Mutations in STXBP1 have been identified in a subset of patients with early 
onset epileptic encephalopathy (EE), but the full phenotypic spectrum remains to 
be delineated. Therefore, we screened a cohort of 160 patients with an 
unexplained EE, including patients with early myoclonic encephalopathy (EME), 
Ohtahara syndrome, West syndrome, nonsyndromic EE with onset in the first year, 
and Lennox-Gastaut syndrome (LGS). We found six de novo mutations in six 
patients presenting as Ohtahara syndrome (2/6, 33%), West syndrome (1/65, 2%), 
and nonsyndromic early onset EE (3/64, 5%). No mutations were found in LGS or 
EME. Only two of four mutation carriers with neonatal seizures had Ohtahara 
syndrome. Epileptic spasms were present in five of six patients. One patient 
with normal magnetic resonance imaging (MRI) but focal seizures underwent 
epilepsy surgery and seizure frequency dropped drastically. Neuropathology 
showed a focal cortical dysplasia type 1a. There is a need for additional 
neuropathologic studies to explore whether STXBP1 mutations can lead to 
structural brain abnormalities.