Hyperekplexia: A Single-Center Experience.

Background: Hyperekplexia is a rare neurogenetic disorder that is classically characterized by an exaggerated startle response to sudden unexpected stimuli. This study aimed to determine clinical and genetic characteristics of our patients with hyperekplexia.

Methods: The age of onset and diagnosis, familial and perinatal history, clinical course, complications, metabolic screening tests, magnetic resonance imaging (MRI), medications, neuropsychometric evaluations, and gene mutations of patients diagnosed with hyperekplexia were reviewed retrospectively.

Results: All hyperekplexia patients had displayed neonatal excessive startle response and muscle stiffness, which we accepted as the major form of the disorder. Sixteen patients had mutations in genes associated with hyperekplexia. The ages at clinical diagnosis and genetic confirmation ranged from newborn to 16 years old and from 2.5 to 19 years, respectively. Nine patients (56.25%) were initially misdiagnosed with epilepsy. Seven patients (43.75%) carried a diagnosis of intellectual disability, defined here as a total IQ <80. Delayed gross motor development was detected in 4 patients (25%), and speech delay was reported in 3 (18.75%). Mutations in GLRA1 (NM_000171.4) and SLC6A5 (NM_004211.5) were identified in 13 (81.25%) and 3 patients (18.75%), respectively. Fifteen of the 16 patients (93.75%) showed autosomal recessive inheritance. Only 1 patient (6.25%) showed autosomal dominant inheritance.

Conclusion: Although hyperekplexia is a potentially treatable disease, it can be complicated by delayed speech and/or motor acquisition and also by intellectual disability. This study shows that hyperekplexia is not always a benign condition and that all patients diagnosed with hyperekplexia should be evaluated for neuropsychiatric status and provided with genetic testing.