Hyperekplexia

Overview

Hyperekplexia is a rare condition that affects how the nervous system reacts to surprises. People with it have a startle reflex that is much stronger than usual. A sudden noise, a light touch, or a quick movement can make the whole body stiffen or jerk. In babies, this stiffness can be very noticeable, and it can sometimes cause short pauses in breathing. Hyperekplexia is not epilepsy, and it is not caused by something the person did wrong. It happens because of a change in how certain nerve signals are controlled. Some people have a mild form with mainly a big startle, and others have a form with stiffness and breathing problems, especially in infancy.

No, it is rare. Doctors and hospitals see it only occasionally, and many general doctors may never see a case in their whole career. Because it is rare, families sometimes wait a while before getting the right diagnosis.

Hyperekplexia can affect anyone. The most serious form usually shows up in the first days or weeks of life, so newborn babies and young infants are the group most often diagnosed. Milder forms may not be noticed until childhood or even adulthood. It affects boys and girls, and people of all ethnic backgrounds. In some families it runs from parent to child, and in others it appears for the first time in one person.

Symptoms

Common symptoms

• A startle reaction that is far bigger than expected — the whole body jumps or stiffens
• Brief stiffness of the arms, legs, or whole body after a surprise
• Jerking movements that can make the person drop things or fall
• Falling stiffly, like a log, without putting out the hands to break the fall
• Being easily startled by everyday sounds such as a door closing or a phone ringing
• Night-time jerks or sudden body jerks when falling asleep
• Feeling generally tense or stiff, especially when anxious or in busy places

Symptoms in children

• In newborns: a very strong startle to sound or touch, with the arms and legs going rigid for a few seconds
• Stiffness that makes nappy changing, dressing, or feeding harder
• Short pauses in breathing during a startle, which can be frightening for parents
• Frequent startling that disturbs sleep and feeding
• Delayed head control or slower reaching of motor milestones in some children
• Hernias (a bulge in the groin or around the tummy button) are more common in babies with the condition
• Older children may seem clumsy or fall often, and may avoid noisy places or groups

Symptoms in older adults

• Startle-induced falls, which can lead to injuries
• Stiffness or a heavy, tense feeling in the legs and body
• Sudden jerks when drifting off to sleep
• Feeling anxious about crowded or noisy places because of the risk of startling
• Mild forms may only be recognised in adulthood after a careful neurological review

Causes

Main causes

• Most cases are genetic. They are caused by changes in genes that help build the proteins which respond to glycine — a natural chemical that helps calm nerve signals in the spinal cord and brainstem.
• When these signals do not work as they should, the nervous system stays 'switched on' a little too much, so surprises cause a much bigger reaction.
• Some cases run in families. Some forms need only one changed copy of a gene from one parent, and other forms need a changed copy from both parents.
• In some people the genetic cause is not found, even after thorough testing.
• Very rarely, a similar problem can be caused by damage or another condition affecting the brainstem, but this is not typical hyperekplexia.

Risk factors

• Having a parent or sibling with the condition
• Parents who are close blood relatives, which makes some recessive forms more likely
• A known gene change in the family, even if the parents have no symptoms
• Being a newborn — this is simply when the most serious form usually first appears

When to see a doctor

See a doctor urgently if:

• Your baby goes stiff and stops breathing, turns blue, or becomes floppy or unresponsive — call your local emergency number straight away
• Your baby has repeated stiff spells or breathing pauses — get medical help the same day
• A startle causes a fall with a head knock, loss of consciousness, or vomiting
• A child or adult suddenly develops much stronger startles, stiffness, or new weakness

Book a routine appointment if:

• You or your child startle much more than other people and it affects daily life
• Stiffness or jerking is getting in the way of feeding, sleeping, playing, or school
• Frequent falls, or falls where the body goes stiff
• A family member has been diagnosed with hyperekplexia and you would like advice
• You are worried about your child's development or movement skills

Diagnosis

A doctor, usually a neurologist (a specialist in brain and nerve conditions), makes the diagnosis by talking with you, watching the startle response, and examining the muscles, movement, and reflexes. They will ask about when symptoms started, what triggers them, and whether anyone else in the family has similar problems. Because the jerks can look like fits, tests are often done to rule out epilepsy and other conditions before hyperekplexia is confirmed.

Tests that may be done

• A full physical and neurological examination, including watching how the person responds to a sudden sound or tap
• Genetic testing (a blood or saliva sample) to look for changes in the genes linked to hyperekplexia
• An EEG, which records the brain's electrical activity, to check for epilepsy
• Electromyography (EMG), a test that records how muscles and nerves respond to a tap or a startle
• Blood tests to rule out other causes of stiffness or jerking
• A brain scan (MRI) in some cases, especially if the picture is unusual

What to expect at your appointment

The assessment is usually done in a clinic and does not hurt, although your child may find parts of it strange. Genetic test results can take several weeks. In the meantime, your doctor will focus on keeping your child safe and comfortable. If the diagnosis is confirmed, you will usually be offered a referral to a specialist team, and possibly to a clinical geneticist who can explain what the result means for your family and for future pregnancies.

