Genetic and environmental factors of schizophrenia and autism spectrum disorder: insights from twin studies

Abstract

Twin studies of psychiatric disorders such as schizophrenia and autism spectrum disorder have employed epidemiological approaches that determine heritability by comparing the concordance rate between monozygotic twins (MZs) and dizygotic twins. The basis for these studies is that MZs share 100% of their genetic information. Recently, biological studies based on molecular methods are now being increasingly applied to examine the differences between MZs discordance for psychiatric disorders to unravel their possible causes. Although recent advances in next-generation sequencing have increased the accuracy of this line of research, there has been greater emphasis placed on epigenetic changes versus DNA sequence changes as the probable cause of discordant psychiatric disorders in MZs. Since the epigenetic status differs in each tissue type, in addition to the DNA from the peripheral blood, studies using DNA from nerve cells induced from postmortem brains or induced pluripotent stem cells are being carried out. Although it was originally thought that epigenetic changes occurred as a result of environmental factors, and thus were not transmittable, it is now known that such changes might possibly be transmitted between generations. Therefore, the potential possible effects of intestinal flora inside the body are currently being investigated as a cause of discordance in MZs. As a result, twin studies of psychiatric disorders are greatly contributing to the elucidation of genetic and environmental factors in the etiology of psychiatric conditions.

Anti-Inflammatory Diets and Schizophrenia

“…Schizophrenia occurs by interactions between genetic variations and environmental factors, which affect neurotransmission and subsequent behavioral and intellectual changes [ 3 4 ]. Dysregulation of neurotransmission systems (e.g., dopaminergic and glutamatergic neurotransmission) has been considered as a primary hypothesis of schizophrenia [ 5 6 8 ].…”

“…and negative symptoms (flat affect / inappropriate responses, apathy, and lack of speech). Although the causes of schizophrenia have not been evidently identified, interactions among genetic, environmental, and other psychological factors may involve with the development of schizophrenia [ 3 4 ].…”

Optical Coherence Tomography Angiography of Macula and Optic Nerve in Autism Spectrum Disorder: A Pilot Study

“…The etiology of this disorder remains elusive. Several causes and effects have been proposed [ 3 ]. Vascularization and blood flow in a number of regions of interest (ROI) have been studied in ASD.…”

Finding underlying genetic mechanisms of two patients with autism spectrum disorder carrying familial apparently balanced chromosomal translocations

“…Genetic studies on ASD have accelerated over the last decade with the use of next‐generation sequencing and microarray analysis methods and hundreds of genes, hereditary or de novo copy number variations (CNVs), chromosomal abnormalities, etc., have been associated with ASD 6,8–11 . Rare inherited or de novo protein truncation variants (PTVs) that are frameshifts, canonical splice sites, and nonsense single nucleotide variants (SNVs) with large effect size and inherited common SNVs with small effect size have been associated with the genetic etiology of ASD in many studies to date 9,12 .…”