SELENON-related myopathy (SELENON-RM)

SELENON-related myopathy (SELENON-RM) is a condition that affects the muscles and is part of a group of genetic muscle conditions called congenital myopathies. These conditions are present from birth or in infancy and lead to muscle weakness.

The main features of SELENON-RM include muscle weakness, especially in the head, neck, and torso, breathing difficulties, and spine rigidity. SELENON-RM is caused by a change in the SELENON gene (previously known as SEPN1).

The first signs of SELENON-RM may appear at birth or in the first few months of life, but it may not be diagnosed until later in childhood. Early signs include low muscle tone (hypotonia), poor head control, or delays in achieving motor milestones like sitting up, crawling, or walking. Some children may struggle to gain weight and grow at the expected rate.

Muscle weakness

In SELENON-RM, weakness mainly affects the muscles of the head, neck, and torso, and is expected to be slowly progressive. It can also affect the upper arms and legs. This can make some tasks difficult, such as standing up, climbing stairs, or lifting objects.

The severity and speed of progression can vary greatly. Most children learn to walk and continue to be able to walk throughout their lives. Some may need walking aids or a wheelchair if their muscles become much weaker over time.

Respiratory

Weak respiratory muscles can cause breathing problems early in life and should be regularly monitored. Even if muscle weakness is mild and a person can walk, they can still experience severe breathing problems.

Some people develop frequent chest infections, aspiration pneumonia (a lung infection caused by food or fluid entering the airway), and nocturnal hypoventilation (shallow breathing at night). Night-time breathing issues may cause morning headaches, daytime sleepiness, poor appetite, and unplanned weight loss. As children grow into teenagers, non-invasive ventilation (NIV) at night is usually required to help with breathing.

Joints and spine

People with SELENON-RM can develop stiff joints, called contractures, especially in the ankles and elbows. This happens when muscles tighten and shorten, reducing movement and flexibility of joints.

Scoliosis, where the spine twists and curves to the side, is common in SELENON-RM. It usually develops in childhood and can worsen quickly, so it’s important that the spine is monitored in a specialist clinic with regular X-rays. This may be every year from when initial curvature is first noticed, or when recommended by the specialist. A spinal brace may be needed to improve posture and slow the progression of scoliosis. In some cases, scoliosis surgery may also be needed. Many people also develop spinal rigidity, which makes it difficult to bend forward.

Feeding and swallowing

Some people with SELENON-RM have weakness in the muscles used for chewing and swallowing. This can make it hard to chew food properly and may lead to choking or aspiration (food or liquid entering the airway). As a result, eating can take longer, and it can be difficult to gain weight.

A significant number of children and some adults may have low weight. This should be managed with support from a dietitian, who advises on nutrition and weight management, and dietary supplements. A speech and language therapist, who assesses swallowing difficulties, can help identify any problems and suggest a modified diet or other interventions if needed.

Genetic changes

SELENON-RM is caused by changes in the SELENON gene (previously called SEPN1). This gene provides instructions to make a protein called selenoprotein N. This protein helps control calcium levels in a part of cells called the endoplasmic reticulum. Changes in the SELENON gene disrupt the production or function of selenoprotein N, leading to problems with calcium regulation. This causes muscle weakness and other related symptoms.

Inheritance

SELENON-RM is typically inherited in an autosomal recessive pattern. This means that a person needs to inherit two copies of the changed gene, one from each parent, to develop the condition. The parents are carriers, meaning they each have one copy of the changed gene but don’t have the condition themselves.

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. The neurologist will investigate symptoms and typically use physical examination and genetic testing to make a diagnosis. Genetic testing uses a blood sample to check for changes in the SELENON gene. In some cases, a muscle biopsy may also be done. This involves taking a small sample of muscle to examine under a microscope and look for changes in the muscles associated with SELENON-RM.

For more information, see our diagnosis page.

A diagnosis of SELENON-related myopathy is usually given, but depending on symptoms and tests done, some healthcare professionals may use other names for related conditions.

Conditions associated with changes in the SELENON gene include:

• Congenital muscular dystrophy with rigid spine
• Multiminicore disease (MmD)
• Desmin-related myopathy with Mallory body-like inclusions
• Congenital fibre type disproportion (CFTD)

A multi-disciplinary approach, which involves different healthcare professionals working together, is not only important in managing the condition and symptoms but in improving wellbeing too.

Access to a healthcare team

People with SELENON-RM should have access to a multi-disciplinary healthcare team. Usually, the lead professional will be a neurologist in a specialist neuromuscular clinic. If you don’t have contact with a neurologist or specialist doctor, speak to your GP about getting access to one.

Exercise and physiotherapy

People with SELENON-RM are encouraged to stay as active as possible. 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 help keep muscles engaged and prevent or slow the progression of joint stiffness. Moderate exercise, like swimming, walking, and pedalling is recommended because this type of aerobic exercise helps 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. For advice for adults, see exercising with a muscle wasting condition. Physiotherapists can also provide advice on walking aids and wheelchairs if needed.

Respiratory

Respiratory function and lung capacity should be checked regularly using a spirometry test. Overnight sleep studies are used to assess breathing while sleeping and check for night-time breathing problems. This is usually nocturnal hypoventilation, where low oxygen levels and high carbon dioxide levels while sleeping can cause symptoms of morning headaches and fatigue during the day. Nocturnal hypoventilation can be treated using non-invasive ventilation (NIV) during sleep to help maintain adequate ventilation.

It’s also recommended to get a flu vaccination every year. People who need NIV at night should also ask their GP about getting the pneumococcal vaccine.

Orthopaedics

Orthopaedic management refers to the treatment and care of bones, joints, and muscles and can help with contractures and scoliosis. This might include using splints, braces, and other tailored orthotic devices. For scoliosis, spinal surgery may be necessary to realign the spine. It’s important to discuss all your options with a specialist.

Swallowing and diet

A significant proportion of children and some adults may have low weight. This should be managed with support from a dietitian, who advises on nutrition and weight management, and dietary supplements. A speech and language therapist, who assesses swallowing difficulties, can help identify any problems with the ability to swallow and suggest a modified diet or other interventions if needed.