Missense dopamine transporter mutations associate with adult parkinsonism and ADHD
Freja H. Hansen, … , Lisbeth B. Møller, Ulrik Gether
Freja H. Hansen, … , Lisbeth B. Møller, Ulrik Gether
Published June 9, 2014
Citation Information: J Clin Invest. 2014;124(7):3107-3120. https://doi.org/10.1172/JCI73778.
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Research Article Neuroscience

Missense dopamine transporter mutations associate with adult parkinsonism and ADHD

Abstract

Parkinsonism and attention deficit hyperactivity disorder (ADHD) are widespread brain disorders that involve disturbances of dopaminergic signaling. The sodium-coupled dopamine transporter (DAT) controls dopamine homeostasis, but its contribution to disease remains poorly understood. Here, we analyzed a cohort of patients with atypical movement disorder and identified 2 DAT coding variants, DAT-Ile312Phe and a presumed de novo mutant DAT-Asp421Asn, in an adult male with early-onset parkinsonism and ADHD. According to DAT single-photon emission computed tomography (DAT-SPECT) scans and a fluoro-deoxy-glucose-PET/MRI (FDG-PET/MRI) scan, the patient suffered from progressive dopaminergic neurodegeneration. In heterologous cells, both DAT variants exhibited markedly reduced dopamine uptake capacity but preserved membrane targeting, consistent with impaired catalytic activity. Computational simulations and uptake experiments suggested that the disrupted function of the DAT-Asp421Asn mutant is the result of compromised sodium binding, in agreement with Asp421 coordinating sodium at the second sodium site. For DAT-Asp421Asn, substrate efflux experiments revealed a constitutive, anomalous efflux of dopamine, and electrophysiological analyses identified a large cation leak that might further perturb dopaminergic neurotransmission. Our results link specific DAT missense mutations to neurodegenerative early-onset parkinsonism. Moreover, the neuropsychiatric comorbidity provides additional support for the idea that DAT missense mutations are an ADHD risk factor and suggests that complex DAT genotype and phenotype correlations contribute to different dopaminergic pathologies.

Authors

Freja H. Hansen, Tina Skjørringe, Saiqa Yasmeen, Natascha V. Arends, Michelle A. Sahai, Kevin Erreger, Thorvald F. Andreassen, Marion Holy, Peter J. Hamilton, Viruna Neergheen, Merete Karlsborg, Amy H. Newman, Simon Pope, Simon J.R. Heales, Lars Friberg, Ian Law, Lars H. Pinborg, Harald H. Sitte, Claus Loland, Lei Shi, Harel Weinstein, Aurelio Galli, Lena E. Hjermind, Lisbeth B. Møller, Ulrik Gether

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Figure 6

Molecular modeling of hDAT.

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Molecular modeling of hDAT. (A) Homology model of hDAT based on the outw...
(A) Homology model of hDAT based on the outward-open crystal structure of LeuT, a bacterial homolog. (B) I312, indicated in green in TM 6, was seen to have no direct contact with dopamine or ion binding sites. (C) D421, indicated in green in TM 8, was involved in coordinating binding of sodium at the second sodium binding site (Na2). Sodium and chloride ions are indicated in purple and turquoise, respectively. (D) Sodium dependence of [3H]-dopamine uptake. Dopamine uptake was evaluated at increasing concentrations of sodium. The sodium dependence of DAT-I312F–mediated uptake was comparable to that of WT (Kd = 70 ± 20 mM for DAT-I312F vs. Kd = 30 ± 4 mM for WT). DAT-D421N, on the other hand, showed impaired binding of sodium, seen as a linear sodium dependence curve with no tendency to saturate at 200 mM of NaCl. (E) Sodium dependence of [3H]-CFT binding. Sodium dependence of [3H]-CFT binding to DAT-I312F was similar to that of WT (Kd = 29 ± 3.6 mM for DAT-I312F vs. Kd = 46 ± 10 mM for WT), while specific binding of [3H]-CFT to DAT-D421N could not be detected. The curves of D and E are average curves from 3 and 4 experiments, respectively, each performed in triplicate and normalized to WT Bmax. ChoCl was used for equimolar cation substitution of sodium to obtain indicated sodium concentrations. Bmax and Kd values were derived using a one-site–specific binding model.