IQGAP3 (IQ motif containing GTPase activating protein 3) is a 1,631 amino acid protein that acts as an effector of Cdc42 and Rac 1, linking their activation to the cytoskeleton during neuronal morphogenesis. A novel member of the IQGAP family, IQGAP3 is highly expressed in brain where it localizes to axons of hippocampal neurons. IQGAP3 contains one Ras-GAP domain, a CH (calponin-homology) domain, four IQ domains and is encoded by a gene located on human chromosome 1, which spans 260 million base pairs, contains over 3,000 genes and comprises nearly 8% of the human genome. Chromosome 1 houses a large number of disease-associated genes, including those that are involved in familial adenomatous polyposis, Stickler syndrome, Parkinson’s disease, Gaucher disease, schizophrenia and Usher syndrome. Aberrations in chromosome 1 are found in a variety of cancers, including head and neck cancer, malignant melanoma and multiple myeloma.