Anne Kästner

A myelin gene causative of a catatonia-depression syndrome upon aging

Severe mental illnesses have been linked to white matter abnormalities, documented by postmortem studies. However, cause and effect have remained difficult to distinguish. CNP (2′,3′‐cyclic nucleotide 3′‐phosphodiesterase) is among the oligodendrocyte/myelin‐associated genes most robustly reduced on mRNA and protein level in brains of schizophrenic, bipolar or major depressive patients. This suggests that CNP reduction might be critical for a more general disease process and not restricted to a single diagnostic category. We show here that reduced expression of CNP is the primary cause of a distinct behavioural phenotype, seen only upon aging as an additional ‘pro‐inflammatory hit’. This phenotype is strikingly similar in Cnp heterozygous mice and patients with mental disease carrying the AA genotype at CNP SNP rs2070106. The characteristic features in both species with their partial CNP ‘loss‐of‐function’ genotype are best described as ‘catatonia‐depression’ syndrome. As a consequence of perturbed CNP expression, mice show secondary low‐grade inflammation/neurodegeneration. Analogously, in man, diffusion tensor imaging points to axonal loss in the frontal corpus callosum. To conclude, subtle white matter abnormalities inducing neurodegenerative changes can cause/amplify psychiatric diseases.

Heterozygous Ambra1 deficiency in mice: A genetic trait with autism-like behavior restricted to the female gender.

Autism-spectrum disorders (ASD) are heterogeneous, highly heritable neurodevelopmental conditions affecting around 0.5% of the population across cultures, with a male/female ratio of approximately 4:1. Phenotypically, ASD are characterized by social interaction and communication deficits, restricted interests, repetitive behaviors, and reduced cognitive flexibility. Identified causes converge at the level of the synapse, ranging from mutation of synaptic genes to quantitative alterations in synaptic protein expression, e.g., through compromised transcriptional or translational control. We wondered whether reduced turnover and degradation of synapses, due to deregulated autophagy, would lead to similar phenotypical consequences. Ambra1, strongly expressed in cortex, hippocampus, and striatum, is a positive regulator of Beclin1, a principal player in autophagosome formation. While homozygosity of the Ambra1 null mutation causes embryonic lethality, heterozygous mice with reduced Ambra1 expression are viable, reproduce normally, and lack any immediately obvious phenotype. Surprisingly, comprehensive behavioral characterization of these mice revealed an autism-like phenotype in Ambra1+/− females only, including compromised communication and social interactions, a tendency of enhanced stereotypies/repetitive behaviors, and impaired cognitive flexibility. Reduced ultrasound communication was found in adults as well as pups, which achieved otherwise normal neurodevelopmental milestones. These features were all absent in male Ambra1+/− mice. As a first hint explaining this gender difference, we found a much stronger reduction of Ambra1 protein in the cortex of Ambra1+/− females compared to males. To conclude, Ambra1 deficiency can induce an autism-like phenotype. The restriction to the female gender of autism-generation by a defined genetic trait is unique thus far and warrants further investigation.

Circulating damage marker profiles support a neuroprotective effect of erythropoietin in ischemic stroke patients

The German Multicenter EPO Stroke Trial, which investigated safety and efficacy of erythropoietin (EPO) treatment in ischemic stroke, was formally declared a negative study. Exploratory subgroup analysis, however, revealed that patients not receiving thrombolysis most likely benefited from EPO during clinical recovery, a result demonstrated in the findings of the Göttingen EPO Stroke Study. The present work investigated whether the positive signal on clinical outcome in this patient subgroup was mirrored by respective poststroke biomarker profiles. All patients of the German Multicenter EPO Stroke Trial nonqualifying for thrombolysis were included if they (a) were treated per protocol and (b) had at least two of the five follow-up blood samples for circulating damage markers drawn (n = 163). The glial markers S100B and glial fibrillary acid protein (GFAP) and the neuronal marker ubiquitin C-terminal hydrolase (UCH-L1) were measured by enzyme-linked immunosorbent assay in serum on d 1, 2, 3, 4 and 7 poststroke. All biomarkers increased poststroke. Overall, EPO-treated patients had significantly lower concentrations (area under the curve) over 7 d of observation, as reflected by the composite score of all three markers (Cronbach α = 0.811) and by UCH-L1. S100B and GFAP showed a similar tendency. To conclude, serum biomarker profiles, as an outcome measure of brain damage, corroborate an advantageous effect of EPO in ischemic stroke. In particular, reduction in the neuronal damage marker UCH-L1 may reflect neuroprotection by EPO.

