SN/VTA neuromelanin signal is associated with subclinical paranoia irrespective of familial risk for psychosis

Subclinical paranoia is present in the relatives of patients with psychosis but it is also relatively common in the general population. Dopamine neurotransmission is increased in people with psychosis and is linked with positive symptoms, such as paranoia. Here, we examined if neuromelanin-sensitive MRI, a proxy of long-term dopamine turnover, is different between those with (n = 25) and without (n = 77) a first-degree relative with psychosis (N = 102). We further tested whether neuromelanin-sensitive MRI was associated with the experience of subclinical paranoia as measured by the paranoia checklist. We found that there was no difference in neuromelanin-sensitive MRI signal between those with and without a first-degree relative. However, neuromelanin-sensitive MRI was significantly associated with the frequency subscore of the paranoia checklist, irrespective of familial risk (255 of 1879 voxels at p < 0.05, p_corrected = 0.03). This relationship was further supported by the association of neuromelanin-sensitive MRI and community assessment of psychic experience paranoia frequency subscore (316 of 1879 voxels at p < 0.05, p_corrected = 0.01). In summary, we show that subclinical paranoid thoughts are associated with a proxy of long-term dopamine turnover regardless of whether the person has a relative with psychosis or not. Thus, neuromelanin-MRI associates with positive subclinical symptomatology in those without psychotic illness, in addition to the link observed in patients.