Editing Trichotillomania (section)

== Causes ==
[[Anxiety]], [[clinical depression|depression]] and [[obsessive–compulsive disorder]] are more frequently encountered in people with trichotillomania.<ref name="Chamberlain"/><ref name="pmid8698680">{{cite journal | vauthors = Christenson GA, Crow SJ | title = The characterization and treatment of trichotillomania | journal = The Journal of Clinical Psychiatry | volume = 57 | issue = Suppl 8 | pages = 42–7; discussion 48–9 | year = 1996 | pmid = 8698680 }}</ref> Trichotillomania has a high overlap with [[post traumatic stress disorder]],<ref>{{Cite journal |last1=Özten |first1=Eylem |last2=Sayar |first2=Gökben Hızlı |last3=Eryılmaz |first3=Gül |last4=Kağan |first4=Gaye |last5=Işık |first5=Sibel |last6=Karamustafalıoğlu |first6=Oğuz |date=2015 |title=The relationship of psychological trauma with trichotillomania and skin picking |journal=Neuropsychiatric Disease and Treatment |volume=11 |pages=1203–1210 |doi=10.2147/NDT.S79554 |doi-access=free |issn=1176-6328 |pmc=4440428 |pmid=26028973}}</ref> and some cases of trichotillomania may be triggered by stress. Another school of thought emphasizes hair pulling as addictive or negatively reinforcing, as it is associated with rising tension beforehand and relief afterward.<ref name="Chamberlain"/> A neurocognitive model — the notion that the [[basal ganglia]] play a role in habit formation and that the [[frontal lobe]]s are critical for normally suppressing or inhibiting such habits — sees trichotillomania as a habit disorder.<ref name="Chamberlain"/>

In several [[MRI]] studies, it has been found that people with trichotillomania have more [[gray matter]] on average than those who do not have the disorder.<ref>{{cite journal | vauthors = Chamberlain SR, Menzies LA, Fineberg NA, Del Campo N, Suckling J, Craig K, Müller U, Robbins TW, Bullmore ET, Sahakian BJ | display-authors = 6 | title = Grey matter abnormalities in trichotillomania: morphometric magnetic resonance imaging study | journal = The British Journal of Psychiatry | volume = 193 | issue = 3 | pages = 216–221 | date = September 2008 | pmid = 18757980 | pmc = 2806575 | doi = 10.1192/bjp.bp.107.048314 }}</ref> One study found that individuals with trichotillomania have decreased [[cerebellar]] volume on average,<ref name="Chamberlain"/><ref name="pmid16945351">{{cite journal | vauthors = Keuthen NJ, Makris N, Schlerf JE, Martis B, Savage CR, McMullin K, Seidman LJ, Schmahmann JD, Kennedy DN, Hodge SM, Rauch SL | display-authors = 6 | title = Evidence for reduced cerebellar volumes in trichotillomania | journal = Biological Psychiatry | volume = 61 | issue = 3 | pages = 374–381 | date = February 2007 | pmid = 16945351 | doi = 10.1016/j.biopsych.2006.06.013 | s2cid = 28202399 }}</ref> which suggests some differences between OCD and trichotillomania.<ref name="Chamberlain"/> An [[fMRI]] study reported decreased activation in the [[basal ganglia]], [[dorsolateral prefrontal cortex]], and [[dorsal anterior cingulate cortex]] in people with trichotillomania.<ref>{{cite journal | vauthors = Dougherty DD, Peters AT, Grant JE, Peris TS, Ricketts EJ, Migó M, Chou T, O'Neill J, Stein DJ, Lochner C, Keuthen N, Piacentini J, Deckersbach T | display-authors = 6 | title = Neural basis of associative learning in Trichotillomania and skin-picking disorder | journal = Behavioural Brain Research | volume = 425 | pages = 113801 | date = May 2022 | pmid = 35183617 | doi = 10.1016/j.bbr.2022.113801 | pmc = 8940679 }}</ref> Abnormalities in the [[caudate nucleus]] are noted in OCD, but there is no evidence to support that these abnormalities can also be linked to trichotillomania.<ref name="Chamberlain"/>

