Polymorphisms at six distinct Alu insertion loci (ACE, APO, FXIIIB, TPA25,
A25 and B65) were examined in three north-east Piedmont human populations:
Postua, a village of 570 inhabitants with partial geographical and, in the past, cultural
isolation, closed to immigration, with a high degree of marriages between relatives; as
control, two neighbouring urban agglomerates, Cavaglià, an agricultural town of
3,680 residents, and Biella, an industrial city of 47,000 inhabitants, were considered.
Significant deviations from the Hardy-Weinberg equilibrium were never
observed, except for the locus ACE in Postua and Cavaglià populations and for the
locus B65 in Biella. Five loci out of six showed for Postua insertion frequency values
lower than those observed for Cavaglià and Biella. Postua presented, for all loci, an
average heterozygosity (0.291±0.003) lower than Cavaglià (0.329±0.002) and Biella
(0.343±0.003). The average FST value were low (0,038), indicating that the variance of
Alu insertion frequencies is mainly due to differences within populations rather than
between populations.
The Alu insertion frequency data were analysed along with data available in the
literature relatively to other 7 European populations, and a Neighbor-Joining tree was
constructed: Postua occupied a basal position, followed by Cavaglià and Biella.
Moreover, the principal components analysis places Postua in a relatively isolated
position with respect to Cavaglià, Biella and the other European populations.
Our analysis depicts Postua as characterised by low genetic heterogeneity, with
lower Alu insertion frequencies and average heterozigosity values, compared to the
control populations. Cultural factors, like the tradition to get married within the
community, with consequent increasing of the consanguinity among inhabitants, and a
partial isolation that Postua maintained, at least in the past, could have contributed to
determine the current genetic structure of this population.
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