The involvement of GSK3beta in bipolar disorder: integrating evidence from multiple types of genetic studies

We aimed to get a comprehensive insight into the genetic evidence supporting the role of GSK3beta in bipolar disorder (BD). Using broad searches in NCBI's PubMed and the Genetic Association Database we looked for association, whole-genome linkage, genome-wide association, gene expression, pharmocogenomic, epigenetic, cytogenetic, and mouse model studies performed for BD until July 2009. Per gene, we rated the degree of converging evidence across these types of genetic studies. The genes most consistently associated with BD in the genetic studies we reviewed were GSK3beta , GRK3, 5-HTTLPR, GRIN3, COMT, and GLUR3. GSK3beta stood out as it was implicated in at least five types of genetic studies. Although our results are limited by design differences of included studies and possibly by publication bias, GSK3beta is a plausible candidate gene for BD from a pharmacological and a genetic perspective. Future studies investigating the effects of GSK3beta manipulation in BD seem warranted.

"Forward genetics" as a method to maximize power and cost-efficiency in studies of human complex traits

There is increasing interest in methods to disentangle the relationship between genotype and (endo)phenotypes in human complex traits. We present a population-based method of increasing the power and cost-efficiency of studies by selecting random individuals with a particular genotype and then assessing the accompanying quantitative phenotypes. Using statistical derivations, power- and cost graphs we show that such a “forward genetics” approach can lead to a marked reduction in sample size and costs. This approach is particularly apt for implementing in epidemiological studies for which DNA is already available but the phenotyping costs are high.

An association screen of myelin-related genes implicates the chromosome 22q11 PIK4CA gene in schizophrenia

Several lines of evidence, including expression analyses, brain imaging and genetic studies suggest that the integrity of myelin is disturbed in schizophrenia patients. In this study, we first reconstructed a pathway of 138 myelin-related genes, all involved in myelin structure, composition, development or maintenance. Then we performed a two-stage association analysis on these 138 genes using 771 single nucleotide polymorphisms (SNPs). Analysis of our data from 310 cases vs 880 controls demonstrated association of 10 SNPs from six genes. Specifically, we observed highly significant P-values for association in PIK4CA (observed P=6.1 x 10(-6)). These findings remained significant after Bonferroni correction for 771 tests. The PIK4CA gene is located in the chromosome 22q11 deletion syndrome region, which is of particular interest because it has been implicated in schizophrenia. We also report weak association of SNPs in PIK3C2G, FGF1, FGFR1, ARHGEF10 and PSAP (observed P<or=0.01). Our approach--of screening genes involved in a particular pathway for association--resulted in identification of several, mostly novel, genes associated with the risk of developing schizophrenia in the Dutch population.

The genetics of symptom dimensions of schizophrenia: review and meta-analysis

BACKGROUND

The use of symptom dimensions of schizophrenia as quantitative phenotypes has been proposed as a mean to reduce the heterogeneity of schizophrenia and facilitate genetic research. However, the genetic background of symptom dimensions is not clear.

AIM

We aim to investigate whether the symptom dimensions "reality distortion", "psychomotor poverty" and "disorganization" are heritable phenotypes.

METHOD

We performed a Medline search including all papers from 1980 to August 2007. In addition to reviewing the articles, we performed meta-analyses on these studies where possible.

RESULTS

We identified 18 relevant papers. Only the studies on affected sibling pairs were suitable for meta-analysis. Data from twin and affected sibling studies are consistent with a genetic contribution to the disorganization dimension. However these studies did not unequivocally support a large genetic contribution to neither the reality distortion symptom dimension nor to the psychomotor poverty symptom dimension. In contrast several molecular genetic studies did report associations of genes with psychomotor poverty.

CONCLUSIONS

These data suggest that only the disorganization symptom dimension may provide an useful alternative phenotype for genetic research. More research is required to make any definitive conclusions.

