Summary
We have previously reported that the 3363 inserted (Ins) C mutation in exon 6 of the
protein C gene was present in four unrelated French patients and in four French Canadian
families with type I protein C deficiency as well as in a large Vermont protein C
deficient kindred of French Canadian origin. The present study was designed to investigate
the likelihood of the existence of a founder effect for this mutation in protein C
deficient individuals of French origin living in France, Québec and Vermont. In order
to demonstrate a possible founder effect for the 3363 InsC mutation, we have previously
constructed a high-resolution genetic map to locate several highly polymorphic markers
close to the protein C locus. Thereafter, the markers D2S347, D2S2339, D2S383, D2S2271
and D2S2215 were genotyped in 117 heterozygotes from France (n = 7), Québec (n = 36)
or Vermont (n = 74). The allelic frequency distribution of these five markers was
also determined in fifty control French Canadian subjects and thirty-two unaffected
members of the Vermont kindred with normal protein C levels and compared with their
frequency in our cohort of heterozygotes. Our data suggest that patients from Québec
and Vermont carry a common haplotype at the protein C locus. Moreover, in order to
study the evolutionary history of the 3363 InsC mutation, we traced back the ascending
genealogy of one proband in each of the families with this mutation. These results
showed that the 3363 InsC mutation was most probably introduced in North America by
a couple of French settlers who established themselves in 1669 on Isle d‘Orleans located
near Québec City. All heterozygotes for the 3363 InsC mutation living in North America
are related to these founders within 10 generations. Thus, these families afford a
unique opportunity to evaluate the role of the protein C system in thrombophilia due
to the high degree of linkage disequilibrium at the protein C gene, which in essence
holds that variable more constant than in a more heterogeneous population.
Keywords
Protein C deficiency - thrombophilia - genetics