Association between the DAOA/G72 gene and bipolar disorder and meta-analyses in bipolar disorder and schizophrenia

Müller DJ, Zai CC, Shinkai T, Strauss J, Kennedy JL. Association between the DAOA/G72 gene and bipolar disorder and meta‐analyses in bipolar disorder and schizophrenia.
Bipolar Disord 2011: 13: 198–207. © 2011 The Authors.
Journal compilation © 2011 John Wiley & Sons A/S. Objective: The d ‐amino acid oxidase activator (DAOA, or G72) is involved in the oxidation of d ‐serine, an endogenous modulator of N‐methyl‐d ‐aspartate receptors and thus represents an important candidate in psychotic disorders. Several studies reported the DAOA/G72 gene to be associated with schizophrenia (SZ) and bipolar disorder (BD); however, the associated polymorphisms varied between SZ and BD. This study attempts to replicate the DAOA/G72 findings in BD and to conduct subgroup analyses based on the presence or absence of psychotic symptoms. Methods: Five polymorphisms of the DAOA/G72 gene (rs1341402, rs1935062, rs2391191, rs947267, and rs778294) were analysed for association with BD in a family‐based study design (303 core families including 916 individuals). We also conducted a meta‐analysis of DAOA/G72 polymorphisms in BD and SZ. Results: Marker rs1935062 was significantly associated with BD diagnosis in our sample (Z‐score for C‐allele = ?2.33, p = 0.02, uncorrected for genome‐wide multiple comparisons). When we examined the subset of BD patients with psychotic symptoms (157 families), no significant results were obtained. Our meta‐analysis yielded negative findings for DAOA/G72 markers in BD and positive findings for marker rs2391191 in SZ in East Asians. However, significant heterogeneity across studies limits interpretation. Conclusions: Our results provide evidence that suggests a possible role of the DAOA/G72 gene in BD and SZ. Marker rs1935062 may be specifically associated with BD, while marker rs2391191 may be associated with SZ but not with BD. Together with previous studies, these findings suggest that the DAOA/G72 gene confers susceptibility to both BD and SZ, but that different polymorphisms may potentially differentiate between these two disorders.     

Increased inferior frontal activation during word generation: A marker of genetic risk for schizophrenia but not bipolar disorder?

During verbal‐fluency tasks, impairments in performance and functional abnormalities in the inferior frontal cortex have been observed in both schizophrenia patients and their unaffected relatives. We sought to examine whether such functional abnormalities are a specific marker of genetic vulnerability to schizophrenia. We studied a sample of 132 subjects, comprising 39 patients with schizophrenia, 10 unaffected monozygotic (MZ) cotwins of schizophrenia probands, 28 patients with bipolar disorder, 7 unaffected MZ cotwins of bipolar disorder probands and 48 healthy controls. Blood oxygen level‐dependent response was measured using functional magnetic resonance imaging during the performance of an overt verbal‐fluency task with two levels of task difficulty, in a cytoarchitectonic region of interest encompassing Brodmann areas 44 and 45 bilaterally. Patients with schizophrenia and the unaffected MZ cotwins of schizophrenia probands showed increased activation in the inferior frontal cortex relative to healthy controls and bipolar patients. Increased engagement of the inferior frontal cortex during verbal‐fluency may thus be a marker of genetic vulnerability to schizophrenia. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.     

Genetic variation in the G72 (DAOA) gene affects temporal lobe and amygdala structure in subjects affected by bipolar disorder

Background:  Variation in the G72 (DAOA) gene is understood to convey susceptibility for bipolar disorder through an uncertain mechanism. Little is known about the structural brain phenotypes associated with this gene. We hypothesised that reductions in temporal lobe and amygdala gray matter would be associated with variation at two loci in the gene for which evidence of genetic linkage has been repeatedly demonstrated.
Methods:  We examined the temporal lobe and amygdala gray matter associations of the risk variants M23 and M24 at the 5' end of the gene encoding G72 in 81 controls and 38 people with bipolar disorder.
Results:  Genetic variation at both the M23 and M24 loci in G72 were associated with decreased gray matter density within the left temporal pole in people with bipolar disorder. M23 was also associated with reductions in right amygdala gray matter density. The genetic imaging associations were found only in patients with bipolar disorder.
Conclusions:  Genetic variation at single nucleotide polymorphisms in the G72 gene previously associated with bipolar disorder is related to reductions in temporal pole and amygdala gray matter structure in people with bipolar disorder.     

