Variants and Polymorphisms of DNA Repair Genes and Neurodegenerative Diseases

Abstract

Oxidative DNA damage is one of the earliest detectable events in several neurodegenerative diseases, often preceding the onset of the clinical symptoms. Moreover, neurons in the adult human brain can re-enter the cell division cycle, likely allowing DNA repair. Impairments of DNA repair pathways are reported in neurons of patients suffering from one of several neurodegenative diseases and might result in the accumulation of mutations critical for neurodegeneration. Current investigation aims at understanding the causes of such impairment (Coppede & Migliore, 2010). One of the most robust set of data that demonstrates association between DNA repair and neurodegenerative diseases comes from studies on early onset ataxia with ocular motor apraxia and hypoalbuminemia/ataxia with oculomotor apraxia type 1 (EAOH/AOA1), an autosomal recessive form of cerebellar ataxia caused by mutations in the aprataxin (APTX) gene. It was shown that aprataxin participates in DNA repair suggesting that genes involved in DNA repair pathways might have a role in neurodegeneration (Hirano et al., 2007; Takahashi et al., 2007). Also parkin, encoded by one of the causative genes of Parkinson’s disease (PD), seems to contribute to DNA repair (Kao, 2009). Variants and polymorphisms of DNA repair genes, particularly DNA base excision repair (BER) genes, have been investigated as possible risk factors for Alzheimer’s disease (AD), Parkinson’s disease, amyotrophic lateral sclerosis (ALS), and other neurodegenerative diseases (Coppede & Migliore, 2010). There is also evidence that BER could contribute to CAG repeat expansion in Huntington’s disease (HD) (Kovtun et al., 2007). Most of the genetic association studies have been performed in the last few years and gave often conflicting or inconclusive results, their power was limited by the sample size of casecontrol groups, gene-gene interactions were missing, and only common polymorphisms have been included with little or no attention paid to rare gene variants (Coppede, 2011). In this chapter I discuss the current knowledge on DNA repair gene variants and polymorphisms and major neurodegenerative disorders.