Elevated risks for amyotrophic lateral sclerosis and blood disorders in Ashkenazi schizophrenic pedigrees suggest new candidate genes in schizophrenia

Cooccurrences of Putative Endogenous Retrovirus-Associated Diseases

At least 8% of the human genome is composed of endogenous retrovirus (ERV) sequences. ERVs play a role in placental morphogenesis and can sometimes protect the host against exogenous viruses. On the other hand, ERV reactivation has been found to be associated with different diseases, for example, multiple sclerosis (MS), schizophrenia, type 1 diabetes mellitus (T1D), or amyotrophic lateral sclerosis (ALS). Little is known about the cooccurrence of these diseases. If all these diseases are caused by ERV, antiretroviral therapy should perhaps also show some effects in the other diseases. Here, we summarize literature demonstrating that some ERV-associated diseases seem to appear together more often than expected, for example, MS and ALS, MS and T1D, MS and schizophrenia, or ALS and T1D. In contrast, some ERV-associated diseases seem to appear together less frequently than expected, for example, schizophrenia and T1D. Besides, some reports demonstrate amelioration of MS, ALS, or schizophrenia under antiretroviral therapy in human immunodeficiency virus-infected patients. If such results could be confirmed in larger studies, alternative therapy strategies for ERV-associated diseases like MS and schizophrenia might be possible.

Altered levels of acute phase proteins in the plasma of patients with schizophrenia

Schizophrenia is a relatively common psychiatric syndrome that affects virtually all brain functions. We investigated the plasma proteome of 22 schizophrenia male patients and 20 healthy male controls using two-dimensional gel electrophoresis and mass spectrometry. In total, we have identified 66 protein spots in human plasma and found that seven of them showed altered changes in schizophrenia patients, as compared to healthy controls, which mainly were acute phase proteins (APPs). Among these APPs, haptoglobin alpha2 chain (p < 0.001), haptoglobin beta chain (p < 0.001), alpha1-antitrypsin (p = 0.001), and complement factor B precursor (p = 0.022) showed overexpression in schizophrenia patients, whereas apolipoprotein A-I (p = 0.034) and transthyretin (p = 0.035) were found to be significantly decreased in patients. In addition, the expression of apolipoprotein A-IV (p = 0.018) was significantly up-regulated in schizophrenia patients, as compared to controls. We also found these APP genes, which were differentially expressed in this study, overlap in the schizophrenia susceptibility loci. Our findings further support the hypothesis that the inflammatory response system is linked to the pathophysiology of schizophrenia.

Identification of candidate genes for schizophrenia based on natural resistance to infectious diseases

BACKGROUND

Identification of candidate genes for schizophrenia may be more successful than genome screens as the latter have not found consistent linkages.

OBJECTIVE

To assist in the gene search, a model of schizophrenia based on resistance to infectious diseases, rather than susceptibility, is proposed. The theory blends the geography of schizophrenia with the assumption that genes that cause schizophrenia likely evolved and persist from selection pressure. The theory includes the notion that schizophrenia enhances biological survival at the cost of psychological and social functioning.

METHOD

To demonstrate the utility of using this model, the Medline literature was searched for resistance genes, mostly identified in mice.

RESULTS

Based on homologous locations in the human genome, these resistance genes are shown to be located in human chromosome regions linked significantly, in at least one genome screen, with schizophrenia or some physiologically related function or condition associated with schizophrenia.

CONCLUSIONS

The infectious disease resistance theory of schizophrenia is offered as a viable model for understanding the origins of schizophrenia. The theory also allows for the inclusion of persistent infections, seasonal variability and translational pathophysiology to contribute to the etiology of schizophrenia.

