Multiple origins of a mitochondrial mutation conferring deafness

Area of Science:

• Genetics
• Mitochondrial DNA Research
• Human Evolution

Background:

• A specific mitochondrial DNA (mtDNA) point mutation (1555G) is linked to maternally inherited streptomycin hypersensitivity and sensorineural deafness.
• This mutation has been observed in diverse populations across China, Japan, Israel, and Africa.

Purpose of the Study:

• To investigate whether the widespread distribution of the 1555G mutation resulted from a single or multiple independent mutational events.
• To analyze the evolutionary origins and phylogenetic relationships of the 1555G mutation in different human populations.

Main Methods:

• Genetic distance analysis of 10 independent mtDNA D-loop sequences from Africa and Asia.
• Phylogenetic analysis to determine the evolutionary placement of 1555G-bearing haplotypes.
• Comparison of genetic distances between mtDNAs with the 1555G mutation and those with neutral or weakly deleterious mutations.

Main Results:

• High mtDNA sequence diversity (2.21%) was observed.
• Phylogenetic analysis placed 1555G-bearing haplotypes at divergent points in the human mtDNA evolutionary tree.
• The 1555G mutation frequently occurred on race-specific mtDNA haplotypes, inconsistent with recent introgression.

Conclusions:

• The simplest interpretation is that the 1555G mutation has multiple independent origins.
• The large genetic distance among mtDNAs bearing the 1555G mutation supports its origin on disparate mtDNA lineages subject to negative selection.
• The consistent association of the 1555G mutation with deafness across diverse genetic backgrounds confirms its pathogenicity.