CNTNAP2 gene dosage variation is associated with schizophrenia and epilepsy

A homozygous mutation of the CNTNAP2 gene has been associated with a syndrome of focal epilepsy, mental retardation, language regression and other neuropsychiatric problems in children of the Old Order Amish community. Here we report genomic rearrangements resulting in haploinsufficiency of the CNTNAP2 gene in association with epilepsy and schizophrenia. Genomic deletions of varying sizes affecting the CNTNAP2 gene were identified in three non-related Caucasian patients. In contrast, we did not observe any dosage variation for this gene in 512 healthy controls. Moreover, this genomic region has not been identified as showing large-scale copy number variation. Our data thus confirm an association of CNTNAP2 to epilepsy outside the Old Order Amish population and suggest that dosage alteration of this gene may lead to a complex phenotype of schizophrenia, epilepsy and cognitive impairment.

Investigating gene environment interaction in complex diseases: increasing power by selective sampling for environmental exposure

BACKGROUND

The often limited influence of disease associated alleles on the vulnerability to complex diseases has lead to increased interest in environmental interaction with genotype. However, gene environmental interactions (GEIs) are not easily studied, since high numbers of subjects are required to detect GEI.

METHODS AND RESULTS

This study provides a potential useful method to increase the power of such studies through selective sampling for environmental exposure. We show that selecting the top and bottom 10% regarding environmental exposure can lead to a 70% reduction in the required number of subjects for genotyping.

CONCLUSION

This study demonstrates the potential usefulness of selective sampling in the study of the interplay between genes and environment. The reduction of required subjects can be particularly advantageous in studies where genotyping is extensive, such as in whole genome screens or in studies where phenotyping is expensive.

Involvement of the CACNA1A gene containing region on 19p13 in migraine with and without aura

OBJECTIVE

To assess the involvement of the 19p13 familial hemiplegic migraine (FHM) locus in migraine with and without aura.

BACKGROUND

Migraine with and without aura are likely to be polygenetic multifactorial disorders. FHM is a rare dominantly inherited type of migraine with aura. In about 50% of families, FHM is caused by mutations in the P/Q-type calcium channel alpha(1A)-subunit (CACNA1A) gene on chromosome 19p13. The CACNA1A gene is thus a good candidate gene for "nonhemiplegic" migraine with or without aura.

METHODS

The authors performed an affected sibpair analysis using flanking and CACNA1A intragenic markers. The authors assessed the occurrence of shared parental marker alleles among 189 affected siblings from 36 extended families with typical migraine with or without aura.

RESULTS

Sibling pairs with any form of migraine had inherited the same 19p13 CACNA1A-containing region significantly more frequently than expected by chance (maximum multipoint lod score = 1.22). This result was almost exclusively dependent on the increased sharing found in sibling pairs with migraine with aura (maximum multipoint lod score = 1.41). The locus-specific relative risk for a sibling (lambda(s)) to suffer from migraine with aura, defined as the increase in risk of the trait attributable to the 19p13 locus, was lambda(s) = 1.56. When combining migraine with and without aura, lambda(s) was 1.22.

CONCLUSIONS

The increased allele sharing in the CACNA1A gene region on 19p13 is consistent with an important involvement of this region in migraine, especially migraine with aura.

The genome-wide distribution of background linkage disequilibrium in a population isolate

Recent interest in using association studies to investigate complex traits has focused attention on understanding linkage disequilibrium (LD) in the human genome. We examined the genome-wide distribution and magnitude of such background LD (BLD) using 1036 densely spaced microsatellites, in a sample from the demographically well characterized population of the Central Valley of Costa Rica. High levels of BLD were found between linked markers several centiMorgans apart, and although BLD was significantly related to genetic distance between markers it was not spread uniformly throughout the genome. Understanding the forces governing the distribution of BLD in the genome will require similar investigations using a standard set of markers in other populations.

