On 2017 Mar 15, KEVIN BLACK commented:

We proposed that "the most likely cause for the" excess prevalence of depression in PD was "that both syndromes arise from similar causes, with either appearing first in a given individual. ... [O]ne may reasonably search for such shared causative factors among the known risk factors for" either disease, "such as genes (probably plural), aging, chemical toxins, or psychologically stressful life events" (Black KJ, Pandya A. Depression in Parkinson disease. Pp. 199-237 in Gilliam F, Kanner AM, Sheline YI: Depression and Brain Dysfunction. New York: Taylor & Francis, 2006, at pp. 216-217).

Arabia and colleagues (2007) found that depressive and anxious disorders were much more likely in first-degree relatives of PD patients than of controls (doi: 10.1001/archpsyc.64.12.1385). One gene that may contribute to that finding is the serotonin transporter, discussed in the review cited above. Cagni et al here identify an additional gene that may also be a shared risk factor: the G/G phenotype of the Val66Met polymorphism of the BDNF gene.

Studies such as these may contribute useful information not only to the etiology of depression and anxiety but also to the etiology of Parkinson disease.

On 2017 Mar 15, KEVIN BLACK commented:

We proposed that "the most likely cause for the" excess prevalence of depression in PD was "that both syndromes arise from similar causes, with either appearing first in a given individual. ... [O]ne may reasonably search for such shared causative factors among the known risk factors for" either disease, "such as genes (probably plural), aging, chemical toxins, or psychologically stressful life events" (Black KJ, Pandya A. Depression in Parkinson disease. Pp. 199-237 in Gilliam F, Kanner AM, Sheline YI: Depression and Brain Dysfunction. New York: Taylor & Francis, 2006, at pp. 216-217).

Arabia and colleagues (2007) found that depressive and anxious disorders were much more likely in first-degree relatives of PD patients than of controls (doi: 10.1001/archpsyc.64.12.1385). One gene that may contribute to that finding is the serotonin transporter, discussed in the review cited above. Cagni et al here identify an additional gene that may also be a shared risk factor: the G/G phenotype of the Val66Met polymorphism of the BDNF gene.

Studies such as these may contribute useful information not only to the etiology of depression and anxiety but also to the etiology of Parkinson disease.