Genetic Influence on Eye Movements to Complex Scenes at Short Timescales

Where one looks within their environment constrains one's visual experiences, directly affects cognitive, emotional, and social processing [1-4], influences learning opportunities [5], and ultimately shapes one's developmental path. While there is a high degree of similarity across individuals with regard to which features of a scene are fixated [6-8], large individual differences are also present, especially in disorders of development [9-13], and clarifying the origins of these differences is essential to understand the processes by which individuals develop within the complex environments in which they exist and interact. Toward this end, a recent paper [14] found that "social visual engagement"-namely, gaze to eyes and mouths of faces-is strongly influenced by genetic factors. However, whether genetic factors influence gaze to complex visual scenes more broadly, impacting how both social and non-social scene content are fixated, as well as general visual exploration strategies, has yet to be determined. Using a behavioral genetic approach and eye tracking data from a large sample of 11-year-old human twins (233 same-sex twin pairs; 51% monozygotic, 49% dizygotic), we demonstrate that genetic factors do indeed contribute strongly to eye movement patterns, influencing both one's general tendency for visual exploration of scene content, as well as the precise moment-to-moment spatiotemporal pattern of fixations during viewing of complex social and non-social scenes alike. This study adds to a now growing set of results that together illustrate how genetics may broadly influence the process by which individuals actively shape and create their own visual experiences.

A cerebellar learning model of vestibulo-ocular reflex adaptation in wild-type and mutant mice

Mechanisms of cerebellar motor learning are still poorly understood. The standard Marr-Albus-Ito theory posits that learning involves plasticity at the parallel fiber to Purkinje cell synapses under control of the climbing fiber input, which provides an error signal as in classical supervised learning paradigms. However, a growing body of evidence challenges this theory, in that additional sites of plasticity appear to contribute to motor adaptation. Here, we consider phase-reversal training of the vestibulo-ocular reflex (VOR), a simple form of motor learning for which a large body of experimental data is available in wild-type and mutant mice, in which the excitability of granule cells or inhibition of Purkinje cells was affected in a cell-specific fashion. We present novel electrophysiological recordings of Purkinje cell activity measured in naive wild-type mice subjected to this VOR adaptation task. We then introduce a minimal model that consists of learning at the parallel fibers to Purkinje cells with the help of the climbing fibers. Although the minimal model reproduces the behavior of the wild-type animals and is analytically tractable, it fails at reproducing the behavior of mutant mice and the electrophysiology data. Therefore, we build a detailed model involving plasticity at the parallel fibers to Purkinje cells' synapse guided by climbing fibers, feedforward inhibition of Purkinje cells, and plasticity at the mossy fiber to vestibular nuclei neuron synapse. The detailed model reproduces both the behavioral and electrophysiological data of both the wild-type and mutant mice and allows for experimentally testable predictions.

Viewing social scenes: a visual scan-path study comparing fragile X syndrome and Williams syndrome

Fragile X syndrome (FXS) and Williams syndrome (WS) are both genetic disorders which present with similar cognitive-behavioral problems, but distinct social phenotypes. Despite these social differences both syndromes display poor social relations which may result from abnormal social processing. This study aimed to manipulate the location of socially salient information within scenes to investigate the visual attentional mechanisms of: capture, disengagement, and/or general engagement. Findings revealed that individuals with FXS avoid social information presented centrally, at least initially. The WS findings, on the other hand, provided some evidence that difficulties with attentional disengagement, rather than attentional capture, may play a role in the WS social phenotype. These findings are discussed in relation to the distinct social phenotypes of these two disorders.

