Editing Causes of mental disorders (section)

==Biological factors==
Biological factors consist of anything physical that can cause adverse effects on a person's mental health. Biological factors include genetics, prenatal damage, infections, exposure to toxins, brain defects or injuries, and substance abuse. Many professionals believe that the cause of mental disorders is the biology of the brain and the nervous system.{{cn|date=October 2024}}

[[Mind (charity)|''Mind'']] mentions genetic factors, long-term physical health conditions, and head injuries or epilepsy (affecting behavior and mood) as factors that may trigger an episode of mental illness.

===Genetics===

Some rare mental disorders are caused only by genetics such as [[Huntington's disease]].

Family linkage and some [[twin studies]] have indicated that [[psychiatric genetics|genetic factors often play a role]] in the heritability of mental disorders. The reliable identification of specific genetic variation can cause indication of higher risk to particular disorders, through [[Genetic linkage|linkage]], Genome Wide Association Scores<ref>https://www.genome.gov/genetics-glossary/Genome-Wide-Association-Studies Genome-wide association studies (GWAS). Genome.gov. (n.d.). Retrieved August 8, 2022</ref> or [[Genetic association|association studies]], has proven difficult. This is due to the complexity of interactions between genes, environmental events, and early development or the need for new research strategies. No specific gene results in a complex trait disorder, but specific variations of alleles result in higher risk for a trait. The [[heritability]] of behavioral traits associated with a mental disorder may be in permissive than in restrictive environments, and susceptibility genes probably work through both "within-the-skin" (physiological) pathways and "outside-the-skin" (behavioral and social) pathways. Investigations increasingly focus on links between genes and endophenotypes because they are more specific traits. Some include neurophysiological, biochemical, endocrinological, neuroanatomical, cognitive, or neuropsychological, rather than disease categories. Concerning a well-known mental disorder, [[schizophrenia]], it is said with certainty {{by whom|date=October 2024}} that [[alleles]] (forms of genes) were responsible for this disorder. Some research has indicated only multiple, rare mutations are thought to alter neurodevelopmental pathways that can ultimately contribute to schizophrenia; virtually every rare structural mutation was different in each individual.{{cn|date=October 2024}}

Research has shown that many conditions are polygenic meaning there are multiple defective genes rather than only one that is responsible for a disorder, and these genes may also be pleiotropic meaning that they cause multiple disorders, not just one.<ref>{{cite journal | vauthors = Lu H, Qiao J, Shao Z, Wang T, Huang S, Zeng P | title = A comprehensive gene-centric pleiotropic association analysis for 14 psychiatric disorders with GWAS summary statistics | journal = BMC Medicine | volume = 19 | issue = 1 | pages = 314 | date = December 2021 | pmid = 34895209 | pmc = 8667366 | doi = 10.1186/s12916-021-02186-z | doi-access = free }}</ref> [[Schizophrenia]] and [[Alzheimer's]] are both examples of hereditary mental disorders.{{cn|date=March 2025}} When exonic genes encode for proteins, these proteins do not just affect one trait. The pathways that contribute to complex traits and phenotypes interact with multiple systems, even though proteins have specific functions.<ref>Lynch M. (2005). Simple evolutionary pathways to complex proteins. Protein science: a publication of the Protein Society, 14(9), 2217–2227. https://doi.org/10.1110/ps.041171805</ref> 
[[Neuroplasticity|brain plasticity (neuroplasticity)]] raises questions of whether some brain differences may be caused by mental illnesses or by pre-existing and then causing them.
====Attention deficit hyperactivity disorder====
{{excerpt|Attention deficit hyperactivity disorder|Genetics}}
====Bipolar disorder====
{{excerpt|Bipolar disorder|Genetic}}

===Prenatal damage===
Any damage that occurs to a fetus while still in its mother's womb is considered prenatal damage. Mental disorders can develop if the pregnant mother uses drugs or alcohol or is exposed to illnesses or infections during pregnancy. {{cn|date=October 2024}}
Environmental events surrounding [[pregnancy]] and [[Childbirth|birth]] have increased the development of mental illness in the [[offspring]]. Some events may include maternal exposure to [[Stress (medicine)|stress]] or [[Psychological trauma|trauma]], conditions of famine, [[Obstetric|obstetric birth]] complications, infections, and [[Pregnancy|gestational]] exposure to [[Alcohol (drug)|alcohol]] or [[cocaine]]. These factors have been hypothesized to affect areas of neurodevelopment, general development, and restrict [[neuroplasticity]].{{cn|date=October 2024}}

===Infection, disease and toxins===
====Infection====
There have been some findings of links between infection by the parasite [[Toxoplasma gondii]] and schizophrenia.<ref name="Contopoulos-Ioannidis Gianniki Ai-Nhi Truong Montoya 2022 pp. 48–60">{{cite journal | vauthors = Contopoulos-Ioannidis DG, Gianniki M, Ai-Nhi Truong A, Montoya JG | title = Toxoplasmosis and Schizophrenia: A Systematic Review and Meta-Analysis of Prevalence and Associations and Future Directions | journal = Psychiatric Research and Clinical Practice | volume = 4 | issue = 2 | pages = 48–60 | year = 2022 | pmid = 36254187 | doi = 10.1176/appi.prcp.20210041 | publisher = American Psychiatric Association Publishing | pmc = 9558922 | s2cid = 248354624 }}</ref>

