in individuals where the region on at least one copy of chromosome 6 contains 39 or more continuous repeats of glutamine in which more repeats are correlated to earlier onset and faster progression. Histidine interruptions in the polygluatamine tract can mitigate or prevent SCA1. SCA1 is known to exhibit genetic anticipation, where one generation with the disease may exhibit earlier onset and faster progression than the previous generation. This is typically caused by expansions in the polyglutamine tract between generations and is more common in cases of patrilineal inheritance. This non-Mendelian inheritance is similar to that observed in Huntington's disease and is believed to be caused by differences in various mechanisms in gamete production between the sexes that result in increased mosaicism in the male germline. DNA with CAG repeats are prone to forming secondary structures, including hairpin loops and R-loops, which can result in mutations and mosaicism if DNA repair mechanisms fail. These secondary structures cause somatic mosaicism by lagging DNA polymerase in Okazaki fragments and by disrupting DNA mismatch repair, base excision repair, nucleotide excision repair and double strand break repair mechanisms. The mechanism for germline expansions is not well understood, but it is believed that only mismatch repair pathways effect germline instability and the MSH2 repair protein has been linked to expansions in male gametes in mice models. Pathophysiology Normal ataxin 1 is intimately involved in a number of signaling pathways, in protein ubiquitination, RNA metabolism, in transcription regulation, protein transformation, and protein stabilization. Among other interactions, it forms a transcription complex with Retinoid-related Orphan nuclear-receptor transcription factor α (RORα) following interactions with an activator, Histone acetyltransferase KAT5, sometimes referred to as TIP60, and it is in the signaling mediated by metabotropic glutamate receptor 1 (mGluR1). Resonant Recognition Modeling of the ataxin 1 protein has shown possible binding sites for growth factor independent transcription repressor 1 (Gfi-1). The predictions of this computational model reveal an interaction that could play a role in SCA1 pathology, because the Gfi-1 protein is known to cause selective degradation of Purkinje cells. It is the extensive involvement of ataxin 1 in many different functions that make understanding the biochemical pathophysiology of its mutant form difficult to identify and understand. The mechanism by which expanded CAG repeat regions in ataxin 1 cause neuronal degeneration is unclear. It was historically believed to be caused by aggregation and deposition of the affected protein similar to