The protocadherin 17 gene affects cognition, personality, amygdala structure and function, synapse development and risk of major mood disorders.

Major mood disorders, which primarily include bipolar disorder and major depressive disorder, are the leading cause of disability worldwide and pose a major challenge in identifying robust risk genes. Here, we present data from independent large-scale clinical data sets (including 29 557 cases and 32 056 controls) revealing brain expressed protocadherin 17 (PCDH17) as a susceptibility gene for major mood disorders. Single-nucleotide polymorphisms (SNPs) spanning the PCDH17 region are significantly associated with major mood disorders; subjects carrying the risk allele showed impaired cognitive abilities, increased vulnerable personality features, decreased amygdala volume and altered amygdala function as compared with non-carriers. The risk allele predicted higher transcriptional levels of PCDH17 mRNA in postmortem brain samples, which is consistent with increased gene expression in patients with bipolar disorder compared with healthy subjects. Further, overexpression of PCDH17 in primary cortical neurons revealed significantly decreased spine density and abnormal dendritic morphology compared with control groups, which again is consistent with the clinical observations of reduced numbers of dendritic spines in the brains of patients with major mood disorders. Given that synaptic spines are dynamic structures which regulate neuronal plasticity and have crucial roles in myriad brain functions, this study reveals a potential underlying biological mechanism of a novel risk gene for major mood disorders involved in synaptic function and related intermediate phenotypes.

Adjunctive raloxifene treatment improves attention and memory in men and women with schizophrenia.

There is increasing clinical and molecular evidence for the role of hormones and specifically estrogen and its receptor in schizophrenia. A selective estrogen receptor modulator, raloxifene, stimulates estrogen-like activity in brain and can improve cognition in older adults. The present study tested the extent to which adjunctive raloxifene treatment improved cognition and reduced symptoms in young to middle-age men and women with schizophrenia. Ninety-eight patients with a diagnosis of schizophrenia or schizoaffective disorder were recruited into a dual-site, thirteen-week, randomized, double-blind, placebo-controlled, crossover trial of adjunctive raloxifene treatment in addition to their usual antipsychotic medications. Symptom severity and cognition in the domains of working memory, attention/processing speed, language and verbal memory were assessed at baseline, 6 and 13 weeks. Analyses of the initial 6-week phase of the study using a parallel groups design (with 39 patients receiving placebo and 40 receiving raloxifene) revealed that participants receiving adjunctive raloxifene treatment showed significant improvement relative to placebo in memory and attention/processing speed. There was no reduction in symptom severity with treatment compared with placebo. There were significant carryover effects, suggesting some cognitive benefits are sustained even after raloxifene withdrawal. Analysis of the 13-week crossover data revealed significant improvement with raloxifene only in attention/processing speed. This is the first study to show that daily, oral adjunctive raloxifene treatment at 120 mg per day has beneficial effects on attention/processing speed and memory for both men and women with schizophrenia. Thus, raloxifene may be useful as an adjunctive treatment for cognitive deficits associated with schizophrenia.

Intrinsic and synaptic homeostatic plasticity in motoneurons from mice with glycine receptor mutations.

Inhibitory synaptic inputs to hypoglossal motoneurons (HMs) are important for modulating excitability in brainstem circuits. Here we ask whether reduced inhibition, as occurs in three murine mutants with distinct naturally occurring mutations in the glycine receptor (GlyR), leads to intrinsic and/or synaptic homeostatic plasticity. Whole cell recordings were obtained from HMs in transverse brainstem slices from wild-type (wt), spasmodic (spd), spastic (spa), and oscillator (ot) mice (C57Bl/6, approximately postnatal day 21). Passive and action potential (AP) properties in spd and ot HMs were similar to wt. In contrast, spa HMs had lower input resistances, more depolarized resting membrane potentials, higher rheobase currents, smaller AP amplitudes, and slower afterhyperpolarization current decay times. The excitability of HMs, assessed by "gain" in injected current/firing-frequency plots, was similar in all strains whereas the incidence of rebound spiking was increased in spd. The difference between recruitment and derecruitment current (i.e., ΔI) for AP discharge during ramp current injection was more negative in spa and ot. GABAA miniature inhibitory postsynaptic current (mIPSC) amplitude was increased in spa and ot but not spd, suggesting diminished glycinergic drive leads to compensatory adjustments in the other major fast inhibitory synaptic transmitter system in these mutants. Overall, our data suggest long-term reduction in glycinergic drive to HMs results in changes in intrinsic and synaptic properties that are consistent with homeostatic plasticity in spa and ot but not in spd. We propose such plasticity is an attempt to stabilize HM output, which succeeds in spa but fails in ot.

