Genetic heterogeneity may in part explain sex differences in the familial risk for schizophrenia

Sex-Dependent Shared and Nonshared Genetic Architecture Across Mood and Psychotic Disorders

BACKGROUND

Sex differences in incidence and/or presentation of schizophrenia (SCZ), major depressive disorder (MDD), and bipolar disorder (BIP) are pervasive. Previous evidence for shared genetic risk and sex differences in brain abnormalities across disorders suggest possible shared sex-dependent genetic risk.

METHODS

We conducted the largest to date genome-wide genotype-by-sex (G×S) interaction of risk for these disorders using 85,735 cases (33,403 SCZ, 19,924 BIP, and 32,408 MDD) and 109,946 controls from the PGC (Psychiatric Genomics Consortium) and iPSYCH.

RESULTS

Across disorders, genome-wide significant single nucleotide polymorphism-by-sex interaction was detected for a locus encompassing NKAIN2 (rs117780815, p = 3.2 × 10-8), which interacts with sodium/potassium-transporting ATPase (adenosine triphosphatase) enzymes, implicating neuronal excitability. Three additional loci showed evidence (p < 1 × 10-6) for cross-disorder G×S interaction (rs7302529, p = 1.6 × 10-7; rs73033497, p = 8.8 × 10-7; rs7914279, p = 6.4 × 10-7), implicating various functions. Gene-based analyses identified G×S interaction across disorders (p = 8.97 × 10-7) with transcriptional inhibitor SLTM. Most significant in SCZ was a MOCOS gene locus (rs11665282, p = 1.5 × 10-7), implicating vascular endothelial cells. Secondary analysis of the PGC-SCZ dataset detected an interaction (rs13265509, p = 1.1 × 10-7) in a locus containing IDO2, a kynurenine pathway enzyme with immunoregulatory functions implicated in SCZ, BIP, and MDD. Pathway enrichment analysis detected significant G×S interaction of genes regulating vascular endothelial growth factor receptor signaling in MDD (false discovery rate-corrected p < .05).

CONCLUSIONS

In the largest genome-wide G×S analysis of mood and psychotic disorders to date, there was substantial genetic overlap between the sexes. However, significant sex-dependent effects were enriched for genes related to neuronal development and immune and vascular functions across and within SCZ, BIP, and MDD at the variant, gene, and pathway levels.

Neuropsychiatric Features in Primary Mitochondrial Disease

Mitochondrial diseases are a clinically heterogeneous group of disorders that ultimately result from dysfunction of the mitochondrial respiratory chain. There is some evidence to suggest that mitochondrial dysfunction plays a role in neuropsychiatric illness; however, the data are inconclusive. This article summarizes the available literature published in the area of neuropsychiatric manifestations in both children and adults with primary mitochondrial disease, with a focus on autism spectrum disorder in children and mood disorders and schizophrenia in adults.

Sex differences in the genetic risk for schizophrenia: history of the evidence for sex-specific and sex-dependent effects

Although there is a long history to examinations of sex differences in the familial (and specifically, genetic) transmission of schizophrenia, there have been few investigators who have systematically and rigorously studied this issue. This is true even in light of population and clinical studies identifying significant sex differences in incidence, expression, neuroanatomic and functional brain abnormalities, and course of schizophrenia. This review highlights the history of work in this arena from studies of family transmission patterns, linkage and twin studies to the current molecular genetic strategies of large genome-wide association studies. Taken as a whole, the evidence supports the presence of genetic risks of which some are sex-specific (i.e., presence in one sex and not the other) or sex-dependent (i.e., quantitative differences in risk between the sexes). Thus, a concerted effort to systematically investigate these questions is warranted and, as we argue here, necessary in order to fully understand the etiology of schizophrenia.

The genetics of sex differences in brain and behavior

Biological differences between men and women contribute to many sex-specific illnesses and disorders. Historically, it was argued that such differences were largely, if not exclusively, due to gonadal hormone secretions. However, emerging research has shown that some differences are mediated by mechanisms other than the action of these hormone secretions and in particular by products of genes located on the X and Y chromosomes, which we refer to as direct genetic effects. This paper reviews the evidence for direct genetic effects in behavioral and brain sex differences. We highlight the 'four core genotypes' model and sex differences in the midbrain dopaminergic system, specifically focusing on the role of Sry. We also discuss novel research being done on unique populations including people attracted to the same sex and people with a cross-gender identity. As science continues to advance our understanding of biological sex differences, a new field is emerging that is aimed at better addressing the needs of both sexes: gender-based biology and medicine. Ultimately, the study of the biological basis for sex differences will improve healthcare for both men and women.

