PHYHIP (Phytanoyl-CoA hydroxylase-interacting protein) is a 330 amino acid protein that is strongly expressed in brain, with weak expression in ovary, small intestine and ovary. In transgenic mice, overexpression of PHYHIP in heart results in tachycardia and tachyarrhythmia. PHYHIP interacts with the Refsum disease gene product, PAHX, indicating that PHYHIP may play a role in the CNS deficits of Refsum disease, which is characterized by cerebellar degeneration, neurologic damage and peripheral neuropathies. PHYHIP also interacts with Dyrk1A, a protein that that is overexpressed in brain of Down-syndrome patients, therefore PHYHIP may participate in some of the neurological abnormalities of Down syndrome. Significantly, the gene encoding PHYHIP is localized to a region of the short arm of human chromosome 8 that is frequently found deleted in prostate, breast and several other types of cancers.