Molecular evidence of N-methyl-D-aspartate receptor hypofunction in schizophrenia.

Blockade of N-methyl-D-aspartate receptors (NMDARs) produces behavior in healthy people that is similar to the psychotic symptoms and cognitive deficits of schizophrenia and can exacerbate symptoms in people with schizophrenia. However, an endogenous brain disruption of NMDARs has not been clearly established in schizophrenia. We measured mRNA transcripts for five NMDAR subunit mRNAs and protein for the NR1 subunit in the dorsolateral prefrontal cortex (DLPFC) of schizophrenia and control (n=74) brains. Five NMDAR single-nucleotide polymorphisms (SNPs) previously associated with schizophrenia were tested for association with NMDAR mRNAs in postmortem brain and for association with cognitive ability in an antemortem cohort of 101 healthy controls and 48 people with schizophrenia. The NR1 subunit (mRNA and protein) and NR2C mRNA were decreased in postmortem brain from people with schizophrenia (P=0.004, P=0.01 and P=0.01, respectively). In the antemortem cohort, the minor allele of NR2B rs1805502 (T5988C) was associated with significantly lower reasoning ability in schizophrenia. In the postmortem brain, the NR2B rs1805502 (T5988C) C allele was associated with reduced expression of NR1 mRNA and protein in schizophrenia. Reduction in NR1 and NR2C in the DLPFC of people with schizophrenia may lead to altered NMDAR stoichiometry and provides compelling evidence for an endogenous NMDAR deficit in schizophrenia. Genetic variation in the NR2B gene predicts reduced levels of the obligatory NR1 subunit, suggesting a novel mechanism by which the NR2B SNP may negatively influence other NMDAR subunit expression and reasoning ability in schizophrenia.

Preclinical trials in autosomal dominant AD: implementation of the DIAN-TU trial.

The Dominantly Inherited Alzheimer's Network Trials Unit (DIAN-TU) was formed to direct the design and management of interventional therapeutic trials of international DIAN and autosomal dominant Alzheimer's disease (ADAD) participants. The goal of the DIAN-TU is to implement safe trials that have the highest likelihood of success while advancing scientific understanding of these diseases and clinical effects of proposed therapies. The DIAN-TU has launched a trial design that leverages the existing infrastructure of the ongoing DIAN observational study, takes advantage of a variety of drug targets, incorporates the latest results of biomarker and cognitive data collected during the observational study, and implements biomarkers measuring Alzheimer's disease (AD) biological processes to improve the efficiency of trial design. The DIAN-TU trial design is unique due to the sophisticated design of multiple drugs, multiple pharmaceutical partners, academics servings as sponsor, geographic distribution of a rare population and intensive safety and biomarker assessments. The implementation of the operational aspects such as home health research delivery, safety magnetic resonance imagings (MRIs) at remote locations, monitoring clinical and cognitive measures, and regulatory management involving multiple pharmaceutical sponsors of the complex DIAN-TU trial are described.

Axonal damage and astrocytosis are biological correlates of grey matter network integrity loss: a cohort study in autosomal dominant Alzheimer disease.

Brain development and maturation leads to grey matter networks that can be measured using magnetic resonance imaging. Network integrity is an indicator of information processing capacity which declines in neurodegenerative disorders such as Alzheimer disease (AD). The biological mechanisms causing this loss of network integrity remain unknown. Cerebrospinal fluid (CSF) protein biomarkers are available for studying diverse pathological mechanisms in humans and can provide insight into decline. We investigated the relationships between 10 CSF proteins and network integrity in mutation carriers (N=219) and noncarriers (N=136) of the Dominantly Inherited Alzheimer Network Observational study. Abnormalities in Aß, Tau, synaptic (SNAP-25, neurogranin) and neuronal calcium-sensor protein (VILIP-1) preceded grey matter network disruptions by several years, while inflammation related (YKL-40) and axonal injury (NfL) abnormalities co-occurred and correlated with network integrity. This suggests that axonal loss and inflammation play a role in structural grey matter network changes. Key points: Abnormal levels of fluid markers for neuronal damage and inflammatory processes in CSF are associated with grey matter network disruptions.The strongest association was with NfL, suggesting that axonal loss may contribute to disrupted network organization as observed in AD.Tracking biomarker trajectories over the disease course, changes in CSF biomarkers generally precede changes in brain networks by several years.

