The ATN1 gene has a segment of DNA called the CAG trinucleotide repeat.[9] It is made up of cytosine, adenine, and guanine.[9] The number of CAG repeats in the ATN1 gene in a healthy person will range from six to thirty-five repeats.[9] CAG repeats that exceed thirty-five can cause a gain-of-function mutation in ATN1.[10] Studies have supported the idea that mutated Atrophin-1 gathers in neurons and disrupts cell function.[11] The sequence of the ATN1 gene contains a nuclear localizing signal (NLS) and a nuclear export signal (NES).[11] It has been shown that a mutation of the NES in ATN1 can change where ATN1 localizes, and can cause aggregation to occur in the nucleus.[11] This can lead to an increase in cellular toxicity.[11]
Mutations in ATN1 are associated with a form of trinucleotide repeat disorder known as "dentatorubral-pallidoluysian atrophy" or "dentatorubropallidoluysian atrophy". Dentatorubral-pallidoluysian atrophy (DRPLA) is a rare neurodegenerative disorder characterized by cerebellar ataxia, myoclonic epilepsy, choreoathetosis, and dementia.[5] The disorder is related to the expansion of a trinucleotide repeat within this gene.[5] In patients with DRPLA, truncated ATN1 has been observed forming intranuclear aggregates that cause cell death.[11] The symptoms of this disorder can be credited to the significant reduction of brain and spinal tissue observed in those afflicted with DRPLA.[12] There are both juvenile-onset and late adult-onset variants of DRPLA, which show differing degrees of severity of specific symptoms.[12]
