Analysis of NOS Gene Polymorphisms in Relation to Cluster Headache and Predisposing Factors in Sweden

Combined genotype of HCRTR2 and CLOCK variants in a large family of cluster headache with familial periodicity phenotype

PURPOSE

Cluster headache (CH) is a debilitating condition with severe and recurrent headaches characterized by circannual and circadian rhythms. A genetic contingent was suggested, and several loci were described in large cohorts. However, no variant associated with CH for multiplex families has been described. The purpose of our study was to examine candidate genes and new genetic variants in a multigenerational family of cluster headaches in which two members have original chronobiological characteristics that we have called the phenomenon of "family periodicity".

METHODS AND RESULTS

We performed a whole genome sequencing in four patients in a large multigenerational family of cluster headache to identify additional loci associated with CH. This allowed us to replicate the genomic association of HCRTR2 and CLOCK as candidate genes. In two family members with the same phenotypic circadian pattern (familial periodicity) the association of polymorphism NM_001526.4:c.922G > A was shown in the HCRTR2 gene, and NM_004898.4:c.213T > C in the CLOCK gene.

INTERPRETATION

This whole genome sequencing reproduced two genetic risk loci for CH already involved in its pathogenicity. This is the first time that the combination of HCRTR2 and CLOCK gene variants is identified in a multigenerational family of CH with striking periodicity characteristics. Our study supports the hypothesis that the combination of HCRTR2 and CLOCK gene variants can contribute to the risk of cluster headache and offer the prospect of a new area of research on the molecular circadian clock.

Association of Single-Nucleotide Polymorphisms Rs2779249 (chr17:26128581 C>A) and Rs rs2297518 (chr17: chr17:27769571 G>A) of the NOS2 Gene with Tension-Type Headache and Arterial Hypertension Overlap Syndrome in Eastern Siberia

Inducible nitric oxide (NO) synthase (iNOS), encoded by the NOS2 gene, promotes the generation of high levels of NO to combat harmful environmental influences in a wide range of cells. iNOS can cause adverse effects, such as falling blood pressure, if overexpressed. Thus, according to some data, this enzyme is an important precursor of arterial hypertension (AH) and tension-type headache (TTH), which are the most common multifactorial diseases in adults. The purpose of this study was to investigate the association of rs2779249 (chr17:26128581 C>A) and rs2297518 (chr17: chr17:27769571 G>A) of the NOS2 gene with TTH and AH overlap syndrome (OS) in Caucasians in Eastern Siberia. The sample size was 91 participants: the first group-30 patients with OS; the second group-30 patients AH; and the third group-31 healthy volunteers. RT-PCR was used for the determination of alleles and genotypes of the SNPs rs2779249 and rs2297518 of the NOS2 gene in all groups of participants. We showed that the frequency of allele A was significantly higher among patients with AH compared with healthy volunteers (p-value < 0.05). The frequency of the heterozygous genotype CA of rs2779249 was higher in the first group vs. the control (p-value = 0.03), and in the second group vs. the control (p-value = 0.045). The frequency of the heterozygous genotype GA of rs2297518 was higher in the first group vs. the control (p-value = 0.035), and in the second group vs. the control (p-value = 0.001). The allele A of rs2779249 was associated with OS (OR = 3.17 [95% CI: 1.31-7.67], p-value = 0.009) and AH (OR = 2.94 [95% CI: 1.21-7.15], p-value = 0.015) risks compared with the control. The minor allele A of rs2297518 was associated with OS (OR = 4.0 [95% CI: 0.96-16.61], p-value = 0.035) and AH (OR = 8.17 [95% CI: 2.03-32.79], p-value = 0.001) risks compared with the control. Therefore, our pilot study demonstrated that the SNPs rs2779249 and rs229718 of the NOS2 gene could be promising genetic biomarkers for this OS risk in Caucasians from Eastern Siberia.

Evidence That HFE H63D Variant Is a Potential Disease Modifier in Cluster Headache

Cluster headache (CH) is a primary headache disorder with a complex genetic background. Several studies indicate a potential link between iron homeostasis and the pathophysiology of primary headaches. The HFE gene encodes for a protein involved in iron metabolism, while genetic variants in HFE have been associated with hereditary hemochromatosis (HH), an iron overload disorder. The objective of the current study was to examine the association of the more common HFE H63D variant, with the susceptibility to develop CH and diverse clinical phenotypes in a population of Southeastern European Caucasian (SEC) origin. Genomic DNA samples from 128 CH patients and 294 neurologically healthy controls were genotyped for the HFE rs1799945 (H63D) variant. H63D genotypic and allelic frequency distribution did not differ significantly between patients and controls (p > 0.05). Subgroup analysis revealed a significantly more frequent occurrence of the variant G allele in chronic compared to episodic CH patients, indicative for a possible correlation of the HFE gene with the susceptibility for disease chronification. Although homozygosity for the less prevalent H63D variant G allele was minimal in the CH cohort, the results of the present study are in accordance with previous studies in CH and migraine patients, suggesting that HFE H63D variant modifies the disease clinical characteristics. Hence, despite the absence of a per se association with CH susceptibility in the current SEC cohort, variability in HFE gene may be potentially regarded as a disease modifier genetic factor in CH.