West Syndrome, Severe Developmental Retardation, and Intermittent Horizontal Saccade Failure: An Expanded Spectrum of STXBP1-Epileptic Encephalopathy

Background/Purpose: Mutations in the STXBP1 gene, encoding the syntaxin binding protein 1, have been described in Ohtahara syndrome or early infantile epileptic encephalopathy with suppression burst pattern and in other early epileptic encephalopathies, like West syndrome.

Methods: We describe a patient with de novo STXBP1 mutations presenting with West syndrome, severe developmental retardation and ocular motor apraxia.

Results: A 4-month-old boy presented with infantile spasms. The child showed normal cognitive and motor development until the age of 4 months. EEG showed a hypsarrhythmia pattern during awake state and during sleep. Seizures stopped and EEG improved with high dose vigabatrin. The child remained seizure-free even after cessation of vigabatrin at the age of 16 months. From the age of 10 months, the child developed ocular motor apraxia. The cognitive profile at the age of 19 months showed a severe developmental retardation corresponding to a developmental age of 5 to 6 months. Genetic analysis (epilepsy panel) showed a novel de novo mutation in the STXBP1 gene: c.1461G > A; p.E487E (het.). The now 2.5-year-old boy had severe developmental retardation, motor coordination problems and intermittent horizontal saccade failure (ocular motor apraxia) but no seizures.

Conclusion: Ocular motor apraxia has so far not been described in STXBP1 encephalopathy and might be a new clinical features in patients with STXBP1 mutations.