The Lundbeck Foundation Integrative Psychiatric Research (iPSYCH) consortium has almost doubled its Danish population-based Case-Cohort sample (iPSYCH2012). The newly updated cohort, named iPSYCH2015, expands the study base with 56,233 samples, to a combined total of 141,265 samples. The cohort is nested within the Danish population born between 1981 and 2008 and is a Case-cohort design including 50,615 population controls. We added more cases to the existing phenotypes identified with, schizophrenia (Nnew=4,131/Ntotal=8,113), autism (Nnew=8,056 / Ntotal=24,975), attention-deficit/hyperactivity disorder (Nnew=10,026/Ntotal=29,668) and affective disorder (Nnew=13,999/Ntotal=40,482) of which a subset has bipolar affective disorder (N-new=1,656/Ntotal=3,819). We also added two additional focus phenotypes, schizophrenia spectrum disorder (N=16,008) and post-partum disorder (N=3,421). In total, the expanded iPSYCH2015 sample consists of 93,608 unique individuals in the case groups and 50,615 population controls. For the sample expansion, DNA was extracted and amplified from dried blood spots samples stored within the Danish Neonatal Screening Biobank and genotyped using the Illumina Global Screening Array. The Biobank sample retrieval rate was 95%, and the genotyping success rate was 92% (97% of retrieved). We expanded the follow-up period by three years, including data such as longitudinal information on health, prescribed medicine, social and socioeconomic information.

BackgroundPatients 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).MethodsWe sequenced the candidate genes SLC6A4 (SERT), SLC29A4 (PMAT), and GCHFR (GFRP), followed by whole exome analysis.ResultsThe 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.ConclusionsOur 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.