TABLE 1. CLASSIFICATION OF SCA VARIANTS.
There are currently 24 genetically distinct forms of SCA. The trinucleotide repeat disorders, SCA1-8, comprise 65–80% of diagnosed patients. The classifications labeled in grey are those tested for in Athena Diagnostic's Complete Ataxia Panel ($7,300). Adapted from Zumrova A. Problems and possibilities in the differential diagnosis of syndrome spinocerebellar ataxia. Neuro Endocrinol Lett 2005. 26(2): 98–108.
| SCA Class |
Percent of all ADCA |
Average Onset (years) |
Average Duration (year) |
ATAXIA and | Genetic/ Biochemical Defects |
|---|---|---|---|---|---|
| SCA1 | 6% (5–27) |
4th decade (<10 to >60) |
15 (10–28) |
Peripheral neuropathy Pyramidal signs |
6p23 CAG expansion Ataxin-1 |
| SCA2 | 15% (13–24) |
3rd-4th decade (<10 to >60) |
10 (1–30) |
Abnormal ocular saccades dementia Peripheral neuropathy |
12q24.1 CAG expansion Ataxin-2 |
| SCA3 | 21% (11–36) |
4th decade (10–70) | 10 (1–20) |
Pyramidal and extrapyramidal signs; lid retraction, nystagmus, decreased saccade velocity; amyotrophy sensory neuropathy |
14q24.3-q32.2 CAG expansion |
| SCA4 | Rare | 4th-5th decade (19–59) |
Decades | Sensory axonal neuropathy |
16q22.1 |
| SCA5 | Rare | 3rd-4th decade (10–68) |
>25 | Myokymia, nystagmus, and altered vibration sense; Early onset, slow course |
11p11.q11 CAG expansion not demonstrated as yet |
| SCA6 | 15% | 5th-6th decade (19–71) |
>25 | Slowly progressive ataxia; Sometimes episodic ataxia |
19p13 CAG expansion with altered alpha 1A subunit of the voltage-dependent calcium channel (CACLN1A4) |
| SCA7 | 5% | 3rd-4th decade (0.5–60) |
20 (1–45) |
Visual loss with retinopathy | 3p21.1-pl2 CAG expansion Ataxin-7 |
| SCA8 | 2–5% | 39 (18–65) |
Normal lifespan | Hyperreflexia, decreased vibration sense |
13q21 CTG expansion |
| SCA9 | Category not assigned | ||||
| SCA10 | Rare | 36 | nystagmus, occasional seizures | 22q13 | |
| SCA11 | Rare | 30 (15–70) |
Normal lifespan | Mild disorder ataxia | 1Sq14-q21.3 Mutation not identified |
| SCA12 | Rare | 33 (8–55) |
Pure spinocerebellar ataxia, late dementia |
5q31–q33 CAG expansion Protein phosphatase |
|
| SCA13 | Rare | Childhood | Unknown | Mild mental retardation, short stature |
19ql3.3–ql3.4 |
| SCA14 | Rare | 28 (12–42) |
Decades (1–30) |
Early axial myoclonus | 19ql3.4 Protein Kinase C, gamma type |
| SCA15 | Rare | 10–50 | Decades | Pure ataxia, very slow progression |
3pter-3p24.2 |
| SCA16 | Rare | 39 (20–66) |
1–40 | Head tremor | 8q22.1–q24.1 |
| SCA17 | Rare | 6–34 | >8 years | Mental deterioration | 6q27 TATA-box binding protein |
| SCA19 | Rare | 34 (20–45) |
Decades | Cognitive impairment, myoclonus, tremor |
1p21–q21 |
| SCA20 | Rare | 46 (19–64) |
Decades | Earlydysarthria, dystonia, dentate calcification |
11cen |
| SCA21 | Rare | 6–30 | Decades | Mild cognitive impairment | 7p21–15 |
| SCA22 | Rare | 10–46 | Decades | Slowly progressive ataxia | 1p21–q23 |
| SCA23 | Rare | 5th-6th decade |
>10years | Late-onset ataxia and sensory loss |
20p13–12.3 |
| SCA25 | Rare | 1.5–39 | Unknown | Sensory neuropathy | 2p21–p13 |
| DRPLA | Rare Japan – 20% |
8–20 or 40–60 |
Early onset correlates with shorter duration |
chorea, seizures, myoclonus, and dementia |
12p13.31 CAG expansion Atrophin-1 |