HPCA and Dystonia: Thus, it is plausible to hypothesize that the homozygous p.Asn75Lys variant, by impairing or even preventing Ca2+ binding to EF-hand domain 2, would be expected to reduce the likelihood of conformational change of hippocalcin in response to Ca2+ signals and, by extension, result in a defect in cellular Ca2+ signal transduction in the striatum, an area of the brain intimately connected with movement disorders, such as dystonia.