Rare Inherited and De Novo CNVs Reveal Complex Contributions to ASD Risk in Multiplex Families

Abstract

Rare mutations, including copy-number variants (CNVs), contribute significantly to autism spectrum disorder (ASD) risk. Although their importance has been established in families with only one affected child (simplex families), the contribution of both de novo and inherited CNVs to ASD in families with multiple affected individuals (multiplex families) is less well understood. We analyzed 1,532 families from the Autism Genetic Resource Exchange (AGRE) to assess the impact of de novo and rare CNVs on ASD risk in multiplex families. We observed a higher burden of large, rare CNVs, including inherited events, in individuals with ASD than in their unaffected siblings (odds ratio [OR] = 1.7), but the rate of de novo events was significantly lower than in simplex families. In previously characterized ASD risk loci, we identified 49 CNVs, comprising 24 inherited events, 19 de novo events, and 6 events of unknown inheritance, a significant enrichment in affected versus control individuals (OR = 3.3). In 21 of the 30 families (71%) in whom at least one affected sibling harbored an established ASD major risk CNV, including five families harboring inherited CNVs, the CNV was not shared by all affected siblings, indicating that other risk factors are contributing. We also identified a rare risk locus for ASD and language delay at chromosomal region 2q24 (implicating NR4A2) and another lower-penetrance locus involving inherited deletions and duplications of WWOX. The genetic architecture in multiplex families differs from that in simplex families and is complex, warranting more complete genetic characterization of larger multiplex ASD cohorts.

Figure 1

Overview of the Analysis Pipeline We started by renormalizing intensities according to manufacturer recommendations and continued with the CNVision pipeline, followed by quality control (QC) with strict recommended criteria. After QC, we proceeded to annotate CNVs by type and annotate samples by family structure and analyzed the samples in multiplex (at least two affected children) and combined (all samples and family types) analyses for rare (<1% frequency in the DGV) and de novo CNVs. Families in whom the child or children failed QC were excluded from the analyses. Analyses were performed by CNV size (≥500 kb, 100–500 kb, and combined) in the mentioned CNV categories. Inheritance patterns for CNVs could be determined only in families with both parents, and only these families were included in the de novo analyses.

Figure 2

Summary of CNV Association Results in the AGRE Summary of results for all samples combined (simplex and multiplex) and multiplex families only. Detailed sample sizes and summaries by array are available in Table S2. CNVs over 500 kb were considered large, and CNVs with a population frequency below 1% in the DGV were considered rare. CNVs found in a child but not in the parents were considered de novo. Analyses for large, rare CNVs contained inherited or de novo CNVs, whereas de novo analyses contained only de novo CNVs. Only p values smaller than 0.05 are shown in the figure. The fraction of deletions is shown in blue, and the fraction of duplications is shown in green. Abbreviations are as follows: Aff, affected sibling; and Sib, unaffected sibling.

Figure 3

Distribution of Large, Rare CNVs The majority of large, rare de novo CNVs in the AGRE are in loci considered to be associated with ASD (55%), and only a minority of the CNVs are loci of unknown pathogenicity (not presently associated with ASD). Inherited CNVs, however, are mostly of unknown pathogenicity, and only 28% are in known ASD-associated loci. Most ASD-associated CNV loci have been identified through the recurrence of de novo events, which would bias our findings toward de novo CNVs. Also, because these loci have large effect sizes on behavior and cognition, we would expect a larger percentage of the CNVs to be de novo at these loci as a result of potential effects on fecundity. Table 1 shows a breakdown of all known ASD-associated loci found in the AGRE, Table S3 shows all large, rare de novo CNVs, and Table S4 shows large, rare inherited CNVs.

Figure 4

The Non-segregation of Established ASD Risk CNVs in Multiplex Families We observed non-segregation of known pathogenic CNVs in multiplex families: all affected children in the same family did not necessarily share the CNV. Most of these (n = 17/21) were de novo CNVs and were present in only one affected child. The cause of ASD in the other affected child remains unknown. Thorough sequencing of all family members will be beneficial for determining the exact phenotypic effects of the pathogenic CNVs and assessing other possible genetic causes of ASD in these families. Plus signs indicate samples with available DNA for testing.

Figure 5

The 2q24.1 Recurrent De Novo Deletion Locus and NR4A2 Expression in the Fetal Brain (A) AGRE, DECIPHER, and ClinGen CNVs in 2q24.1 all overlap two genes: NR4A2 and GDP2. All samples from DECIPHER or ClinGen were reviewed for additional CNVs, and only samples with no additional ASD risk CNVs were included. The minimal overlap area between gray dashed lines contains all of NR4A2 and the beginning of GPD2. De novo deletions are marked in dark red, and deletions with no information on the mode of inheritance are marked in coral red. (B–D) Using in situ hybridization, we looked at the localization of NR4A2 expression in fetal brains from 19–20 gestational weeks. Coronal sections (B and C) showed strong expression in the deep layers of the cortical plate (CP; especially in the perisylvian temporal cortex [PSTC]), in the stratified transitional field (STF) (C) that runs through the claustrum and habenula (H) (B) and in the sagittal section (D) of the CP, especially in the frontal (FL) and temporal (TL) lobes.

Figure 6

Raven's NVIQ Is Correlated with the Number of Rare De Novo CNVs in ASD Overall, the effect of rare de novo CNVs (A) and large, rare de novo CNVs (B) on NVIQ is modest between de novo CNV carriers (light blue) and non-carriers (dark blue), but the effect is stronger in females with de novo CNVs (light green, C) than in females without de novo CNVs (dark green, D). The midline in the boxplots (A–D and E) represents the median, the notches show the 95% confidence interval, the solid box represents the middle 50% of the data points (quantiles two and three), the whiskers extend to show 1.5× the interquartile rage, and the individual dots are outlier values. The number of rare de novo CNVs (E) or large, rare de novo CNVs (F) correlates clearly with NVIQ, more so in females (green) than in males (gray) or the total affected population (black line). SDs are shown with dashed lines. However, there is neither a difference in Raven’s NVIQ between affected females (green) and males (gray) (G) nor an increased number of de novo CNVs in affected females (H) (the portion of large [≥500 kb], rare, de novo CNVs is shown in green, and rare, 100–500 kb de novo CNVs are in blue).