Retinoic acid deficiency impairs the vestibular function

The retinaldehyde dehydrogenase 3 (Raldh3) gene encodes a major retinoic acid synthesizing enzyme and is highly expressed in the inner ear during embryogenesis. We found that mice deficient in Raldh3 bear severe impairment in vestibular functions. These mutant mice exhibited spontaneous circling/tilted behaviors and performed poorly in several vestibular-motor function tests. In addition, video-oculography revealed a complete loss of the maculo-ocular reflex and a significant reduction in the horizontal angular vestibulo-ocular reflex, indicating that detection of both linear acceleration and angular rotation were compromised in the mutants. Consistent with these behavioral and functional deficiencies, morphological anomalies, characterized by a smaller vestibular organ with thinner semicircular canals and a significant reduction in the number of otoconia in the saccule and the utricle, were consistently observed in the Raldh3 mutants. The loss of otoconia in the mutants may be attributed, at least in part, to significantly reduced expression of Otop1, which encodes a protein known to be involved in calcium regulation in the otolithic organs. Our data thus reveal a previously unrecognized role of Raldh3 in structural and functional development of the vestibular end organs.

Genomic profiling reveals Pitx2 controls expression of mature extraocular muscle contraction-related genes

PURPOSE

To assess the influence of the Pitx2 transcription factor on the global gene expression profile of extraocular muscle (EOM) of mice.

METHODS

Mice with a conditional knockout of Pitx2, designated Pitx2(Δflox/Δflox) and their control littermates Pitx2(flox/flox), were used. RNA was isolated from EOM obtained at 3, 6, and 12 weeks of age and processed for microarray-based profiling. Pairwise comparisons were performed between mice of the same age and differentially expressed gene lists were generated. Select genes from the profile were validated using real-time quantitative polymerase chain reaction and protein immunoblot. Ultrastructural analysis was performed to evaluate EOM sarcomeric structure.

RESULTS

The number of differentially expressed genes was relatively small. Eleven upregulated and 23 downregulated transcripts were identified common to all three age groups in the Pitx2-deficient extraocular muscle compared with littermate controls. These fell into a range of categories including muscle-specific structural genes, transcription factors, and ion channels. The differentially expressed genes were primarily related to muscle contraction. We verified by protein and ultrastructural analysis that myomesin 2 was expressed in the Pitx2-deficient mice, and this was associated with development of M lines evident in their orbital region.

CONCLUSIONS

The global transcript expression analysis uncovered that Pitx2 primarily regulates a relatively select number of genes associated with muscle contraction. Pitx2 loss led to the development of M line structures, a feature more typical of other skeletal muscle.

Associations between serotonin transporter gene promoter region (5-HTTLPR) polymorphism and gaze bias for emotional information

The serotonin transporter promoter region polymorphism (5-HTTLPR) is associated with neural response to negative images in brain regions involved in the experience of emotion. However, the behavioral implications of this sensitivity have been studied far less extensively. The current study used eye-tracking methodology to examine how individuals genotyped for the 5-HTTLPR, including the single nucleotide polymorphism (SNP) rs25531, allocated attention during prolonged (30-s) exposure to face stimuli depicting positive and negative emotion. Short 5-HTTLPR allele carriers and carriers of the long allele with guanine at the sixth nucleotide (S/LG) displayed a stronger gaze bias (total fixation time, number of fixations, mean fixation length) for positive than for sad, threat, or neutral stimuli. In contrast, those homozygous for the long 5-HTTLPR allele with adenine at the sixth nucleotide (LA) viewed the emotion stimuli in an unbiased fashion. Time course analyses indicated no initial 5-HTTLPR group differences; however, S/LG 5-HTTLPR allele carriers were more likely than LA 5-HTTLPR homozygotes to direct gaze toward happy than toward sad stimuli over time. This bias toward positive stimuli during the later stages of information processing likely reflects a strategic effort to downregulate heightened reactivity to negative stimuli among 5-HTTLPR S/LG allele carriers.

