The SNAP25 gene encodes a protein involved in exocytosis, a complex mechanism by which molecules such as insulin and neurotransmitters are secreted from a cell.  Exocytosis involves carrying the secretory vesicle to the plasma membrane, docking of the vesicle, vesicle priming, and subsequently, vesicle fusion with the cell membrane.  SNAP25, a SNARE protein (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) forms a SNARE complex with syntaxin 1A and synaptobrevin.  The selective binding of these proteins is essential for vesicle docking and fusion to occur at the correct location.  SNAP25 also modulates the activity of potassium voltage gated ion channels.

As SNAP25 is involved in the secretion of insulin and neurotransmitters, it is easy to understand how mutations in the gene can have pathological consequences.  The gene has been associated with Congenital Myasthenic Syndrome 18, a neuromuscular disorder characterized by muscle weakness, ataxia, delayed psychomotor development, and easy fatigability.  The gene may also play a role in Alzheimer’s disease, Autism and Type 2 Diabetes Mellitus.  

The SNAP25 gene is located on the short arm of chromosome 20.  It spans a length of 88 kb and its coding sequence consists of 17 exons.  The protein encoded by the gene is 23 kDa in size and is made up of 206 amino acids.  Alternative splicing results in two protein isoforms, named SNAP25A and SNAP25B.  The gene is highly expressed in the frontal cortex and in the brain in general.