Hyperekplexia and the alpha1 subunit glycine receptor gene (GLRA1)

Hyperekplexia: Treatment of a Severe Phenotype and Review of the Literature

Hyperekplexia is a rare disorder caused by autosomal dominant or recessive modes of inheritance and characterized by episodes of exaggerated startle. Five causative genes have been identified to date. The syndrome has been recognized for decades and due to its rarity, the literature contains mostly descriptive reports, many early studies lacking molecular genetic diagnoses. A spectrum of clinical severity exists. Severe cases can lead to neonatal cardiac arrest and death during an episode, an outcome prevented by early diagnosis and clinical vigilance. Large treatment studies are not feasible, so therapeutic measures continue to be empiric. A marked response to clonazepam is often reported but refractory cases exist. Herein we report the clinical course and treatment response of a severely affected infant homozygous for an SLC6A5 nonsense mutation and review the literature summarizing the history and genetic understanding of the disease as well as the described comorbidities and treatment options.

Major and minor form of hereditary hyperekplexia

Hyperekplexia is a hereditary neurological disorder characterized by excessive startle responses. Within the disorder two clinical forms can be distinguished. The major form is characterized by continuous generalized stiffness in the first year of life and an exaggerated startle reflex, accompanied by temporary generalized stiffness and falls, whereas in the minor form only excessive startle and hypnic jerks have been described. Mutations in the gene encoding the alpha-1 subunit of the glycine receptor (GLRA1) are responsible for the major form of hyperekplexia but no mutation was detected in patients with the minor form in the large Dutch pedigree originally described by Suhren and colleagues. Here we describe the genetic analysis of the GLRA1 gene of two English families in which both forms of hyperekplexia were present. Mutation analysis revealed no genetic defect in the GLRA1 gene in patients carrying either the minor or major forms. This is further evidence that the minor form of hyperekplexia is seldom due to a genetic defect in the GLRA1 gene.

Hypertonia, hyperreflexia, and excessive startle response in a neonate

Following an uneventful gestation, a newborn girl presented with hypertonia, hyperreflexia, tremor, and excessive startle response. Nose tap elicited a dramatic head recoil. Her mother had similar symptoms beginning as a child that improved but persisted into adulthood. In addition, several members of mother's family died unexpectedly in infancy. Hypertonia in the newborn period indicates central nervous system dysfunction of several possible causes, most of which are associated with severe cognitive deficits and limited neurological development.