Measuring the optokinetic response of zebrafish larvae

Our laboratory screens for visual mutants by examining larval eye movements in response to rotating illuminated stripes. This behavior, which is termed an optokinetic response (OKR), is a reflex that appears in zebrafish at the same time as the development of the visual system. The OKR can be accurately measured by 4 d post-fertilization, which is the age when larvae begin foraging for food. The OKR requires approximately 1 min per larva analyzed. After identifying fish with defective eye movements, we conduct secondary screens (such as histological analysis and electroretinography) to identify the subset of fish with disruptions in the function of the outer retina. This paper describes our protocol for the OKR. Our setup is simple to construct and the materials needed are inexpensive. This makes our system especially useful for new undergraduate and graduate students, as well as introductory science lecturers.

Oculomotor instabilities in zebrafish mutant belladonna: a behavioral model for congenital nystagmus caused by axonal misrouting

A large fraction of homozygous zebrafish mutant belladonna (bel) larvae display a reversed optokinetic response (OKR) that correlates with failure of the retinal ganglion cells to cross the midline and form the optic chiasm. Some of these achiasmatic mutants display strong spontaneous eye oscillations (SOs) in the absence of motion in the surround. The presentation of a stationary grating was necessary and sufficient to evoke SO. Both OKR reversal and SO depend on vision and are contrast sensitive. We built a quantitative model derived from bel fwd (forward) eye behaviors. To mimic the achiasmatic condition, we reversed the sign of the retinal slip velocity in the model, thereby successfully reproducing both reversed OKR and SO. On the basis of the OKR data, and with the support of the quantitative model, we hypothesize that the reversed OKR and the SO can be completely attributed to RGC misrouting. The strong resemblance between the SO and congenital nystagmus (CN) seen in humans with defective retinotectal projections implies that CN, of so far unknown etiology, may be directly caused by a projection defect.

Mutations in FRMD7, a newly identified member of the FERM family, cause X-linked idiopathic congenital nystagmus

Idiopathic congenital nystagmus is characterized by involuntary, periodic, predominantly horizontal oscillations of both eyes. We identified 22 mutations in FRMD7 in 26 families with X-linked idiopathic congenital nystagmus. Screening of 42 singleton cases of idiopathic congenital nystagmus (28 male, 14 females) yielded three mutations (7%). We found restricted expression of FRMD7 in human embryonic brain and developing neural retina, suggesting a specific role in the control of eye movement and gaze stability.

Heritability and Reliability of P300, P50 and Duration Mismatch Negativity

BACKGROUND

Event-related potentials (ERPs) have been suggested as possible endophenotypes of schizophrenia. We investigated the test-retest reliabilities and heritabilities of three ERP components in healthy monozygotic and dizygotic twin pairs.

METHODS

ERP components (P300, P50 and MMN) were recorded using a 19-channel electroencephalogram (EEG) in 40 healthy monozygotic twin pairs, 19 of them on two separate occasions, and 30 dizygotic twin pairs. Zygosity was determined using DNA genotyping.

RESULTS

High reliabilities were found for the P300 amplitude and its latency, MMN amplitude, and P50 suppression ratio components. ICC=0.86 and 0.88 for the P300 amplitude and P300 latency respectively. Reliability of MMN peak amplitude and mean amplitude were 0.67 and 0.66 respectively. P50 T/C ratio reliability was 0.66. Model fitting analyses indicated a substantial heritability or familial component of variance for these ERP measures. Heritability estimates were 63 and 68% for MMN peak amplitude and mean amplitude respectively. For P50 T/C ratio, 68% heritability was estimated. P300 amplitude heritability was estimated at 69%, and while a significant familiality effect was found for P300 latency there was insufficient power to distinguish between shared environment and genetic factors.

CONCLUSIONS

The high reliability and heritability of the P300 amplitude, MMN amplitude, and P50 suppression ratio components supports their use as candidate endophenotypes for psychiatric research.

A concordance study of three electrophysiological measures in schizophrenia

OBJECTIVE

The authors evaluated concordance rates among three electrophysiological measures in patients with schizophrenia, nonschizophrenic first-degree relatives of schizophrenia patients, and healthy comparison subjects. The purpose of the study was to provide data for defining a common endophenotype for genetic studies of schizophrenia and for improving the criteria for diagnosis.

