SNP Shot: Genomic Insights

Hereditary hyperekplexia is a disorder characterized by heightened muscle stiffness (hypertonia) and an extreme startle response to sudden stimuli, particularly loud sounds, in infants. After being startled, babies experience a short phase of extreme rigidity and immobility. This rigidity can sometimes cause them to stop breathing, which can be life-threatening if prolonged. Infants with this condition exhibit hypertonia constantly, except during sleep.

Additional symptoms of hereditary hyperekplexia may include muscle jerks while falling asleep (hypnagogic myoclonus) and limb movements during sleep. Some infants demonstrate a reaction to a tap on the nose, extending their head forward along with spasms in the limb and neck muscles. In rare instances, infants with hereditary hyperekplexia can develop recurring seizures (epilepsy).

The characteristic signs of hereditary hyperekplexia usually lessen by the age of one. However, older individuals may retain an exaggerated startle response and episodes of rigidity, potentially leading to falls. Hypnagogic myoclonus or sleep movements may persist. As individuals with this condition age, they might develop a sensitivity to crowded environments and loud sounds. Individuals with hereditary hyperekplexia who also have epilepsy will continue to experience seizures throughout their lives.

Hereditary hyperekplexia could be a contributing factor in some cases of sudden infant death syndrome (SIDS), a leading cause of unexplained infant mortality in babies under one year old.

Inheritance:

Hereditary hyperekplexia exhibits various inheritance patterns. It can be inherited in an autosomal dominant manner, meaning a mutation in just one copy of a related gene within each cell is enough to cause the condition. Sometimes, an affected person inherits this mutation from a parent who also has the condition. Other times, the mutation arises spontaneously in the gene, in which case there is no family history of the disorder. Hereditary hyperekplexia can also be inherited in an autosomal recessive manner, meaning both copies of a related gene in each cell must have mutations. In autosomal recessive inheritance, the parents usually each carry a single copy of the mutated gene, but don't show any symptoms of the disorder themselves.