We describe the discovery of genetic and phenotypic associations with “nail biting,” technically known as onychophagia. Over 180,000 participants who consented to research in the 23andMe customer base responded to the question “How often do you bite your nails”; 37% reported biting their nails and 7% said they bite very often. Consistent with the literature, “nail biting” was correlated with “conscientiousness” and “neuroticism” of our five dimensional personality questionnaires. Individuals who become nervous easily or are moody report a higher frequency of nail biting.
Our genome-wide scan identified 21 significant associations (p < 5e-8) with nail biting. We identified a loss of function variant (rs117612447, p=4.6e-22) in KRT31, a keratin gene involved in hair and nail formation, and a variant (rs10876505, p=5.5e-9) near HOXC13, a gene linked to nail and hair developmental disorders. Six of the identified loci (rs713843, p=4.2e-26; rs35754740, p=4.8e-11; rs4776970, p=7.4e-11; rs4775313, p=8.4e-11; rs62264775, p=9.4e-9; rs149994299, p=2e- 8) were also associated with BMI in the same direction. Five of the identified loci (rs1442883, p=3.8e-19; rs8095324, p=1.7e-13; rs7837754, p=3.3e-12; rs7411445 [NEGR1], p=8.6e-10; rs2977694 [CSMD1], p=7.2e-8) were also associated with “sweet tooth," but in the different directions. The NEGR1 and CSMD1 regions that have been previously implicated in psychiatric disorders. We also identified variants near GRIN2A in 16p13.2 (rs2014151, p=6e-19) and near NRG1 (rs13255543, p=5.7e-13). Mutations in these two regions have previously been linked to diseases such as autism, schizophrenia, and bipolar disorder.
We estimated a positive genetic correlation between nail biting and BMI (LD score rg=0.17, p=1.46e-14). We found a near-zero genetic correlation between nail biting and sweet tooth. Although they shared many associations, the effects from those pleiotropic loci are not in the same direction. Overall, our findings revealed genetic contributions to nail biting. They also point to a possible connection between nail biting, BMI, and taste perception, which is interesting in light of prior findings that BMI GWASes implicate neural regulations; personality factors such as anxiety and the ability to cope with stress have been discovered to change hormones and act on taste. Our study may provide molecular evidence for neural mechanisms underlying personality and taste.C. Tian, J. Tung, and D. Hinds of 23andme "Genome- and phenome-wide study of “nail biting”: Not just a habit." ASHG Conference Presentation 276 (October 2016)/