Common and rare variants of microRNA genes in autism spectrum disorders

<div><p></p><p><i>Objectives.</i> MicroRNAs (miRNAs) are post-transcriptional regulators that have been shown to be involved in disease susceptibility. Here we explore the possible contribution of common and rare variants in miRNA genes in autism spectrum disorders (ASD). <i>Methods.</i> A total of 350 tag SNPs from 163 miRNA genes were genotyped in 636 ASD cases and 673 controls. A replication study was performed in a sample of 449 ASD cases and 415 controls. Additionally, rare variants in 701 miRNA genes of 41 ASD patients were examined using whole-exome sequencing. <i>Results.</i> The most significant association in the discovery sample was obtained for the miR-133b/miR-206 cluster (rs16882131, <i>P = </i>0.00037). The replication study did not reach significance. However, the pooled analysis (1,085 cases and 1,088 controls) showed association with two miRNA clusters: miR-133b/miR-206 (rs16882131, <i>permP = </i>0.037) and miR-17/miR-18a/miR-19a/miR-20a/miR-19b-1/miR92a-1 (rs6492538, <i>permP = </i>0.019). Both miR-133b and miR-206 regulate the <i>MET</i> gene, previously associated with ASD. Rare variant analysis identified mutations in several miRNA genes, among them miR-541, a brain-specific miRNA that regulates <i>SYN1</i>, found mutated in ASD. <i>Conclusions.</i> Although our results do not establish a clear role for miRNAs in ASD, we pinpointed a few candidate genes. Further exome and GWAS studies are warranted to get more insight into their potential contribution to the disorder.</p></div

Table3_Dissecting the multifaceted contribution of the mitochondrial genome to autism spectrum disorder.xlsx

Autism spectrum disorder (ASD) is a clinically heterogeneous class of neurodevelopmental conditions with a strong, albeit complex, genetic basis. The genetic architecture of ASD includes different genetic models, from monogenic transmission at one end, to polygenic risk given by thousands of common variants with small effects at the other end. The mitochondrial DNA (mtDNA) was also proposed as a genetic modifier for ASD, mostly focusing on maternal mtDNA, since the paternal mitogenome is not transmitted to offspring. We extensively studied the potential contribution of mtDNA in ASD pathogenesis and risk through deep next generation sequencing and quantitative PCR in a cohort of 98 families. While the maternally-inherited mtDNA did not seem to predispose to ASD, neither for haplogroups nor for the presence of pathogenic mutations, an unexpected influence of paternal mtDNA, apparently centered on haplogroup U, came from the Italian families extrapolated from the test cohort (n = 74) when compared to the control population. However, this result was not replicated in an independent Italian cohort of 127 families and it is likely due to the elevated paternal age at time of conception. In addition, ASD probands showed a reduced mtDNA content when compared to their unaffected siblings. Multivariable regression analyses indicated that variants with 15%–5% heteroplasmy in probands are associated to a greater severity of ASD based on ADOS-2 criteria, whereas paternal super-haplogroups H and JT were associated with milder phenotypes. In conclusion, our results suggest that the mtDNA impacts on ASD, significantly modifying the phenotypic expression in the Italian population. The unexpected finding of protection induced by paternal mitogenome in term of severity may derive from a role of mtDNA in influencing the accumulation of nuclear de novo mutations or epigenetic alterations in fathers’ germinal cells, affecting the neurodevelopment in the offspring. This result remains preliminary and needs further confirmation in independent cohorts of larger size. If confirmed, it potentially opens a different perspective on how paternal non-inherited mtDNA may predispose or modulate other complex diseases.</p

Table1_Dissecting the multifaceted contribution of the mitochondrial genome to autism spectrum disorder.xlsx

