The protein encoded by this gene catalyzes the conversion of isopentenyl diphosphate to dimethylallyl diphosphate, which is a precursor for the synthesis of cholesterol and other isoprenoids. This gene, which is a product of an ancestral gene duplication event, encodes a protein that may be involved in the aggregation of alpha-synuclein in the cerebral cortex of patients with Lewy body disease. In addition, segmental copy number gains in this locus have been associated with sporadic amyotrophic lateral sclerosis.