How can feeding problems be managed to ensure my baby gets enough nutrition?

Place the infant in a semi‑upright position, use a specialized nipple (slow‑flow or pre‑term) to reduce aspiration risk, and consider a nasogastric tube or gastrostomy (G‑tube) if oral intake remains 5 % of body weight in a week), or a change in muscle tone (more floppiness or new contractures). Any of these changes warrant immediate contact with the neuromuscular or respiratory specialist.

What respiratory support is recommended for an infant diagnosed with actin‑accumulation myopathy?

Most infants require non‑invasive ventilation (NIV) such as bilevel positive airway pressure (BiPAP) during sleep, and many progress to invasive ventilation via tracheostomy if hypoventilation worsens. Continuous pulse‑oximetry and capnography help guide settings; early involvement of a pediatric pulmonologist and a sleep‑study team is essential.

Actin-accumulation myopathy

Actin-accumulation myopathy is a rare genetic muscle disorder that causes profound muscle weakness and life-threatening breathing difficulties starting in infancy.

Overview

Actin-accumulation myopathy is a rare congenital disorder that primarily affects skeletal muscles, which are the muscles the body uses for movement. Affected infants exhibit severe muscle weakness (myopathy) and poor muscle tone (hypotonia) throughout the body, often being described as "floppy" and unable to move on their own.

Symptoms

Signs and symptoms of actin-accumulation myopathy are apparent at birth or during infancy and can include:

Severe muscle weakness and poor muscle tone (hypotonia)
Feeding and swallowing difficulties
A weak cry
Difficulty controlling head movements
Shallow breathing (hypoventilation), particularly during sleep
Frequent respiratory infections
Life-threatening breathing difficulties due to weakness of the respiratory muscles
Delayed development of motor skills, such as sitting, crawling, standing, and walking, in surviving individuals

Due to severe respiratory complications, most affected individuals do not survive past infancy.

Frequency

Actin-accumulation myopathy is an extremely rare disorder. It has been identified in only a small number of individuals, and its exact prevalence is currently unknown.

Causes & Risk Factors

The condition is caused by mutations in the ACTA1 gene, which provides instructions for producing a protein called skeletal alpha (α)-actin. This protein belongs to the actin family, which is essential for cell movement and muscle contraction. In skeletal muscles, thin filaments made of actin and thick filaments made of myosin overlap and interact to allow muscles to contract.

Mutations in the ACTA1 gene disrupt how skeletal α-actin binds to ATP (adenosine triphosphate), the molecule that supplies energy for cellular activities. This faulty binding impairs the formation of thin filaments and prevents normal muscle contraction, leading to severe muscle weakness. Under a microscope, these abnormal accumulations of actin filaments can be seen within the muscle cells of affected individuals.

In some diagnosed individuals, no mutations in the ACTA1 gene have been identified, and the cause of the disorder remains unknown.

Inheritance

This condition is inherited in an autosomal dominant pattern, meaning a single copy of the altered gene in each cell is sufficient to cause the disorder. However, most cases are not inherited from a parent; instead, they result from new (de novo) mutations in the gene and occur in individuals with no family history of the disease.

Other Names for This Condition

Actin filament aggregate myopathy
Actin myopathy
Congenital myopathy with excess of thin filaments
Nemaline myopathy 3