This chapter uses the phrase nail biting rather than onychophagia because nail biting is more easily understood. Although most nail biters bite only their fingernails, some people bite their toenails as well or overclip their toenails. Occasionally, people may bite their nails as part of a behavioral disorder occasioned by intense pain. Nail biting can be reliably and simply measured by using calipers. For older teenagers and adults, the data from Malone and Massler's study indicate that fewer girls and women than boys and men bite their nails. Studies of obsessive-compulsive spectrum disorders have often revealed quite high levels of nail biting, among other habits. Only one trial of pharmacological agents has been described, in which clomipramine and desimipramine were compared in a double-blind, randomized study. A number of interventions have been proposed, but none has shown clear superiority in adequately designed trials.

This chapter discusses the components of the behavioral phenotype in velo-cardio-facial syndrome (VCFS), namely, the high rates of behavioral and psychiatric disorder seen in VCFS children and adults. It summarizes the principal studies of the psychiatric phenotype in VCFS individuals. The most reliable criteria to determine whether the association between VCFS and schizophrenia is valid should involve: increased frequency of schizophrenia in VCFS individuals, increased frequency of VCFS in people with schizophrenia and susceptibility locus for schizophrenia should map to 22q11.2. A major goal of psychiatric and especially schizophrenia research over the past three decades has been the identification of precursor symptoms and areas of dysfunction in children and adolescents which precede the later development of major psychiatric disorder in adults. Difficult behaviors seen in children with VCFS can be approached using behavioral modification techniques including the use of token economies and reward schemes.