Probing glycine receptor stoichiometry in superficial dorsal horn neurones using the spasmodic mouse.

Inhibitory glycine receptors (GlyRs) are pentameric ligand gated ion channels composed of α and ß subunits assembled in a 2:3 stoichiometry. The α1/ßheteromer is considered the dominant GlyR isoform at 'native' adult synapses in the spinal cord and brainstem. However, the α3 GlyR subunit is concentrated in the superficial dorsal horn (SDH: laminae I-II), a spinal cord region important for processing nociceptive signals from skin, muscle and viscera. Here we use the spasmodic mouse, which has a naturally occurring mutation (A52S) in the α1 subunit of the GlyR, to examine the effect of the mutation on inhibitory synaptic transmission and homeostatic plasticity, and to probe for the presence of various GlyR subunits in the SDH.We usedwhole cell recording (at 22-24◦C) in lumbar spinal cord slices obtained from ketamine-anaesthetized (100 mg kg⁻¹, I.P.) spasmodic and wild-type mice (mean age P27 and P29, respectively, both sexes). The amplitude and decay time constants of GlyR mediated mIPSCs in spasmodic micewere reduced by 25% and 50%, respectively (42.0 ± 3.6 pA vs. 31.0 ± 1.8 pA, P <0.05 and 7.4 ± 0.5 ms vs. 5.0 ± 0.4 ms, P <0.05; means ± SEM, n =34 and 31, respectively). Examination of mIPSC amplitude versus rise time and decay time relationships showed these differences were not due to electrotonic effects. Analysis of GABAAergic mIPSCs and A-type potassium currents revealed altered GlyR mediated neurotransmission was not accompanied by the synaptic or intrinsic homeostatic plasticity previously demonstrated in another GlyR mutant, spastic. Application of glycine to excised outside-out patches from SDH neurones showed glycine sensitivity was reduced more than twofold in spasmodic GlyRs (EC50 =130 ± 20 µM vs. 64 ± 11 µM, respectively; n =8 and 15, respectively). Differential agonist sensitivity and mIPSC decay times were subsequently used to probe for the presence of α1-containing GlyRs in SDHneurones.Glycine sensitivity, based on the response to 1-3 µM glycine, was reduced in>75% of neurones tested and decay times were faster in the spasmodic sample. Together, our data suggest most GlyRs and glycinergic synapses in the SDH contain α1 subunits and few are composed exclusively of α3 subunits. Therefore, future efforts to design therapies that target the α3 subunit must consider the potential interaction between α1 and α3 subunits in the GlyR.

Community interest in predictive genetic testing for susceptibility to major depressive disorder in a large national sample.

BACKGROUND: Despite international concern about unregulated predictive genetic testing, there are surprisingly few data on both the determinants of community interest in such testing and its psychosocial impact. METHOD: A large population-based public survey with community-dwelling adults (n=1046) ascertained through random digit dialling. Attitudes were assessed by structured interviews. RESULTS: The study found strong interest in predictive genetic testing for a reported susceptibility to depression. Once the benefits and disadvantages of such testing had been considered, there was significantly greater interest in seeking such a test through a doctor (63%) compared to direct-to-consumer (DTC; 40%) (p<0.001). Personal history of mental illness [odds ratio (OR) 2.58, p<0.001], self-estimation of being at higher than average risk for depression (OR 1.92, p<0.001), belief that a genetic component would increase rather than decrease stigma (OR 1.62, p<0.001), and endorsement of benefits of genetic testing (OR 3.47, p<0.001) significantly predicted interest in having such a test. CONCLUSIONS: Despite finding attitudes that genetic links to mental illness would increase rather than decrease stigma, we found strong community acceptance of depression risk genotyping, even though a predisposition to depression may only manifest upon exposure to stressful life events. Our results suggest that there will be a strong demand for predictive genetic testing.

Interactions between BDNF Val66Met polymorphism and early life stress predict brain and arousal pathways to syndromal depression and anxiety.

