Ohtahara syndrome (OS) is one of the most severe and earliest forms of epilepsy. 
We have recently identified that the de novo mutations of STXBP1 are important 
causes for OS. Here we report a paternal somatic mosaicism of an STXBP1 
mutation. The affected daughter had onset of spasms at 1 month of age, and 
interictal electroencephalogram showed suppression-burst pattern, leading to the 
diagnosis of OS. She had a heterozygous c.902+5G>A mutation of STXBP1, which 
affects donor splicing of exon 10, resulting in 138-bp insertion of intron 10 
sequences in the transcript. The mutant transcript had a premature stop codon, 
and was degraded by nonsense-mediated mRNA decay in lymphoblastoid cells derived 
from the patient. High-resolution melting analysis of clinically unaffected 
parental DNAs suggested that the father was somatic mosaic for the mutation, 
which was also suggested by sequencing. Cloning of PCR products amplified with 
the paternal DNA samples extracted from blood, saliva, buccal cells, and nails 
suggested that 5.3%, 8.7%, 11.9%, and 16.9% of alleles harbored the mutation, 
respectively. This is a first report of somatic mosaicism of an STXBP1 mutation, 
which has implications in genetic counseling of OS.