The hypothesis that OCD may be genetically heterogeneous, with some individuals and families segregating OCD without tics and others a subtype of OCD with tics that may share genetic risk with TS, was originally proposed by Pauls and colleagues in 1986 (27), and more recent epidemiologic studies have provided additional support for this concept (9, 26, 28). Although not yet studied, these genetic differences may also correlate with well-documented differences in treatment outcomes of patients with OCD alone compared to OCD with tics, in which the latter are more refractory to treatment and may require neuroleptic augmentation (29–31).
