakness. Breathing and swallowing difficulties are common, often needing continuous ventilator support, alongside a raised risk of chest infections and respiratory failure. Facial weakness, an elongated face, drooping eyelids, scoliosis and joint stiffness are also frequent features; some babies don't survive the first months, and those who do usually need substantial ongoing medical support.

Autosomal dominant CNM tends to start later — adolescence or early adulthood — with a milder, progressive weakness in the legs that can eventually lead to needing a wheelchair. Autosomal recessive CNM usually starts in infancy or early childhood, ranging from severe to mild; weakness typically affects the muscles closest to the trunk first, and more severe cases involve swallowing and breathing difficulties, facial weakness, restricted eye movement, scoliosis and an elongated face.

Inheritance

XLMTM follows an X-linked recessive pattern (the MTM1 gene), mainly affecting boys; the other CNM forms can be autosomal dominant (most often the DNM2 gene) or autosomal recessive (genes including BIN1, RYR1, TTN, SPEG and CACNA1S).

Getting a diagnosis

Diagnosis draws on a physical exam, family history, genetic blood testing, muscle imaging, and sometimes a muscle biopsy — which characteristically shows nuclei sitting in the centre of muscle fibres rather than at the edges.

Management and outlook

Multidisciplinary care led by a neurologist is standard. Respiratory support is often central to management, particularly for XLMTM, up to and including long-term ventilation; annual flu and pneumococcal vaccination is recommended. Speech and language therapy helps with swallowing, and a feeding tube may be needed for adequate nutrition. Physiotherapy supports breathing capacity and helps manage scoliosis and joint stiffness — daily respiratory physiotherapy is often recommended for anyone using a ventilator.

Cardiac monitoring is worthwhile where TTN or SPEG gene changes are involved, given a rare associated risk of cardiomyopathy. Anaesthetic planning matters too: RYR1-related forms carry a raised malignant hyperthermia risk, so anaesthetists need advance warning and dantrolene should be available; suxamethonium and certain other agents are best avoided.