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Heterozygous FA2H Mutations in Autism Spectrum Disorders

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Heterozygous FA2H Mutations in Autism Spectrum Disorders Scheid et al. BMC Medical Genetics 2013, 14:124 http://www.biomedcentral.com/1471-2350/14/124 RESEARCH ARTICLE Open Access Heterozygous FA2H mutations in autism spectrum disorders Isabelle Scheid1,2,3†, Anna Maruani1,2,3†, Guillaume Huguet1,2, Claire S Leblond1,2, Gudrun Nygren4, Henrik Anckarsäter5, Anita Beggiato1,2,3,6, Maria Rastam5, Fréderique Amsellem3,7, I Carina Gillberg4, Monique Elmaleh8, Marion Leboyer6,7, Christopher Gillberg4,9, Catalina Betancur10,11,12, Mary Coleman13, Hiroko Hama14, Edwin H Cook15, Thomas Bourgeron1,2,16 and Richard Delorme1,2,3* Abstract Background: Widespread abnormalities in white matter development are frequently reported in cases of autism spectrum disorders (ASD) and could be involved in the disconnectivity suggested in these disorders. Homozygous mutations in the gene coding for fatty-acid 2-hydroxylase (FA2H), an enzyme involved in myelin synthesis, are associated with complex leukodystrophies, but little is known about the functional impact of heterozygous FA2H mutations. We hypothesized that rare deleterious heterozygous mutations of FA2H might constitute risk factors for ASD. Methods: We searched deleterious mutations affecting FA2H, by genotyping 1256 independent patients with ASD genotyped using Genome Wide SNP arrays, and also by sequencing in independent set of 186 subjects with ASD and 353 controls. We then explored the impact of the identified mutations by measuring FA2H enzymatic activity and expression, in transfected COS7 cells. Results: One heterozygous deletion within 16q22.3-q23.1 including FA2H was observed in two siblings who share symptoms of autism and severe cognitive impairment, axial T2-FLAIR weighted MRI posterior periventricular white matter lesions. Also, two rare non-synonymous mutations (R113W and R113Q) were reported. Although predictive models suggested that R113W should be a deleterious, we did not find that FA2H activity was affected by expression of the R113W mutation in cultured COS cells. Conclusions: While our results do not support a major role for FA2H coding variants in ASD, a screening of other genes related to myelin synthesis would allow us to better understand the role of non-neuronal elements in ASD susceptibility. Keywords: Autism, Brain, Gene, Myelin Background components of ASD arising from multiple independently Autism spectrum disorders (ASD) are characterized by regulated genes. One of these mechanisms is abnormal impairments in reciprocal social interactions, language myelin development, which could explain the wide- impairments and repetitive, stereotyped and ritualistic spread abnormalities in white matter development that verbal and non-verbal behaviors. Beyond this unifying are thought to affect functional frontotemporal, fronto- definition lies an extreme degree of clinical heterogen- limbic, frontoparietal and inter-hemispheric connections eity, ranging from mild to profound impairments [1,2]. in patients with ASD [3]. Indeed, transcriptomics Some of this heterogeneity might be due to heritable coupled to pathway analyses have shown that immune- glial genes could contribute to the disorder [4]. Further evidence for connectivity abnormalities comes from dys- * Correspondence: [email protected] † CNTNAP2 Equal contributors regulation in certain genes, such as and 1Human Genetics and Cognitive Functions, Institut Pasteur, Paris, France CNTN4, that code for proteins located at the nodes of 2 CNRS URA2182, Paris, France Ranvier that organize the tight junctions between axons Full list of author information is available at the end of the article © 2013 Scheid et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Scheid et al. BMC Medical Genetics 2013, 14:124 Page 2 of 9 http://www.biomedcentral.com/1471-2350/14/124 and myelinating glia [5]. It has been hypothesized that Ethics statement reduced long-range connectivity and excess local con- This study was approved by the local Institutional Re- nectivity may affect system-wide integration of brain ac- view Board (IRB) and written inform consents were ob- tivity, which has been suggested to explain some tained from all participants of the study. The local IRB symptoms of autism such as poor central coherence [6]. are the “Comité de Protection des Personnes” (Île-de- FA2H gene codes for fatty acid 2-hydroxylase (FA2H) France Hôpital Pitié-Salpêtrière Paris) for France; the [2], an enzyme that produces 2-hydroxylated fatty acids Sahlgrenska Academy Ethics committee, University of for incorporation into 2-hydroxydihydroceramide and 2- Gothenburg for Sweden. Written