What is Hyperekplexia?
Hyperekplexia is an extremely rare neurological disorder that is inherited and is seen mostly in newborns but children and adults may also have it. It is characterized by the person having excessive startle response or reflex consisting of eye blinking and body spasms. These responses are noted even to slightest of sound, light, or touch. A baby with Hyperekplexia will have significant muscle tension which will prevent any voluntary motion of the body. In children and adults, Hyperekplexia may cause extreme muscle stiffness to an extent that the person may just fall but will not lose consciousness. Due to exaggerated reflexes, person with Hyperekplexia will also have an abnormal gait pattern.[1,2,3]
Hyperekplexia is normally inherited in an autosomal dominant fashion meaning that only one copy of the defective gene from either parent is good enough to cause this condition. However, there have been rare cases of Hyperekplexia being inherited in autosomal recessive fashion meaning that two copies of the defective gene one from each parent is needed to get the condition.[1,2,3]
There is also data of Hyperekplexia being caused in rare cases due to X-linked inheritance. Due to the symptoms and muscle stiffness that Hyperekplexia causes, most often it is misdiagnosed as a form of epilepsy and hence the correct diagnosis is often at times delayed. Treatment for Hyperekplexia is usually straightforward and involves use of anxiolytics and antispastic medications. Additionally, physical and cognitive therapy is also quite effective in the treatment of Hyperekplexia.[1,2,3]
What Causes Hyperekplexia?
As stated, Hyperekplexia is an inherited condition. In most cases, it is inherited in an autosomal dominant fashion. This means that only one copy of the defective gene is good enough to cause it but rarely autosomal recessive and X-linked form of inheritance have been observed. The genes responsible for Hyperekplexia are the GLRA1, SLC6A5, GLRB, and GPHN genes.
In majority of the cases it is the mutation of GLRA1 or the SLC6A5 gene that is responsible for Hyperekplexia. The genes that cause Hyperekplexia are responsible for making glycine protein. This protein reduces the action of the nerve cells in the brain and spinal cord to external stimuli. In cases of Hyperekplexia, the mutation of the gene interferes with the production of glycine protein. This results in the nerve cells being hyperactive and react very easily even to the slightest of stimulus.
What are the Symptoms of Hyperekplexia?
There are basically two forms of Hyperekplexia, namely major and minor. In the major form of this condition, the patient has abnormally excessive startle response to sudden sound, movement, or touch. The patient will have arching of the head, myoclonic jerks, and in cases of children and adults falling to the ground with the whole body abnormally stiff without loss of consciousness. All these symptoms are observed when the patient is startled. The frequency and severity of the symptoms tend to become worse in periods of stress and fatigue. The myoclonic jerks can also be seen when the patient is trying to fall asleep.
Hypertonia is something which is quite common in newborns with Hyperekplexia at the time of birth. Babies with Hyperekplexia will not move at all and even if they do it will be a very slow movement. Hyperreflexia, intermittent apneic episodes, and unstable gait are some of the other symptoms that children and adults with Hyperekplexia show. There have also been some reports of the presence of inguinal hernia in people with Hyperekplexia.
In the minor form of Hyperekplexia, there will be far less symptoms seen when compared to the major form of this disease. In newborns, the startle response may be brought on by fever and in children and adults stress or anxiety may cause it. The onset of symptoms of Hyperekplexia can be observed right from the time of birth but in some cases symptoms may not be evident until the child reaches adolescence of adulthood.
How is Hyperekplexia Treated?
Clonazepam is one medication that has been found to be extremely effective in managing the symptoms of Hyperekplexia in everyone with Hyperekplexia. Clonazepam is an anxiolytic and an antispastic drug. Some of the other medications that can be given to treat Hyperekplexia include carbamazepine, phenobarbital, phenytoin, and diazepam.
For people who have a family history of Hyperekplexia or who have a family member with this condition, it is important to get genetic testing done to check for the chances of their offspring getting Hyperekplexia.