title: Autism spectrum disorder associated with low serotonin in CSF and mutations in the SLC29A4 plasma membrane monoamine transporter (PMAT) gene.
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.
authors: Division of Metabolism, Department of Pediatrics, University of Zürich, Zürich 8032, Switzerland.|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.
authors: Dea
authors: D
authors: Adamsen
authors: Centre of Autism Liège and Division of Pediatric Neurology, University Hospital Liège, Liège 4000, Belgium.
authors: Vincent
authors: V
authors: Ramaekers
authors: Department of Pharmaceutics, University of Washington, Seattle 98195, WA, USA.
authors: Horace Tb
authors: HT
authors: Ho
authors: Division of Clinical Chemistry and Biochemistry, Department of Pediatrics, University of Zürich Zürich 8032, Switzerland.
authors: Corinne
authors: C
authors: Britschgi
authors: Division of Metabolism, Department of Pediatrics, University of Zürich, Zürich 8032, Switzerland.
authors: Véronique
authors: V
authors: Rüfenacht
authors: Division of Clinical Chemistry and Biochemistry, Department of Pediatrics, University of Zürich Zürich 8032, Switzerland.
authors: David
authors: D
authors: Meili
authors: University Clinics of Child and Adolescent Psychiatry, University of Zürich, Zürich 8050, Switzerland.
authors: Elise
authors: E
authors: Bobrowski
authors: Centre of Autism Liège and Division of Pediatric Neurology, University Hospital Liège, Liège 4000, Belgium.
authors: Paule
authors: P
authors: Philippe
authors: Department of Genetics, Cytogenetics and human Genetics, Pitié-Salpêtrière Hospital, Paris 75651, France.
authors: Caroline
authors: C
authors: Nava
authors: Centre for Human Genetics, University of Franche-Comté, Besançon 25030, France.
authors: Lionel
authors: L
authors: Van Maldergem
authors: Functional Genomics Center Zürich, ETH Zürich/University of Zürich, Zürich 8057, Switzerland.|current address: Interfaculty Bioinformatics Unit, University of Bern/Swiss Institute of Bioinformatics, Bern 3012, Switzerland.
authors: Rémy
authors: R
authors: Bruggmann
authors: University Clinics of Child and Adolescent Psychiatry, University of Zürich, Zürich 8050, Switzerland.|Affiliated with the Neuroscience Center Zürich, University of Zürich and ETH Zürich (ZNZ), Zürich 8000, Switzerland.|Affiliated with the Zürich Center for Integrative Human Physiology (ZIHP), University of Zürich, Zürich 8000, Switzerland.
authors: Susanne
authors: S
authors: Walitza
authors: Department of Pharmaceutics, University of Washington, Seattle 98195, WA, USA.
authors: Joanne
authors: J
authors: Wang
authors: University Clinics of Child and Adolescent Psychiatry, University of Zürich, Zürich 8050, Switzerland.|Affiliated with the Neuroscience Center Zürich, University of Zürich and ETH Zürich (ZNZ), Zürich 8000, Switzerland.
authors: Edna
authors: E
authors: Grünblatt
authors: Division of Metabolism, Department of Pediatrics, University of Zürich, Zürich 8032, Switzerland.|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.|Division of Clinical Chemistry and Biochemistry, Department of Pediatrics, University of Zürich Zürich 8032, Switzerland.|Affiliated with the Zürich Center for Integrative Human Physiology (ZIHP), University of Zürich, Zürich 8000, Switzerland.
authors: Beat
authors: B
authors: Thöny
keywords: Autism spectrum disorder; PMAT; SERT; Serotonin end-metabolite 5-hydroxyindolacetic acid