Xiehe Liu

Preferential transmission of the high activity allele of Comt in schizophrenia

Catechol-O-methyl transferase (COMT) metabolizes a variety of catecholamines such as dopamine, adrenaline and nor-adrenaline. It exists in common high and low activity forms. The low activity form is the result of an amino acid substitution (val-108-met) which reduces the thermostability of the enzyme [Lotta et al. (1994) Biochemistry, 34, 4202–4210]. We have genotyped this polymorphism in 178 trios consisting of Han Chinese schizophrenic subjects and their parents in order to test the hypothesis that the high activity allele is transmitted more often to affected subjects. The data were analysed using the transmission disequilibrium test (TDT), a robust method of detecting linkage in the presence of allelic associations. Of the 131 parents heterozygous at this locus, 80 transmitted the high activity allele (val-108) to affected offspring, while the remaining 51 transmitted the low activity allele (p = 0.005, one-tailed). Combining this result with that of a previous TDT study of the same polymorphism in familial schizophrenia [Kunugi et al. (1996) submitted] gives significant evidence for linkage disequilibrium (p = 0.0015). However, val-108 is frequent in the Han Chinese population, and in the present sample, 239 of the 350 non-transmitted parental alleles were val-108 (68%). It is therefore unlikely that val-108 allele of COMT has a major effect on susceptibility to schizophrenia. Our results suggest that either val-108 is a minor risk factor for schizophrenia, that the COMT gene has additional polymorphisms with greater effect on risk, or that this region of chromosome 22 contains a susceptibility gene which is in linkage disequilibrium with the COMT gene.

Distinct transcriptional regulation and function of the human BACE2 and BACE1 genes

Amyloid β protein (Aβ) is the principal component of neuritic plaques in Alzheimers disease (AD). Aβ is derived from β amyloid precursor protein (APP) by β‐ and γ‐secretases. Beta‐site APP cleaving enzyme 1 (BACE1) has been identified as the major β‐secretase. BACE2 is the homolog of BACE1. The BACE2 gene is on chromosome 21 and has been implicated in the pathogenesis of AD. However, the function of BACE2 in Aβ generation is controversial. Some studies have shown that BACE2 cleaved APP at the β‐site whereas other studies showed it cleaved around the α‐secretase site. To elucidate the involvement of BACE2 in AD pathogenesis, we compared BACE2 and BACE1 gene regulation and their functions in Aβ generation. We cloned and functionally characterized the human BACE2 promoter. The BACE2 gene is controlled by a TATA‐less promoter. Though Sp1 can regulate both BACE1 and BACE2 genes, comparative sequence analysis and transcription factor prediction showed little similarity between the two promoters. BACE1 increased APP cleavage at the β‐site and Aβ production whereas BACE2 did not. Overexpression of BACE2 significantly increased sAPP levels in conditioned media but markedly reduced Aβ production. Knockdown of BACE2 resulted in increased APP C83. Our data indicate that despite being homologous in amino acid sequence, BACE2 and BACE1 have distinct functions and transcriptional regulation. BACE2 is not a β‐secretase, but processes APP within the Aβ domain at a site downstream of the α‐secretase cleavage site. Our data argue against BACE2 being involved in the formation of neuritic plaques in AD.—Sun, X., Wang, Y., Qing, H., Christensen, M. A., Liu, Y., Zhou, W., Tong, Y., Xiao, C., Huang, Y., Zhang, S., Liu, X., Song, W. Distinct transcriptional regulation and function of the human BACE2 and BACE1 genes. FASEB J. 19, 739–749 (2005)

ASSOCIATION ANALYSIS OF THE DOPAMINE D4 GENE EXON III VNTR AND HEROIN ABUSE IN CHINESE SUBJECTS

Although social and cultural influences are clearly important, family, twin and adoption studies indicate that genes contribute significantly to substance abuse.1–3 Substance abuse is associated with novelty seeking, a heritable human personality trait which may be influenced by alleles of the dopamine D4 (DRD4) gene exon III VNTR.4,5 Consequently Kotler et al6 analysed the DRD4 VNTR in opiate-dependent subjects from Israel, and found a significant excess of the 7-repeat allele. We have attempted to replicate this finding using a Han Chinese case-control sample of 121 heroin-dependent subjects and 154 normal controls. We found two 7-repeat alleles which occurred exclusively in the patient group, and overall there was an excess of longer alleles, which did not reach significance (χ2 = 7.04; P = 0.07). When the D4 VNTR was divided into ‘long’ (5–7 repeats) and ‘short’ (2–4 repeats), a significant excess of long alleles was observed in the patient group (P = 0.023, one-tailed), with an odds ratio of 2.30 (95% CI 1.07–4.93). We conclude that our findings support the hypothesis that alleles of the DRD4 exon III VNTR are susceptibility factors for heroin abuse.

