Disrupted‐in‐schizophrenia 1 functional polymorphisms and D 2 /D 3 receptor availability: A [ 11 C]‐(+)‐PHNO imaging study

The disrupted‐in‐schizophrenia 1 (DISC1) protein has been implicated in a range of biological mechanisms underlying chronic mental disorders such as schizophrenia. Schizophrenia is associated with abnormal striatal dopamine signalling, and all antipsychotic drugs block striatal dopamine 2/3 receptors (D_{2/3}Rs). Importantly, the DISC1 protein directly interacts and forms a protein complex with the dopamine D_{2} receptor (D_{2}R) that inhibits agonist‐induced D_{2}R internalisation. Moreover, animal studies have found large striatal increases in the proportion of D_{2}R receptors in a high affinity state (D_{2}^{high}R in DISC1 rodent models. Here, we investigated the relationship between the three most common polymorphisms altering the amino‐acid sequence of the DISC1 protein (Ser704Cys (rs821616), Leu607Phe (rs6675281) and Arg264Gln (rs3738401)) and striatal D_{2/3}R availability in 41 healthy human volunteers, using [{11}^C] ‐(+)‐PHNO positron emission tomography. We found no association between DISC1 polymorphisms and D_{2/3}R availability in the striatum and D_{2}R availability in the caudate and putamen. Therefore, despite a direct interaction between DISC1 and the D_{2}R, none of its main functional polymorphisms impact striatal D_{2/3}R binding potential, suggesting DISC1 variants act through other mechanisms.