Treatment

There is no cure for hyperekplexia, but there is a lot that can help. Treatment aims to reduce the startle and stiffness, prevent injuries, support breathing and feeding in babies, and help the person take part in everyday life. Care is usually led by a specialist team and tailored to the person's age and how much the condition affects them.

Self-care at home

• Learn your own or your child's triggers and, where possible, reduce them — for example, avoid sudden loud noises, and ask people to speak before touching
• Cushion hard floors and corners at home, and keep floors clear of clutter
• Use a helmet or protective padding if falls are frequent, as advised by your team
• For babies, follow safe sleep advice and ask your health visitor or paediatric team about monitoring at home if breathing pauses have occurred
• Keep a symptom diary to spot patterns and to share with your doctor
• Pace activities and build in quiet time if busy places make stiffness worse

Medical treatments

Treatment is planned by a specialist and usually focuses on medicines that help calm overactive nerve signals and reduce stiffness and startle. These are started at a low level and adjusted carefully, because the right balance differs from person to person. Babies with breathing pauses may need close monitoring in hospital at first. Other support can include physiotherapy to keep muscles and joints flexible, speech and feeding support for babies who find feeding hard, and occupational therapy for practical day-to-day help. Your specialist will explain the options, the possible side effects, and how often follow-up is needed. Never start, stop, or change any medicine without talking to your prescriber first.

When is surgery considered?

Surgery is not a treatment for hyperekplexia itself. It may occasionally be needed for related problems, such as repairing a hernia in a baby, or for an injury caused by a fall. Your team will discuss any operation with you in detail if it becomes relevant.

Living with this condition

Life with hyperekplexia is often about small, practical adjustments. Many families find that warning people before a greeting, keeping environments a bit quieter, and having a plan for falls makes daily life calmer. Children may need extra support at nursery or school, and a short letter or care plan from your specialist can help staff understand what to do if a stiff spell happens. Adults may find that pacing busy days and choosing quieter social settings helps a lot.

Lifestyle tips

• Build a routine that includes quiet wind-down time before sleep
• Tell close friends, teachers, and carers about the condition and what helps during a startle
• Keep a simple emergency plan handy, especially if breathing pauses have ever happened
• Make your home safer: rugs secured, sharp corners padded, good lighting on stairs
• Ask about support at school or work if symptoms affect attendance or concentration
• Connect with other families through a rare disease support group if you would like to

Diet and exercise

There is no special diet for hyperekplexia, but eating well and staying hydrated supports general health and energy. Gentle, regular movement is helpful — walking, swimming, and stretching can ease stiffness and keep joints flexible. A physiotherapist can suggest safe exercises for you or your child. Avoid very tiring or high-impact activity if it seems to trigger more startles, and always warm up slowly. Ask your team before starting a new exercise programme, especially if falls are a concern.

Mental health and emotional wellbeing

Living with a rare condition can be worrying and isolating, both for the person affected and for parents and carers. It is very common to feel anxious about the next startle or fall, and some people become nervous about going out. These feelings matter and deserve support. Talking to a counsellor or psychologist, or to other families in a similar situation, can really help. If you or someone you care for is having thoughts of self-harm or suicide, contact your local emergency number or a crisis support service in your area straight away — you do not have to cope alone.

Prevention

You cannot prevent hyperekplexia in most cases, because it is usually caused by gene changes present from birth. What you can do is reduce the chance of injuries and breathing problems by knowing the triggers, planning ahead for safety, and getting medical advice early. If you have a family history and are planning a pregnancy, genetic counselling can explain the options and the chance of passing the condition on.

Screening programmes

There is no routine screening for the general public. Genetic testing may be offered to relatives of someone with a confirmed gene change, and prenatal testing can be discussed during pregnancy if a family gene change is known. Ask your doctor about a referral to genetic services if this applies to you.

Complications

If left untreated

• Injuries from stiff falls, including head knocks and fractures
• Breathing pauses in babies, which can be serious if not recognised and managed
• Feeding difficulties and slow weight gain in infancy
• Delay in some motor milestones, such as head control or walking
• Hernias in babies
• Anxiety, low mood, and social withdrawal related to the fear of startling or falling
• Disrupted sleep from night-time jerks

Long-term outlook

The outlook is often encouraging. Many people find that symptoms ease as they get older, and treatment plus sensible safety steps can help most people live a full and active life. Some people continue to have a strong startle and need ongoing specialist follow-up, but with the right support, school, work, relationships, and independence are all very possible. Your specialist team can give you a clearer sense of what to expect for your own situation.

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