Individual risk markers for depression and anxiety disorders have been identified but the explicit pathways that link genes and environment to these markers remain unknown. Here we examined the explicit interactions between the brain-derived neurotrophic factor (BDNF) Val66Met gene and early life stress (ELS) exposure in brain (amygdala-hippocampal-prefrontal gray matter volume), body (heart rate), temperament and cognition in 374 healthy European volunteers assessed for depression and anxiety symptoms. Brain imaging data were based on a subset of 89 participants. Multiple regression analysis revealed main effects of ELS for body arousal (resting heart rate, P=0.005) and symptoms (depression and anxiety, P<0.001) in the absence of main effects for BDNF. In addition, significant BDNF-ELS interactions indicated that BDNF Met carriers exposed to greater ELS have smaller hippocampal and amygdala volumes (P=0.013), heart rate elevations (P=0.0002) and a decline in working memory (P=0.022). Structural equation path modeling was used to determine if this interaction predicts anxiety and depression by mediating effects on the brain, body and cognitive measures. The combination of Met carrier status and exposure to ELS predicted reduced gray matter in hippocampus (P<0.001), and associated lateral prefrontal cortex (P<0.001) and, in turn, higher depression (P=0.005). Higher depression was associated with poorer working memory (P=0.005), and slowed response speed. The BDNF Met-ELS interaction also predicted elevated neuroticism and higher depression and anxiety by elevations in body arousal (P<0.001). In contrast, the combination of BDNF V/V genotype and ELS predicted increases in gray matter of the amygdala (P=0.003) and associated medial prefrontal cortex (P<0.001), which in turn predicted startle-elicited heart rate variability (P=0.026) and higher anxiety (P=0.026). Higher anxiety was linked to verbal memory, and to impulsivity. These effects were specific to the BDNF gene and were not evident for the related 5HTT-LPR polymorphism. Overall, these findings are consistent with the correlation of depression and anxiety, yet suggest that partially differentiated gene-brain cognition pathways to these syndromes can be identified, even in a nonclinical sample. Such findings may aid establishing an evidence base for more tailored intervention strategies.

A genome screen of 35 bipolar affective disorder pedigrees provides significant evidence for a susceptibility locus on chromosome 15q25-26.

Bipolar affective disorder is a heritable, relatively common, severe mood disorder with lifetime prevalence up to 4%. We report the results of a genome-wide linkage analysis conducted on a cohort of 35 Australian bipolar disorder families which identified evidence of significant linkage on chromosome 15q25-26 and suggestive evidence of linkage on chromosomes 4q, 6q and 13q. Subsequent fine-mapping of the chromosome 15q markers, using allele frequencies calculated from our cohort, gave significant results with a maximum two-point LOD score of 3.38 and multipoint LOD score of 4.58 for marker D15S130. Haplotype analysis based on pedigree-specific, identical-by-descent allele sharing, supported the location of a bipolar susceptibility gene within the Z(max-1) linkage confidence interval of 17 cM, or 6.2 Mb, between markers D15S979 and D15S816. Non-parametric and affecteds-only linkage analysis further verified the linkage signal in this region. A maximum NPL score of 3.38 (P=0.0008) obtained at 107.16 cM (near D15S130), and a maximum two-point LOD score of 2.97 obtained at marker D15S1004 (affecteds only), support the original genome-wide findings on chromosome 15q. These results are consistent with four independent positive linkage studies of mood and psychotic disorders, and raise the possibility that a common gene for susceptibility to bipolar disorder, and other psychiatric disorders may lie in this chromosome 15q25-26 region.

Transient expression shows ligand gating and allosteric potentiation of GABAA receptor subunits.

Human gamma-aminobutyric acid A (GABAA) receptor subunits were expressed transiently in cultured mammalian cells. This expression system allows the simultaneous characterization of ligand-gated ion channels by electrophysiology and by pharmacology. Thus, coexpression of the alpha and beta subunits of the GABAA receptor generated GABA-gated chloride channels and binding sites for GABAA receptor ligands. Channels consisting of only alpha or beta subunits could also be detected. These homomeric channels formed with reduced efficiencies compared to the heteromeric receptors. Both of these homomeric GABA-responsive channels were potentiated by barbiturate, indicating that sites for both ligand-gating and allosteric potentiation are present on receptors assembled from either subunit.

Distinct agonist- and antagonist-binding sites on the glycine receptor.

The distinction between receptor-binding sites for agonists and antagonists underpins the pharmacological differences between these two classes of ligands. In the glycine receptor, antagonist (strychnine) binding requires an interaction with residues Lys-200 and Tyr-202. We now demonstrate that the agonist-binding site of this receptor is located at the residue Thr-204. The agonist-binding site interaction is thus likely to be mediated by hydrogen bonding and not by ionic interactions. Our results demonstrate that, in contrast to other studies of ligand-gated ion channel receptors, agonist- and antagonist-binding sites are composed of distinct amino acid residues.

