In the present article, we address whether the
1278insTATC mutation had a single origin in the AJ
population and, if so, what the age is of the most recent
common ancestor (MRCA) of the mutation-bearing AJ
chromosomes. We have carried out this research through
haplotype analysis and modeling of the decay of allelic
association (linkage disequilibrium, LD) over time in a
2.8-cM region encompassing the HEXA locus. To this end,
we have used the observed distribution of allelic variants
of five flanking short tandem-repeat (STR) markers
(D15S981, D15S131, D15S1050, D15S197, D15S188) in
a sample of mutant and control chromosomes. In addition,
we have compared the estimated age with the minimum
age of the mutation that is compatible with the probability
of the current AJ frequency of 1278insTATC as a function
of its age, assuming no positive selection. This comparison
provides evidence for the non-compelling strength of
the heterozygote-advantage hypothesis.