Hair Cortisol Level as a Biomarker for Altered Hypothalamic-Pituitary-Adrenal Activity in Female Adolescents with Posttraumatic Stress Disorder After the 2008 Wenchuan Earthquake

BACKGROUND The present study evaluated the accumulated changes in hair cortisol levels of patients with posttraumatic stress disorder (PTSD) attributed to the 2008 Wenchuan earthquake in China. METHODS Sixty-four female adolescents from two townships who experienced the earthquake were recruited 7 months after the disaster, including 32 subjects with PTSD (PTSD group) and 32 subjects without PTSD (non-PTSD group). Twenty matched adolescents were recruited from an area that was not affected significantly by the earthquake as the control group. Hair cortisol concentrations were measured by the electrochemiluminescence immunoassay in each 3-cm segment of hair sample from the scalp. RESULTS There was no significant difference at the baseline hair cortisol level in the three groups before the traumatic event (p > .6). Hair cortisol levels changed over time and differed among groups (p = .0042). The hair cortisol levels among the PTSD and non-PTSD subjects were elevated, suggesting increasing levels in response to stress. However, these two groups differed in their response. The non-PTSD subjects showed a significantly higher cortisol level than the PTSD group between month 2 and month 4 (p = .0137) and also between month 5 and month 7 (p = .0438) after the traumatic event. CONCLUSIONS This study revealed a blunted response curve to the disaster among PTSD subjects compared with subjects without PTSD. These findings suggest that hair cortisol level could be used to assess the integrated hypothalamic-pituitary-adrenal activity over a period of months after traumatic events and be used to serve as a biomarker in patients with PTSD.

Catechol-O-methyltransferase Val158Met polymorphism : frequency analysis in Han Chinese subjects and allelic association of the low activity allele with bipolar affective disorder

Catechol-O-methyltransferase catalyses the O-methylation of biologically active or toxic catechols and is a major component of the metabolism of drugs and neurotransmitters such as L-dopa, noradrenaline, adrenaline, and dopamine. Human catechol-O-methyltransferase activity is an autosomal partially dominant trait and is strongly associated with a valine to methionine substitution at codon 158 of the protein. About 25% of Caucasians have low activity, 50% intermediate activity and 25% high activity as determined by either phenotypic or genotypic measurement. In black populations, the low activity allele (Met158; COMTL) is less frequent with about 7% being homozygous. Using a PCR based genotyping assay, we report that the Met158 allele is also less frequent in normal Han Chinese subjects with about 3% of the population being homozygous. Because of its role in catecholamine metabolism and several lines of evidence pointing to a locus for psychosis near the COMT gene on chromosome 22q11, we have analysed the COMT Val158Met polymorphism as a candidate susceptibility factor for bipolar affective disorder. We report an association between bipolar affective disorder and the Met158 allele (p = 0.004) and genotype (p = 0.01) in 93 affected Chinese subjects and 98 controls. We hypothesize that either the low activity allele of catechol-O-methyltransferase is a risk factor for bipolar affective disorder in Chinese populations or is in linkage disequilibrium with a nearby susceptibility gene or polymorphism.

Evidence for association between novel polymorphisms in the PRODH gene and schizophrenia in a Chinese population

Haploinsufficiency for or mutation in at least one gene from the velocardiofacial syndrome (VCFS) region at chromosome 22q11 is implicated in psychosis. Linkage disequilibrium mapping of the region in patients identified a segment containing two genes, proline dehydrogenase (PRODH) and DGCR6, as candidates [Liu et al., 2002a ] and by analysis of additional polymorphisms the PRODH gene was associated with schizophrenia in adult and early onset patients. In the present study we provide additional evidence in support of genetic association between PRODH and schizophrenia in a Chinese population. We analyzed the PRODH gene in a samples of schizophrenic patients and their families from Sichuan, SW China consisting of 528 family trios and sibling pairs. We genotyped six SNPs, PRODH*1195C → T, PRODH*1482C → T, PRODH*1483A → G, PRODH*1766A → G, PRODH*1852G → A PRODH*1945T → C, two of which (PRODH*1483A → G and PRODH*1852G → A) have not been previously reported. We found association with schizophrenia for two haplotypes consisting of PRODH*1945T → C and PRODH*1852G → A (Global P = 0.006), and PRODH*1852G → A and PRODH*1766A → G (Global P = 0.01) which include one of the newly identified markers. After six‐fold Bonferroni correction for multiple testing the PRODH*1945T‐C/PRODH*1852G‐A haplotypes remained significant. This is a sub‐haplotype of the PRODH haplotype previously associated with schizophrenia and it also maps to the 3′ region of the gene, indicating that this is the region most likely to contain the underlying risk alleles. Overall this finding supports a role for the PRODH locus in schizophrenia.

