Elongation protein 4 homolog (S. cerevisiae), also known as ELP4, is a protein which in humans is encoded by the ELP4 gene. This gene encodes a component of the six subunit elongator complex, a histone acetyltransferase complex that associates directly with RNA polymerase II during transcriptional elongation. The human gene can partially complement sensitivity phenotypes of yeast ELP4 deletion mutants. Alternatively spliced variants that encode different protein isoforms have been described but the full-length nature of only one has been determined. In a study published in February 2009, researcher linked this gene to the most common form of human epilepsy, namely Rolandic epilepsy. This is the first gene to be linked with rolandic epilepsy. The Elongator Protein Complex (ELP) is what regulates the growth of cortical projection neurons. This means that it helps cortical neurons to exhibit dendrite branching and radial migration of neurons to form the close knit neural network of the cerebral cortex. If ELP is not working properly or is not being expressed at the correct levels (too low) then the neurons in that region in particular would not be properly situated in relation to each other for proper brain activity. The expression of ELP and the fourth sub-unit (ELP4) in particular is the cause of Rolandic epilepsy and possibly other cognitive impairment later in life if the condition is severe enough or if it is not treated effectively.