Luk W. Ho

Genetic associations with clinical characteristics in bipolar affective disorder and recurrent unipolar depressive disorder

Genetic factors may be associated with disease subtype as well as susceptibility. We have therefore typed polymorphisms at the serotonin transporter, dopamine receptor, tryptophan hydroxylase, tyrosine hydoxylase, and monoamine oxidase A (MAOA) loci in 139 unipolar and 131 bipolar patients and investigated associations with gender, number of episodes, age of onset, history of psychotic symptoms, history of suicidal behavior, and history of substance abuse. In bipolar subjects, the promoter variable number tandem repeat (VNTR) allele 132 of MAOA was associated with history of suicide attempts, P = 0.029, particularly in females, P = 0.006. The Fnu4HI allele 1 of MAOA was also associated with history of suicide attempts in females, P = 0.0162. The serotonin transporter promoter allele 2 was associated with increasing number of manic episodes, P = 0.02, and history of psychotic symptoms, P = 0.0243. One significant association was found in the unipolar group: dopamine D2 receptor promoter allele 2 with history of psychotic symptoms, P = 0. 0165. We have tested multiple loci for a variety of different clinical variables and performed 228 tests of significance in total. It is possible that these preliminary findings are type 1 errors, because one would expect 11 of the 228 tests to reach a nominal significance level of P < 0.05 by chance alone if all the tests were independent. The associations with the MAOA and serotonin transporter loci are consistent with previous data suggesting associations with susceptibility to bipolar affective disorder. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:36-42, 2000

Analysis of the monoamine oxidase A (MAOA) gene in bipolar affective disorder by association studies, meta-analyses, and sequencing of the promoter

Monoamine oxidases catalyse the oxidative degradation of biogenic amines including neurotransmitters such as noradrenaline, dopamine, and 5-hydroxytryptamine (5-HT). Three groups have reported positive associations of the monoamine oxidase A (MAOA) gene with bipolar affective disorder although other studies have been negative. In an extension of a previous study [Rubinsztein et al., 1996: Human Molec Genet 5:779-782] we report association studies of MAOA polymorphic markers and affective disorders. The polymorphisms comprised a CA-repeat microsatellite in intron 2 and a Fnu4HI G/T silent polymorphism at position 941 of the cDNA sequence. No significant differences were found when the control allele frequencies were compared with those in bipolar, unipolar, or combined bipolar + unipolar groups. Meta-analyses were then performed to include the data of all published studies using the MAOA microsatellite and Fnu4HI polymorphisms. Separate meta-analyses were performed for Caucasian and Japanese studies, as allele frequencies of the microsatellite in these populations were markedly different. Associations of bipolar affective disorder in pooled male and female groups were found with the MAOA microsatellite in both the Caucasian (P < 0.02) and the Japanese (P < 0.02) meta-analyses. In view of these positive associations, and as previous results have shown that coding variants do not account for the normal population variation in MAOA activity, over 1,300 bp of the promoter were sequenced in 22 bipolar cases and 1 control. A novel polymorphic promoter variable number of tandem repeats (VNTR) located approximately 1,200 bp upstream from the translation start site was demonstrated. However, there was no association of this promoter VNTR with affective disorder. These results suggest that there may be functional variants in other regions of the MAOA gene or neighbouring genes that affect bipolar affective disorder risk.

No association of the tryptophan hydroxylase gene with bipolar affective disorder, unipolar affective disorder, or suicidal behaviour in major affective disorder

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the synthesis of 5-hydroxytryptamine (5-HT). An association study in bipolar affective disorder I or unipolar major affective disorder was performed by using a Bfa I restriction site polymorphism within intron 7 of the tryptophan hydroxylase gene. A total of 118 bipolar, 125 unipolar, and 437 control subjects were used in the study (1:3.7 bipolar:control, 1:3.5 unipolar:control). There were no significant differences in TPH allele or genotype frequencies between the affective disorder and control groups. In addition, bipolar and/or unipolar subjects with or without a history of suicide attempts were compared for the TPH polymorphism. No significant differences were found between suicidal and non-suicidal groups in major affective disorder, in contrast to a previous study suggesting an association of this polymorphism with a history of suicide attempts among alcoholic violent offenders.

Wild type huntingtin reduces the cellular toxicity of mutant huntingtin in mammalian cell models of Huntington's disease

OBJECTIVES Recent data suggest that wild type huntingtin can protect against apoptosis in the testis of mice expressing full length huntingtin transgenes with expanded CAG repeats. It is not clear if this protective effect was confined to particular cell types, or if wild type huntingtin exerted its protective effect in this model by simply reducing the formation of toxic proteolytic fragments from mutant huntingtin. METHODS We cotransfected neuronal (SK-N-SH, human neuroblastoma) and non-neuronal (COS-7, monkey kidney) cell lines with HD exon 1 (containing either 21 or 72 CAG repeats) construct DNA and either full length wild type huntingtin or pFLAG (control vector). RESULTS Full length wild type huntingtin significantly reduced cell death resulting from the mutantHD exon 1 fragments containing 72 CAG repeats in both cell lines. Wild type huntingtin did not significantly modulate cell death caused by transfection of HD exon 1 fragments containing 21 CAG repeats in either cell line. CONCLUSIONS Our results suggest that wild type huntingtin can significantly reduce the cellular toxicity of mutant HD exon 1 fragments in both neuronal and non-neuronal cell lines. This suggests that wild type huntingtin can be protective in different cell types and that it can act against the toxicity caused by a mutant huntingtin fragment as well as against a full length transgene.

