Early diagnosis of spinocerebellar ataxia
Spinocerebellar ataxia (SCA) consists of a community of multisystem neurodegenerative disorders, whose key feature is progressive ataxia. It is caused by mutations in more than 25 genes of which 14.2–4 In seven subtypes, including the most prevalent genotypes (SCA1, SCA2, SCA3, and SCA6), the expansion of a CAG trinucleotide repeat in the coding region of the respective gene triggers the disease. SCA is a phenotypically heterogeneous latent condition characterized by slowly progressive gait ataxia and additional variable symptoms including visual problems, dysarthria, dysphagia, limb ataxia, spasticity, parkinsonism, dystonia, peripheral neuropathy, restless leg syndrome and urge incontinence. Because of its genetic existence, it is likely that the pathogenic process begins early in life or even before birth. Nevertheless, the precise origin of the disease still remains unclear.
It is hard to define the initiation of genetically determined neurodegenerative diseases because of their gradual and slowly progressive nature. This is particularly true for spinocerebellar ataxia (SCA) due to differing affection of many parts of the nervous system and tremendous symptom variability. In 287 patients with SCA1, SCA2, SCA3 or SCA6, we investigated early symptoms and calculated the influence of CAG repeat length on age of onset depending on (1) the definition of onset of disease, (2) the definition of onset, and (3) the duration of the symptoms. The primary symptom in two-thirds of patients was discomfort with gait. In 4% of patients, respectively, ataxia accompanied double vision, dysarthria, poor hand writing and episodic vertigo. Data on on onset of disease ranged for 1 year or more in 44 percent of cases between patients and family