Comorbid Migraine with Aura, Anxiety, and Depression Is Associated with Dopamine D2 Receptor (DRD2) NcoI Alleles

Abstract

Background

Unrelated individuals (n = 242) were interviewed directly for the presence of migraine, anxiety disorders, and major depression.

Materials and Methods

The data described in this study are derived from a clinical genetic relational database that was developed initially for the genetic analysis of migraine. Genotyping of the DRD2 NcoI C to T polymorphism located in exon 6 (His313His) was performed using previously described primers.

Results

A significantly increased incidence of migraine with aura (MWA), major depression, generalized anxiety disorder (GAD), panic attacks, and phobia was observed in individuals with the DRD2 NcoI C/C genotype compared with individuals with an DRD2 NcoI T allele. SpecificaUy, 69% (91/131) of DRD2 NcoI C/C individuals in the present study met criteria for at least one of these neuropsychiatrie disorders versus only 22% (4/18) of the DRD2 NcoI T/T individuals (Chi-square = 15.29; p < 0.00005). The DRD2 Atol C allele frequency is significantly higher (Chi-square = 17.13; p < 0.00002) in individuals with MWA, anxiety disorders, and/or major depression (C allele frequency = 0.80) than in individuals who have none of these disorders (C allele frequency = 0.67).

Conclusions

These data indicate that MWA, anxiety disorders, and major depression can be components of a distinct clinical syndrome associated with allelic variations within the DRD2 gene. Clinical recognition of this genetically based syndrome has significant diagnostic and therapeutic implications.

Introduction

Striking similarities exist between the epidemiological characteristics of migraine, anxiety, and depression (1–5). All three disorders afflict approximately 10% to 25% of the general population at some point in life and are approximately twice as common in females as in males. Prophylactic medications for all three disorders have a subacute onset of action, requiring 3 to 6 weeks of therapy to measure clinical improvement. In epidemiological studies, a clinical diagnosis of migraine significantly increases the risk of comorbid anxiety and depression (5–15). Taken together, these data suggest that a common metabolic variation may underlie comorbid migraine, anxiety and depression.

In a recent molecular genetic study, an association was observed between the NcoI polymorphism in exon 6 of the dopamine D2 receptor (DRD2) and the clinical susceptibility to migraine with aura (MWA) (16). We therefore performed an association analysis of DRD2 NcoI alleles in a group of 242 unrelated individuals, approximately half of whom suffer from MWA, anxiety disorders, and/or major depression. The present study was designed to analyze the possible association of DRD2 NcoI alleles with comorbid neuropsychiatrie disorders.

Materials and Methods

The data described in this study are derived from a clinical genetic relational database that was developed initially for the genetic analysis of migraine (17). Potential subjects were identified by physician or self-referral for a migraine genetic study. Subjects were evaluated using a semi-structured interview for migraine. Migraine evaluations were conducted by a neurologist and/or trained interviewer. The lifetime presence or absence was determined for each of the criteria in the International Headache Society (IHS) definition of MWA (18).

A semi-structured interview based on the Structured Clinical Interview for DSM-III-R (SCID) (19), modified to include the criteria of the Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) (20, 21) was used to evaluate anxiety and depressive disorders in the same individuals interviewed for migraine. The interview included questions that were appropriate to establish a DSM-IV-based diagnosis of generalized anxiety disorder (GAD), phobias, panic attacks, panic disorder, obsessive-compulsive disorder (OCD), and major depression. Interviews were performed by physicians or trained psychiatric nurses. Diagnoses required the concurrence of at least three physicians.

Genomic DNA was isolated using the Puregene DNA isolation kit (Gentra Systems, Research Triangle Park, NC). Genotyping of the DRD2 NcoI C to T polymorphism located in exon 6 (His313His) was performed using previously described primers (22). Briefly, 40 ng of genomic DNA was amplified in 10 µL of a solution containing IX Perkin Elmer PCR amplification buffer, 400 µM each dNTP, 0.5 U TaqGold polymerase (Perkin Elmer, Foster City, CA) and 1 µM primers DRD2.35 (ATCCTGCAGCCATGG) and DRD2.38 (ATTGTCCGGCTTTACC). The enzyme was activated with an initial incubation at 94°C for 10 min, followed by 14 cycles of amplification with denaturation at 94°C for 20 sec, annealing at 63°C for 1 min, elongation at 72°C for 30 sec with a decrease of 0.5°C and 3 sec for each annealing step, and an additional 40 cycles of denaturation at 94°C for 30 sec, annealing at 56°C for 30 sec and elongation at 72°C for 1 min. After amplification, 10 µL of a solution containing 2× NEB4 buffer and 2 U NcoI (New England Biolabs, Beverly, MA) were added directly to the amplification reaction and incubated at 37°C for greater than 4 hr. The digested products were separated on a 1.2% agarose SFR gel (Amresco, Solon, OH). Analysis of the genotype was performed by two individuals blinded to the clinical status.