Autism spectrum disorder (ASD) is a clinically heterogeneous class of neurodevelopmental conditions with a strong, albeit complex, genetic basis. The genetic architecture of ASD includes different genetic models, from monogenic transmission at one end, to polygenic risk given by thousands of common variants with small effects at the other end. The mitochondrial DNA (mtDNA) was also proposed as a genetic modifier for ASD, mostly focusing on maternal mtDNA, since the paternal mitogenome is not transmitted to offspring. We extensively studied the potential contribution of mtDNA in ASD pathogenesis and risk through deep next generation sequencing and quantitative PCR in a cohort of 98 families. While the maternally-inherited mtDNA did not seem to predispose to ASD, neither for haplogroups nor for the presence of pathogenic mutations, an unexpected influence of paternal mtDNA, apparently centered on haplogroup U, came from the Italian families extrapolated from the test cohort (n = 74) when compared to the control population. However, this result was not replicated in an independent Italian cohort of 127 families and it is likely due to the elevated paternal age at time of conception. In addition, ASD probands showed a reduced mtDNA content when compared to their unaffected siblings. Multivariable regression analyses indicated that variants with 15%–5% heteroplasmy in probands are associated to a greater severity of ASD based on ADOS-2 criteria, whereas paternal super-haplogroups H and JT were associated with milder phenotypes. In conclusion, our results suggest that the mtDNA impacts on ASD, significantly modifying the phenotypic expression in the Italian population. The unexpected finding of protection induced by paternal mitogenome in term of severity may derive from a role of mtDNA in influencing the accumulation of nuclear de novo mutations or epigenetic alterations in fathers’ germinal cells, affecting the neurodevelopment in the offspring. This result remains preliminary and needs further confirmation in independent cohorts of larger size. If confirmed, it potentially opens a different perspective on how paternal non-inherited mtDNA may predispose or modulate other complex diseases.</p

DataSheet1_Dissecting the multifaceted contribution of the mitochondrial genome to autism spectrum disorder.docx

Autism spectrum disorder (ASD) is a clinically heterogeneous class of neurodevelopmental conditions with a strong, albeit complex, genetic basis. The genetic architecture of ASD includes different genetic models, from monogenic transmission at one end, to polygenic risk given by thousands of common variants with small effects at the other end. The mitochondrial DNA (mtDNA) was also proposed as a genetic modifier for ASD, mostly focusing on maternal mtDNA, since the paternal mitogenome is not transmitted to offspring. We extensively studied the potential contribution of mtDNA in ASD pathogenesis and risk through deep next generation sequencing and quantitative PCR in a cohort of 98 families. While the maternally-inherited mtDNA did not seem to predispose to ASD, neither for haplogroups nor for the presence of pathogenic mutations, an unexpected influence of paternal mtDNA, apparently centered on haplogroup U, came from the Italian families extrapolated from the test cohort (n = 74) when compared to the control population. However, this result was not replicated in an independent Italian cohort of 127 families and it is likely due to the elevated paternal age at time of conception. In addition, ASD probands showed a reduced mtDNA content when compared to their unaffected siblings. Multivariable regression analyses indicated that variants with 15%–5% heteroplasmy in probands are associated to a greater severity of ASD based on ADOS-2 criteria, whereas paternal super-haplogroups H and JT were associated with milder phenotypes. In conclusion, our results suggest that the mtDNA impacts on ASD, significantly modifying the phenotypic expression in the Italian population. The unexpected finding of protection induced by paternal mitogenome in term of severity may derive from a role of mtDNA in influencing the accumulation of nuclear de novo mutations or epigenetic alterations in fathers’ germinal cells, affecting the neurodevelopment in the offspring. This result remains preliminary and needs further confirmation in independent cohorts of larger size. If confirmed, it potentially opens a different perspective on how paternal non-inherited mtDNA may predispose or modulate other complex diseases.</p

Table2_Dissecting the multifaceted contribution of the mitochondrial genome to autism spectrum disorder.xlsx