Mutation of an arginine residue in the human glycine receptor transforms beta-alanine and taurine from agonists into competitive antagonists.

Agonist binding to the inhibitory glycine receptor (GlyR) initiates the opening of a chloride-selective channel that modulates the neuronal membrane potential. Point mutations of the GlyR, substituting Arg-271 with either Leu or Gln, have been shown to underlie the inherited neurological disorder startle disease (hyperekplexia). We show that these substitutions result in the redistribution of GlyR single-channel conductances to lower conductance levels. Additionally, the binding of the glycinergic agonists beta-alanine and taurine to mutated GlyRs does not initiate a chloride current, but instead competitively antagonizes currents activated by glycine. These findings are consistent with mutations of Arg-271 resulting in the uncoupling of the agonist binding process from the channel activation mechanism of the receptor.

Functional chloride channels by mammalian cell expression of rat glycine receptor subunit.

Cultured human cells were transfected with cloned rat glycine receptor (GlyR) 48 kd subunit cDNA. In these cells glycine elicited large chloride currents (up to 1.5 nA), which were blocked by nanomolar concentrations of strychnine. However, no corresponding high-affinity binding of [3H]strychnine was detected in membrane preparations of the transfected cells. Analysis by monoclonal antibodies specific for the 48 kd subunit revealed high expression levels of this membrane protein. After solubilization, the 48 kd subunit behaved as a macromolecular complex when analyzed by sucrose density centrifugation. Approximately 50% of the solubilized complex bound specifically to a 2-aminostrychnine affinity column, indicating the existence of low-affinity antagonist binding sites on most of the expressed GlyR protein. Thus, the 48 kd strychnine binding subunit efficiently assembles into high molecular weight complexes, resembling the native spinal cord GlyR. However, formation of functional receptor channels of high affinity for strychnine occurs with low efficiency.

Two novel GABAA receptor subunits exist in distinct neuronal subpopulations.

Two cDNAs encoding novel GABAA receptor subunits were isolated from a rat brain library. These subunits, gamma 2 and delta, share approximately 35% sequence identity with alpha and beta subunits and form functional GABA-gated chloride channels when expressed alone in vitro. The gamma 2 subunit is the rat homolog of the human gamma 2 subunit recently shown to be important for benzodiazepine pharmacology. Cellular localization of the mRNAs encoding the gamma 2 and delta subunits in rat brain revealed that largely distinct neuronal subpopulations express the two subunits. The delta subunit distribution resembles that of the high affinity GABAA receptor labeled with [3H]muscimol; the gamma 2 subunit distribution resembles that of GABAA/benzodiazepine receptors labeled with [3H]flunitrazepam. These findings have implications for the composition of two different GABAA receptor subtypes and for information processing in networks using GABA for signaling.

Chromosomal localization of GABAA receptor subunit genes: relationship to human genetic disease.

Hybridization of GABAA receptor probes to human chromosomes in situ and to DNA from sorted human chromosomes has localized the genes encoding a beta subunit and three isoforms of the alpha subunit. The alpha 2 and beta genes are both located on chromosome 4 in bands p12-p13 and may be adjacent. The alpha 1 gene is on chromosome 5 (bands q34-q35) and the alpha 3 gene is on the X chromosome. The alpha 3 locus was mapped also on the mouse X chromosome using genetic break-point analysis in an interspecies pedigree. The combined results locate the human alpha 3 gene within band Xq28, in a location that makes it a candidate gene for the X-linked form of manic depression.

Altered motor activity, exploration and anxiety in heterozygous neuregulin 1 mutant mice: implications for understanding schizophrenia.

