Nemaline myopathy (NM) is also known as rod myopathy. It happens when rod-like structures form in the muscle cells. Symptoms include muscle weakness, as well as breathing and feeding problems.

NM is part of a group of genetic muscle conditions called congenital myopathies. These conditions are usually present from birth or in infancy and lead to muscle weakness.

Symptoms will usually appear at birth or early childhood. Some congenital (at birth) types of NM can be life-threatening, while others will have a normal life expectancy. In rare cases, symptoms may not appear until adulthood. There are several types of NM that can be very similar to each other and may be considered as part of a spectrum.

Symptoms of NM listed below by type:

Adult-onset nemaline myopathy

This is the mildest type of NM, and symptoms are typically noticed during adolescence or adulthood. Muscle weakness is across most of the body and muscle pain can occur. The condition can be rapidly progressive. Neck muscles may be severely affected, making it difficult to hold the head up.

Childhood-onset nemaline myopathy

This type is milder than congenital types, and symptoms are typically noticed around the ages of 8 to 15. The symptoms and severity vary from person to person. Weakness is more noticeable at the lower part of the calf.

Typical congenital nemaline myopathy

This is the most common type of NM. Symptoms include muscle weakness and low muscle tone from birth and infancy. It often leads to delays in reaching motor milestones, like sitting, crawling, or walking, and respiratory and feeding difficulties may occur. The severity of symptoms will vary among those affected.

Intermediate congenital nemaline myopathy

This type has the same features as typical NM that also begins at birth and infancy, but with more severe progression. There is usually early development of joint stiffness (contractures) and the use of ventilatory support. Wheelchair use is also expected in childhood.

Severe congenital nemaline myopathy

This is the most severe type of NM and is life-threatening. Affected babies have severely low muscle tone and weakness. They will show little spontaneous movement (natural movement such as kicking, wriggling, and moving limbs) and will have difficulties with breathing and feeding. Respiratory support will be necessary.

Amish congenital nemaline myopathy

This type of NM is specific to Amish communities. Onset is at birth and babies will have severely low muscle tone, stiff and tight joints (contractures), breathing problems, and tremors. This type of NM is life-threatening and often the child will die within two years of life.

Genetic changes

NM is caused by changes in certain inherited genes that make proteins important for muscle tone and movement. In NM, these changes lead to the formation of rod-like structures in muscle cells. These structures disrupt the normal shape of the muscle fibers and prevent them from working properly, causing weakness and other symptoms.

There are at least 12 genes identified that cause this condition, and the most common changes are in the ACTA1 gene and NEB gene. Other genes that can cause NM include TPM2, TPM3, KBTBD13, CFL-2, KLHL40, KLHL41, LMOD3, MYPN, TNNT1, TNNT3, and MY018B.

Inheritance

NM can be inherited in both an autosomal dominant and autosomal recessive pattern. This means that the changed gene could be inherited from one parent who has the condition, or two parents who are carriers but do not have the condition themselves. In rare cases, a new genetic change may occur where there is no family history of the condition.

For more information, see our inheritance and genetics page.

A GP can make a referral to a neurologist for testing – a neurologist is a doctor who specialises in conditions that affect the muscles and nervous system. NM is usually diagnosed with a medical assessment and genetic testing. Genetic testing uses a blood sample to identify changes in the genes known to cause NM. Once the genetic change has been identified in the affected family member, it’s possible to use this sequence to diagnose other family members and identify unaffected carriers (in case of recessive genes).

A muscle biopsy may be needed if genetic testing is inconclusive. This is when doctors take a small sample of muscle and examine it under a microscope. Muscle from a person affected by NM has a distinctive pattern with thin thread-like or rod-like structures in the muscle cells.

For more information, see our diagnosis page.

A multi-disciplinary approach is important in not only managing the condition and symptoms but in improving wellbeing too. It involves different healthcare professionals working together. Children with severe types of NM will need to stay in hospital to begin breathing support, and many will also need feeding and nutritional support.

It’s generally accepted that the earlier the onset, the more severe the symptoms are.

Access to a healthcare team

People with NM should have access to a multi-disciplinary healthcare team. Usually, the lead professional will be a neurologist. If you do not have contact with a neurologist or specialist doctor, speak to your GP about getting access.

Respiratory

Breathing problems are common, and so respiratory function should be regularly monitored. Overnight sleep studies can assess breathing while sleeping and diagnose night-time breathing problems, such as nocturnal hypoventilation. This is when there are low oxygen and high carbon dioxide levels while sleeping, which can cause symptoms of morning headaches and daytime fatigue. Treating nocturnal hypoventilation involves using non-invasive ventilation (NIV) during sleep. Weakness in the muscles that help with breathing make it harder to clear mucus from the lungs. This increases the risk of chest infections, and antibiotics are needed to treat this. Respiratory function may improve over time.

Swallowing and diet

The ability to swallow may be affected. This can cause coughing, choking, or feeling like food is stuck in the throat. It can lead to weight loss and dehydration. A dietitian may suggest changes to the texture of food or avoiding foods that are tough to chew and swallow. If the problem is severe, they may prescribe food supplements or suggest a procedure called a gastrostomy. This is when doctors make a small surgical opening through the abdomen and into the stomach and insert a feeding tube (also known as a PEG tube). Having this tube means enough nutrition and hydration can be put directly into the stomach.

Exercise and physiotherapy

Physiotherapy and mild exercise are crucial in maintaining muscle strength and mobility. They can also help maintain breathing capacity, delay the onset of curvature of the spine (scoliosis), and slow the progression of joint tightness (contractures). A physiotherapist is a healthcare professional who helps manage symptoms through movement, exercise, and manual therapy. They can put together a suitable exercise plan to follow. Recommended exercises include moderate swimming and walking, as this sort of aerobic exercise can help maintain a healthy cardiovascular system and a steady weight. Before starting any new form of exercise, it’s important to discuss this with a clinician. To find out more about advice for adults, see exercising with a muscle wasting condition. Physiotherapists can also provide advice on walking aids and wheelchairs where necessary.

Cardiac

There is a risk of problems with the heart in some genetic changes – but not all. If heart problems are considered likely, a cardiologist (heart doctor) should perform regular heart checks. This includes an electrocardiogram (ECG) and echocardiogram (ECHO).