Saccades and Eye–Head Coordination in Ataxia with Oculomotor Apraxia Type 2
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Ataxia with oculomotor apraxia type 2 (AOA2) is one of the most frequent autosomal recessive cerebellar ataxias. Oculomotor apraxia refers to horizontal gaze failure due to deficits in voluntary/reactive eye movements. These deficits can manifest as increased latency and/or hypometria of saccades with a staircase pattern and are frequently associated with compensatory head thrust movements. Oculomotor disturbances associated with AOA2 have been poorly studied mainly because the diagnosis of oculomotor apraxia was based on the presence of compensatory head thrusts. The aim of this study was to characterise the nature of horizontal gaze failure in patients with AOA2 and to demonstrate oculomotor apraxia even in the absence of head thrusts. Five patients with AOA2, without head thrusts, were tested in saccadic tasks with the head restrained or free to move and their performance was compared to a group of six healthy participants. The most salient deficit of the patients was saccadic hypometria with a typical staircase pattern. Saccade latency in the patients was longer than controls only for memory-guided saccades. In the head-free condition, head movements were delayed relative to the eye and their amplitude and velocity were strongly reduced compared to controls. Our study emphasises that in AOA2, hypometric saccades with a staircase pattern are a more reliable sign of oculomotor apraxia than head thrust movements. In addition, the variety of eye and head movements’ deficits suggests that, although the main neural degeneration in AOA2 affects the cerebellum, this disease affects other structures.
KeywordsAOA2 Oculomotor apraxia Staircase saccade Eye–head coordination Cerebellum
The authors thank the patients and the healthy subjects for contributing to this study. The authors thank Pr S. Thobois, Dr I. Roullet-Solignac and Dr A. Poisson for referring the patients. The authors are really grateful to Pr. D. Zee for a helpful discussion. This work was promoted by the Hospices Civils de Lyon (2002–303).
Conflict of interest
The authors declare that there is no conflict of interest
- 2.Bomont P, Watanabe M, Gershoni-Barush R, Shizuka M, Tanaka M, Sugano J, et al. Homozygosity mapping of spinocerebellar ataxia with cerebellar atrophy and peripheral neuropathy to 9q33-34, and with hearing impairment and optic atrophy to 6p21-23. Eur J Hum Genet. 2000;8:986–90.PubMedCrossRefGoogle Scholar
- 10.Leigh RJ, Zee DS. The neurology of eye movements. New York: Oxford University Press; 2006.Google Scholar
- 12.Asaka T, Yokoji H, Ito J, Yamaguchi K, Matsushima A. Autosomal recessive ataxia with peripheral neuropathy and elevated AFP: novel mutations in SETX. Neurology. 2006;63:1581.Google Scholar
- 18.R Development Core Team. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2012.Google Scholar
- 20.Hothorn T, Hornik K, van de Wiel MA, Zeilis A. Implementing a class of permutation tests: the coin package. J Stat Soft. 2008;28(8):1–23.Google Scholar
- 21.Brunner E, Domhof S, Langer F. Nonparametric analysis of longitudinal data in factorial experiments. New York: Wiley; 2002.Google Scholar
- 22.Brunner E, Munzel U. The nonparametric Behrens–Fisher problem: asymptotic theory and a small sample approximation. Biomed J. 2000;42:17–25.Google Scholar
- 31.Solomon D, Ramat S, Leigh RJ, Zee D. A quick look at slow saccades after cardiac surgery: where is the lesion? In: Kennard C, Leigh RJ, editors. Using eye movements as an experimental probe of brain function—a symposium in honor of Jean Buttner-Ennever, vol. 171. Amsterdam: Elsevier; 2008. p. 587–90.CrossRefGoogle Scholar