The brain as immunoprecipitator of serum autoantibodies against N-Methyl-D-aspartate receptor subunit NR1

Autoantibodies (AB) against N‐methyl‐D‐aspartate receptor subunit NR1 (NMDAR1) are highly seroprevalent in health and disease. Symptomatic relevance may arise upon compromised blood–brain barrier (BBB). However, it remained unknown whether circulating NMDAR1 AB appear in the cerebrospinal fluid (CSF). Of n = 271 subjects with CSF–serum pairs, 26 were NMDAR1 AB seropositive, but only 1 was CSF positive. Contrariwise, tetanus AB (non–brain‐binding) were present in serum and CSF of all subjects, with CSF levels higher upon BBB dysfunction. Translational mouse experiments proved the hypothesis that the brain acts as an ‘immunoprecipitator’; simultaneous injection of NMDAR1 AB and the non–brain‐binding green fluorescent protein AB resulted in high detectability of the former in brain and the latter in CSF. ANN NEUROL 2016;79:144–151

The brain as ′immunoprecipitator′ of serum autoantibodies against NMDAR1

Autoantibodies (AB) against N‐methyl‐D‐aspartate receptor subunit NR1 (NMDAR1) are highly seroprevalent in health and disease. Symptomatic relevance may arise upon compromised blood–brain barrier (BBB). However, it remained unknown whether circulating NMDAR1 AB appear in the cerebrospinal fluid (CSF). Of n = 271 subjects with CSF–serum pairs, 26 were NMDAR1 AB seropositive, but only 1 was CSF positive. Contrariwise, tetanus AB (non–brain‐binding) were present in serum and CSF of all subjects, with CSF levels higher upon BBB dysfunction. Translational mouse experiments proved the hypothesis that the brain acts as an ‘immunoprecipitator’; simultaneous injection of NMDAR1 AB and the non–brain‐binding green fluorescent protein AB resulted in high detectability of the former in brain and the latter in CSF. ANN NEUROL 2016;79:144–151

A single gene defect causing claustrophobia

Claustrophobia, the well-known fear of being trapped in narrow/closed spaces, is often considered a conditioned response to traumatic experience. Surprisingly, we found that mutations affecting a single gene, encoding a stress-regulated neuronal protein, can cause claustrophobia. Gpm6a-deficient mice develop normally and lack obvious behavioral abnormalities. However, when mildly stressed by single-housing, these mice develop a striking claustrophobia-like phenotype, which is not inducible in wild-type controls, even by severe stress. The human GPM6A gene is located on chromosome 4q32-q34, a region linked to panic disorder. Sequence analysis of 115 claustrophobic and non-claustrophobic subjects identified nine variants in the noncoding region of the gene that are more frequent in affected individuals (P=0.028). One variant in the 3′untranslated region was linked to claustrophobia in two small pedigrees. This mutant mRNA is functional but cannot be silenced by neuronal miR124 derived itself from a stress-regulated transcript. We suggest that loosing dynamic regulation of neuronal GPM6A expression poses a genetic risk for claustrophobia.

Common Variants of the Genes Encoding Erythropoietin and Its Receptor Modulate Cognitive Performance in Schizophrenia

Erythropoietin (EPO) improves cognitive performance in clinical studies and rodent experiments. We hypothesized that an intrinsic role of EPO for cognition exists, with particular relevance in situations of cognitive decline, which is reflected by associations of EPO and EPO receptor (EPOR) genotypes with cognitive functions. To prove this hypothesis, schizophrenic patients (N > 1000) were genotyped for 5′ upstream-located gene variants, EPO SNP rs1617640 (T/G) and EPOR STR(GA)n. Associations of these variants were obtained for cognitive processing speed, fine motor skills and short-term memory readouts, with one particular combination of genotypes superior to all others (p < 0.0001). In an independent healthy control sample (N > 800), these associations were confirmed. A matching preclinical study with mice demonstrated cognitive processing speed and memory enhanced upon transgenic expression of constitutively active EPOR in pyramidal neurons of cortex and hippocampus. We thus predicted that the human genotypes associated with better cognition would reflect gain-of-function effects. Indeed, reporter gene assays and quantitative transcriptional analysis of peripheral blood mononuclear cells showed genotype-dependent EPO/EPOR expression differences. Together, these findings reveal a role of endogenous EPO/EPOR for cognition, at least in schizophrenic patients.

