Late development of OCD-like phenotypes in Dlgap1 knockout mice.

Rationale: Despite variants in the Dlgap1 gene having the two lowest p-value in a genome-wide association study of obsessive compulsive disorder (OCD), previous studies reported the absence of OCD-like phenotypes in Dlgap1 knockout (KO) mice. Since these studies observed behavioral phenotypes only for a short period, development of OCD-like phenotypes in these mice at older ages was still plausible.

Objective: To examine the presence or absence of development of OCD-like phenotypes in Dlgap1 KO mice and their responsiveness to fluvoxamine.

Methods and results: Newly produced Dlgap1 KO mice were observed for a year. Modified SHIRPA primary screen in 2-month-old homozygous mutant mice showed only weak signs of anxiety, stress conditions and aggression. At older ages, however, these mutant mice exhibited excessive self-grooming characterized by increased scratching which led to skin lesions. A significant sex difference was observed in this scratching behavior. The penetrance of skin lesions reached 50% at 6-7 months of age and 90% at 12 months of age. In the open-field test performed just after the appearance of these lesions, homozygous mutant mice spent significantly less time in the center, an anxiety-like behavior, than did their wild-type and heterozygous littermates, none and less than 10% of which showed skin lesions at 1 year, respectively. The skin lesions and excessive self-grooming were significantly alleviated by two-week treatment with fluvoxamine.

Conclusion: Usefulness of Dlgap1 KO mice as a tool for investigating the pathogenesis of OCD-like phenotypes and its translational relevance was suggested.