Phobic anxiety disorder in hereditary hyperekplexia – Comorbidity or a coincidence: Case reports of two siblings

Hyperekplexia (startle disease) is a rare non-epileptic neurological entity resulting from gene mutation. The onset of this disorder is usually in infancy, but can be delayed until early adulthood. Patients with this disorder usually have normal mental development. Patients with hyperekplexia may present with symptoms ranging from sub-syndromal anxiety, to symptoms of syndromal anxiety disorder. This case report is about two siblings with hyperekplexia, in whom phobic anxiety disorder was a prominent manifestation. Neurology Asia 2013; 18(2) : 213 – 215 Address correspondence to: Sujit Kumar Kar, MD (Psy), Department of Psychiatry, King George’s Medical University, Lucknow, Uttar Pradesh, 226003, India. Tel: 09910812247, [email protected] INTRODUCTION Familial or hereditary hyperekplexia is an infrequent disorder, which usually presents with abnormal startle reaction to auditory or somatosensory stimuli. This disorder exists in two clinical forms – “major form” and “minor form”. Hyperekplexia is associated with genetic mutation of alpha-1 subunit of glycine receptor which can be either dominant or recessive. In some studies it has been found that the above genetic mutation is linked more to the “major” form of hyperekplexia rather than the “minor” form. Both “major” and “minor” forms of hyperekplexia have excessive startle reaction, but the “minor” form of hyperekplexia differs from the “major” form by not having generalized stiffness in the course of the disorder. Jerky muscle stiffness usually resolves itself by the end of the fi rst year of life whereas the startle response to auditory and somatosensory stimuli usually persist for life. The “minor” form of hyperekplexia is associated with behavioural manifestations and is of neuropsychiatric signifi cance. Hyperekplexia may follow familial or sporadic pattern. Chromosome 5 is associated with this disorder. Usually the disorder presents in infancy, with minimal impairment to mental development. Clonazepam is effective in the treatment of hyperekplexia. Familial hyperekplexia is frequently associated with serious falls, which in the long run may produce hesitant gait disorder and phobic disorders (particularly fear of open spaces). Neuropsychiatric comorbidities like specifi c phobia are also associated with “stiff-man syndrome” which is a similar condition of exaggerated startle response. In this case report, hyperekplexia and its associated neuropsychiatric manifestations in two biological siblings are discussed.