Autism spectrum disorder (ASD) is a clinically heterogeneous class of neurodevelopmental conditions with a strong, albeit complex, genetic basis. The genetic architecture of ASD includes different genetic models, from monogenic transmission at one end, to polygenic risk given by thousands of common variants with small effects at the other end. The mitochondrial DNA (mtDNA) was also proposed as a genetic modifier for ASD, mostly focusing on maternal mtDNA, since the paternal mitogenome is not transmitted to offspring. We extensively studied the potential contribution of mtDNA in ASD pathogenesis and risk through deep next generation sequencing and quantitative PCR in a cohort of 98 families. While the maternally-inherited mtDNA did not seem to predispose to ASD, neither for haplogroups nor for the presence of pathogenic mutations, an unexpected influence of paternal mtDNA, apparently centered on haplogroup U, came from the Italian families extrapolated from the test cohort (n = 74) when compared to the control population. However, this result was not replicated in an independent Italian cohort of 127 families and it is likely due to the elevated paternal age at time of conception. In addition, ASD probands showed a reduced mtDNA content when compared to their unaffected siblings. Multivariable regression analyses indicated that variants with 15%–5% heteroplasmy in probands are associated to a greater severity of ASD based on ADOS-2 criteria, whereas paternal super-haplogroups H and JT were associated with milder phenotypes. In conclusion, our results suggest that the mtDNA impacts on ASD, significantly modifying the phenotypic expression in the Italian population. The unexpected finding of protection induced by paternal mitogenome in term of severity may derive from a role of mtDNA in influencing the accumulation of nuclear de novo mutations or epigenetic alterations in fathers’ germinal cells, affecting the neurodevelopment in the offspring. This result remains preliminary and needs further confirmation in independent cohorts of larger size. If confirmed, it potentially opens a different perspective on how paternal non-inherited mtDNA may predispose or modulate other complex diseases.</p

Genetic alterations identified in the control subject SWE_Q56_508.

<p>A. <i>SHANK2</i> splice mutation (IVS22+1G>T) detected in a Swedish female control, SWE_Q56_508. The mutation altered the donor splicing site of exon 22 and led to a premature stop in all <i>SHANK2</i> isoforms except for the <i>AF1411901</i> isoform, where it altered the protein sequence (G263V). B. CNVs in the same individual altering <i>LOC339822</i>, <i>SNTG2</i>, <i>PXDN</i> and <i>MYT1L</i>. The two close duplications span 264 kb and 245 kb on chromosome 2 and altered <i>LOC339822</i> and <i>SNTG2</i>, and <i>PXDN</i> and <i>MYT1L</i>, respectively. Dots show the B allele frequency (BAF; in green), Log R ratio (LRR; in red), and QuantiSNP score (in blue). Lower panel: all CNVs listed in the Database of Genomic Variants (DGV) are represented: loss (in red), gain (in blue), gain or loss (in brown). H, homer binding site; D, dynamin binding site; C, cortactin binding site.</p

Characterization of the functional impact of <i>SHANK2</i> mutations in cultured neuronal cells.

<p>A. The colocalization of <i>ProSAP1A/SHANK2</i>-EGFP (postsynaptic marker) and Bassoon (presynaptic marker) indicated that the mutations did not disturb the formation of SHANK2 clusters at excitatory synapses along the dendrites. B. The quantification of synapse density was performed on 20 transfected hippocampal neurons per construct from at least three independent experiments. The majority of the <i>ProSAP1A</i> variants affecting a conserved amino acid among SHANK proteins reduced significantly the synaptic density compared with the variants that affect amino acid non conserved among SHANK proteins (Mann-Whitney U-test: n_WT = 20, n_mut = 20; U_S557N = 82.5, p_S557N = 0.001; U_R569H = 124, p_R569H = 0.04; U_L629P = 149, p_L629P = 0.17; U_V717F = 114, p_V717F = 0.02; U_A729T = 73, p_A729T = 0.000; U_K780Q = 154, p_K780Q = 0.221; U_R818H = 108, p_R818H = 0.012; U_A822T = 154.5, p_A822T = 0.224; U_V823M = 129, p_V823M = 0.056; U_Y967C = 134, p_Y967C = 0.076; U_G1170R = 78, p_G1170R = 0.001; U_R1290W = 142, p_R1290W = 0.121; U_Q1308R = 162, p_Q1308R = 0.314; U_D1535N = 97, p_D1535N = 0.005; U_P1586L = 137, p_P1586L = 0.910; U_L1722P = 79, p_L1722P = 0.001, *p<0.05, **p<0.01, ***p<0.001). <b>C.</b> Effect of the variants on synaptic density. The y-axis represents −log P compared to WT (P obtained with Mann-Whitney test). After Bonferroni correction for 16 tests, only P values<0.003 were considered as significant. Variants represented in red were specific to ASD, in orange were shared by ASD and controls, and in green were specific to the controls. Open circles and filled circles represent non conserved and conserved amino acids, respectively. Prim, primary; second, secondary.</p

<i>SHANK2</i> mutations in patients with ASD.

