Timothy C. Hain, MD Page last modified: September 13, 2016
Supplemental material on the site DVD: Video of rebound nystagmus in SCA-6, (courtesy of Dr. Dario Yacovino).
SCA6 is an autosomal dominant ataxia associated with small expansions of a trinucleotide repeat (CAG) in the gene CACNL1A4, which encodes a voltage-gated calcium channel (Zoghbi, 1997). Another part of this gene also interacts with the cerebellum.
Patients with SCA6 can have at least three different syndromes: episodic ataxia, cerebellar ataxia plus brainstem or long tract degeneration, or pure cerebellar ataxia. Calcium channels are identified in Purkinje and granule neurons. Clinically they have a coarse gaze-evoked nystagmus, downbeat nystagmus on lateral gaze, and poor visual suppression (Gomez et al, 1997). The movie above shows a variant of their gaze-evoked nystagmus (rebound nystagmus).
SCA6 accounts for about 30% of dominant ataxias in Japan, and between 5-15% of dominantly inherited ataxia in the United States (Geshwind et al, 1997; Mosely et al, 1998). Imaging studies reveal cerebellar atrophy with relative sparing of the brainstem. In Japan, ataxia is the most common initial symptom.
Patients with prolonged courses exhibit dystonic postures, involuntary movements and abnormalities in tendon reflexes (Ikeuchi et al, 1997). Takeichi et al (2000) reported that while ocular smooth pursuit is diminished, vestibular cancellation is normal. This may be a distinctive finding of this condition. As mentioned above, patients with calcium channelopathies including SCA-6 and EA2 have deficient ocular responses to otolith input.
In Chicago, at Chicago Dizziness and Hearing, our otoneurologists are well equiped and ready to measure the oculomotor and balance consequences of SCA-6. Additionally, in Chicago, we are fortunate to have Dr. Christopher Gomez in the ataxia clinic at the University of Chicago, who is an expert on SCA6. (e.g. Gomez, 1993; Gomez et al, 1997)