Lack of association between a polymorphism in the promoter region of the dopamine-2 receptor gene and clozapine response

Dopamine receptors are strong candidates for involvement in schizophrenia and are targeted by a wide variety of antipsychotics. We hypothesized that genetic variation in these neurotransmitter receptors may influence clinical response to clozapine, an antipsychotic which displays high affinity for dopamine D2 receptors in the limbic system. To test this hypothesis, we studied a functional polymorphism in the promoter region of the D2 receptor gene (-141C Ins/Del) in a sample of 151 clozapine treated patients of British origin. In addition, the influence of this polymorphism on antipsychotic response in general was investigated on a sample of 146 Han Chinese schizophrenic patients treated with a variety of antipsychotics. No association was found between this polymorphism and clinical response in either of the two samples suggesting that genetic variation in D2 receptors does not play a major role in determining clinical response to antipsychotic treatment.

Neurocognitive deficits in first-episode schizophrenic patients and their first-degree relatives

Some neuropsychological abilities, particularly those affecting memory, attention and executive function, are impaired amongst both schizophrenic patients and their unaffected relatives, implying that these deficits are at least partly genetic in origin. However neuropsychological performance can be altered by medication, and has rarely been examined in first onset, drug naive patients. The objective of this study was to determine whether selected neurocognitive abilities are impaired in first‐onset schizophrenic patients and their relatives compared to controls. We examined attention and speed of information processing, memory and learning, verbal function, visuoconstructive abilities and executive function in 207 first‐episode schizophrenic patients (163 of whom were drug naïve), 322 of their first‐degree relatives and 133 unrelated normal controls. The data were subjected to multilevel modeling to compare neurocognitive performance between schizophrenic probands, relatives and controls while taking into account potential correlations among members of the same family; age, gender, and years of education were included as covariates. Of the three groups, schizophrenic patients performed poorest at all neuropsychological tests, suggestive of a broad range of neurocognitive deficits. Their first‐degree relatives showed a narrower pattern of poor performance at Digit Symbol, Digit Span, Trail Making, Verbal Fluency test, Tower of Hanoi, and WCST‐M tests. Our findings show that selected neurocognitive deficits especially attention and executive function are impaired in the families of schizophrenic patients. These patterns of neurocognitive deficits may represent “endophenotypes” denoting varying degrees of vulnerability to schizophrenia and may be of value in future molecular genetic studies.

Association analysis between dopamine receptor genes and bipolar affective disorder.

We have performed a case-control analysis of dopamine D2-like receptor (DRD2, DRD3 and DRD4) gene polymorphisms in 118 Han Chinese cases with bipolar affective disorder and 196 control subjects, and replication analysis in 157 English cases and 143 control subjects. We found association between a functional DRD2 promoter variant (P = 0.03 by allele) and the DRD2 taq1A polymorphism (P = 0.001 by allele) in Chinese bipolar disorder patients. However, this finding was not replicated in the Caucasian subjects, indicating that the significant association we observed in the Chinese population is a false positive finding. An alternative explanation is that these polymorphisms are risk factors in Chinese but not Caucasian populations, a hypothesis which seems unlikely in view of the similarity of the clinical characteristics of bipolar disorder in the two populations. We also report a novel, rare one-repeat variant of the DRD4 exon 3 VNTR repeat in Chinese populations, which appears to be absent in Caucasians and is not associated with disease.

Association analysis of the RGS4 gene in Han Chinese and Scottish populations with schizophrenia

We investigated the RGS4 as a susceptibility gene for schizophrenia in Chinese Han (184 trios and 138 sibling pairs, a total of 322 families) and Scottish (580 cases and 620 controls) populations using both a family trio and case‐control design. Both the samples had statistical power greater than 70% to detect a heterozygote genotype relative risk of >1.2 for frequent RGS4‐risk alleles. We genotyped four single nucleotide polymorphisms (SNPs) which have previously been associated with schizophrenia as either individually or part of haplotypes. Allele frequencies and linkage disequilibrium between the SNPs was similar in the two populations. In the Chinese sample, no individual SNPs or any of their haplotypes were associated with schizophrenia. In the Scottish population, one SNP (SNP7) was significantly over‐represented in the cases compared with the controls (0.44 vs. 0.38; A allele; χ2 7.08, P = 0.011 after correction for correlation between markers by permutation testing). One two‐marker haplotype, composed of alleles T and A of SNP4 and SNP7, respectively, showed individual significance after correction by permutation testing (χ2 6.8; P = 0.04). None of the full four‐marker haplotypes showed association, including the G‐G‐G‐G haplotype previously associated with schizophrenia in more than one sample and the A‐T‐A‐A haplotype. Thus, our data do not directly replicate previous associations of RGS4, but association with SNP 7 in the Scottish population provides some support for a role in schizophrenia susceptibility. We cannot conclusively exclude RGS4, as associated haplotypes are likely to be surrogates for unknown causative alleles, whose relationship with overlying haplotypes may differ between the population groups. Differences in the association seen across the two populations could result from methodological factors such as diagnostic differences but most likely result from ethnic differences in haplotype structures within RGS4.