Another meta-analysis observed an increased risk in those with the homozygous S allele, but found the LS genotype to be inversely associated with OCD.A genome-wide association study found OCD to be linked with single-nucleotide polymorphisms (SNPs) near BTBD3, and two SNPs in DLGAP1 in a trio-based analysis, but no SNP reached significance when analyzed with case-control data.One meta-analysis found a small but significant association between a polymorphism in SLC1A1 and OCD.The relationship between OCD and Catechol-O-methyltransferase (COMT) has been inconsistent, with one meta-analysis reporting a significant association, albeit only in men, and another meta analysis reporting no association.It has been postulated by evolutionary psychologists that moderate versions of compulsive behavior may have had evolutionary advantages. Examples would be moderate constant checking of hygiene, the hearth, or the environment for enemies. Similarly, hoarding may have had evolutionary advantages. In this view, OCD may be the extreme statistical tail of such behaviors, possibly the result of a high number of predisposing genes. Brain structure and functioning
Imaging studies have shown differences in the frontal cortex and subcortical structures of the brain in patients with OCD. There appears to be a connection between the OCD symptoms and abnormalities in certain areas of the brain, but such a connection is not clear.
Pneumoretroperitoneum is the presence of air in the retroperitoneum. It is always a pathological condition and can be caused by a perforation of a retroperitoneal hollow organ such as the duodenum, colon or rectum. Pneumoretroperitoneum can best be identified by CT scan. See also
Pneumoperitoneum


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