Sophie Molloy

Staging of serotonergic dysfunction in Parkinson's Disease: An in vivo 11C-DASB PET study

Thirty Parkinsons disease (PD) patients were divided into three equal groups according to their disease duration while 10 normal healthy volunteers matched for age and sex served as a control group. Striatal and extrastriatal serotonergic function was studied with (11)C-DASB PET, a marker of serotonin transporter availability. (11)C-DASB binding was correlated with disease disability and exposure to dopaminergic therapy. We found significant (11)C-DASB binding reductions in striatal, brainstem, and cortical regions in PD but no correlations were evident between (11)C-DASB binding and UPDRS scores, Hoehn &Yahr staging, disease duration and level of exposure to dopaminergic therapy. Our results suggest that progressive non-linear serotonergic dysfunction occurs in PD but it does not determine levels of disability. Additionally, chronic exposure to dopaminergic therapy does not appear to influence SERT binding.

Depressive symptoms in PD correlate with higher 5-HTT binding in raphe and limbic structures

Background: Depression associated with Parkinson disease (PD) has a different symptom profile to endogenous depression. The etiology of depression in PD remains uncertain though abnormal serotonergic neurotransmission could play a role. Objective: To assess with PET serotonergic function via in vivo serotonin transporter (5-HTT) availability in antidepressant-naive patients with PD. Methods: Thirty-four patients with PD and 10 healthy matched control subjects had a clinical battery of tests including the patient-report Beck Depression Inventory–II (BDI-II), the clinician-report Hamilton Rating Scale for Depression (HRSD), and the structured clinical interview for DSM-IV Axis I Disorders (SCID-I). They underwent 11C-DASB PET, a selective in vivo marker of 5-HTT binding in humans. Results: BDI-II scores correlated with HRSD scores. Ten of 34 patients with PD (29.4%) had BDI-II and HRSD scores above the discriminative cutoff for PD depression though only half of these patients could be classed on SCID-I criteria as having an anxiety/mood disorder. Patients with PD with the highest scores for depression symptoms showed significantly raised 11C-DASB binding in amygdala, hypothalamus, caudal raphe nuclei, and posterior cingulate cortex compared to low score cases, while 11C-DASB binding values in other regions were similarly decreased in depressed and nondepressed patients with PD compared to healthy controls. Conclusion: Depressive symptoms in antidepressant-naive patients with PD correlate with relatively higher 5-HTT binding in raphe nuclei and limbic structures possibly reflecting lower extracellular serotonin levels. Our data are compatible with a key role of abnormal serotonergic neurotransmission contributing to the pathophysiology of PD depression and justify the use of agents acting on 5-HTT.

Serotonergic mechanisms responsible for levodopa-induced dyskinesias in Parkinson's disease patients.

Levodopa-induced dyskinesias (LIDs) are the most common and disabling adverse motor effect of therapy in Parkinsons disease (PD) patients. In this study, we investigated serotonergic mechanisms in LIDs development in PD patients using 11C-DASB PET to evaluate serotonin terminal function and 11C-raclopride PET to evaluate dopamine release. PD patients with LIDs showed relative preservation of serotonergic terminals throughout their disease. Identical levodopa doses induced markedly higher striatal synaptic dopamine concentrations in PD patients with LIDs compared with PD patients with stable responses to levodopa. Oral administration of the serotonin receptor type 1A agonist buspirone prior to levodopa reduced levodopa-evoked striatal synaptic dopamine increases and attenuated LIDs. PD patients with LIDs that exhibited greater decreases in synaptic dopamine after buspirone pretreatment had higher levels of serotonergic terminal functional integrity. Buspirone-associated modulation of dopamine levels was greater in PD patients with mild LIDs compared with those with more severe LIDs. These findings indicate that striatal serotonergic terminals contribute to LIDs pathophysiology via aberrant processing of exogenous levodopa and release of dopamine as false neurotransmitter in the denervated striatum of PD patients with LIDs. Our results also support the development of selective serotonin receptor type 1A agonists for use as antidyskinetic agents in PD.

Sleep problems and hypothalamic dopamine D3 receptor availability in Parkinson disease

Objective: To investigate the relationship between hypothalamic D3 dopamine receptor availability and severity of sleep problems in Parkinson disease (PD). Methods: Twelve patients were assessed with PET and the high-affinity dopamine D3 receptor radioligand [11C]-propyl-hexahydro-naphtho-oxazin ([11C]-PHNO). Severity of sleep problems was rated with appropriate subitems of the Unified Parkinsons Disease Rating Scale part I (patient questionnaire) and the Epworth Sleepiness Scale. Results: We found that lower dopamine D3 receptor availability measured with [11C]-PHNO PET was associated with greater severity of excessive daytime sleepiness but not with problems of falling asleep or insomnia. Conclusion: In our cohort of patients with PD, the occurrence of excessive daytime sleepiness was linked to reductions in hypothalamic dopamine D3 receptor availability. If these preliminary findings are confirmed in larger cohorts of patients with polysomnographic characterization, selective pharmacologic modulation of the dopaminergic D3 system could be used to increase daytime alertness in patients with PD.

Atypical Parkinsonism-Dystonia Syndrome Caused by a Novel DJ1 Mutation

We describe a sporadic case of atypical parkinsonism‐dystonia of subacute onset at the age of 16 years in a male from a consanguineous family. He showed marked orofacial dystonia, levodopa‐induced dyskinesia, and a stereotyped bilateral eye‐pressing movement disorder. We combined Sanger sequencing of candidate genes, homozygosity mapping, and whole‐exome sequencing. A homozygous mutation was identified disrupting a splice site in exon 5 of the DJ1 (PARK7) gene. Clinical details and a video are provided. DJ1 mutations are a rare cause of atypical complex parkinsonism. Exome sequencing is efficacious in identifying the causal gene variant.