These results derive from prevalence and incidence studies based on clinic records and databases (Pringsheim et al, 2012).

Some of the prevalence ranges and incidences may be overestimated because molecular genetic testing was discovered in mid-1990s and Huntington’s disease phenocopies could not be distinguished before.

The prevalence is lower in Asia (0.40 per 100000) than in Australia, North America and Europe (5.7 per 100000).

This is due to differences in CAG size and Huntingtin haplotypes distribution.

 

 

 

Venezuelan HD kindreds

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The highest prevalence in the world has been described in the Lake Maracaibo region of Venezuela. The Venezuelan HD kindreds encompass 18.149 individuals spanning 10 generations. (Wexler et al, 2004).

 

 

 

 

CAG repeat differences

 

 

CAG repeat size varies according to the country and these differences are statically significant (p<0.05). 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CAG allele distribution is biased in the different populations and this is explained by the ethnic and geographic differences in prevalence. For instance, 26 CAG repeat alleles are more frequent in a specific haplogroup. Protected haplogroup variants are more frequent in China and Japan and high-risk variants are more frequent in Europe.

 

 

 

 

CCG repeat sequence

 

 

CCG repeat sequence, which is adjacent to CAG repeat, is associated with prevalence.

 

CCG7 has been found in 85 % of Huntington’s disease alleles. It is in linkage disequilibrium with HD mutation (Pecheux et al, 1995). The CCG7 region is highly associated with CAG repeat in non-Asian population and CCG10 is strongly associated with CAG repeat in China and Japan. It might mean that ancestral lineages are different.