Table 2. [SCAs with a Pure Cerebellar Phenotype to Consider in the Differential Diagnosis of SCA37]. - GeneReviews®

Disorder	Gene	Phenotype	Comments
SCA5 (OMIM 600224)	SPTBN2	Pure slowly progressive cerebellar syndrome Onset age range: 10-68 yrs; congenital & infantile onset also reported Downbeat nystagmus, impaired smooth pursuit, & gaze-evoked nystagmus	Slower progression than in SCA37; persons w/SCA5 remain ambulatory despite long disease duration.
SCA6	CACNA1A	Adult-onset slowly progressive ataxia Mild vibratory sensory loss Occasional dysphagia Horizontal & vertical nystagmus Abnormal vestibuloocular reflex Rare oculomotor findings in presymptomatic persons: Low-amplitude horizontal gaze-evoked nystagmus Significantly ↓ eye velocity for upward saccades Abnormal frequency of square-wave jerks ↓ gain for pursuit tracking	Positional vertigo, downbeat nystagmus, & external ophthalmoplegia also reported in SCA6; not reported in SCA37. Persons w/presymptomatic SCA37 may also have ↓ gain for pursuit tracking, but in SCA37 saccade velocity is normal & eye movement abnormalities initially affect the vertical axis.
SCA11	TTBK2	Relatively pure form of SCA
SCA26 (OMIM 609306)	EEF2	Pure SCA Irregular visual pursuit movements	Dysmetric ocular saccades, slow optokinetic nystagmus, & anticipation not reported in SCA26
SCA30 (OMIM 613371)	Unknown ¹	Relatively pure, slowly progressive SCA Hypermetric saccades (typically horizontal & into downgaze) Normal vestibuloocular reflex gain	Phenotype overlaps w/SCA37.
SCA31 (OMIM 117210)	BEAN1	Pure cerebellar syndrome Variable hearing loss of cochlear origin	Hearing loss of cochlear origin was reported in 1 person w/SCA37 but did not appear related to SCA37.

Disorder

Gene

Phenotype

Comments

SCA5 (OMIM 600224)

SPTBN2

Pure slowly progressive cerebellar syndrome
Onset age range: 10-68 yrs; congenital & infantile onset also reported
Downbeat nystagmus, impaired smooth pursuit, & gaze-evoked nystagmus

Slower progression than in SCA37; persons w/SCA5 remain ambulatory despite long disease duration.

SCA6

CACNA1A

Adult-onset slowly progressive ataxia
Mild vibratory sensory loss
Occasional dysphagia
Horizontal & vertical nystagmus
Abnormal vestibuloocular reflex
Rare oculomotor findings in presymptomatic persons:
- Low-amplitude horizontal gaze-evoked nystagmus
- Significantly ↓ eye velocity for upward saccades
- Abnormal frequency of square-wave jerks
- ↓ gain for pursuit tracking

Positional vertigo, downbeat nystagmus, & external ophthalmoplegia also reported in SCA6; not reported in SCA37.
Persons w/presymptomatic SCA37 may also have ↓ gain for pursuit tracking, but in SCA37 saccade velocity is normal & eye movement abnormalities initially affect the vertical axis.

SCA11

TTBK2

Relatively pure form of SCA

SCA26 (OMIM 609306)

EEF2

Pure SCA
Irregular visual pursuit movements

Dysmetric ocular saccades, slow optokinetic nystagmus, & anticipation not reported in SCA26

SCA30 (OMIM 613371)

Unknown ¹

Relatively pure, slowly progressive SCA
Hypermetric saccades (typically horizontal & into downgaze)
Normal vestibuloocular reflex gain

Phenotype overlaps w/SCA37.

SCA31 (OMIM 117210)

BEAN1

Pure cerebellar syndrome
Variable hearing loss of cochlear origin

Hearing loss of cochlear origin was reported in 1 person w/SCA37 but did not appear related to SCA37.

From: Spinocerebellar Ataxia Type 37

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Adam MP, Feldman J, Mirzaa GM, et al., editors.

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