Origins and Spread of Machado-Joseph Disease Ancestral Mutations Events

Area of Science:

• Genetics and Human Evolution
• Neurology and Neurodegenerative Diseases

Background:

• Machado-Joseph disease (MJD), an autosomal dominant spinocerebellar ataxia, exhibits significant global prevalence disparities.
• Understanding MJD's ancestral origins and mutation spread is key to explaining its varied geographic distribution.

Purpose of the Study:

• To investigate the ancestral origins and evolutionary pathways of Machado-Joseph disease mutational events.
• To elucidate the genetic factors contributing to the differential prevalence of MJD across populations.

Main Methods:

• Phylogenetic analysis utilizing SNP-based haplotypes (TTACAC, GTGGCA, TTAGAC, TTGGAC, GTGCCA).
• Comparative analysis of flanking markers to assess the independence of mutational events.
• Haplotype studies to trace the geographic origins and dispersal of MJD lineages.

Main Results:

• Identified two primary independent MJD expansion events on distinct haplotype backgrounds: Joseph (TTACAC) and Machado (GTGGCA).
• The Joseph lineage, likely Asian in origin, spread to Europe, with founder effects driving high prevalence in specific Portuguese populations.
• The Machado lineage is primarily found in Portugal; other observed haplotypes suggest introduction, not independent origins, with low mutation rates at the locus.

Conclusions:

• Machado-Joseph disease arose from at least two distinct mutational events.
• The global distribution of MJD is largely explained by the dispersal of the Joseph lineage from Asia and subsequent founder effects in Europe.
• Evidence supports a very low mutation rate at the MJD repeat expansion locus.