A Twin Concordance Study of Trichotillomania
Health Partners, St. Paul, Minneapolis, USA.American Journal of Medical Genetics Part B Neuropsychiatric Genetics (Impact Factor: 3.42). 10/2009; 150B(7):944-9. DOI: 10.1002/ajmg.b.30922
Trichotillomania (TTM) is a disorder with putative genetic underpinnings. Family studies report higher than expected rates of TTM among relatives of affected individuals, but no twin concordance studies have been completed to estimate heritability rates. Same-sex twin pairs with hair pulling in at least one co-twin were included. Subjects were recruited following phone screens and questionnaire completion for zygosity and hair pulling variables. Three sets of criteria were used to define hair pulling and TTM. Two other sets of criteria were widened to include skin picking and bothersome hair manipulation. Fisher exact tests assessed pairwise concordance rates for monozygotic and dizygotic twin pairs and heritability estimates were calculated where significant differences existed. Among 34 identified twin pairs, 24 were monozygotic (MZ) and 10 were dizygotic (DZ). Respective concordance rates for MZ and DZ twin pairs were significantly different at 38.1% and 0% for DSM-IV TTM criteria, 39.1% and 0% using modified DSM criteria, and 58.3% and 20% for noticeable non-cosmetic hair pulling (heritability estimates 76.2%). MZ and DZ concordance rates were not significantly different when broadening hair pulling criteria to include skin picking or when including bothersome hair manipulation. Concordance rates from this study suggest that genetic factors play a significant role in the etiology of TTM. Given the reported discordance rates among the MZ twins, further research is required to fully understand contributory non-genetic factors.
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- "Although most characteristic of disorders such as trichotillomania (TTM) and skin picking disorder, BFRBs are also associated with body-dysmorphic disorder, autism spectrum disorders , and stereotypic movement disorders. Due to their high prevalence rates (Teng et al., 2002), proposed biological overlap (Bienvenu et al., 2009; Novak et al., 2009), and significant risk for impairment, research focused on the identification of factors responsible for the development and maintenance of BFRBs is essential. "
ABSTRACT: Body-focused repetitive behaviors (BFRBs), including hair pulling, nail biting, and skin picking are repetitive, habitual, and compulsive in nature. Although characteristic of disorders such as trichotillomania and skin picking disorder, BFRBs are associated with other psychiatric conditions as well. To date, research has failed to examine neurocognitive risk factors, particularly executive functioning, implicated in BFRBs utilizing a transdiagnostic approach. The present study recruited 53 participants (n = 27 demonstrating BFRBs and n = 26 randomly selected controls) from a larger sample of young adults. Participants completed an automated neurocognitive test battery including tasks of cognitive flexibility, working memory, and planning and organization. Results revealed that participants in the BFRB group demonstrated significantly poorer cognitive flexibility (d = 0.63) than controls. No differences were noted in other neurocognitive domains. However, planning and organization demonstrated a significant relationship with various BFRB severity measures. Implications, limitations, and avenues for further research are discussed.
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- "Trichotillomania is a highly familial illness (Keuthen et al., 2014). Genetic and environmental factors and their interactions are likely important in its pathogenesis (Keuthen et al., 2014; Novak et al., 2009; Chattopadhyay, 2012), but the precise nature of these factors and their relation with cognitive function and brain structure have not yet been identified. There is a search in psychiatry for objective intermediate biological markers, ideally grounded in the neurosciences, which signal 'risk' of developing a given disorder (termed 'endophenotypes') (Gottesman and Gould, 2003). "
ABSTRACT: Trichotillomania is characterized by repetitive pulling out of one's own hair. Impaired response inhibition has been identified in patients with trichotillomania, along with gray matter density changes in distributed neural regions including frontal cortex. The objective of this study was to evaluate impaired response inhibition and abnormal cortical morphology as candidate endophenotypes for the disorder. Subjects with trichotillomania (N = 12), unaffected first-degree relatives of these patients (N = 10), and healthy controls (N = 14), completed the Stop Signal Task (SST), a measure of response inhibition, and structural magnetic resonance imaging scans. Group differences in SST performance and cortical thickness were explored using permutation testing. Groups differed significantly in response inhibition, with patients demonstrating impaired performance versus controls, and relatives occupying an intermediate position. Permutation cluster analysis revealed significant excesses of cortical thickness in patients and their relatives compared to controls, in right inferior/middle frontal gyri (Brodmann Area, BA 47 & 11), right lingual gyrus (BA 18), left superior temporal cortex (BA 21), and left precuneus (BA 7). No significant differences emerged between groups for striatum or cerebellar volumes. Impaired response inhibition and an excess of cortical thickness in neural regions germane to inhibitory control, and action monitoring, represent vulnerability markers for trichotillomania. Future work should explore genetic and environmental associations with these biological markers.
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- "Knowledge of the etiologic factors involved in trichotillomania (TTM) remains rudimentary. The only twin study of TTM [Novak et al., 2009] suggests a role for the importance of genetic factors with heritability estimates ranging from 0.76 to 0.78. However, the small sample size of this study limits interpretability. "
ABSTRACT: Little is known about the etiology of hair pulling (HP) and its relationship to other obsessive compulsive (OC) spectrum disorders. In a large-sample family study, we examined the familial aggregation of HP and co-transmission of obsessive compulsive disorder (OCD) and skin picking (SP). Our sample consisted of 110 proband cases with HP and 48 controls without HP, plus 128 first-degree case relatives and 50 first-degree control relatives. Case versus control relatives had higher recurrence risk estimates for both HP and OCD but not SP. The finding that HP is familial is consistent with the only existing twin study. Additional analyses suggest that there may be a familial subtype of HP with comorbid OCD. Those adult proband cases with HP + OCD had more anxiety and depression than cases without OCD. Probands with HP + OCD also had earlier onset of OCD. Identification of an HP subtype with comorbid OCD may have significant theoretical and treatment implications. The data did not provide evidence for an etiologic relationship between HP and SP. Replication of these findings in future studies with larger cohorts of case and control relatives is warranted. © 2014 Wiley Periodicals, Inc.
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