[[Signs and symptoms of HIV/AIDS#Neurological and psychiatric|AIDS]] has been linked to some mental disorders. Research shows that infections and exposure to toxins such as [[HIV]]<ref name=HIV/> and [[streptococcus]] cause dementia.<ref>{{cite journal | vauthors = Ebert S, Goos M, Rollwagen L, Baake D, Zech WD, Esselmann H, Wiltfang J, Mollenhauer B, Schliebs R, Gerber J, Nau R | display-authors = 6 | title = Recurrent systemic infections with Streptococcus pneumoniae do not aggravate the course of experimental neurodegenerative diseases | journal = Journal of Neuroscience Research | volume = 88 | issue = 5 | pages = 1124–1136 | date = April 2010 | pmid = 19859962 | doi = 10.1002/jnr.22270 | s2cid = 35148634 }}</ref> This HIV infection that makes its way to the brain is called encephalopathy which spreads itself through the brain leading to dementia.<ref name=HIV>{{Cite web |date=2021-08-08 |title=HIV and Dementia | archive-url=https://web.archive.org/web/20200803202732/https://www.hopkinsmedicine.org/health/conditions-and-diseases/hiv-and-aids/hiv-and-dementia  | archive-date=2020-08-03 |url=https://www.hopkinsmedicine.org/health/conditions-and-diseases/hiv-and-aids/hiv-and-dementia |access-date=2022-05-04 |publisher=The Johns Hopkins University, The Johns Hopkins Hospital, and Johns Hopkins Health System  | location=Baltimore MD |website=www.hopkinsmedicine.org |language=en}}</ref> The infections or toxins that trigger a change in the brain chemistry can develop into a mental disorder.

Depression and emotional liability may be also be caused by [[babesiosis]].

There is some evidence that there may be a relationship between [[Borna disease#Psychiatric disease|BoDV-1 infection and psychiatric disease]].

The research on Lyme disease caused by a deer tick and toxins is expanding the link between bacterial infections and mental illness.<ref>{{cite web | url=https://www.cugmhp.org/five-on-friday-posts/lyme-disease-and-mental-health/ | title=Lyme Disease and Mental Health | date=17 August 2018 }}</ref>

====Disease====
Depression, anxiety, mania, psychosis, vegetative symptoms, cognitive deficit and consciousness impairment may be caused by internal disease as well as endocrine and metabolic disorders, deficiency states and neurologic disorders.<ref name="A R S L p.">{{cite journal |last1=A |first1=Testa |last2=R |first2=Giannuzzi |last3=S |first3=Daini |last4=L |first4=Bernardini |last5=L |first5=Petrongolo |last6=N |first6=Gentiloni Silveri |title=Psychiatric emergencies (part III): psychiatric symptoms resulting from organic diseases |url=https://pubmed.ncbi.nlm.nih.gov/23436670/ |journal=European Review for Medical and Pharmacological Sciences |date=February 2013 |publisher=Eur Rev Med Pharmacol Sci |volume=17 |issue=Suppl 1 |pages=86–99 |issn=1128-3602 |pmid=23436670 |access-date=2023-08-11}}</ref>

===Injury and brain defects===
{{more sources needed section|date=October 2024}}
Any damage to the brain can cause a mental disorder. The brain is the control system for the nervous system and the rest of the body. Without it, the body cannot function properly.<ref>{{Cite web |title=Brain Death - Brain, Spinal Cord, and Nerve Disorders |url=https://www.msdmanuals.com/home/brain,-spinal-cord,-and-nerve-disorders/coma-and-impaired-consciousness/brain-death |access-date=2023-03-24 |website=MSD Manual Consumer Version |language=en}}</ref>

Increased mood swings, insane behavior, and substance abuse disorders are [[traumatic brain injury]] (TBI) examples. Findings on the relationship between TBI severity and prevalence of subsequent psychiatric disorders have been inconsistent, and occurrence relates to prior mental health problems. Direct neurophysiological effects in a complex interaction with personality, attitude, and [[social influences]].