The impact of pharmacogenetics for migraine

Migraine is a paroxysmal neurological disorder affecting up to 12% of males and 24% of females in the general population. As migraine has been demonstrated to have a strong, but complex, genetic component, pharmacogenetics bears great promise in providing new targets for drug development and optimization of individual specific therapy. Better, preferably prophylactic, treatment of migraine patients is desired because the drugs now used are not effective in all patients, allow recurrence of the headache in a high percentage of patients and sometimes have severe adverse side-effects. With the recent identification of the brain-specific P/Q-type Ca(2+)channel gene CACNA1A as a pivotal player in the pathogenesis of migraine, the first step has been taken to identify primary biochemical pathways leading to migraine. The work on migraine can also have implications for the increasing number of additional neurological episodic disorders having the common denominator of channelopathy.

Alternating hemiplegia of childhood: no mutations in the familial hemiplegic migraine CACNA1A gene

INTRODUCTION

Alternating hemiplegia of childhood (AHC) is a rare disorder mainly characterized by attacks of hemiplegia and mental retardation. It has been often associated with migraine. The CACNA1A gene on chromosome 19 is involved in familial hemiplegic migraine and other episodic cerebral disorders, but also with progressive neuronal damage.

METHODS

We performed mutation analysis in this gene in four AHC patients, using single strand conformation polymorphism analysis.

RESULTS

We found nine polymorphisms, but no mutations in any of the 47 exons.

CONCLUSIONS

Other cerebral ion channel genes remain candidate genes for AHC.

Migraine, ataxia and epilepsy: a challenging spectrum of genetically determined calcium channelopathies. Dutch Migraine Genetics Research Group

Clinical and genetic heterogeneity as well as influence of environmental factors have hampered identification of the genetic factors which are involved in episodic diseases such as migraine, episodic ataxia and epilepsy. The study of rare, but clearly genetically determined subtypes, may help to unravel the pathogenesis of the more common forms. Recently, different types of mutation in the brain-specific P/Q type calcium channel alpha 1A subunit gene (CACNA1A) on chromosome 19p13 were shown to be involved in three human disorders: familial hemiplegic migraine (FHM), episodic ataxia type 2 (EA2), and chronic spinocerebellar ataxia type 6 (SCA6). In addition, evidence is accumulating that the same gene is also involved in the common forms of migraine with and without aura. In the tottering and leaner mouse, which are characterised by epilepsy and ataxia, similar mutations were identified in the mouse homologue of the calcium channel alpha 1A subunit gene. These findings add to the growing list of episodic (and now also chronic) neurological disorders, which are caused by inherited abnormalities of voltage-dependent ion channels. The findings in migraine illustrate that rare, but monogenic variants of a disorder, may be successfully used to identify candidate genes for the more common, but genetically more complex, forms.

Genetics and pathology of voltage-gated Ca2+ channels

Neurotransmitter release, neuronal excitation, and a whole variety of other neuronal functions are controlled by the intra/extra cellular Ca2+ gradient. The major pathway for entry of Ca2+ into the excitable cells is mediated by voltage-gated Ca2+ channels. Several functional subclasses of voltage-dependent Ca2+ channels have been identified, based on their pharmacological, biophysical properties, and molecular cloning. Recently, three human diseases (familial hemiplegic migraine, episodic ataxia type 2, and spinocerebellar ataxia 6) were added to the growing list of ion-channel disorders, all caused by different mutations in the P/Q-type Ca2+ channel alpha 1 subunit. Molecular analysis of the Ca2+ channelopathies will provide new insights into the role, function and pathology of these voltage-gated Ca2+ channels.

Chromosomal localization of the 5-HT1F receptor gene: no evidence for involvement in response to sumatriptan in migraine patients

The 5-HT1F receptor, which is present in both human vascular and neuronal tissue, may mediate the therapeutic effect and/or side-effects of sumatriptan. We investigated the chromosomal localization of the 5-HT1F receptor gene and the relation between eventually existing polymorphisms and the clinical response to sumatriptan in migraine patients. The 5-HT1F receptor gene was localized using a monochromosomal mapping panel, followed by a radiation-reduced hybrid mapping and fluorescent in situ hybridization. The results of these techniques show that the 5-HT1F receptor gene is localized at 3p12. We investigated the presence of polymorphisms by single strand conformation polymorphism analysis in 14 migraine patients who consistently responded well to sumatriptan, 12 patients who consistently experienced recurrence of the headache after initial relief, 12 patients with no response to sumatriptan, and in 13 patients who consistently experienced chest symptoms after use of sumatriptan. No polymorphisms were detected in any of the patients. We therefore conclude that genetic diversity of the 5-HT1F receptor gene is most probably not responsible for the variable clinical response to sumatriptan.

