[10][11] In the retina and cerebellum, an alternatively spliced transcript variant is expressed, containing an additional exon and totaling 603 amino acids.

It is essential for neurotransmission and binds syntaxin, a component of the synaptic vesicle fusion machinery probably in a 1:1 ratio.

[16][13] Mutations in the STXBP1 cause early infantile epileptic encephalopathy type 4 (EIEE4), a severe form of epilepsy characterized by frequent tonic seizures or spasms beginning in infancy with a specific EEG finding of suppression-burst patterns, characterized by high-voltage bursts alternating with almost flat suppression phases.

Affected individuals have neonatal or infantile onset of seizures, profound intellectual disability, and MRI evidence of brain hypomyelination.

[8][17] STXBP1 variants are increasingly being identified in people with wider neurological problems, including intellectual disability or movement disorders without epilepsy.