Psychiatric symptoms and CAG repeats in neurologically asymptomatic Huntington's disease gene carriers

The putative relationship between the psychiatric profile of a sample of neurologically asymptomatic Huntingtons disease gene carriers and CAG repeats was investigated. The psychiatric assessments (by consultant psychiatrist and computerised battery) were undertaken before the genetic testing was carried out. In this way, the informational distortions caused by neurological and cognitive deficits were avoided. The hypothesis that there is a relationship between psychiatric and CAG repeats was tested by seeking direct correlations between psychiatric systems and CAG repeats, and also by correcting the correlation by the number of years above or below the estimated age of onset in Huntingtons disease. Scores for irritability and cognitive failures were high in the sample. There was no correlation between any psychiatric variable and CAG repeats. Possible explanations for this lack of correlations are discussed.

A rare coding variant within the wolframin gene in bipolar and unipolar affective disorder cases.

A recent report has shown that Wolfram syndrome carriers (heterozygotes) are 26-fold more likely to require psychiatric hospitalization compared with non-carriers, and that Wolfram syndrome heterozygotes may constitute approximately 25% of individuals hospitalized with depression and suicide attempts. We analyzed a His611Arg polymorphism of the wolframin gene by the polymerase chain reaction (PCR) and HhaI restriction digestion, in 158 bipolar I and 163 unipolar major affective disorder cases, and 316 controls. Statistical analyses of allele or genotype frequencies do not support a major role for wolframin in affective disorder. HhaI restriction digestion and sequencing of PCR products from four affective disorder cases showed a heterozygous Ala559Thr change. The Ala559Thr variant was not detectable in 382 controls tested. Thus, the rare wolframin 559Thr allele deserves consideration as a risk allele for affective disorder.

No association of a functional polymorphism in the dopamine D2 receptor promoter region with bipolar or unipolar affective disorders.

The dopaminergic system, along with the serotonergic and noradrenergic systems, has been implicated in the etiology of mood disorders. An association study of a functional variant in the promoter region of the dopamine D2 receptor (DRD2) with bipolar affective disorder I or unipolar major affective disorders was performed. Variable expression of the DRD2 gene in vitro has been shown with this promoter polymorphism. One hundred and thirty-one unrelated bipolar patients, 128 unrelated unipolar patients, and 262 controls were used in the study. There were no significant differences in DRD2 allele or genotype frequencies between the affective disorder and control groups. These results do not support a major role for the DRD2 gene in the etiology of either bipolar or unipolar affective disorders.

Candidate gene association studies of genes involved in neuronal cholinergic transmission in Alzheimer's disease suggests choline acetyltransferase as a candidate deserving further study

Consistent deficits in the cholinergic system are evident in the brains of Alzheimers Disease (AD) patients, including reductions in the activities of acetylcholine, acetylcholinesterase (AChE), and choline acetyltransferase (ChAT), increased butyrylcholinesterase (BChE) activity, and a selective loss of nicotinic acetylcholine receptors (nAChRs). Accordingly, we have analyzed polymorphisms in the genes encoding AChE, ChAT, BChE, and several of the subunit genes from neuronal nAChRs, for genetic associations with late‐onset AD. A significant association for disease was detected for a non‐coding polymorphism in ChAT (allele χ12 = 12.84, P = 0.0003; genotype χ22 = 11.89, P = 0.0026). Although replication analysis did not confirm the significance of this finding when the replication samples were considered alone (allele χ12 = 1.02, P=0.32; genotype χ22 = 1.101, P = 0.58) the trends were in the correct direction and a significant association remained when the two sample sets were pooled (allele χ12 = 12.37, P = 0.0004; genotype χ22 = 11.61, P = 0.003). Previous studies have reported significant disease associations for both the K‐variant of BChE and the coding ChAT rs3810950 polymorphism with AD. Replication analyses of these two loci failed to detect any significant association for disease in our case‐control samples.

Candidate gene association studies of the alpha 4 (CHRNA4) and beta 2 (CHRNB2) neuronal nicotinic acetylcholine receptor subunit genes in Alzheimer's disease

Consistent deficits in the cholinergic system are evident in Alzheimers disease (AD) patients, including selective loss of alpha4beta2 nicotinic acetylcholine receptors in the brains of AD patients. Knockout mice for the beta2 subunit have impaired neuronal survival in ageing. Accordingly, we have analysed polymorphisms in the genes that encode the alpha4 and beta2 subunits, CHRNA4 and CHRNB2 respectively, for genetic associations with late-onset AD. A significant association for disease was observed for a non-coding polymorphism in CHRNB2 (odds ratio=0.57, 95% confidence interval=0.35-0.95, P=0.024). Replication analysis was performed in two further sample sets. While these did not individually yield significant results, a significant association remained when all samples were pooled (odds ratio=0.70, 95% confidence interval=0.52-0.95, P=0.019). These data suggest that this variant warrants further examination in large case-control series.

No association of an insertion/deletion polymorphism in the angiotensin I converting enzyme gene with bipolar or unipolar affective disorders.

A recent Japanese study on the angiotensin I converting enzyme gene (ACE) insertion/deletion polymorphism reported that both the D allele (P < 0.02) and the DD genotype (P < 0.002) were significantly more frequent in affective disorder cases than in controls [Arinami et al., 1996: Biol Psychiatry 40:1122-1127]. A replication study was performed by using 157 bipolar I affective disorder cases, 169 major depressive disorder cases, and 313 controls. No significant association with this polymorphism was found in either disorder or in a combined affective disorder group. These results do not support the ACE gene having a major role in the etiology of either bipolar or unipolar affective disorders. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:733-735, 2000.