Head trauma classifies as either open or closed head injury. In [[open head injury]], the skull is punctured and the brain tissue is demolished. [[Closed head injury]] is more common, the skull is not punctured because there is an impact of the brain against the skull that creates permanent structural damage ([[subdural hematoma]]). With both types, symptoms may disappear or persist over time. Typically the longer the length of time spent unconscious and the length of [[post-traumatic amnesia]] the worse the prognosis for the individual. The cognitive residual symptoms of head trauma are associated with the type of injury (either an open head injury or closed head injury) and the amount of tissue destroyed. Closed injury head trauma symptoms include; Deficits in [[Abstract reasoning|abstract reasoning ability]], judgment, memory, and marked personality changes. Open injury head trauma symptoms tend to be the experience of classic neuropsychological syndromes like [[aphasia]], visual-spatial disorders, and types of memory or [[Sensory processing disorder|perceptual disorders]].{{cn|date=October 2024}}

[[Brain tumor]]s are classified as either [[malignant]] and [[benign]], and as [[intrinsic]] (directly infiltrate the [[parenchyma]] of the brain) or [[extrinsic]] (grows on the external surface of the brain and produces symptoms as a result of pressure on the brain tissue). Progressive cognitive changes associated with brain tumors may include confusion, poor comprehension, and even [[dementia]]. Symptoms tend to depend on the location of the tumor in the brain. For example, tumors on the [[Frontal lobe|frontal lobe tend]] to be associated with the sign of impairment of judgment, apathy, and loss of the ability to regulate/modulate behavior.<ref>{{Cite journal |last1=Madhusoodanan |first1=Subramoniam |last2=Ting |first2=Mark Bryan |last3=Farah |first3=Tara |last4=Ugur |first4=Umran |date=2015-09-22 |title=Psychiatric aspects of brain tumors: A review |journal=World Journal of Psychiatry |volume=5 |issue=3 |pages=273–285 |doi=10.5498/wjp.v5.i3.273 |doi-access=free |issn=2220-3206 |pmc=4582304 |pmid=26425442}}</ref>

Findings have indicated abnormal functioning of [[brainstem]] structures in individuals with mental disorders such as [[schizophrenia]], and other disorders that have to do with impairments in maintaining sustained attention. Some abnormalities in the average size or shape of some regions of the brain have been found in some disorders, reflecting genes and experiences. Studies of schizophrenia have tended to find enlarged [[Ventricular system|ventricles]] and sometimes reduced volume of the [[cerebrum]] and [[hippocampus]], while studies of (psychotic) [[bipolar disorder]] have sometimes found increased [[amygdala]] volume. Findings differ over whether volumetric abnormalities are risk factors or are only found alongside the course of mental health problems, possibly reflecting neurocognitive or emotional stress processes and medication use or substance use. Some studies have also found reduced hippocampal volumes in [[major depression]], possibly worsening with time depression.{{cn|date=October 2024}}

[[File:Generic Neurotransmitter System.jpg|thumb|Generic Neurotransmitter System]]

===Neurotransmitter systems===
Abnormal levels of [[dopamine]] activity correspond with several disorders (reduced in [[ADHD]] and [[OCD]], and increased in schizophrenia). The dysfunction in [[serotonin]] and other [[monoamine]] neurotransmitters ([[norepinephrine]] and [[dopamine]]) correspond with certain mental disorders and their associated neural networks. Some include [[Major depressive disorder|major depression]], [[Obsessive compulsive disorder|obsessive-compulsive disorder]], [[phobias]], [[post-traumatic stress disorder]], and [[generalized anxiety disorder]]. Studies of depleted levels of [[monoamine]] neurotransmitters show an association with depression and other psychiatric disorders, but "... it should be questioned whether 5-HT [serotonin] represents just one of the final and not the main, factors in the neurological chain of events underlying psychopathological symptoms...."

Simplistic "chemical imbalance" explanations for mental disorders have never received empirical support; and most prominent psychiatrists, neuroscientists, and psychologists have not espoused such ill-defined, facile etiological theories. Instead, neurotransmitter systems have been understood in the context of the [[Diathesis–stress model|diathesis-stress]] or [[Biopsychosocial|biopsychosocial models]]. The following 1967 quote from renowned psychiatric and neuroscience researchers exemplifies this more sophisticated understanding (in contrast to the woolly "chemical imbalance" notion).

Whereas specific genetic factors may be of importance in the etiology of some, and possibly all, depressions, it is equally conceivable that early experiences of the infant or child may cause enduring biochemical changes, that may predispose some individuals to depressions in adulthood. It is not likely that changes in the metabolism of the biogenic amines alone will account for the complex phenomena of normal or pathological affect.

===Substance abuse===
{{no sources section|date=October 2024}}
Substance abuse, especially long-term abuse, can cause or exacerbate many mental disorders. [[Alcoholism]] is linked to [[Depression (mood)|depression]] while abuse of [[amphetamines]] and [[LSD]] can leave a person feeling [[paranoid]] and [[anxious]].

Correlations of mental disorders with drug use include [[Cannabis (drug)|cannabis]], alcohol, and [[caffeine]]. At more than 300&nbsp;mg, [[caffeine]] may cause [[anxiety]] or worsen anxiety disorders. Illicit drugs can stimulate particular parts of the brain that can affect development in adolescence. Cannabis has also been found to worsen depression and lessen an individual's [[motivation]]. Alcohol has the potential to damage "[[white matter]]" in the brain that affects [[thinking]] and [[memory]]. Alcohol is a problem in many countries due to many people participating in excessive drinking or [[binge drinking]].