Some highlights of major findings from our studies:

• The OCD Family Study reported that the prevalence of OCD was significantly greater in relatives of OCD cases than in relatives of controls (12% vs 3%). OCD cases with earlier age at onset of symptoms were more likely to have relatives with OCD. (Archives of General Psychiatry 2000; 57:358-363).
   
• In the first large genome-wide linkage scan of OCD, the OCD Collaborative Genetics Association Study reported evidence for OCD-susceptibility loci on chromosomes 3, 7, 15, 6, and 1 in 219 families with OCD (Molecular Psychiatry 2006; 11:763-770).
   
• We found evidence that compulsive hoarding behavior was linked to chromosome 14 in these 219 OCD families. In families with 2 or more relatives who hoarded, there was significant linkage of OCD to chromosome 14, whereas in families with fewer than 2 relatives who hoarded, there was linkage to chromosome 3 (American Journal of Psychiatry 2007; 164:493-499).
   
• Using a statistical technique called latent class analysis, we found that OCD can be classified into 3 subtypes, based on co-occurring conditions: 1) an OCD simplex class, in which major depressive disorder is most frequent; 2) a tic- related class, in which tics are prominent; and 3) an affective related class, in which panic disorder and mood disorders are prominent .(Psychological Medicine, 2009:39:1491-1501).
   
• The SAPAP3 gene codes for a protein found in certain neurons in the brain. A recent study found that mice with a deletion of this gene groom themselves excessively. We conducted a family-based association analysis to determine if SAPAP3 is associated with grooming in 383 OCD families. We found that grooming disorders, especially hair pulling (trichotillomania) were significantly associated with SAPAP3 in these families. (American Journal of  Medical  Genetics Part B  (Neuropsychiatric Genetics) 2009; 150B(5):710-720).

• In a family-based association analysis, we investigated the association between OCD and single nucleotide polymorphisms (SNPs) in, or near, the glutamate transporter gene SLC1A1, which is a promising positional and functional candidate gene for OCD. this gene. We found a strong association with a SNP outside this gene, which was significant in families with male but not female probands. ( American Journal of Medical Genetics Part B. (American Journal of Medical Genetics Part B (Neuropsychiatric Genetics) 2011; 156:472-477).
   
• In the genome-wide association study, the most significant finding was for a genetic marker on chromosome 9, near the protein tyrosine phosphatase receptor type D gene (PTPRD). This gene is involved in the differentiation of glutamatergic synapses (Molecular Psychiatry 2015; 20:337-244).