Results

Clinical Characteristics of Individuals in this Study

Direct diagnostic interviews were completed on 242 unrelated individuals in the present study. The ethnic background of the study group was 98% Caucasian, 1% Asian, and 1% African-American A diagnosis was made only if the individual met DSM or IHS criteria for the disorders listed in Table 1. If a clear clinical diagnosis could not be made, the subject was not included in any further statistical analyses for that particular disorder. For each of the conditions analyzed, a diagnosis was made in at least 98% of the individuals. In the overall dataset, 55% (134/ 242) of individuals were diagnosed with at least one of the clinical disorders analyzed. As shown in Table 1, anxiety disorders are the most common diagnosis, being present in 46% (122/242) of the current dataset. Major depression is the single most common diagnosis (i.e., 38%) amongst the group of analyzed disorders in the present study. The incidences of panic attacks (31%) and phobia (29%) are similar. MWA is present in 21 % of the individuals. Panic disorder, GAD, and OCD are present in less than 20% of the current study group.

Table 1 Incidence of migraine with aura, anxiety disorders, and major depression

A distribution of the comorbidities is provided in Table 2. These data are consistent with previous reports on neuropsychiatrie comorbidities. For example, approximately 50% of individuals with MWA report a history of major depression (13, 13, 23). Individuals with panic attacks have the highest incidence of comorbid MWA (78%) in the present study.

Table 2 Comorbid incidence of migraine with aura, anxiety disorders, and major depression

Frequency of Neuropsychiatrie Disorders Based on DRD2 NcoI Genotypes

The incidences of the various clinical diagnoses based on DRD2 NcoI genotypes is provided in Table 3. A present or past history of MWA, anxiety disorders, or major depression is present in 69% of the C/C individuals, 53% of the C/T individuals, and 22% of the T/T individuals. The incidence of any of these neuropsychiatrie diagnoses is significantly higher in the C/C individuals when compared to either the C/T individuals (Chi-square = 6.53; p < 0.005), T/T individuals (Chi-square = 15.29; p < 0.00005), or the combined T/any group of individuals (Chi-square = 12.72; p < 0.0002).

Table 3 Incidence of migraine with aura, anxiety disorders, and major depression in current database based on DRD2 NcoI genotypes

The presence of an anxiety disorder is significantly more frequent in the C/C individuals than in either the C/T individuals (Chi-square = 3.87; p < 0.02), T/T individuals (Chi-square = 8.92; p < 0.001), or the combined T/any group of individuals (Chi-square = 7.20; p < 0.004). A similar pattern is seen with GAD. Major depression, panic attacks, MWA, and phobia are also all increased significantly in the C/C versus T/any individuals (Table 3). Although both panic disorder and OCD are more frequent in the C/C versus T/any individuals, the difference does not reach statistical significance. However, OCD is more frequent in the C/C individuals than in the T/T individuals (Chi-square = 2.84; p < 0.05).

DRD2 NcoI Allele Frequencies in Neuropsychiatrie Disorders in this Study

DRD2 NcoI allele frequencies were determined in individuals based on the presence or absence of the neuropsychiatrie disorders analyzed in the present study (Table 4). In individuals with MWA, anxiety disorders, and/or major depression, the C allele frequency is 0.80 and the T allele frequency is 0.20. In individuals who have none of these neuropsychiatrie disorders, the C allele frequency is 0.63, and the T allele frequency is 0.37. The difference in the DRD2 NcoI C allele frequencies between these two groups of individuals is highly significant (Chi-square = 17.13; p < 0.00002). These data are consistent with the allele frequencies reported in the general Caucasian population where the C allele frequency was reported to be 0.69 and the T allele frequency was reported to be 0.31 (22).

Table 4 DRD2 Nco I allele frequencies in individuals with or without migraine with aura, anxiety disorders, or major depression

Discussion

The major finding of the present study is that the incidence of the clinical diagnoses of MWA, anxiety disorders, and major depression are comor-bidly associated with the NcoI polymorphism within the DRD2 gene. This is the first known association study of the DRD2 NcoI polymorphism in neuropsychiatrie disorders. As demonstrated in the present study, individuals with migraine, anxiety, and/or depression display an increased frequency of the DRD2 NcoI C/C genotype compared to individuals with the C/T or T/T genotype. These data represent the first direct evidence to suggest that a specific genetic variant may, at least partially, underlie the well-documented comorbidity of migraine, anxiety disorders, and major depression (5–15).

