Editing Causes of mental disorders (section)

===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}}