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Lancet Neurol. 2019 Aug;18(8):748-759. doi: 10.1016/S1474-4422(19)30140-1. Epub 2019 Jun 19.

Serotonergic pathology and disease burden in the premotor and motor phase of A53T α-synuclein parkinsonism: a cross-sectional study.

Author information

1
Neurodegeneration Imaging Group, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK.
2
University of Athens Medical School, 1st Department of Neurology, University of Athens Hospital Attikon, Greece.
3
Center for Neurodegenerative Diseases (CEMAND), Department of Medicine, Neuroscience Section, University of Salerno, Italy.
4
Nuclear Medicine Department, King's College Hospital NHS Foundation Trust, London, UK.
5
University of Athens Medical School, 1st Department of Neurology, University of Athens Hospital Attikon, Greece; Department of Neurology, Philipps University, Marburg, Germany; Parkinson's Disease and Movement Disorders Department, HYGEIA Hospital, Athens, Greece.
6
Division of Brain Sciences, Department of Medicine, Imperial College London, London, UK; Invicro LLC, Centre for Imaging Sciences, Hammersmith Hospital, London, UK.
7
Centre for Neuroimaging Sciences, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK; Invicro LLC, Centre for Imaging Sciences, Hammersmith Hospital, London, UK.
8
University of Athens Medical School, 1st Department of Neurology, University of Athens Hospital Attikon, Greece; Center of Clinical Research, Experimental Surgery and Translational Research, Biomedical Research Foundation of the Academy of Athens, Athens, Greece.
9
Neurodegeneration Imaging Group, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK. Electronic address: marios.politis@kcl.ac.uk.

Abstract

BACKGROUND:

Because of the highly penetrant gene mutation and clinical features consistent with idiopathic Parkinson's disease, carriers of the autosomal dominant Ala53Thr (A53T; 209G→A) point mutation in the α-synuclein (SNCA) gene are an ideal population to study the premotor phase and evolution of Parkinson's pathology. Given the known neurochemical changes in the serotonergic system and their association with symptoms of Parkinson's disease, we hypothesised that carriers of the A53T SNCA mutation might show abnormalities in the serotonergic neurotransmitter system before the diagnosis of Parkinson's disease, and that this pathology might be associated with measures of Parkinson's burden.

METHODS:

In this cross-sectional study, we recruited carriers of the A53T SNCA mutation from specialist Movement Disorders clinics in Athens, Greece, and Salerno, Italy, and a cohort of healthy controls with no personal or family history of neurological or psychiatric disorders from London, UK (recruited via public advertisement) who were age matched to the A53T SNCA carriers. We also recruited one cohort of patients with idiopathic Parkinson's disease (cohort 1) from Movement Disorders clinics in London, UK, and retrieved data on a second cohort of such patients (cohort 2; n=40) who had been scanned with a different scanner. 7-day continuous recording of motor function was used to determine the Parkinson's disease status of the A53T carriers. To assess whether serotonergic abnormalities were present, we used [11C]DASB PET non-displaceable binding to quantify serotonin transporter density. We constructed brain topographic maps reflecting Braak stages 1-6 and used these as seed maps to calculate [11C]DASB non-displaceable binding potential in our cohort of A53T SNCA carriers. Additionally, all participants underwent a battery of clinical assessments to determine motor and non-motor symptoms and cognitive status, and [123I]FP-CIT single-photon emission CT (SPECT) to assess striatal dopamine transporter binding and MRI for volumetric analyses to assess whether pathology is associated with measures of Parkinson's disease burden.

FINDINGS:

Between Sept 1, 2016, and Sept 30, 2018, we recruited 14 A53T SNCA carriers, 25 healthy controls, and 25 patients with idiopathic Parkinson's disease. Seven (50%) of 14 A53T SCNA carriers were confirmed to have motor symptoms and confirmed to have Parkinson's disease, and the absence of motor symptoms was confirmed in seven (50%) A53T SCNA carriers (ie, premotor), in whom [123I]FP-CIT SPECT confirmed the absence of striatal dopaminergic deficits. Compared with healthy controls, premotor A53T SNCA carriers showed loss of [11C]DASB non-displaceable binding potential in the ventral (p<0·0001) and dorsal (p=0·0002) raphe nuclei, caudate (p=0·00015), putamen (p=0·036), thalamus (p=0·00074), hypothalamus (p<0·0001), amygdala (p=0·0041), and brainstem (p=0·046); and in A53T SNCA carriers with Parkinson's disease this loss was extended to the hippocampus (p=0·0051), anterior (p=0·022) and posterior cingulate (p=0·036), insula (p=0·0051), frontal (p=0·0016), parietal (p=0·019), temporal (p<0·0001), and occipital (p=0·0053) cortices. A53T SNCA carriers with Parkinson's disease showed a loss of striatal [123I]FP-CIT-specific binding ratio compared with healthy controls (p<0·0001). Premotor A53T SNCA carriers had loss of [11C]DASB non-displaceable binding potential in brain areas corresponding to Braak stages 1-3, whereas [11C]DASB non-displaceable binding potential was largely preserved in areas corresponding to Braak stages 4-6. Except for one participant who was diagnosed with Parkinson's disease in the past year, all A53T SNCA carriers with Parkinson's disease had decreases in [11C]DASB non-displaceable binding potential in brain areas corresponding to Braak stages 1-6. Decreases in [11C]DASB non-displaceable binding potential in the brainstem were associated with increased Movement Disorder Score-Unified Parkinson's Disease Rating Scale total scores in all A53T SNCA carriers (r -0·66, 95% CI -0·88 to -0·20; p=0·0099), idiopathic Parkinson's disease cohort 1 (r -0·66, -0·84 to -0·36; p=0·00031), and idiopathic Parkinson's disease cohort 2 (r -0·71, -0·84 to -0·52; p<0·0001).

INTERPRETATION:

The presence of serotonergic pathology in premotor A53T SNCA carriers preceded development of dopaminergic pathology and motor symptoms and was associated with disease burden, highlighting the potential early role of serotonergic pathology in the progression of Parkinson's disease. Our findings provide evidence that molecular imaging of serotonin transporters could be used to visualise premotor pathology of Parkinson's disease in vivo. Future work might establish whether serotonin transporter imaging is suitable as an adjunctive tool for screening and monitoring progression for individuals at risk or patients with Parkinson's disease to complement dopaminergic imaging, or as a marker of Parkinson's burden in clinical trials.

FUNDING:

Lily Safra Hope Foundation and National Institute for Health Research (NIHR) Biomedical Research Centre at King's College London.

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