Multiple previous association studies of other DRD2 polymorphisms have focused on other neuropsychiatrie disorders. For example, the DRD2 TaqI A1 allele was reported to be a risk factor in the polygenic inheritance of Tourette’s syndrome, stuttering, attention deficit hyperactivity, conduct and oppositional defiant disorder (24). In the early 1990s, numerous groups reported an association between the DRD2 TaqI A1 allele and alcoholism (25–34), although the putative association was not confirmed by other investigators (35–39). Numerous reviews of all available data have tended to conclude that an association probably does exist between the DRD2 variants and certain forms of alcoholism (40–43).

Significant associations have also been reported between DRD2 polymorphisms and poly-substance substance abuse (43–47). A single report suggested an association between the S311C variant of the DRD2 receptor and schizophrenia (48), although this finding was not confirmed by other investigators (49–51). Individuals with the DRD2 HphI B2 allele were reported to display a decrease in mature, and an increase in neurotic and immature, defense styles compared to individuals without this DRD2 allele (52). Thus, a variety of DRD2 polymorphisms have been associated with numerous neuropsychiatrie disorders. A key unanswered question concerns the possible mechanism by which these polymorphisms might affect gene function.

In postmortem brain samples, Taq A DRD2 alleles are associated with variations in the density of DRD2 binding sites (26). No data exist at present on the effect of NcoI polymorphisms on DRD2 expression. Conceivably, intragenic nucleotide variations may result in functional variations in RNA stability or efficacy in transcription (53), thus resulting in alterations in the density of the expressed receptor protein. For example, recent data suggest that noncoding region variations within the 5-hydroxytryptamine transporter (5-HTT) gene may alter expression of the transporter (54). Specifically, the transcriptional efficiency of the short variant of the 5-HTT gene is reduced compared to the long version of the gene (55). In addition, intragenic nucleotide variations may also exist within a gene that could result in functional variations in splicing and/or RNA stability (53), thus resulting in alterations in the density of the expressed protein. In the case of monoamine oxidase A, for example, noncoding region variations have been shown to result in a 30-fold difference in enzymatic activity (56). Alternatively, the NcoI polymorphism analyzed in the present report may lie in linkage disequilibrium with a more directly causative mutation. However, a specific molecular variation within the DRD2 gene which could underlie functional variations in the expressed receptor protein remains unidentified (57). Future studies are needed to more clearly define the possible functional significance of noncoding region variations within the DRD2 gene.

The association data reported in the present study confirm and extend multiple previous epidemiological studies on migraine and psychiatric comorbidities (5–15). In a study of 133 index cases with major depression versus control index cases and their first-degree relatives (6), a strong association was observed between migraine and depression. Specifically, in the first-degree relatives of control subjects, the incidence of migraine (7%) and depression (10%) was significantly lower than the incidence of migraine (22%) and depression (19%) in the first-degree relatives of depressed subjects. If an index case had both migraine and depression, the individual had a 75% chance of having a comorbid anxiety disorder (6). No association with migraine was found for alcoholism, substance abuse, antisocial personality, obsessive-compulsive disorder or schizophrenia. The authors concluded that“depression may be either a sequela of migraine or the diathesis which results in both migraine and depression.”However, they“could not definitely resolve whether the source of correlation between the two disorders was attributable to a transmissible or a non-transmissible common component or both.”

An association between migraine and depression was also demonstrated in a study of an unselected epidemiological sample with a standardized assessment of psychiatric diagnoses (7). Migraine patients were noted to have a significantly increased incidence of major depression, bipolar spectrum, general anxiety, panic disorder and phobias. The migraine subjects reported a significantly earlier onset of anxiety symptoms than nonmigraine subjects as evidenced by a high incidence of being more anxious than their peers during childhood. The authors suggested that“migraine with anxiety and depression may constitute a distinct syndrome comprising anxiety, often manifested in early childhood, followed by the occurrence of migraine headaches, and then by discrete episodes of depressive disorder in adulthood”(7).

A prospective study has also documented an association between migraine and depression/ anxiety (23) wherein a history of migraine was found to carry a 4-fold increased incidence of depression. These authors also found a temporal pattern with anxiety preceding migraine, followed by depression (8) and concluded that migraine, anxiety disorders and major depression might share common predispositions,“although the nature of these predispositions remains to be determined”(23). By contrast, the present study provides strong evidence for a shared genetic predisposition to comorbid migraine, anxiety and depression.

In conclusion, the present data indicate that MWA, anxiety disorders and major depression are comorbidly associated with the NcoI polymorphism within the DRD2 gene. As a result, these disorders should not necessarily be considered as independent disorders. Rather, the data indicate that a distinct clinical syndrome may be expressed as a manifestation of a single underlying genetic variation. The clinical recognition that all three disorders may be associated with the same genetic variant has significant diagnostic and therapeutic implications since DRD2 antagonists have been shown to be effective therapeutic agents for a subset of individuals with these common disorders.