METHOD

P50 event-related potential inhibition, antisaccade, and smooth pursuit eye tracking paradigms were measured. Data for all three paradigms were available for 81 patients with schizophrenia, 25 parents of patients with schizophrenia, and 60 healthy comparison subjects.

RESULTS

The schizophrenia patients and the patients' parents showed a high rate of inhibitory deficits measured by the P50 inhibition and antisaccade paradigms. Both groups had a high prevalence of eye tracking dysfunction. Smooth pursuit gain and the error rate in the antisaccade paradigm were significantly correlated in the schizophrenia patients and the parents, whereas P50 inhibition showed no correlation with smooth pursuit gain or antisaccade paradigm measurements.

CONCLUSIONS

Despite superficial similarities, two paradigms designed to measure central inhibition processes (antisaccade and P50 inhibition) do not appear to reflect the same neurobiological substrates. In contrast, the convergence in performance data for the antisaccade and eye tracking paradigms suggests that the neural circuitry underlying these tasks may overlap. P50 inhibition and antisaccade errors were the optimal paradigms for discrimination between comparison subjects, patients with schizophrenia, and the parents of patients with schizophrenia.

Variation in catechol-o-methyltransferase val158 met genotype associated with schizotypy but not cognition: a population study in 543 young men

BACKGROUND

Increased catechol-O-methyltransferase activity associated with variation in catechol-O-methyltransferase valine158 methionine genotypes may result in reduced dopamine neurotransmission in the prefrontal cortex and thus contribute to the poor performance of frontally mediated cognitive tasks and the occurrence of associated negative symptoms observed in patients with schizophrenia; however, reported associations between catechol-O-methyltransferase valine158 methionine genotypes and measures of cognition have not been consistent.

METHODS

Catechol-O-methyltransferase genotyping, measures of schizotypy, cognitive measures of memory and attention, as well as the antisaccade eye movement task, a measure sensitive to prefrontal cortical function, were obtained in a sample of 543 young men representative for that age group (mean age 21 years).

RESULTS

None of the cognitive measures was associated with catechol-O-methyltransferase valine158 methionine genotypes; however, there was an effect of high-activity allele loading on schizotypy, in particular the negative and disorganization dimensions.

CONCLUSIONS

Previously reported inconsistencies in the relationship between catechol-O-methyltransferase valine158 methionine genotypes and cognition were not resolved; however, catechol-O-methyltransferase genotype may affect expression of negative schizotypy by direct or indirect effects on central dopamine neurotransmitter signaling.

Optokinetic test to evaluate visual acuity of each eye independently

A previously described optokinetic testing apparatus [Nat. Neurosci. 5 (2002) 53] was modified to measure vision in each eye separately for evaluation of monocular treatments. This apparatus consists also of a striped rotating drum. Ca. 170 degrees of the drum are illuminated from outside and ca. 190 degrees of the drum move behind a stationary black wall. The rat sits unrestrained in the drum center in a tube so that one eye is unexposed to the rotating stripes. Normal pigmented and retinal degenerate transgenic S334ter-3 rats were tested with the original and the modified apparatus. The usefulness of this method was tested in retinal degenerate rats with retinal transplants in one eye. In retinal degenerate animals, the amount of time (seconds) spent for head-tracking tended to be higher with the original method, possibly due to simultaneous stimulation of both eyes. In rats with retinal transplants, visual responses were significantly preserved in transplanted eyes at late stages of retinal degeneration. In conclusion, contributions from the fellow eye to the optokinetic tracking response can be limited by this testing modification, which is useful for evaluation of treatment effects to one eye.

Defining and quantifying the social phenotype in autism

OBJECTIVE

Genetic and neurofunctional research in autism has highlighted the need for improved characterization of the core social disorder defining the broad spectrum of syndrome manifestations.

METHOD

This article reviews the advantages and limitations of current methods for the refinement and quantification of this highly heterogeneous social phenotype.