informed consent was hydroxyceramide [7]. These ceramides, in turn, serve as obtained from all participating subjects. If the proband precursors for the synthesis of galactosylceramide and was under 18 years old, the proband's consent and writ- sulfatides, essential lipid components of myelin sheaths. ten parental consent were obtained. Homozygous mutations of the FA2H gene in humans are associated with three neurodegenerative disorders in- volving a wide variety of symptoms: complicated spastic CNV detection and validation paraplegia (SPG35) [8], leukodystrophy with spastic Two CNV calling algorithms, QuantiSNP and PennCNV, paraparesis and dystonia [9,10], and neurodegeneration and the CNV viewer, SnipPeep (http://snippeep.source- associated with brain iron accumulation [11]. Although forge.net/) were used. To obtain high-confidence calls, the little is known about the effects of heterozygous muta- CNVs identified by QuantiSNP were validated by visual in- tions or deletions of FA2H, and its relations with ASD, spection of the Log R ratio and B allele frequency values. we hypothesized that deleterious heterozygous muta- PennCNV was used to confirm inheritance status of the tions of FA2H might constitute a risk factor for this CNV calls. group of disorders. Using Genome Wide SNP arrays, we CNVs were validated by quantitative PCR (qPCR) ana- genotyped 1256 independent patients with ASD. We de- lysis using the Universal Probe Library (UPL) system from tected one heterozygous 167.1 kb deletion within Roche. UPL probes and primers were designed using the 16q22.3-q23.1 including FA2H, in two siblings who share UPL assay Design center from Rochar Applied Scicence. symptoms of autism and severe cognitive impairment, UPL probes were labeled with 6-FAMTM fluorescein and axial T2-FLAIR weighted MRI posterior periventricular the fluorescence was read with the Applied Biosystems white matter lesions. We then sequenced the FA2H gene 7500 Real-Time PCR System. Each assay was conducted in in 186 patients with ASD and 353 controls, finding one four replicates for target region probe-set and control re- non-synonymous mutation (R113W) shared by the af- gion probe-set. Relative levels of region dosage were deter- fected siblings and transmitted by the mother who may mined using the comparative CT method assuming that carry a somatic mosaicism. there were two copies of DNA in the control region. The relative copy number for each target region was calculated ΔΔ ΔΔ Methods as 2- CT with confidence interval as 2-( CT±SD). Sample Nine hundred and ninety six patients from the Autism Genome Project (www.autismgenome.org) and 260 patients DNA sequencing from the Paris Autism Research International Sibpair Study The genomic structure of FA2H was obtained from (PARIS) not included in the AGP, meeting stringent quality http://genome.ucsc.edu/ (hg18). Primers spanning all control (QC) criteria, were included in the study. Informa- seven intron-exon boundaries of FA2H were designed tion concerning the phenotypic assessment of patients en- and used to amplify the regions of interest. Amplicons rolled was described previously (for details see [12] and were produced from genomic DNA, and sequencing was [13]). In brief, patients were recruited by the PARIS study performed using ABI 3730 DNA sequencer (Aplied Bio- at specialized clinical centers disposed in Paris (France) and systems, Foster City, CA). Sequence comparison to ref- Goteborg (Sweden). The Autism Diagnostic Interview- erence sequence was performed using GenalysCarbon Revised (ADI-R) and Autism Diagnostic Observation 2.8.2b (http://www.cng.fr). Schedule (ADOS) were used for clinical evaluation and diagnosis. In Sweden, in some cases, the Diagnostic Inter- view for Social and Communication Disorders (DISCO-10) In silico protein function analysis was applied instead of the ADI-R. Patients were included Multiple in silico applications were used to predict after a clinical and medical check-up with psychiatric and the functional effect of the amino acid substitutions, includ- neuropsychological examination, standard karyotyping, ing SIFT (http://sift.jcvi.org/www/SIFT_seq_submit2.html), fragile-X testing and brain imaging and EEG whenever pos- Polyphen-2 (http://genetics.bwh.harvard.edu/pph2/), and sible. All patients were from Caucasian ancestry. SNAP (http://rostlab.org/services/snap/). Scheid et al. BMC Medical Genetics 2013, 14:124 Page 3 of 9 http://www.biomedcentral.com/1471-2350/14/124 Cloning of PCR products quantification of FA2H expression, the cells were har- Exon 2 PCR products from genomic DNA derived from vested 24 hours after transfection and processed for blood and buccal swabs were cloned using the Strata- western blot analysis
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