Geographical and seasonal correlation of multiple sclerosis to sporadic schizophrenia

BACKGROUND: Clusters by season and locality reveal a striking epidemiological overlap between sporadic schizophrenia and multiple sclerosis (MS). As the birth excesses of those individuals who later in life develop schizophrenia mirror the seasonal distribution of Ixodid ticks, a meta analysis has been performed between all neuropsychiatric birth excesses including MS and the epidemiology of spirochaetal infectious diseases. RESULTS: The prevalence of MS and schizophrenic birth excesses entirely spares the tropical belt where human treponematoses are endemic, whereas in more temperate climates infection rates of Borrelia garinii in ticks collected from seabirds match the global geographic distribution of MS. If the seasonal fluctuations of Lyme borreliosis in Europe are taken into account, the birth excesses of MS and those of schizophrenia are nine months apart, reflecting the activity of Ixodes ricinus at the time of embryonic implantation and birth. In America, this nine months' shift between MS and schizophrenic births is also reflected by the periodicity of Borrelia burgdorferi transmitting Ixodes pacificus ticks along the West Coast and the periodicity of Ixodes scapularis along the East Coast. With respect to Ixodid tick activity, amongst the neuropsychiatric birth excesses only amyotrophic lateral sclerosis (ALS) shows a similar seasonal trend. CONCLUSION: It cannot be excluded at present that maternal infection by Borrelia burgdorferi poses a risk to the unborn. The seasonal and geographical overlap between schizophrenia, MS and neuroborreliosis rather emphasises a causal relation that derives from exposure to a flagellar virulence factor at conception and delivery. It is hoped that the pathogenic correlation of spirochaetal virulence to temperature and heat shock proteins (HSP) might encourage a new direction of research in molecular epidemiology.

No evidence to support an association between the oestrogen receptor beta gene and bipolar disorder

Oestrogen, a sex steroid hormone, has long been hypothesized to be involved in alterations to pathways involved in neurotransmission, and therefore may be involved in neuropsychiatric conditions including bipolar disorder. Indeed, certain depressive disorders in women have been found to be associated with low levels of oestrogen and can be much improved by the administration of this hormone. As the effects of oestrogen are most probably mediated through the oestrogen receptors (ER alpha and ER beta), the genes encoding these receptors may be possible candidates for association studies with bipolar disorder and other neuropsychiatric disorders. A number of studies, including previous results from this group, have reported modest evidence of linkage between both bipolar disorder and schizophrenia and a region of chromosome 14 (q22-q24), where the ER beta gene has been localized. In the present study, a sample of 102 Irish parent-proband trios were genotyped for a single nucleotide polymorphism within the ER beta gene (3' untranslated region, A1730G). However, the transmission/disequilibrium test failed to reveal evidence of a distortion in allele transmission to bipolar I (BPI) probands.

Comparative proteome analysis of the hippocampus implicates chromosome 6q in schizophrenia

Comparative brain proteome analysis is a new strategy to discover proteins and therefore genes whose altered expression may underlie schizophrenia. This strategy does not require an a priori theory of the pathogenesis or the mode of inheritance of schizophrenia. Using proteome analysis we previously compared the hippocampal proteome, that is, those proteins expressed by the hippocampal genome, of seven schizophrenic individuals with the hippocampal proteome of seven control individuals, matched for age and post mortem delay.1 We found 18 proteins that were significantly altered in concentration in the schizophrenic hippocampus (P < 0.05), when compared to control tissue. One of these proteins was characterised, by N-terminal sequencing, as diazepam binding inhibitor whose gene maps to 6q12-q21. Here we characterise a further three of the 18 proteins as: manganese superoxide dismutase, 6q25.3, T-complex protein 1, 6q25.3-q26 and collapsin response mediator protein 2, 8p21. That three of these four characterised proteins should map to the long arm of the same chromosome is significant (P < 0.002) and suggests the importance of chromosome 6q in schizophrenia. These results indicate that antioxidant defence is altered in the schizophrenic hippocampus and suggest that segregation distortion, of schizophrenia susceptibility genes, may be a possible causative factor in the high incidence of schizophrenia. Molecular Psychiatry (2000) 5, 85-90.

c-Fos basal immunoreactivity decreases in rat spinal cord during normal ageing

The pattern of distribution in rat spinal cord and changing pattern during normal ageing of c-Fos expression were investigated by immunohistochemical staining in male Sprague-Dawley rats at the age of 1 week, 5 months and 2 years. c-Fos immunoreactivity was observed diffusely in gray matters in neonatal rats, preferentially located in deep dorsal horn and around central canal. Compared with those of neonatal rats, these cells decreased prominently in adult rats. In aged rats, immunoreactive cells were not seen in any segments. c-Fos immunoreactivity in spinal cord may be related to stress response, functional differentiation, and in part, neuronal death with target dependence. In conclusion, we demonstrated for the first time that c-Fos expression patterns change during normal ageing.