RESULTS

The study of social visual pursuit by use of eye-tracking technology is offered as a paradigm for novel tools incorporating these requirements and as a research effort that builds on the emerging synergy of different branches of social neuroscience.

CONCLUSIONS

Advances in the area will require increased consideration of processes underlying experimental results and a closer approximation of experimental methods to the naturalistic demands inherent in real-life social situations.

Neurophysiological markers of vulnerability to schizophrenia: sensitivity and specificity of specific quantitative eye movement measures

Eye-tracking deficits in schizophrenic patients and relatives have generated interest in using eye movements to mark schizophrenia liability. Efforts to develop specific quantitative measures have provided insight into the nature of the deficit and suggested what underlying neurophysiological mechanisms are involved. This study used receiver operating characteristic curve analyses to evaluate and compare the sensitivity, specificity, and overall accuracy of predicting disease liability using single and combined specific and global quantitative measures. Results indicate that measures of predictive pursuit and leading saccades significantly increased predictive accuracy compared with traditional global measures. Combining specific measures provided greater predictive accuracy compared with single measures. Implications for the use of specific eye movement measures to define schizophrenia-related phenotypes in genetic studies are discussed.

Calcium channelopathy mutants and their role in ocular motor research

Thanks to technical advances in eye movement recording, the mouse is destined to become increasingly important in ocular motor research. An advantage of this species is the wide range of existing mutant strains and techniques to generate new mutations affecting specific cell types. Mutations of ion channels may be used to modulate the intrinsic properties of neurons, and this approach may generate insight into the degree to which neuronal computations depend upon those intrinsic properties as opposed to the properties of circuits of neurons. Dendritic calcium currents carried by P-type voltage-activated calcium channels have been widely postulated to perform important computational functions in cerebellar Purkinje cells. Mutations of this channel lead to human diseases, and several ataxic strains of mice are now known to harbor mutations of this calcium channel. Murine P-channel mutants such as rocker are ataxic, but have normal or near-normal numbers of cerebellar Purkinje cells and thus offer the opportunity to study the effects of biophysical perturbations as opposed to outright cell destruction or inactivation. Initial studies of rocker mice reveal an array of ocular motor abnormalities, including static hyperdeviation of the eyes and an attenuation of vestibulo-ocular reflex gains at high stimulus frequencies. The pattern of gain and phase abnormalities is entirely different in lurcher, an ataxic mutant in which Purkinje cells degenerate. The ocular motor abnormalities of rocker progress with animal age, underscoring the importance of careful attention to animal age when performing ocular motor studies in this short-lived species.

Loss of adaptability of horizontal optokinetic response eye movements in mGluR1 knockout mice

Metabotropic glutamate receptor subtype 1 (mGluR1) plays an essential role in the cerebellar long-term depression (LTD). We examined the dynamic characteristics and adaptability of horizontal vestibulo-ocular reflex (HVOR) and optokinetic response (HOKR) eye movements in mGluR1 knockout mice. A mild difference was seen in the HOKR/HVOR dynamics between the wild-type and mGluR1(-/-) mice. Exposure to 1 h of sustained screen oscillation, which induced HOKR adaptation in wild-type mice, induced no change in mutant mice. These results suggest that the mGluR1 plays an essential role in the adaptation of HOKR, and LTD underlies the adaptation of ocular reflexes.