An fMRI study of prefrontal dysfunction and symptomatic recovery in schizophrenia

Smee C, Krabbendam L, O’Daly O, Prins A‐M, Nalesnik N, Morley L, Samson G, Shergill S. An fMRI study of prefrontal dysfunction and symptomatic recovery in schizophrenia. Objective: Prefrontal cortical dysfunction has been implicated in the pathophysiology of schizophrenia but it is unclear to what extent these are related to changes in symptomatology as well as task demand. Method: We examined the neural correlates of symptom change and task demand during a longitudinal functional magnetic resonance imaging (fMRI) study using a verbal fluency task with differential task demands in patients with schizophrenia and matched healthy control subjects. The fMRI data were acquired using clustered acquisition technique, enabling ongoing monitoring of behavioural responses, in the patient group on two occasions separated by 6–8 weeks, and the control group at baseline. Results: Positive psychotic symptoms were significantly reduced over the 6–8‐week duration of the study. This change was associated with increased activation within the left middle frontal gyrus and decreased activation of the left precuneus. An interaction between symptom change and task demand was evident in the activation of the left middle frontal gyrus. The decrease in positive symptoms was associated with normalisation of activation in the dorsolateral prefrontal cortex and a decrease in parietal activation during the verbal fluency task. Conclusion: The data supports the role of dysfunctional prefronto‐parietal relationships in the genesis of positive psychotic symptoms.     

精神分裂症与G72基因多态性的关联分析

目的:探讨精神分裂症与G72基因多态性的关系,是否有混合家族史精神分裂症在G72基因多态性的区别。方法:采用聚合酶链反应技术分别检测162例无混合家族史精神分裂症、62例有混合家族史精神分裂症、88名正常对照的G72基因单核苷酸多态性rs947267、rs2181953,进行关联分析。结果:不同性别及发病年龄的无混合家族史精神分裂症组与对照组rs947267、rs2181953基因型及等位基因分布差异均无显著性(P均>0.05);不同性别及发病年龄的有混合家族史精神分裂症组与对照组rs947267基因型及等位基因分布差异无显著性(P>0.05);不同性别及早发型(发病年龄≤25岁)有混合家族史精神分裂症组与对照组rs2181953基因型及等位基因分布差异无显著性(P>0.05);晚发型(发病年龄>25岁)有混合家族史精神分裂症与对照组rs2181953基因型及等位基因分布差异显著(χ2=9.121,P=0.01与χ2=6.804,P=0.01),基因型A/A、T/T及等位基因A、T的OR值分别为7.083(P=0.007)、0.357(P=0.049)、2.531(P=0.009)、0.395(P=0.009)。结论:G72基因多态性可能与晚发型有混合家族史精神分裂症存在关联,其中rs2181953的A/A基因型与A等位基因是危险因子。     

The genetic deconstruction of psychosis

Psychiatric research, including the search for predisposing genes, has tended to proceed under the assumptions that schizophrenia and bipolar disorder, as defined in Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, and International Statistical Classification of Diseases, 10th Revision, are discrete disease entities with distinct etiology and pathogenesis and that these disease entities can be identified by current "operational" diagnostic conventions. However, recent findings emerging from genetic studies show increasing evidence for an overlap in genetic susceptibility across the traditional binary classification of psychosis. Moreover, the emerging evidence suggests the possibility of relatively specific relationships between genotype and psychopathology. For example, variation in Disrupted in Schizophrenia 1 (DISC1) and Neuregulin 1 (NRG1) may confer susceptibility to a form of illness with mixed features of schizophrenia and mania. The elucidation of genotype-phenotype relationships is at an early stage, but current findings highlight the need to consider alternative approaches to classification and conceptualization for psychiatric research rather than continuing to rely heavily on the traditional categorical approach. We can expect that, over the coming years, molecular genetics will catalyze a reappraisal of psychiatric nosology as well as contribute in a major way to our understanding of pathophysiology and to the development of improved treatments. However, our understanding of the brain mechanisms that link specific gene actions and products to the subjective experience of psychopathological symptoms is likely to be bridged by employing intermediate (or endo-) phenotypes in the domains such as cognition, neurophysiology, or neuroanatomy rather than relying upon clinical measures alone.     