Expanded (CAG)n, (CGG)n and (GAA)n trinucleotide repeat microsatellites, and mutant purine synthesis and pigmentation genes cause schizophrenia and autism

Unstable (CAG)n trinucleotide repeat microsatellites are hypothesized to cause schizophrenia. The (CAG)n microsatellite of dominant spinal cerebellar ataxia type 1 (SCA1) is a candidate schizophrenia gene. Autism results from expansions of (CGG)n and (GAA)n trinucleotide repeat stretches at fragile X syndrome (FRAXA), and the recessive Friedreich's ataxia (FA). Dominant ataxia genes may cause schizophrenia and recessive ataxia genes may cause autism. Syndromes with autism show purine synthesis defects (PSDs) and/or pigmentation defects (PDs). Autism is caused by very lengthy expansions of (CAG)n, (CGG)n and (GAA)n repeats, while schizophrenia results from much smaller (CAG)n and (CGG)n repeat expansions.

Three independent lines of evidence suggest retinoids as causal to schizophrenia

Retinoid dysregulation may be an important factor in the etiology of schizophrenia. This hypothesis is supported by three independent lines of evidence that triangulate on retinoid involvement in schizophrenia: (i) congenital anomalies similar to those caused by retinoid dysfunction are found in schizophrenics and their relatives; (ii) those loci that have been suggestively linked to schizophrenia are also the loci of the genes of the retinoid cascade (convergent loci); and (iii) the transcriptional activation of the dopamine D2 receptor and numerous schizophrenia candidate genes is regulated by retinoic acid. These findings suggest a close causal relationship between retinoids and the underlying pathophysiological defects in schizophrenia. This leads to specific strategies for linkage analyses in schizophrenia. In view of the heterodimeric nature of the retinoid nuclear receptor transcription factors, e.g., retinoid X receptor beta at chromosome 6p21.3 and retinoic acid receptor beta at 3p24.3, two-locus linkage models incorporating genes of the retinoid cascade and their heterodimeric partners, e.g., peroxisome proliferator-activated receptor alpha at chromosome 22q12-q13 or nuclear-related receptor 1 at chromosome 2q22-q23, are proposed. New treatment modalities using retinoid analogs to alter the downstream expression of the dopamine receptors and other genes that are targets of retinoid regulation, and that are thought to be involved in schizophrenia, are suggested.

Chromosomal fragility may be indicative of altered higher-order DNA organization as the underlying genetic diathesis in complex neurobehavioral disorders

Preliminary observations concerning increased chromosomal fragility in association with behavioural disorders in humans allow an opportunity to suggest a cohesive theory regarding the possible importance of higher-order DNA modifications in the coordination of gene function in brain evolution and during development. Visible or submicroscopic acentric chromosomal fragments are formed as an accompaniment to chromosomal breakage and are associated with sequence amplification. During genomic reintegration of extrachromosomally amplified repeat sequence elements, functional consequences could include unequal crossing over with gain-of-function, and/or deletion with loss-of-function. This process could result in regulatory changes in gene function in association with normal coding regions, since fragile sites appear to be located at or near upstream DNaseI-hypersensitive areas. Earlier research on chromosomal breakage in relation to transposon behaviour in maize has set a precedent by which many elements in a network could be coordinately controlled, a principle which may allow transcriptional control over multiple areas in the genome simultaneously. The hypothesis proposed in this paper implies that a small number of fundamental higher-order changes may be responsible for influencing a wide range of genetic alterations leading to complex phenotypes, sometimes segregating as distinct entities within pedigrees, or alternatively, and perhaps more commonly, presenting with several overlapping phenotypes in some other families. Studying only pure multiplex families in psychiatric genetics may not be sufficient for an understanding of the underlying genetic diathesis in this group of disorders. Validation of the fragile site hypothesis for complex neurobehavioural disorders may offer additional avenues for gene therapy based either on preferential integration of exogenous DNA at fragile sites, or utilizing the acentric fragments to modify sequence amplification extrachromosomally.