Stapedial reflex in myotonic dystrophy type 1 and CTG repeat expansion

The severity of clinical symptoms of myotonic dystrophy type 1 (DM1) has been shown to be closely related to the size of a CTG triplet repeat in the gene encoding myotonin protein kinase. Neuro-otological examinations that include eye movement and stapedial reflex (SR) tests can contribute to the quantitative evaluation of muscular involvement in DM1. We previously found that saccadic eye movement velocity in DM1 patients was significantly lower than that in control subjects and that the saccadic velocity and size of the CTG triplet repeat in DM1 patients had a strong inverse correlation. We now report a case-control study that compared the SR wave form (latency: L, contraction time: C50, and relaxation time: D50) measured by the acoustic impedance method in 13 patients with DM1 and in 14 control subjects matched for age and sex. The correlation between the SR wave form and CTG repeat length in DM1 patients obtained by Southern blot analysis with EcoRI was also examined. We found (1) no significant difference between the pure tone audiometric threshold at 500 Hz in the DM1 patients and that in the control subjects; (2) or between the SR thresholds in the patients and controls (500 Hz stimuli); (3) C50 and D50 in DM1 patients to be significantly prolonged, whereas L was not; (4) C50 and D50 in DM1 patients to be significantly correlated with CTG repeat length, whereas L was not. Measurement of SR by the acoustic impedance method is completely non-invasive, causes no discomfort to the subject, and does not depend on the person's effort or cooperation. Our findings show that SR measurement can be used for a quantitative evaluation of muscle involvement in DM1. We believe that the prolongation of D50 in DM1 is caused by myotonia, which has to be confirmed by further clinical and pathological studies.

Eye-tracking dysfunction (ETD) in families with sporadic and familial schizophrenia

BACKGROUND

Within the field of genetic schizophrenia research, eye-tracking dysfunction can be regarded as a putative trait marker in families with multiple occurrences of the disease (familial schizophrenia). We concentrated on families with single occurrences of schizophrenia (sporadic schizophrenia) to test whether a genetic factor may be present in these families as well.

METHODS

Eye movements were recorded using infrared oculography in eight families with sporadic schizophrenia (44 members), eight families with familial schizophrenia (66 members), and nine nonpsychotic families (77 members). Triangle-wave stimuli at 15 degrees /sec and 30 degrees /sec were used, and gains (eye velocity/target velocity), rates, and amplitudes of saccades (classified as catch-up and anticipatory saccades) were determined.

RESULTS

1) In sporadic-schizophrenia families, gain values, saccade rates, and anticipatory saccade amplitudes at 30 degrees /sec differed in a statistically significant fashion from nonpsychotic families, but not from families with multiple occurrences of schizophrenia, and 2) at 30 degrees /sec, a significant effect of target direction on smooth-pursuit maintenance was observed in both sporadic- and familial-schizophrenia families.

CONCLUSIONS

Our results support the hypothesis that genetic factors may be present even in sporadic-schizophrenia families and may contribute to a more precise and biologically based definition of the schizophrenia phenotype in future molecular genetic analysis.

Neural correlates of eye tracking deficits in first-degree relatives of schizophrenic patients: a positron emission tomography study

BACKGROUND

Schizophrenia is thought to arise from the interaction of genetically mediated and environmentally triggered abnormalities in brain function. Reduced frontal activation, reported in schizophrenic patients, may be one expression of genetic risk. The present study investigated whether frontal activation in relatives of schizophrenic patients would be related to eye tracking deficits (ETD), which are considered a behavioral marker of risk for schizophrenia.

METHODS

Subjects were first-degree relatives of schizophrenic patients (n = 17) and controls (n = 11). Relatives were divided into those with normal and abnormal pursuit based on qualitative ratings. Subjects were scanned using positron emission tomography and the H(2)15O bolus subtraction technique while performing smooth pursuit and fixation. Brain areas more active in pursuit than fixation were identified in the 3 groups. Correlations were used to investigate the relationship between activation of pursuit regions and pursuit gain in the relatives.

RESULTS

Controls significantly activated frontal eye fields (FEFs) and posterior areas, including the motion processing area, V5, and cuneus. The 2 groups of relatives activated the same posterior regions as controls, but differed from each other in activation of FEFs. Relatives with normal tracking activated right dorsal FEFs while relatives with ETD did not. Individual subtractions revealed that 90% of controls and 100% of the relatives with normal tracking activated FEFs during pursuit compared with 42% of relatives with ETD (P = .009). Pursuit gain was significantly and selectively associated with percent activation of right dorsal FEFs (r = 0.74).

