Clinical characteristics of patients with spinocerebellar ataxias 1, 2, 3 and 6 in the US; a prospective observational study

Abstract

Background: All spinocerebellar ataxias (SCAs) are rare diseases. SCA1, 2, 3 and 6 are the four most common SCAs, all caused by expanded polyglutamine-coding CAG repeats. Their pathomechanisms are becoming increasingly clear and well-designed clinical trials will be needed.

Methods: To characterize the clinical manifestations of spinocerebellar ataxia (SCA) 1, 2, 3 and 6 and their natural histories in the United States (US), we conducted a prospective multicenter study utilized a protocol identical to the European consortium study, using the Scale for the Assessment and Rating of Ataxia (SARA) score as the primary outcome, with follow-ups every 6 months up to 2 years.

Results: We enrolled 345 patients (60 SCA1, 75 SCA2, 138 SCA3 and 72 SCA6) at 12 US centers. SCA6 patients had a significantly later onset, and SCA2 patients showed greater upper-body ataxia than patients with the remaining SCAs. The annual increase of SARA score was greater in SCA1 patients (mean ± SE: 1.61 ± 0.41) than in SCA2 (0.71 ± 0.31), SCA3 (0.65 ± 0.24) and SCA6 (0.87 ± 0.28) patients (p = 0.049). The functional stage also worsened faster in SCA1 than in SCA2, 3 and 6 (p = 0.002).

Conclusions: The proportions of different SCA patients in US differ from those in the European consortium study, but as in the European patients, SCA1 progress faster than those with SCA2, 3 and 6. Later onset in SCA6 and greater upper body ataxia in SCA2 were noted. We conclude that progression rates of these SCAs were comparable between US and Europe cohorts, suggesting the feasibility of international collaborative clinical studies.

Figure 1

The SARA Total Score at the baseline and the duration of the disease. The SARA Total Score (Y axis) plotted against the duration of disease (years; X axis) was calculated from the age at the baseline visit and the age at onset for each subject. Blue dots: SCA1 subjects, red dots: SCA2 subjects, green dots: SCA3 subjects, and black dots: SCA6 subjects. The slope of the color-coded linear regression line indicates the estimated average increase rate of the SARA Total Score of the SCA group.

Figure 2

Progression rate of SCA1, 2, 3 and 6. The annual rate of increase of the SARA Total Score is shown. Black bar: Annual rate of increase of the SARA Total Score was estimated from cross-section SARA scores and the durations of the disease at the baseline visit. Grey bar: The observed rate of increase of the SARA Total Score during the longitudinal study. (*: p = 0.003, **: p = 0.049, compared with SCA2, SCA3 and SCA6).