[Channelopathies: a genetic explanation of migraine and other paroxysmal neurologic disorders]

There is increasing evidence of involvement of genes coding for ion channels in the pathogenesis of paroxysmal neurological disorders. Recently for instance, mutations in the calcium channel gene on chromosome 19 were identified in migraine, ataxia, and epilepsy. With the current research into inherited 'channelopathies' a new approach has been established. A better understanding of the pathophysiology of paroxysmal neurological disorders may lead to new therapeutic strategies.

5-HT1B receptor polymorphism and clinical response to sumatriptan

The 5-HT1 receptor agonist, sumatriptan, is highly effective in the treatment of migraine. Some patients, however, do not respond or experience recurrence of the headache. In addition, some patients report chest symptoms after sumatriptan. We investigated whether these different responses could be attributed to genetic diversity of the 5-HT1B receptor, which most likely mediates the therapeutic action and the coronary side effects of sumatriptan. Allele frequencies of two polymorphisms in the 5-HT1B receptor gene (G861C and T-261G) were investigated in migraine patients with consistently good response to sumatriptan (n = 14), with no response (n = 12), with recurrence of the headache (n = 12), with chest symptoms (n = 13), and in patients without chest symptoms (n = 27). Allele frequencies (G:0.74; C:0.26 at nt 861 and T:0.39; G:0.61 at nt -261) did not differ between patient groups, indicating that genetic diversity of the 5-HT1B receptor does not seem to be involved in the different clinical responses to sumatriptan.

Variable clinical expression of mutations in the P/Q-type calcium channel gene in familial hemiplegic migraine. Dutch Migraine Genetics Research Group

Familial hemiplegic migraine (FHM) is an autosomal dominant subtype of migraine with aura, with half of the families being assigned to chromosome 19p13. We identified missense mutations in a brain-specific calcium channel alpha1A-subunit (CACNA1A) gene on 19p13 segregating with FHM and truncating mutations in families with episodic ataxia type 2 (EA-2). Expansions of an intragenic CAG repeat have been shown in autosomal dominant cerebellar ataxia (SCA6). Hence, FHM, EA-2, and SCA6 are allelic ion channel disorders. We analyzed the phenotype-genotype relation in three unrelated FHM families with the calcium channel alpha1A-subunit gene mutations I1811L (two families) and V714A (one family). We found mutations in all but three patients with FHM (i.e., three phenocopies). In addition, the I1811L mutation occurred in two patients with "nonhemiplegic" migraine and in one subject without migraine. Cerebellar ataxia was found in both families with the I1811L mutation but not in the family with the V714A mutation. We failed to find expansions of the intragenic CAG repeat in FHM patients with cerebellar ataxia. We conclude that the I1811L mutation causes both FHM and cerebellar ataxia independent of the number of CAG repeats. The I1811L mutation may also occur in "normal" migraine patients, supporting the hypothesis that FHM is part of the migraine spectrum.

Clinical and genetic analysis of a large Dutch family with autosomal dominant vascular retinopathy, migraine and Raynaud's phenomenon

We describe an extended Dutch family with a new hereditary disorder: autosomal dominant vascular retinopathy, migraine and Raynaud's phenomenon. Information was obtained on 289 family members (151 males, 138 females), of whom 198 were personally interviewed. Retinopathy was found in 20 (6.9%) of the family members, migraine in 65 (22.5%) and Raynaud's phenomenon in 50 (17.3%). A combination of all three symptoms was found in 11 subjects. In a genetic linkage analysis we firstly excluded several candidate loci. Subsequently, 75% of the autosomal genome was excluded in a genome-wide search. The following conclusions were drawn. First, genetic factors are involved in Raynaud's phenomenon. Secondly, the genetic linkage of migraine with vascular retinopathy and Raynaud's phenomenon supports a vascular aetiology of this disorder. Finding the gene for this family may help to elucidate the genetic background of migraine and of vascular disorders in general.