<p>A. A heterozygous deletion of <i>SHANK2</i> was identified with the Illumina Human 1M-Duo SNP array in a patient with autism (AU038_3). The deletion spans 421 kb on chromosome 11q13.3, covers twelve exons of the human <i>SHANK2</i> and is not present in the parents. Each dot shows Log R Ratio (LRR; in red) and B allele frequency (BAF; in green). QuantiSNP score is represented with a blue line and indicates the deletion size. B. Location of the CNV and sequence variants (from this study and Berkel <i>et al.</i> 2010) along the SHANK2 protein: in red the variations specific to ASD, in orange the variations shared by ASD and controls and in green the variations specific to controls <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002521#pgen.1002521-Berkel1" target="_blank">[26]</a>. The breakpoints of the <i>SHANK2</i> deletion in AU038_3 are represented with a dotted line on the protein. Stars indicate the variants affecting conserved amino acids. C. A total of 40 variants were identified and variants affecting conserved amino acids in other SHANK proteins are enriched in patients with ASD (n_conserved = 12 and n_{non-conserved} = 3) compared with controls (n_conserved = 6 and n_{non-conserved} = 11) (Fisher's exact test 1-sided, P = 0.013, OR = 6.83, 95% IC = 1.19–53.40). D. The percentage of carriers of <i>SHANK2</i> variants in patients with ASD and Controls. Variants affecting a conserved amino acid among the SHANK proteins are enriched in patients with ASD (n_conserved = 29 and n_{non-conserved} = 822) compared with controls (n_conserved = 16 and n_{non-conserved} = 1074) (Fisher's exact test 1-sided, P = 0.004, OR = 2.37, 95% CI = 1.23–4.70). Open squares and filled squares represent the non-conserved and conserved amino acids, respectively. ANK, Ankyrin repeat domain; SH3, Src homology 3 domain; PDZ, postsynaptic density 95/Discs large/zona occludens-1 homology domain; SAM, sterile alpha motif domain; BSR, brain specific region; H, homer binding site; D, dynamin binding site; C, cortactin binding site. The proline-rich region is represented as a horizontal gray line.</p

Inherited 15q11–q13 CNVs identified in three ASD patients carrier of a <i>de novo</i> SHANK2 deletion.

<p>Deletions (del) and duplications (dup) are indicated in red and blue, respectively. Paternally and maternally imprinted genes are indicated in yellow and pink, respectively. Genes altered by the CNVs are indicated in blue or red. The bottom part of the figure indicates the location of the deletions/duplications previously associated with neuropsychiatric disorders <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002521#pgen.1002521-Miller1" target="_blank">[43]</a>–<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002521#pgen.1002521-deKovel1" target="_blank">[61]</a>. BP, breakpoint; Inh_M, inherited by mother; Inh_F, inherited by father; AS, Angelman syndrome; ASD, Autism spectrum disorders; ADHD, attention deficit-hyperactivity disorder; BP, bipolar disorder; DD: developmental delay; DBD, disruptive behavior disorder; EPI, epilepsy; GAD, generalized anxiety disorder; OCD, obsessive-compulsive disorder; ID, intellectual disability; PWS, Prader-Willi syndrome; SCZ, schizophrenia.</p

<i>ProSAP1A/SHANK2</i> variations identified in 851 patients with ASD and 1,090 controls.

a<p>Nucleotide positions are according to <i>NM 012309.3</i> from NCBI36/hg18 on the positive DNA strand; The patients with ASD and the controls used for this analysis came from this study (455 ASD & 431 controls) and from the study of Berkel <i>et al.</i> 2010 (396 ASD & 659 controls);</p>b<p>A screening of V717F, A729T, R818H, G1170R, D1535N and L1722P was performed in 948 subjects from the Human Genome Diversity Panel (V717F = 0/948; A729T = 0/948; R818H = 5/948; G1170R = 0/948; D1535N = 0/948; L1722P = 0/948);</p>c<p>A screen of R818H was performed in additional patients and controls (ASD 32/3250 (1.0%); controls 27/2030 (1.33%); Fisher's exact test 2-sided, P = 0.28). Fisher's exact test was used for statistical analysis;</p>d<p>“Yes” indicates if amino acid is conserved in SHANK1 (S1), SHANK3 (S3) or both (S1 & S3); MAF, Minor Allele Frequency.</p