It is likely that a combination of multiple genes confers vulnerability to trichotillomania.<ref name="Chamberlain"/> Mutations in the [[SLITRK1]],<ref name="Chamberlain"/><ref>{{cite journal | vauthors = Zuchner S, Cuccaro ML, Tran-Viet KN, Cope H, Krishnan RR, Pericak-Vance MA, Wright HH, Ashley-Koch A | display-authors = 6 | title = SLITRK1 mutations in trichotillomania | journal = Molecular Psychiatry | volume = 11 | issue = 10 | pages = 887–889 | date = October 2006 | pmid = 17003809 | doi = 10.1038/sj.mp.4001865 | s2cid = 28209408 | doi-access =  }}</ref> [[5HT2A]],<ref>{{cite journal | vauthors = Hemmings SM, Kinnear CJ, Lochner C, Seedat S, Corfield VA, Moolman-Smook JC, Stein DJ | title = Genetic correlates in trichotillomania--A case-control association study in the South African Caucasian population | journal = The Israel Journal of Psychiatry and Related Sciences | volume = 43 | issue = 2 | pages = 93–101 | date = 2006 | pmid = 16910371 | url = https://doctorsonly.co.il/wp-content/uploads/2011/12/2006_2_5.pdf }}</ref> [[SAPAP3]],<ref>{{cite journal | vauthors = Züchner S, Wendland JR, Ashley-Koch AE, Collins AL, Tran-Viet KN, Quinn K, Timpano KC, Cuccaro ML, Pericak-Vance MA, Steffens DC, Krishnan KR, Feng G, Murphy DL | display-authors = 6 | title = Multiple rare SAPAP3 missense variants in trichotillomania and OCD | journal = Molecular Psychiatry | volume = 14 | issue = 1 | pages = 6–9 | date = January 2009 | pmid = 19096451 | pmc = 2803344 | doi = 10.1038/mp.2008.83 }}</ref> and [[FOXP1]]<ref>{{cite journal |last1=Curtis |first1=Kaya L |last2=Lipner |first2=Shari R |title=Body-Focused Repetitive Behaviors in Patients with FOXP1 Syndrome: An International Cross-Sectional Survey-Based Study |journal=Skin Appendage Disorders |date=2 April 2024 |volume=10 |issue=3 |pages=229–231 |doi=10.1159/000537906 |pmid=38835719 |url=https://karger.com/sad/article-pdf/10/3/229/4235859/000537906.pdf}}</ref> genes have been associated with trichotillomania. In addition, [[HOXB8]] [[Gene knockout|knockout]] mice display pathological grooming behavior similar to trichotillomania,<ref>{{cite journal | vauthors = Greer JM, Capecchi MR | title = Hoxb8 is required for normal grooming behavior in mice | journal = Neuron | volume = 33 | issue = 1 | pages = 23–34 | date = January 2002 | pmid = 11779477 | doi = 10.1016/s0896-6273(01)00564-5 | s2cid = 18832852 | authorlink2 = Mario Capecchi | doi-access = free }}</ref><ref>{{cite journal | vauthors = Chen SK, Tvrdik P, Peden E, Cho S, Wu S, Spangrude G, Capecchi MR | title = Hematopoietic origin of pathological grooming in Hoxb8 mutant mice | journal = Cell | volume = 141 | issue = 5 | pages = 775–785 | date = May 2010 | pmid = 20510925 | pmc = 2894573 | doi = 10.1016/j.cell.2010.03.055 | authorlink7 = Mario Capecchi }}</ref> although associations between trichotillomania and the HOXB8 gene have not been demonstrated in humans.<ref>{{cite journal |last1=Reid |first1=Madison |last2=Lin |first2=Ashley |last3=Farhat |first3=Luis C. |last4=Fernandez |first4=Thomas V. |last5=Olfson |first5=Emily |title=The genetics of trichotillomania and excoriation disorder: A systematic review |journal=Comprehensive Psychiatry |date=31 May 2024 |volume=133 |pages=152506 |doi=10.1016/j.comppsych.2024.152506 |pmid=38833896 |quote=Even though studies have been conducted on the mouse Hoxb8 gene, no studies have directly investigated the HOXB8 gene in humans concerning TTM or ED.|doi-access=free |pmc=11513794 }}</ref>