Accumulated common variants in the broader fragile X gene family modulate autistic phenotypes

Fragile X syndrome (FXS) is mostly caused by a CGG triplet expansion in the fragile X mental retardation 1 gene (FMR1). Up to 60% of affected males fulfill criteria for autism spectrum disorder (ASD), making FXS the most frequent monogenetic cause of syndromic ASD. It is unknown, however, whether normal variants (independent of mutations) in the fragile X gene family (FMR1, FXR1, FXR2) and in FMR2 modulate autistic features. Here, we report an accumulation model of 8 SNPs in these genes, associated with autistic traits in a discovery sample of male patients with schizophrenia (N = 692) and three independent replicate samples: patients with schizophrenia (N = 626), patients with other psychiatric diagnoses (N = 111) and a general population sample (N = 2005). For first mechanistic insight, we contrasted microRNA expression in peripheral blood mononuclear cells of selected extreme group subjects with high‐ versus low‐risk constellation regarding the accumulation model. Thereby, the brain‐expressed miR‐181 species emerged as potential “umbrella regulator”, with several seed matches across the fragile X gene family and FMR2. To conclude, normal variation in these genes contributes to the continuum of autistic phenotypes.

Autism beyond diagnostic categories: characterization of autistic phenotypes in schizophrenia.

BackgroundBehavioral phenotypical continua from health to disease suggest common underlying mechanisms with quantitative rather than qualitative differences. Until recently, autism spectrum disorders and schizophrenia were considered distinct nosologic entities. However, emerging evidence contributes to the blurring of symptomatic and genetic boundaries between these conditions. The present study aimed at quantifying behavioral phenotypes shared by autism spectrum disorders and schizophrenia to prepare the ground for biological pathway analyses.MethodsSpecific items of the Positive and Negative Syndrome Scale were employed and summed up to form a dimensional autism severity score (PAUSS). The score was created in a schizophrenia sample (N = 1156) and validated in adult high-functioning autism spectrum disorder (ASD) patients (N = 165). To this end, the Autism Diagnostic Observation Schedule (ADOS), the Autism (AQ) and Empathy Quotient (EQ) self-rating questionnaires were applied back to back with the newly developed PAUSS.ResultsPAUSS differentiated between ASD, schizophrenia and a disease-control sample and substantially correlated with the Autism Diagnostic Observation Schedule. Patients with ADOS scores ≥12 obtained highest, those with scores <7 lowest PAUSS values. AQ and EQ were not found to vary dependent on ADOS diagnosis. ROC curves for ADOS and PAUSS resulted in AuC values of 0.9 and 0.8, whereas AQ and EQ performed at chance level in the prediction of ASD.ConclusionsThis work underscores the convergence of schizophrenia negative symptoms and autistic phenotypes. PAUSS evolved as a measure capturing the continuous nature of autistic behaviors. The definition of extreme-groups based on the dimensional PAUSS may permit future investigations of genetic constellations modulating autistic phenotypes.

Monogenic heritable autism gene neuroligin impacts Drosophila social behaviour

Autism spectrum disorders (ASDs) are characterized by deficits in social interactions, language development and repetitive behaviours. Multiple genes involved in the formation, specification and maintenance of synapses have been identified as risk factors for ASDs development. Among these are the neuroligin genes which code for postsynaptic cell adhesion molecules that induce the formation of presynapses, promote their maturation and modulate synaptic functions in both vertebrates and invertebrates. Neuroligin-deficient mice display abnormal social and vocal behaviours that resemble ASDs symptoms. Here we show for the fly Drosophila melanogaster that deletion of the dnl2 gene, coding for one of four Neuroligin isoforms, impairs social interactions, alters acoustic communication signals, and affects the transition between different behaviours. dnl2-Deficient flies maintain larger distances to conspecifics and males perform less female-directed courtship and male-directed aggressive behaviours while the patterns of these behaviours and general locomotor activity were not different from wild type controls. Since tests for olfactory, visual and auditory perception revealed no sensory impairments of dnl2-deficient mutants, reduced social interactions seem to result from altered excitability in central nervous neuropils that initiate social behaviours. Our results demonstrate that Neuroligins are phylogenetically conserved not only regarding their structure and direct function at the synapse but also concerning a shared implication in the regulation of social behaviours that dates back to common ancestors of humans and flies. In addition to previously described mouse models, Drosophila can thus be used to study the contribution of Neuroligins to synaptic function, social interactions and their implication in ASDs.