Schizotypal, schizoid and paranoid characteristics in the biological parents of social anhedonics

Mounting evidence suggests that social anhedonia may be a marker of genetic liability for schizophrenia-spectrum pathology. To examine this hypothesis, we conducted a study of severity of schizotypal, schizoid and paranoid pathology (i.e., Cluster A personality disorders) in the biological parents of individuals with high levels of social anhedonia and healthy controls. Eighty-six individuals with social anhedonia, 89 healthy controls and their biological parents were recruited from a large community. Structured clinical interviews were conducted to obtain Cluster A diagnoses and symptom ratings for parents. The biological parents of socially anhedonic probands had elevated rates of Cluster A disorders (24%) compared with the parents of control probands (12%). Post hoc analyses revealed that these group differences were the result of elevated rates of diagnoses in the fathers of social anhedonic probands, but not the mothers. This finding was replicated when Cluster A symptoms were examined dimensionally. These findings are consistent with the hypothesis that social anhedonia is a promising indicator of the genetic vulnerability to schizophrenia-spectrum pathology. The unexpected findings of elevated pathology in fathers, but not mothers of socially anhedonic probands, require further exploration.

Emotion processing in persons at risk for schizophrenia

Evidence suggests that individuals with schizophrenia demonstrate emotion-processing deficits. However, the nature and extent of emotion abnormalities in individuals considered at risk for schizophrenia have not been previously summarized. This article provides a review of the recent literature pertaining to emotion processing in 3 at-risk populations: those at familial high risk, those with schizotypal characteristics, and those in the putative prodrome to psychosis. Studies are reviewed across the components of emotion perception, experience, and expression. Further, we discuss investigations into psychophysiology, brain structure, and brain function that employ emotion probes. Review of the literature suggests that individuals at high risk demonstrate similar abnormalities to those with schizophrenia but at an attenuated level. The most robust findings in at-risk groups are in the areas of reduced emotion perception, self-reported anhedonia, and increased negative affect. We conclude with an agenda for future research.

Sex differences in symptoms of psychosis in a non-selected, general population sample

BACKGROUND

Little is known about sex differences in psychosis beyond the borders of clinical disorder.

METHODS

A general population sample of 7,076 subjects was assessed using the Composite International Diagnostic Interview, in order to explore sex differences in the prevalence of any positive and negative symptoms of psychosis, and to examine to what degree any differences could be explained by differences in level of affective symptoms.

RESULTS

Male sex was associated with higher prevalence of negative symptoms (OR = 1.6, 95% CI = 1.0, 2.5), independent of differences in affective symptoms and presence of DSM-III-R psychotic disorder. Women had higher rates of positive psychotic experiences (OR = 0.8, 95% CI = 0.7, 0.9), but this difference disappeared after adjustment for depressive symptoms (adjusted OR = 1.2, 95% CI = 0.9, 1.5).

CONCLUSION

The sex differences in psychopathology that are seen in schizophrenia are expressed beyond the clinical phenotype, suggesting sex-dependent continuous and normal variation of several psychosis dimensions. The higher rates of positive psychotic experiences seen in women may be secondary to differences in the rate of affective symptoms.

P300 subcomponent abnormalities in schizophrenia: III. Deficits In unaffected siblings of schizophrenic probands

BACKGROUND

Reduced P300 amplitude is a robust finding in patients with schizophrenia. In previous investigations, we reported reductions of specific subcomponents of the auditory oddball P300 that were independent of acute symptomatology and persistent over time, consistent with a trait abnormality. To clarify whether these stable deficits represented genetic markers of vulnerability to schizophrenia, event-related brain potentials (ERPs) from patients were compared to those from their own healthy siblings and unrelated control subjects.

METHODS

Auditory P300 ERPs were acquired from 11 schizophrenic patients, 12 healthy siblings and 23 matched control subjects. Five P300 subcomponents were identified using current source density measures: frontal, bilateral parietal, and bilateral temporal.

RESULTS

Consistent with previous reports, patients had reduced parietal and frontal P300 amplitudes. The healthy siblings of the schizophrenic probands had an isolated reduction of the frontal P300.

CONCLUSIONS

Frontal P300 amplitude is a potential endophenotypic marker of genetic vulnerability to schizophrenia in individuals who otherwise show no evidence of clinical symptomatology. Given the functional interpretation of the frontal P300 as a physiological correlate of cognitive orienting, this supports the hypothesis that impairments of the neural substrate underlying attentional mechanisms are selective indicators of genetic susceptibility to schizophrenia in high-risk individuals.

Schizophrenia: genes and environment

The historical and genetic foundations of our current understanding of schizophrenia are reviewed, as are the present and future directions for research. Genetic epidemiological investigations, including family, twin, and adoption studies have confirmed the contributions of genetic and environmental determinants of schizophrenia. For example, identical twins show average concordance rates of only 50%; rates of 100% would be expected on the basis of genetic equivalence alone. Genetic factors may cause errors in brain development and synaptic connections. A broad range of environmental components may further damage the brain. Biological components may include pregnancy and delivery complications, such as intrauterine fetal hypoxia, infections, and malnutrition. Primarily nonbiological components may include psychosocial stressors, such as residence in an urban area and dysfunctional family communication. It is likely that the environmental factors interact with the genetic liability in a negative manner to produce disorders in the schizophrenic spectrum. Genetic and environmental components of the disorder are examined, as well as their interactions in producing either neurodevelopmental syndromes or schizophrenia itself. The implication of these findings for prevention and treatment are considered.