Familial hemiplegic migraine: involvement of a calcium neuronal channel

A gene for familial hemiplegic migraine (FHM), a subtype of migraine with aura, has been assigned to chromosome 19p13. In this region we identified a brain-specific P/Q-type calcium channel alpha 1A-subunit gene, CACNL1A4, with 47 exons covering 300 kb. Sequencing of all exons and their flanking surroundings revealed polymorphic variations, including a (CA)n-repeat, and a (CAG)n-repeat in the 3'-UTR. In FHM patients, we found four different missense mutations in conserved functional domains. One of the mutations has occurred on two different haplotypes in unrelated FHM families. Moreover, in episodic ataxia type-2 (EA-2), we found two mutations disrupting the reading frame. Thus, FHM and EA-2 can be considered as allelic channelopathies. Involvement of this FHM locus in migraine with and without aura was demonstrated by sib-pair analysis. We showed an increase of shared marker alleles of locus D19S394, which is tightly linked to the gene. The association between the alpha 1A calcium channel and FHM, and the increase of shared alleles in migraine affected sib-pairs, have uncovered a new pathway for the pathophysiology of migraine. This finding may provide a rationale for the development of specific prophylactic therapy for migraine and other (paroxysmal) cerebral disorders.

Episodic ataxia type 2 (EA2) and spinocerebellar ataxia type 6 (SCA6) due to CAG repeat expansion in the CACNA1A gene on chromosome 19p

Point mutations of the CACNA1A gene coding for the alpha 1A voltage-dependent calcium channel subunit are responsible for familial hemiplegic migraine (FHM) and episodic ataxia type 2 (EA2). In addition, expansions of the CAG repeat motif at the 3' end of the gene, smaller than those responsible for dynamic mutation disorders, were found in patients with a progressive spinocerebellar ataxia, named SCA6. In the present work, the analysis of two new families with small CAG expansions of the CACNA1A gene is presented. In one family, with a clinical diagnosis of EA2, a CAG23 repeat allele segregated in patients showing different interictal symptoms, ranging from nystagmus only to severe progressive cerebellar ataxia. No additional mutations in coding and intron-exon junction sequences in disequilibrium with the CAG expansion were found. In the second family, initially classified as autosomal dominant cerebellar ataxia of unknown type, an inter-generational allele size change showed that a CAG20 allele was associated with an EA2 phenotype and a CAG25 allele with progressive cerebellar ataxia. These results show that EA2 and SCA6 are the same disorder with a high phenotypic variability, at least partly related to the number of repeats, and suggest that the small expansions may not be as stable as previously reported. A refinement of the coding and intron-exon junction sequences of the CACNA1A gene is also provided.

Wolff Award 1997. Involvement of a Ca2+ channel gene in familial hemiplegic migraine and migraine with and without aura. Dutch Migraine Genetics Research Group

A gene for familial hemiplegic migraine, a subtype of migraine with aura, was assigned to chromosome 19p13. In this region, we identified a brain-specific P/Q-type calcium-channel alpha 1A-subunit gene, CACNA 1A, with 47 exons covering 300 kb. Sequencing of all exons and their flanking surroundings revealed polymorphic variations, including a (CA)n-repeat and a (CAG)n-repeat in the 3' untranslated region. In patients with familial hemiplegic migraine, we found four different missense mutations in conserved functional domains. One of the mutations has occurred on two different haplotypes in unrelated familial hemiplegic migraine families. Moreover, in episodic ataxia type 2, we found two mutations disrupting the reading frame. Thus, familial hemiplegic migraine and episodic ataxia type 2 can be considered as allelic channelopathies. Involvement of this familial hemiplegic migraine locus in migraine with and without aura was demonstrated by sib-pair analysis. We showed an increase of shared marker alleles of locus D19S394, which is tightly linked to the gene. The association between the alpha 1A calcium channel and familial hemiplegic migraine, and the increase of shared alleles in migraine-affected sib-pairs, have uncovered a new pathway for the pathophysiology of migraine. This finding may provide a rationale for the development of specific prophylactic therapy for migraine and other (paroxysmal) cerebral disorders.

