Trichotillomania: Heritable, twin study confirms (if you include skin picking)

I was told that a friend’s mother’s sister’s second ex-husband’s father was a debt collector for the Mafia, affectionately called, “Frank the Eyelash” — he would pull out eyelashes of the debtors. (I previously noted my Skinnerian response to the word “eyelash” now is to run away screaming, “I’ll pay, I’ll pay”)

The premise is that pulling out eyelashes is unpleasant (regardless of the veracity of the story, which is a good one). So, trichotillomania is self-injurious behavior, compulsively so.  But, not lethally so, as there seems to be a genetic component.  (If it were deadly behavior, then there would be no chance to study the genetics, to state the obvious. )

Hair pulling and skin picking are thought to be some kind of  “grooming genes” gone awry, perhaps into the OCD neural pathway. A recent study among monozygous an dizygous twins seems to clinch this theory — the more generalized behavior that is heriditary is skin/hair pulling and picking, rather than just the eyelash or hair pulling itself:

. . . 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. . . .. 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.

Novak CE, Keuthen NJ, Stewart SE, Pauls DL., A twin concordance study of trichotillomania. Am J Med Genet Part B 150B:944-949.