Human genetic studies have shown that neuregulin 1 (NRG1) is a potential susceptibility gene for schizophrenia. Nrg1 influences various neurodevelopmental processes, which are potentially related to schizophrenia. The neurodevelopmental theory of schizophrenia suggests that interactions between genetic and environmental factors are responsible for biochemical alterations leading to schizophrenia. To investigate these interactions and to match experimental design with the pathophysiology of schizophrenia, we applied a comprehensive behavioural phenotyping strategy for motor activity, exploration and anxiety in a heterozygous Nrg1 transmembrane domain mutant mouse model (Nrg1 HET) using different housing conditions and age groups. We observed a locomotion- and exploration-related hyperactive phenotype in Nrg1 HETs. Increased age had a locomotion- and exploration-inhibiting effect, which was significantly attenuated in mutant mice. Environmental enrichment (EE) had a stimulating influence on locomotion and exploration. The impact of EE was more pronounced in Nrg1 hypomorphs. Our study also showed a moderate task-specific anxiolytic-like phenotype for Nrg1 HETs, which was influenced by external factors. The behavioural phenotype detected in heterozygous Nrg1 mutant mice is not specific to schizophrenia per se, but the increased sensitivity of mutant mice to exogenous factors is consistent with the pathophysiology of schizophrenia and the neurodevelopmental theory. Our findings reinforce the importance of carefully controlling experimental designs for external factors and of comprehensive, integrative phenotyping strategies. Thus, Nrg1 HETs may, in combination with other genetic and drug models, help to clarify pathophysiological mechanisms behind schizophrenia.

Heterozygous neuregulin 1 mice are more sensitive to the behavioural effects of Delta9-tetrahydrocannabinol.

RATIONALE: Cannabis use may precipitate schizophrenia especially if the individual has a genetic vulnerability to this mental disorder. Human and animal research indicates that neuregulin 1 (Nrg1) is a susceptibility gene for schizophrenia. OBJECTIVES: The aim of this study was to investigate whether dysfunction in the Nrg1 gene modulates the behavioural effects of Delta(9)-tetrahydrocannabinol (THC), the major psychotropic component of cannabis. MATERIALS AND METHODS: Heterozygous Nrg1 transmembrane-domain knockout mice (Nrg1 HET) were treated with acute THC (0, 5 or 10 mg/kg i.p.) 30 min before being tested using open field (OF), hole board (HB), light-dark (LD), elevated plus maze (EPM), social interaction (SI) and prepulse inhibition (PPI) tests. RESULTS: Nrg1 HET mice showed differences in baseline behaviour with regard to locomotor activity, exploration and anxiety. More importantly, they were more sensitive to the locomotor suppressant actions of THC compared to wild type-like (WT) mice. In addition, Nrg1 HET mice expressed a greater THC-induced enhancement in % PPI than WT mice. The effects of THC on anxiety-related behaviour were task-dependent, with Nrg1 HET mice being more susceptible than WT mice to the anxiogenic effects of THC in LD, but not in the EPM, SI and OF tests. CONCLUSIONS: Nrg1 HET mice were more sensitive to the acute effects of THC in an array of different behaviours including those that model symptoms of schizophrenia. It appears that variation in the schizophrenia-related neuregulin 1 gene alters the sensitivity to the behavioural effects of cannabinoids.

The contribution of apolipoprotein E alleles on cognitive performance and dynamic neural activity over six decades.

Neuroimaging shows brain-functional differences due to apolipoprotein E (APOE) polymorphisms may exist decades before the increased risk period for Alzheimer's disease, but little is known about their effect on cognition and brain function in children and young adults. This study assessed 415 healthy epsilon2 and epsilon4 carriers and matched epsilon3/epsilon3 controls, spanning ages 6-65, on a range of cognitive tests. Subjects were also compared on a new dynamical measure of EEG activity during a visual working memory task using alphabetical stimuli. epsilon4 subjects had better verbal fluency compared to epsilon3, an effect that was strongest in 51-65 year-olds. No epsilon4 deficits in cognition were found. In 6-15 year-olds, there were differences in total spatio-temporal wave activity between epsilon3 and epsilon4 subjects in the theta band, approximately 200ms post-stimulus. Differences in brain function in younger epsilon4 subjects and superior verbal fluency across the entire age range suggest that the APOE epsilon4 allele is an example of antagonistic pleiotropy.

Molecular mechanisms of inherited startle syndromes.

Inherited neurological disorders involving an exaggerated startle response to unexpected sensory stimuli have been identified in mice, cows, dogs, horses and humans. Recent studies of the molecular pathology of a number of these startle syndromes have revealed that they are caused by defects in the inhibitory glycinergic pathways that mediate reciprocal and recurrent inhibition in the spinal cord. These defects arise from various mutations of the receptor for glycine, which either impair its sensitivity to agonists or reduce its expression in vivo. The emergent models of the molecular mechanisms that underlie startle disorders illustrate how diverse mutations can converge physiologically to produce a common phenotype.