Hyperekplexia-like syndromes without mutations in the GLRA1 gene

Hyperekplexia (MIM: 149400), or startle disease, is an autosomal dominant neurological disorder characterized by an extreme generalized stiffness immediately after birth, normalizing during the first years of life. Other features of this disorder are excessive startle reactions to unexpected, particularly auditory, stimuli together with a short period of generalized stiffness during which voluntary movements are impossible. Linkage analysis mapped a gene for this disorder to chromosome 5q33-q35. Subsequently, mutations in the GLRA1 gene encoding the alpha 1-subunit of the glycine receptor proved to be causally related to the disease. In the present study, mutation analysis of all exon and flanking intron sequences of this gene was performed in sporadic patients and their parents. Moreover, a branch of the original Dutch hyperekplexia family with a very severely affected individual was screened for an additional mutation in the GLRA1 gene. Except for two polymorphisms, of which one results in an amino acid change, no potentially disease causing mutations were found in the alpha 1-subunit of the glycine receptor. Together with haplotype analysis these results exclude a recessive inheritance or new mutation etiology in these hyperekplexia-like syndrome and emphasize that hyperekplexia-like syndromes can be caused by other genetic factors. The involvement of other genes encoding subunits of the functional glycine receptor complex has not been excluded.

Towards a unified nomenclature describing voltage-gated calcium channel genes

A unified nomenclature for describing voltage-gated calcium channel genes is proposed. The terminology has been approved by the HUGO/GDB nomenclature committee.

Partial cosegregation of familial hemiplegic migraine and a benign familial infantile epileptic syndrome

PURPOSE

We studied a large Dutch-Canadian family, in which two very rare hereditary paroxysmal neurologic disorders, familial hemiplegic migraine (FHM) and a "benign familial infantile epileptic syndrome" concur and partially cosegregate. FHM is a dominantly inherited subtype of migraine with attacks of hemiparesis, linked to chromosome 19p13 in 50% of the families tested. Recently mutations in a brain-specific P/Q-type Ca2+ channel alpha1 subunit gene (CACNL1A4) were identified in families with chromosome 19-linked FHM. The infantile epileptic syndrome resembles to two other dominantly inherited benign epilepsies occurring in the first year of life, benign familial neonatal convulsions (BFNC), assigned to chromosomes 20q13.2 and 8q, and benign infantile familial convulsions (BIFC), as yet unlinked.

METHODS

Linkage analysis was performed for the known locations of FHM and BFNC. The question whether the two conditions in this family can be caused by a single gene defect was addressed by additional linkage analysis.

RESULTS

We excluded linkage of the infantile convulsions to markers on chromosome 20q13.2, 8q, or 19p13. This indicates the existence of a third locus for benign familial convulsions in the first year of life. Linkage of FHM to these markers was not formally excluded but seems very unlikely. Statistical analysis of whether, in this family, both conditions are caused by a single gene defect was inconclusive.

CONCLUSIONS

We describe a "benign familial infantile epileptic syndrome" with attacks of FHM at a later age. Further genetic studies in this family may help to unravel the genetic basis of epilepsy or migraine or both.

The quest for migraine genes

Research into the genetics of migraine remains difficult because of the involvement of polygenetic and environmental factors. The discovery of the gene for familial hemiplegic migraine on chromosome 19p 13 is an important step forward. This brain specific P/Q-type calcium channel alpha 1-subunit gene opens new avenues for studying the genetics of migraine, the pathophysiology of the onset of migraine attacks and the development of novel specific prophylactic drugs.