CONCLUSIONS

Subtle frontal dysfunction seems to be a pathophysiological substrate of ETD in relatives of schizophrenic patients, and may be one aspect of genetically mediated differences in brain function relevant to schizophrenia.

Linkage of a composite inhibitory phenotype to a chromosome 22q locus in eight Utah families

Eight Utah multigenerational families, each with three to six cases of schizophrenia, were phenotyped with two specific measures of inhibitory neurophysiological functioning, P50 auditory sensory gating (P50), and antisaccade ocular motor performance (AS). A genomewide linkage analysis was performed to screen for loci underlying a qualitative phenotype combining the P50 and AS measures. For this composite inhibitory phenotype, the strongest evidence for linkage was to the D22s315 marker on chromosome 22q (lod score = 3.55, theta = 0) under an autosomal dominant model. Simulation analyses indicate that this 3.55 lod score is unlikely to represent a false positive result. Lod scores were 2.0 or greater for markers flanking D22s315. A nonparametric linkage (NPL) analysis of the chromosome 22 data showed evidence for allele sharing over the broad region surrounding D22s315 with a maximum NPL score of 3.83 (p = .002) for all pedigrees combined.

Progressive cerebellar ataxia, proximal neurogenic weakness and ocular motor disturbances: hexosaminidase A deficiency with late clinical onset in four siblings

Tay-Sachs disease is a genetically determined neurodegenerative disorder, resulting from mutations of the hexosaminidase (Hex) A gene coding for the alpha-subunit of beta-D-N-acetyl-hexosaminidase. Clinically, there is severe encephalomyelopathy leading to death within the first few years of life. Hex A activity is usually absent in tissue and body fluids of these patients. Juvenile and adult Hex A deficiencies are less severe but rare variants with some residual Hex A activity. All these variants are most prevalent among Ashkenazi Jews. We describe a non-Jewish family in which four adult brothers and sisters had markedly reduced Hex A activities and onset of symptoms in the second decade of life. The phenotypical expression was remarkably homogeneous, consisting in a combination of slowly progressive motor neuron disease, ataxia and ocular motor disturbances. None of the patients were demented at this stage of their illness. Magnetic resonance studies showed severe cerebellar atrophy, but were otherwise normal. Hex A deficiency was established by biochemical measurements in the serum and skin fibroblasts using the fluorogenic substrates 4-MUG and 4-MUGS as well as by gel electrophoresis. Molecular genetic studies revealed that the patients are compound heterozygotes for the 'adult' mutation Gly269 --> Ser and the 'infantile' 4-base insertion in exon 11 of the Hex A gene.

Central phenotype and related varieties of spinocerebellar ataxia 2 (SCA2): a clinical and genetic study with a pedigree in the Japanese

The gene for SCA2 has been mapped to chromosome 12q23-q24.1, but the mutant gene remained to be identified. When studying a Japanese family with SCA2, we noted that clinical features and disability varied among patients, with the central feature being progressive ataxia-slow eye movement-hyporeflexia syndrome. Additional symptoms were parkinsonism with minor cerebellar deficits, and severe ataxia with choreoathetosis. Our experience plus related literature documentation indicates that choreoathetosis is not so rare at the advanced stage of the disease, with onset at an early age, and that the variety of SCA2 phenotype depends on age at onset and duration of the disorder.

Eye movements in spectrum personality disorders: comparison of community subjects and relatives of schizophrenic patients

OBJECTIVE

The purpose of the current study was to test the specificity of an association between eye tracking abnormality and schizophrenia spectrum personality symptoms in the family members of schizophrenic patients. The studies of biological markers for genetic vulnerability to schizophrenia, which test an association between a biological measure and schizophrenia spectrum personality symptoms, are constrained, since these personality symptoms may lack the specificity for a schizophrenic phenotype. An association between a behavioral measure and these personality symptoms in general can easily be false (i.e., not related to schizophrenic vulnerability). In contrast, a strong deviant finding in the relatives of schizophrenic patients with spectrum personality symptoms, in the presence of a relatively normal finding in spectrum subjects without a known history of schizophrenia, makes the biobehavioral measure an interesting candidate for such investigations.