Cognitive functioning in siblings discordant for schizophrenia

OBJECTIVE: The objective of this study was to investigate neuropsychological impairment as a genetically mediated risk indicator for schizophrenia while accounting for prevalence of schizotypy signs/symptoms in siblings. METHOD: Cognitive functioning in 25 individuals with schizophrenia, 25 unaffected siblings and 25 unrelated healthy controls, was assessed using neuropsychological tests of sustained attention, memory and learning, executive function, visual-spatial ability and psychomotor performance. RESULTS: Unaffected siblings demonstrated better performance than patients on some measures of memory and learning and executive function. Patients and siblings demonstrated impaired Full Scale IQ and verbal fluency, otherwise siblings performed similarly to healthy controls. Controlling for differences in IQ, the shared deficit in verbal fluency disappeared. CONCLUSION: Patients with schizophrenia and unaffected siblings (without schizotypy personality disorder) shared a neuropsychological deficit in verbal fluency. This deficit appeared to be mediated by IQ. Deficits, which differentiated patients from controls, may not be inherited and perhaps are related to the manifestation or treatment of schizophrenia.     

Genetic models of schizophrenia and bipolar disorder

Abstract Schizophrenia and affective disorder have been considered to be nosologically and etiologically distinct disorders. This postulate is challenged by progress in new biological research. Both disorders are strongly influenced by genetic factors; thus genetic research is a main contributor to this discussion. We review current evidence of the genetic relationship between schizophrenia and affective disorders, mainly bipolar disorder (the various genetic research methods have been particularly applied to bipolar disorder). Recent family and twin studies reveal a growing consistency in demonstrating cosegregation between both disorders which is difficult to detect with certainty given the low base rates. Systematic molecular genetic search for specific genes impacting on either disorder has now identified one gene which is apparently involved in both disorders (G72/G30); other candidate genes reveal some evidence to present as susceptibility genes with very modest effects for each of both disorders, although not consistently so (e. g., COMT, BDNF). There is room for speculation about other common susceptibility genes, given the overlap between candidate regions for schizophrenia and those for bipolar disorder emerging from linkage studies.     

Neural correlates of movement generation in the ‘at‐risk mental state’

Broome MR, Matthiasson P, Fusar‐Poli P, Woolley JB, Johns LC, Tabraham P, Bramon E, Valmaggia L, Williams SCR, Brammer MJ, Chitnis X, McGuire PK. Neural correlates of movement generation in the ‘at‐risk mental state’. Objective: People with ‘prodromal’ symptoms have a very high risk of developing psychosis. We examined the neurocognitive basis of this vulnerability by using functional MRI to study subjects with an at‐risk mental state (ARMS) while they performed a random movement generation task. Method: Cross‐sectional comparison of individuals with an ARMS (n = 17), patients with first episode schizophreniform psychosis (n = 10) and healthy volunteers (n = 15). Subjects were studied using functional MRI while they performed a random movement generation paradigm. Results: During random movement generation, the ARMS group showed less activation in the left inferior parietal cortex than controls, but greater activation than in the first episode group. Conclusion: The ARMS is associated with abnormalities of regional brain function that are qualitatively similar to those in patients who have recently presented with psychosis but less severe.     

Elaborative verbal encoding and altered anterior parahippocampal activation in adolescents and young adults at genetic risk for schizophrenia using FMRI.

BACKGROUND: First-degree relatives of persons with schizophrenia are at elevated risk for the illness, demonstrate deficits in verbal memory, and exhibit structural abnormalities in the medial temporal lobe (MTL). We used functional magnetic resonance imaging (fMRI) to assess brain activity in the MTL during novel and repeated word-pair encoding. METHODS: Participants were 21 non-psychotic, first-degree relatives of persons with schizophrenia and 26 matched healthy controls (ages 13-28). fMRI signal change was measured using a Siemens 1.5T MR scanner, and data were analyzed using SPM-2. Verbal memory was assessed using the Miller Selfridge (MS) Context Memory test prior to scanning. RESULTS: The groups were comparable on demographics, intelligence and post-scan word recognition. Relatives at genetic risk (GR) had significantly more psychopathology than controls and worse performance on the MS test (p < .05). GR participants exhibited greater repetition suppression of activation in the left and right anterior parahippocampus (PHA, in the region of the entorhinal cortex region), after controlling for possible confounders. Controls and GR participants with above-median MS performance showed significantly greater repetition suppression of activation in left inferior frontal gyrus than those scoring below the median. CONCLUSIONS: This is the first study to demonstrate an alteration of brain activity in the PHA in persons at GR for schizophrenia.