Role of factor XIII Val 34 Leu polymorphism in patients with migraine. 
At present, it is contradictory to determine if the combination of certain prothrombotic polymorphisms and migraine increases the risk to develop ischaemic cerebrovascular disease.  Recently, the common Val34Leu polymorphism of the A-chain factor XIII gene, associated with variations in factor XIII activity, has been suggested to play a significant role in the development of arterial and venous thrombotic disorders.  We analysed the prevalence of this polymorphism in 17 patients with coexisting ischaemic cerebrovascular disease and migraine (5 with aura, and 12 without aura), 89 patients with migraine (43 with aura, and 46 without aura), 116 patients with ischaemic cerebrovascular disease, and 467 healthy Caucasian controls from the South of Spain.  Genomic PCR amplification, using a mutated oligonucleotide, and allele-specific restriction assays were used for genotyping.  The factor XIII Leu 34 variant was present in 47.1; 40.5; 34.9; and 35.1% of patients with coexisting ischaemic cerebrovascular disease and migraine, ischaemic cerebrovascular disease, migraine, and control subjects, respectively.  These data suggest that the factor XIII Leu 34 allele does not play a protective role against these disorders in our population.