Figure 1.

Unexpanded genotype frequency distribution at the ataxin-2 gene in 2695 NM Cuban chromosomes and frequency of large ANs in Cuba vs different populations. (a) CAG distribution at the SCA2 locus of the ANs in the Cuban population related to SCA2 families (NM). The distribution is skewed toward large ANs. The shortest alleles found are those sized 13 and 14 CAG and the largest are 30 and 31 CAG. Alleles with >23 CAG repeats are over-represented over all large and short ANs. (b) Comparison of the CAG size frequency of large ANs in Cuba vs other populations. Allele frequencies in Cuba were grouped by CAG size; frequencies of large normal allele (>22 CAG) and other alleles (≤22 CAG) were compared with the frequency of large ANs in other populations by χ² or Fisher's exact test. Frequencies were tabulated in a 2 × 2 contingency table with 2 d.f. for comparison. Because the frequency of alleles sized 22 CAG may be higher with respect to both groups, short (<22 CAG) and large alleles (>22 CAG), we also applied a component analysis by χ² and Fisher's exact test, excluding such alleles, and included in the table only alleles either >22 CAG or <22 CAG. In the table each line shows the frequency of large ANs in each population and the resulting comparison of the frequency of each allele when grouped according to CAG cutoff (ie, >22 CAG, >23 CAG, >24 CAG, and so on). Frequencies of alleles in each region were taken from the literature as shown in the table and the Cuban frequency was determined in the current work.