Table 1 The canonical repeat in the SCA31 locus is a short TAAAA penta-nucleotide repeat, usually of 8–20 repeats

From: Spinocerebellar ataxia type 31 (SCA31)

 

Repeat configurations

Allele frequency(%)

Pathogenic?

Japanese

(TAAAA)8~20

99.6a

No

(TAGAA)n(TAAAATAGAA)n expansion

0.24a

No

(TGGAA)n(TAGAA)n(TAAAATAGAA)n expansion

0.003b

Yes

European Caucasiansc

(TAAAA)8~20

94.5

No

(TACAA)n

5.5

No

(TAACA)n

  

(TGAAA)n

  

(GAAAA)n

  
  1. However, a long, complex repeat consisting of (TAAAA)n(TAGAA)n(TAAAATAGAA)n are rarely seen in Japanese. In SCA31 patients, (TGGAA)n in conjunction with (TAAAA)n(TAGAA)n(TAAAATAGAA)n is seen. Assuming that the disease frequency of SCA31 is around 0.003% of general Japanese population, the frequency of (TAAAA)n(TAGAA)n(TAAAATAGAA)n is much higher than that of SCA31 founder chromosome.
  2. In Caucasian population, different repeats such as (TACAA)n, (GAAAA)n, (TGAAA)n, and (TAACA)n are seen. The frequency of these repeats are very high (5.5% of general population).
  3. aNumbers came from actual data on >1000 chromosomes
  4. bCalculated by assuming the disease frequency of SCA31 as 0.003% of general population, at the very most.
  5. cNumebrs came from actual data on >1400 healthy and ataxia chromosomes
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