Genome-wide association study of migraine implicates a common susceptibility variant on 8q22.1

Migraine is a common episodic neurological disorder, typically presenting with recurrent attacks of severe headache and autonomic dysfunction. Apart from rare monogenic subtypes, no genetic or molecular markers for migraine have been convincingly established. We identified the minor allele of rs1835740 on chromosome 8q22.1 to be associated with migraine (p=5.12 × 10⁻⁹, OR 1.23 [1.150-1.324]) in a genome-wide association study of 2,748 migraineurs from three European headache clinics and 10,747 population-matched controls. The association was replicated in 3,202 cases and 40,062 controls for an overall meta-analysis p-value of 1.60 × 10⁻¹¹ (OR 1.18 [1.127 – 1.244]). rs1835740 is located between the astrocyte elevated gene 1 (MTDH/AEG-1) and plasma glutamate carboxypeptidase (PGCP). In an expression quantitative trait study in lymphoblastoid cell lines transcript levels of the MTDH/AEG-1 were found to have a significant correlation to rs1835740. Our data establish rs1835740 as the first genetic risk factor for migraine.

A visual migraine aura locus maps to 9q21-q22

OBJECTIVE

To identify susceptibility loci for visual migraine aura in migraine families primarily affected with scintillating scotoma type of aura.

METHODS

We included Finnish migraine families with at least 2 affected family members with scintillating scotoma as defined by the International Criteria for Headache Disorders-II. A total of 36 multigenerational families containing 351 individuals were included, 185 of whom have visual aura and 159 have scintillating scotoma. Parametric and nonparametric linkage analyses were performed with 378 microsatellite markers. The most promising linkage loci found were fine-mapped with additional microsatellite markers.

RESULTS

A novel locus on chromosome 9q22-q31 for migraine aura was identified (HLOD = 4.7 at 104 cM). Fine-mapping identified a shared haplotype segment of 12 cM (9.8 Mb) on 9q21-q22 among the aura affected. Four other loci showed linkage to aura: a locus on 12p13 showed significant evidence of linkage, and suggestive evidence of linkage was detected to loci on chromosomes 5q13, 6q25, and 13q14.

CONCLUSIONS

A novel visual migraine aura locus has been mapped to chromosome 9q21-q22. Interestingly, this region has previously been linked to occipitotemporal lobe epilepsy with prominent visual symptoms. Our finding further supports a shared genetic background in migraine and epilepsy and suggests that susceptibility variant(s) to visual aura for both of these traits are located in the 9q21-q22 locus.

Genetic association study of endothelin-1 and its receptors EDNRA and EDNRB in migraine with aura

The effect of endothelin-1 and its receptors EDNRA and EDNRB in migraine with aura (MA) susceptibility is not established yet. We studied the association between the MA end-diagnosis and three migraine trait components and 32 single nucleotide polymorphisms (SNPs) capturing the variation of endothelin genes in 850 Finnish migraine patients and 890 non-migrainous individuals. The SNPs showing evidence of association were further studied in 648 German migraine patients and 651 non-migrainous individuals. No significant association was detected. However, the homozygous minor genotype (5% in cases) of the EDNRA SNP rs2048894 showed nominal association with MA both in the Finnish sample (P = 0.015) and in the pooled sample [odds ratio (OR) 1.61, 95% confidence interval (CI) 1.12-2.32, P = 0.010] when adjusted for gender and sample origin. The trait age of onset < 20 years was also associated with rs2048894 (OR 1.69, 95% CI 1.13-2.54, P = 0.011) in the pooled sample. To confirm this finding studies on even larger samples are required.

Consistently replicating locus linked to migraine on 10q22-q23

Here, we present the results of two genome-wide scans in two diverse populations in which a consistent use of recently introduced migraine-phenotyping methods detects and replicates a locus on 10q22-q23, with an additional independent replication. No genetic variants have been convincingly established in migraine, and although several loci have been reported, none of them has been consistently replicated. We employed the three known migraine-phenotyping methods (clinical end diagnosis, latent-class analysis, and trait-component analysis) with robust multiple testing correction in a large sample set of 1675 individuals from 210 migraine families from Finland and Australia. Genome-wide multipoint linkage analysis that used the Kong and Cox exponential model in Finns detected a locus on 10q22-q23 with highly significant evidence of linkage (LOD 7.68 at 103 cM in female-specific analysis). The Australian sample showed a LOD score of 3.50 at the same locus (100 cM), as did the independent Finnish replication study (LOD score 2.41, at 102 cM). In addition, four previously reported loci on 8q21, 14q21, 18q12, and Xp21 were also replicated. A shared-segment analysis of 10q22-q23 linked Finnish families identified a 1.6-9.5 cM segment, centered on 101 cM, which shows in-family homology in 95% of affected Finns. This region was further studied with 1323 SNPs. Although no significant association was observed, four regions warranting follow-up studies were identified. These results support the use of symptomology-based phenotyping in migraine and suggest that the 10q22-q23 locus probably contains one or more migraine susceptibility variants.

The enhancement of homogenous mass extension reaction: comparison of two enzymes

Reliable and efficient PCR and extension reactions using standardized procedures are key elements for successful single nucleotide polymorphism (SNP) genotyping projects. To improve the cost efficiency and overall performance of SNP genotyping we evaluated two commercial thermostable DNA polymerases used for the extension reaction in the homogeneous mass extension MassARRAY genotyping system. The aim was to study whether the quality, accuracy, and expenses of a new TERMIPol DNA polymerase are competitive to the commonly used ThermoSequenase DNA polymerase. We compared the enzymes by testing 96 SNPs genotyped for DNA samples of 31 unrelated individuals and one water control. The success rates, congruence between the genotypes and completeness of extension reactions support the use of TERMIPol, especially when the amplification of the higher mass allele is difficult. Further, using TERMIPol enabled successful genotyping (>93%) of several SNPs that failed (<80% success) when using ThermoSequenase.