Mineko Hattori

SEROTONIN TRANSPORTER GENE POLYMORPHISMS : ETHNIC DIFFERENCE AND POSSIBLE ASSOCIATION WITH BIPOLAR AFFECTIVE DISORDER

There is some evidence suggesting that a polymorphism of variable number of tandem repeats (VNTR) in the second intron of the serotonin transporter (5-HTT) gene and another variation which lies 1.2 kb upstream of the promoter of the gene (5-HTTLPR) are associated with affective disorders. However, conflicting results have also been reported. We examined an allelic association of these two polymorphisms in a Japanese sample of 191 patients with affective disorders (142 bipolar and 49 unipolar) and 212 controls. Substantial differences in the number and frequency of alleles between Caucasians and Japanese were observed for both polymorphisms. A significant association between the VNTR polymorphism and bipolar disorder (genotypic association: odds ratio 2.2, 95% CI 1.2–4.0; allelic association: odds ratio 1.7, 95% CI 1.0–3.0) was found, but not between the 5-HTTLPR polymorphism and bipolar disorder. No significant association with unipolar depression was detected using either genetic marker, although this may be attributable to the relatively small number of subjects with unipolar depression. Our results suggest that the VNTR itself or another unknown functional polymorphism which would be in linkage disequilibrium to the VNTR has an effect on susceptibility to bipolar disorder.

High and low activity alleles of catechol-O-methyltransferase gene: ethnic difference and possible association with Parkinson's disease

Catechol-O-methyltransferase (COMT) is an enzyme that inactivates catecholamines such as adrenaline, noradrenaline, dopamine, and levodopa. Recently an amino acid change (Val-108-Met) of the COMT protein was found to determine high and low activity alleles of the COMT gene. We genotyped 109 Japanese patients with Parkinsons disease (PD) and 153 controls by using polymerase chain reaction (PCR) amplification and digestion by the restriction enzyme NlaIII. The frequency of low activity allele in the controls was 0.29, which was significantly different from that reported in Caucasians (0.50). When comparison was made between patients with PD and controls, homozygosity for the low activity allele was significantly more common among the patients than among the controls (P = 0.017; odds ratio, 2.8, 95% CI 1.2-6.5), suggesting that homozygosity for the low activity allele may increase susceptibility to PD.

A functional polymorphism in the promoter region of monoamine oxidase-A gene and mood disorders.

A polymorphism of a variable number tandem repeat (VNTR), that was recently found in the promoter region of the monoamine oxidase-A (MAOA) gene, was shown to be associated with its transcriptional activity. This study examined whether this functional polymorphism of the MAOA gene is associated with the risk of developing mood disorders in a Japanese sample of 161 patients with bipolar disorder, 98 with unipolar depression, and 258 controls. There was no significant genotypic or allelic association, suggesting that the functional VNTR polymorphism in the MAOA gene is unlikely to play a major role in the pathogenesis of bipolar disorder or unipolar depression. Furthermore, we found no association between the polymorphism and a history of suicide attempt.

C677T polymorphism in methylenetetrahydrofolate reductase gene and psychoses

A common missense mutation of the methylenetetrahydrofolate reductase (MTHFR) gene (C677T) has been shown to be a risk factor for premature cardiovascular disease and neural tube defect. Deficient activity of MTHFR has also been implicated in the pathogenesis of psychiatric conditions such as schizophrenia and affective disorders. Arinami et al1 found an increased frequency of homozygosity for the mutated type (T677) of the MTHFR gene in schizophrenia and depression. We tried to replicate this finding in a sample of 343 patients with schizophrenia, 143 with bipolar disorder, 71 with unipolar depression, and 258 controls; however, there was no significantly increased frequency of homozygosity for the T677 allele in any of the diagnostic groups, compared to the controls. Our results suggest that homozygosity for the T677 allele of the MTHFR gene is unlikely to play a major role in the pathogenesis of schizophrenia or affective disorders in our sample.

