Similarities and differences in the phenotype, genotype and pathogenesis of different spinocerebellar ataxias

Historically, the differential diagnosis of the autosomal ataxias (ADCAs) h as been difficult. In 1983 Harding proposed a useful clinical classificatio n. Since 1983 ADCAs have been increasingly characterized in terms of their genetic locus and are referred to as spinocerebeller ataxia (SCA). The over lap between the SCA phenotypes and the high variability within SCA subgroup s means that, for individual patients, the underlying mutation cannot be pr edicted reliable purely on the basis of clinical symptoms and so diagnosis should be made on the genotype. However, for executing DNA analyses in orde r of clinical likelihood, neurologists may try to deduce the underlying mut ation by using a clinical algorithm. In this article we not only describe s uch an algorithm but also plot the pathway from clinical presentation, gene tic classification and mutation, abnormal protein to common neuropathology in these disorders.