Congenital anomalies in relatives of schizophrenic probands may indicate a retinoid pathology

Retinoic acid, the morphogenic derivative of vitamin A, has been shown to alter patterns of neurulation and to regulate the expression of many genes involved in central nervous system development. Retinoid toxicity can result in craniofacial, limb, digit, heart and urogenital abnormalities. Hydrocephalus, due to increased ventricular size and/or decreased size of the hind- or forebrain, occurs frequently. Comparison of the frequency and type of congenital anomalies in extended pedigrees of 12 Ashkenazi probands with schizophrenia and seven normal Ashkenazi control probands indicates that relatives of the schizophrenic probands present a gamut of both minor and major congenital anomalies similar to, but less severe than, those caused by retinoid excess or deficiency, and at a frequency significantly greater than in control pedigrees. Within schizophrenic pedigrees, those diagnosed with schizophrenia spectrum illnesses are more likely to present such anomalies than are non-spectrum members. Retinoic acid receptors are present in all parts of the cranial region and delivery of retinoids is exquisitely controlled throughout embryonic and fetal development. Alterations in the functioning of the retinoid cascade may have profound implications for neurodevelopmental disorders like schizophrenia.

Clinical epidemiology of amyotrophic lateral sclerosis

The introduction of palliative therapies in amyotrophic lateral sclerosis (ALS) will alter the epidemiology of ALS as it is known now. Although incidence rates will remain unchanged in the near future, prevalence rates will likely increase dramatically. Better understanding of the age-specific presentation of motor neuron diseases worldwide will shed light on the vexing questions concerning the variable incidence rates in some countries and apparent incidence gradients in North America and Europe.

Chromosomal locations and modes of action of genes of the retinoid (vitamin A) system support their involvement in the etiology of schizophrenia

Vitamin A (retinoid), an essential nutrient for fetal and subsequent mammalian development, is involved in gene expression, cell differentiation, proliferation, migration, and death. Retinoic acid (RA) the morphogenic derivative of vitamin A is highly teratogenic. In humans retinoid excess or deficit can result in brain anomalies and psychosis. This review discusses chromosomal loci of genes that control the retinoid cascade in relation to some candidate genes in schizophrenia. The paper relates the knowledge about the transport, delivery, and action of retinoids to what is presently known about the pathology of schizophrenia, with particular reference to the dopamine hypothesis, neurotransmitters, the glutamate hypothesis, retinitis pigmentosa, dermatologic disorders, and craniofacial anomalies.

A family history study of schizophrenia spectrum disorders suggests new candidate genes in schizophrenia and autism

To limit genetic heterogeneity, this study focused on the widely extended pedigrees of Ashkenazi Jewish schizophrenic and autistic probands, to determine if similar causal mechanisms might obtain for both conditions. At least two previous epidemiological studies have demonstrated increased risk for schizophrenia in Ashkenazi Jews. The hypothesis posed is that increased prevalence of various rare autosomal recessive diseases among the Ashkenazim might contribute to the increased vulnerability to schizophrenia and to autism in this large genetic isolate. Rates of amyotrophic lateral sclerosis (ALS) and bleeding disorders were significantly increased among relatives of schizophrenic and autistic probands, compared to relatives of normal probands. These results suggest new candidate loci in schizophrenia and autism, particularly the chromosome 15q23-24 locus of the hexosaminidase A gene, causing various GM2 gangliosidoses, and the 21q22.1-q22.2 loci of the antioxidant, superoxide dismutase gene, and a cytokine receptor gene.