A study of the association between schizophrenia and the dopamine D3 receptor gene

A study of the genetic association between schizophrenia and aBalI polymorphism in exon 1 of the dopamine D3 (DRD3) gene, a candidate gene for schizophrenia, was conducted. The polymorphism was examined in 91 patients whose symptoms satisfied DSM-III-R for schizophrenia and 90 controls. There were no significant differences between the groups in allele frequencies or genotype counts. Contrary to a previous report, the patients were no more likely to be homozygous than controls. Moreover, no association with the presence of illness could be demonstrated when the patients were grouped according to sex, age of onset, history of admission to psychiatric institutions or positive family history.

Neurotrophin-3 gene polymorphism associated with schizophrenia.

The recent possible neurodevelopmental etiology of schizophrenia makes the neurotrophin‐3 (NT‐3) gene an interesting candidate locus. We studied the allelic distributions of dinucleotide repeat polymorphism at the NT‐3 gene locus in 70 patients with schizophrenia and in 70 controls. A highly significant difference between the two groups was observed at the allele A3. Even Bonferronis correction was used, the difference was still significant. Individuals with homozygous or heterozygous for the allele A3 had a 2.4‐fold increased risk of schizophrenia. Determination of NT‐3 genotype may help to identify those at greater risk of schizophrenia. Furthermore, this finding supports evidence implicating neurodevelopmental deficit in the pathogenesis of this disorder.

Association of apolipoprotein E4 with sporadic Alzheimer's disease is more pronounced in early onset type

Apolipoprotein E genotypes in 88 unrelated Japanese patients with NINCDS-ADRDA sporadic Alzheimers disease (AD) were examined and compared with those of 93 healthy controls. Frequency of epsilon 4 allele was increased in patients with AD (31%) compared with controls (10%), as was reported previously. Individuals homozygous or heterozygous for the allele epsilon 4 had a 5.9-fold increased risk of AD. This tendency was more pronounced in early onset sporadic (= non-familial) type than late onset type. The relative risk was also greater for early onset type (RR = 11.7; 95% CI, 4.9-28.3) than late onset type (RR = 4.3; 95% CI, 2.1-8.8). Moreover, patients with homozygote for the allele epsilon 4 had a 14.7-fold increased risk of early onset sporadic AD (P < 0.005, chi 2 = 9.0, df = 1, 95% CI, 2.5-85.1). Our findings indicated that association of apolipoprotein epsilon 4 with sporadic Alzheimers disease is more pronounced in early onset type than in late onset type.

Genes for interleukin‐2 receptor β chain, interleukin‐1 β, and schizophrenia: No evidence for the association or linkage

We studied a CA repeat polymorphism of the interleukin-2 receptor beta chain (IL-2RB) gene and a C/-514/T variation of the interleukin-1 beta (IL-1B) gene in Japanese schizophrenia patients. Both a case-control association study (54 patients and 54 controls) and a linkage study using six multiplex families (the number of the affected > or =4 in each family) were employed. No evidence for the association or the linkage was obtained either for the IL-2RB or IL-1B gene.

No evidence of linkage or association between tyrosine hydroxylase gene and affective disorder

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of dopamine and norepinephrine, and therefore is of significant interest as a candidate gene in studies of affective disorders. We have carried out the linkage study between the susceptibility gene for affective disorder and tetranucleotide polymorphism of TH gene in five Japanese pedigrees. In addition to the linkage approach, we have undertaken an allelic association study using 74 patients with affective disorder and 78 controls with polymorphisms at the TH gene and the nearby dopamine D4 receptor gene. No evidence for linkage or associations were found. These results indicate that TH gene is less likely to contribute to the genetic component of affective disorders.

No association between Parkinson's disease and monoamine oxidase A and B gene polymorphisms

Parkinsons disease (PD) is thought to be caused by a combination of unknown environmental, genetic and degenerative factors. Among these factors, monoamine oxidase has been considered as a possible factor in the pathophysiology of Parkinsons disease. We have carried out allelic association studies of PD with monoamine oxidase type A (MAOA) and monoamine oxidase type B (MAOB) gene loci using dinucleotide repeat polymorphisms. Distributions of all alleles at MAOA and MAOB gene loci were almost similar in patients and controls. Contrary to previous reports, our findings could not support the hypothesis that susceptibility to PD is associated with MAOA or MAOB polymorphism.