METHOD

Seventy-five subjects recruited from the community who did not have a family history of psychosis completed the study (24 of the 75 had significant schizophrenia spectrum personality symptoms). Thirty-two first-degree relatives of schizophrenic patients (13 with spectrum symptoms) completed the study. Subjects were 18-45 years old and had no DSM-III-R axis I diagnosis.

RESULTS

Qualitative smooth pursuit eye movement score was significantly worse in relatives with the spectrum symptoms than in spectrum subjects without a family history of schizophrenia and the nonspectrum relatives. Schizotypal and schizoid symptoms explained a significant amount of the variance in the eye tracking measure in the relatives (31% and 20%, respectively) but not in the community subjects (less than 2%). Relatives of schizophrenic patients with and without the spectrum symptoms had significantly longer antisaccade latency, in spite of comparable latency for visually guided saccades, than the community subjects.

CONCLUSIONS

Smooth pursuit abnormality in subjects with schizophrenia spectrum personality disorders is specifically associated with a family history of schizophrenia.

The role of psychological probes in genetic studies of schizophrenia

The success of the neurosciences in opening pathways to the understanding of psychotic disorders has led to enormous optimism about solutions to the mysteries of these illnesses. Yet the Holy Grail for this field--the discovery linkage between a chromosomal locus that is linked to a diseased gene--has thus far eluded us, whereas it has been grasped in such disorders as cystic fibrosis, Huntington's disease, and neurofibromatosis. This paper argues that those biological studies that bypass the psychological domain, and have directly attempted to find biochemical measures associated with schizophrenia, probably will not succeed. Seeking direct links from such molar behaviors as psychotic symptoms to molecular events has not worked in the past, and is not likely to work in the future. The approach recommended here focuses on working one's way from the behavioral through the psychological and psychophysiological levels toward the neural, biochemical and molecular levels. Psychology has much strength to contribute in the search for traits that broaden the phenotype of schizophrenia. Examples are given in the study of eye movement abnormalities as aids in the genetic exploration of schizophrenia.

Smooth pursuit eye movement abnormality in severe major depression: effects of ECT and clinical recovery

Smooth pursuit eye movement (SPEM) dysfunction is a putative genetic marker for schizophrenia, but it has also been described in major depression. The authors longitudinally evaluated effects of clinical state on SPEM quality in patients with depression. Prior to ECT, SPEM abnormality characterized 42% of 24 severely depressed patients, 60% of 30 schizophrenia patients, and 5% of 20 control subjects. SPEM was significantly correlated to Hamilton Rating Scale for Depression scores (r = 0.49, P = 0.02) in the depressed patients. Although SPEM was transiently disrupted by an acute ECT treatment, it improved during the treatment course. This improvement of SPEM quality with clinical recovery suggests that SPEM abnormality may be a state marker in severe major depression, in contrast to its invariable trait nature in schizophrenia.

DNA markers and biological vulnerability markers in families multiply affected with schizophrenia

A family is reported in which the monozygotic co-twin of a schizophrenic proband was diagnosed bipolar 1 and their mother had a history of unipolar major depression. Although their clinical manifestations varied, the ill members of this family shared an abnormality in P300 not found in the asymptomatic siblings. In 14 families, linkage to the 5q11-13 region was excluded when affection status was defined solely by P300 latency independently of the clinical findings. Linkage was also excluded when the analysis was restricted to the families that had no cases of bipolar illness and when the schizophrenic phenotype was narrowly or broadly defined. It is concluded that biological markers such as P300 and eye tracking may help to clarify the overlap of different types of psychosis and help to define the phenotype for linkage analyses.