Pathogenic mutations and non-pathogenic DNA polymorphisms in the most common neurodegenerative disorders

In the past, each nucleotide change causing amino acid substitution in a gene in which other mutations responsible for a neurodegenerative disorder had been found was considered as a causative mutation. However, in recent years, mainly due to the progress of the Human Genome Project (HGP), numerous DNA variants have been identified in many neurodegenerative disorders. Some of them likely belong to the class of pathogenic (causative) mutations, whereas others, which may occasionally coexist with the disease phenotype, should be classified as non-pathogenic DNA polymorphisms. How to differentiate between a pathogenic mutation and a harmless DNA polymorphism nowadays, i.e. in the post-genomic era? The question still remains open. Erroneously assumed pathogenicity of a mutation may result in a misdiagnosis of the disease and in consequence lead to inappropriate genetic counselling. The aim of this short review is to present a set of mutations with no clear pathogenic effect that have been identified in some neurodegenerative disorders.