Autism spectrum disorder associated with low serotonin in CSF and mutations in the SLC29A4 plasma membrane monoamine transporter (PMAT) gene

Dea Adamsen; Vincent Ramaekers; Horace Tb Ho; Corinne Britschgi; Véronique Rüfenacht; David Meili; Elise Bobrowski; Paule Philippe; Caroline Nava; Lionel Van Maldergem; Rémy Bruggmann; Susanne Walitza; Joanne Wang; Edna Grünblatt; Beat Thöny

doi:10.1186/2040-2392-5-43

Autism spectrum disorder associated with low serotonin in CSF and mutations in the SLC29A4 plasma membrane monoamine transporter (PMAT) gene

Mol Autism. 2014 Aug 13:5:43. doi: 10.1186/2040-2392-5-43. eCollection 2014.

Authors

Dea Adamsen^#^{1

2}, Vincent Ramaekers^#³, Horace Tb Ho⁴, Corinne Britschgi⁵, Véronique Rüfenacht¹, David Meili⁵, Elise Bobrowski⁶, Paule Philippe³, Caroline Nava⁷, Lionel Van Maldergem⁸, Rémy Bruggmann^{9

10}, Susanne Walitza^{6

11

12}, Joanne Wang⁴, Edna Grünblatt^{6

11}, Beat Thöny^{1

2

5

12}

Affiliations

¹ Division of Metabolism, Department of Pediatrics, University of Zürich, Zürich 8032, Switzerland.
² Affiliated with the Neuroscience Center Zürich, University of Zürich and ETH Zürich (ZNZ), Zürich 8000, and the Children's Research Center (CRC), Zürich 8032, Switzerland.
³ Centre of Autism Liège and Division of Pediatric Neurology, University Hospital Liège, Liège 4000, Belgium.
⁴ Department of Pharmaceutics, University of Washington, Seattle 98195, WA, USA.
⁵ Division of Clinical Chemistry and Biochemistry, Department of Pediatrics, University of Zürich Zürich 8032, Switzerland.
⁶ University Clinics of Child and Adolescent Psychiatry, University of Zürich, Zürich 8050, Switzerland.
⁷ Department of Genetics, Cytogenetics and human Genetics, Pitié-Salpêtrière Hospital, Paris 75651, France.
⁸ Centre for Human Genetics, University of Franche-Comté, Besançon 25030, France.
⁹ Functional Genomics Center Zürich, ETH Zürich/University of Zürich, Zürich 8057, Switzerland.
¹⁰ current address: Interfaculty Bioinformatics Unit, University of Bern/Swiss Institute of Bioinformatics, Bern 3012, Switzerland.
¹¹ Affiliated with the Neuroscience Center Zürich, University of Zürich and ETH Zürich (ZNZ), Zürich 8000, Switzerland.
¹² Affiliated with the Zürich Center for Integrative Human Physiology (ZIHP), University of Zürich, Zürich 8000, Switzerland.

^# Contributed equally.

Abstract

Background: Patients with autism spectrum disorder (ASD) may have low brain serotonin concentrations as reflected by the serotonin end-metabolite 5-hydroxyindolacetic acid (5HIAA) in cerebrospinal fluid (CSF).

Methods: We sequenced the candidate genes SLC6A4 (SERT), SLC29A4 (PMAT), and GCHFR (GFRP), followed by whole exome analysis.

Results: The known heterozygous p.Gly56Ala mutation in the SLC6A4 gene was equally found in the ASD and control populations. Using a genetic candidate gene approach, we identified, in 8 patients of a cohort of 248 with ASD, a high prevalence (3.2%) of three novel heterozygous non-synonymous mutations within the SLC29A4 plasma membrane monoamine transporter (PMAT) gene, c.86A > G (p.Asp29Gly) in two patients, c.412G > A (p.Ala138Thr) in five patients, and c.978 T > G (p.Asp326Glu) in one patient. Genome analysis of unaffected parents confirmed that these PMAT mutations were not de novo but inherited mutations. Upon analyzing over 15,000 normal control chromosomes, only SLC29A4 c.86A > G was found in 23 alleles (0.14%), while neither c.412G > A (<0.007%) nor c.978 T > G (<0.007%) were observed in all chromosomes analyzed, emphasizing the rareness of the three alterations. Expression of mutations PMAT-p.Ala138Thr and p.Asp326Glu in cellulae revealed significant reduced transport uptake activity towards a variety of substrates including serotonin, dopamine, and 1-methyl-4-phenylpyridinium (MPP(+)), while mutation p.Asp29Gly had reduced transport activity only towards MPP(+). At least two ASD subjects with either the PMAT-Ala138Thr or the PMAT-Asp326Glu mutation with altered serotonin transport activity had, besides low 5HIAA in CSF, elevated serotonin levels in blood and platelets. Moreover, whole exome sequencing revealed additional alterations in these two ASD patients in mainly serotonin-homeostasis genes compared to their non-affected family members.

Conclusions: Our findings link mutations in SLC29A4 to the ASD population although not invariably to low brain serotonin. PMAT dysfunction is speculated to raise serotonin prenatally, exerting a negative feedback inhibition through serotonin receptors on development of serotonin networks and local serotonin synthesis. Exome sequencing of serotonin homeostasis genes in two families illustrated more insight in aberrant serotonin signaling in ASD.

Keywords: Autism spectrum disorder; PMAT; SERT; Serotonin end-metabolite 5-hydroxyindolacetic acid.

Grants and funding

R01 GM066233/GM/NIGMS NIH HHS/United States