Combined cis-regulator elements as important mechanism affecting FXII plasma levels.
BACKGROUND
Factor XII (FXII) deficiency is a recessive Mendelian trait due to mutations in the F12 gene. There is no bleeding associated with FXII deficiency, but FXII deficiency has been reported to be associated with risk of thrombosis in some studies.


METHODS
We examined the functional effect of two naturally-occurring mutations in two Spanish FXII deficient families: a C/G substitution at position -8, and a C/T substitution at position -13. Both mutations were located on a putative HNF4 binding site of F12 gene promoter. We also analyzed the F12 C46T polymorphism (rs1801020), associated with a decrease in the FXII levels, which also segregated in both families. A fragment containing each one of both -8 and -13 mutations, was cloned 5' of a reporter gene. We compared the in vitro expression of these constructs to the wild type expression.


RESULTS
Our analyses confirm that the -8C/G and the -13C/T mutations decreased expression levels, demonstrating that both mutations are involved in the observed FXII deficiency. In addition, electrophoretic shift analyses suggest that they alter the union of nuclear proteins to the promoter. Coinheritance of these mutations with the C46T polymorphism, result in a significant genotype-phenotype correlation.


CONCLUSIONS
We have identified two naturally-occurring mutations in the F12 promoter that drastically reduce FXII levels. Knowing rare genetic alterations in the F12 gene, together with the C46T common variant, may yield further understanding about the genetic architecture of FXII levels, which may have a role in the risk of thrombosis.
Unitat de Genòmica de Malalties Complexes, Institut de Recerca de l'Hospital de la Santa Creu i Sant Pau, Barcelona 08025, Spain.
Maria
M
Sabater-Lleal
Miguel
M
Chillón
Carolina
C
Mordillo
Angel
A
Martínez
Estel
E
Gil
José
J
Mateo
John
J
Blangero
Laura
L
Almasy
Jordi
J
Fontcuberta
José Manuel
JM
Soria
D002648:Child; D003001:Cloning, Molecular; D005174:Factor XII / Q000032:analysis* / Q000235:genetics*; D005175:Factor XII Deficiency / Q000097:blood* / Q000235:genetics*; D005260:Female; D017930:Genes, Reporter; D005838:Genotype; D006801:Humans; D008875:Middle Aged; D009154:Mutation; D010375:Pedigree; D010641:Phenotype; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic; D013030:Spain
D005174:Factor XII