Abstract
This case-control study examines the prevalence of rare de novo and inherited sequence variations among children and adolescents with attention-deficit/hyperactivity disorder (ADHD) and siblings and parents without ADHD.
Genomic research on attention-deficit/hyperactivity disorder (ADHD) previously focused on common variants1; however, polygenic heritability (28%) is lower than phenotypic heritability (76%) for ADHD,2 and genome-wide association studies revealed increased burden of rare copy-number variations3 and missense and disruptive variants to constrained genes in pediatric ADHD.3,4 Available genomic repositories for ADHD contain heterogeneous clinical phenotypes.5 Consequently, identification of genetic mechanisms specific to ADHD has been challenging. This study assessed monogenic contributions to pediatric ADHD in a well-characterized familial cohort.
Methods
This case-control study included probands aged 6 to 18 years with a DSM-5 diagnosis of ADHD who had a clinic visit at Boston Children’s Hospital between November 2019 and November 2022; controls were siblings and parents without ADHD. Exclusion criteria were autism spectrum disorder (ASD), moderate-severe intellectual disability (ID) (ICD-10 codes F71, F72, and F73), or known genetic syndromes. The study was approved by the institutional review board of Boston Children’s Hospital. Written informed consent was obtained. We followed the STROBE reporting guideline.
Clinical-grade whole exome sequencing was performed using the IDT xGen research panel with Illumina-based sequencing by GeneDx as part of the Children’s Rare Disease Cohorts initiative. Raw sequencing data were processed using the Illumina DRAGEN Germline Pipeline, including read mapping, quality control, and variant calling. Variants were assessed using our custom pipeline and ACMG guidelines. Data were analyzed using Microsoft Excel, version 2307. Two-sided P < .05 was significant. Contributions of rare, predicted damaging inherited and de novo variants were assessed for individuals with vs family members without ADHD.
Results
We included 77 probands with ADHD (19 [25%] female; 58 [75%] male; mean [SD] age, 10 [3.0] years); 1 (1%) had a diagnosis of mild ID. Participating family members included 58 siblings (15 [26%] with ADHD confirmed via medical record review, 43 [74%] without) and 27 parents with and 115 without ADHD. Two siblings with ADHD (13%) had ASD. Forty families (52%) returned a positive genetic finding, including 9 inherited (11%) and 5 de novo (7%) variants meeting ACMG criteria for likely pathogenic classifications and 26 (34%) arising from variants of uncertain significance in dominant neurodevelopmental disorder (NDD) (14 [18%]) and candidate constrained genes (12 [16%]). Four methylation-related genes had variants in multiple families: DIP2C, DOT1L, KMT2B, and SETD1B (Table).
Table. Candidate Variants Impacting Genes Involved in Methylation and Other NDD-Related Pathways.
| Family identification number | Gene | Variant | Clinical presentation | Segregation | Family history | Variant classification |
|---|---|---|---|---|---|---|
| AD108 | ASXL3 (NM_030632) | c.2801T>G:p.L934X | ADHD | De novo | Paternal ADHD; maternal dyslexia | Pathogenic |
| AD214 | DOT1L (NM_032482) | c.766C>T:p.R256W | ADHD, frontal lobe and executive function deficit | De novo | None | Likely pathogenic |
| AD216 | DOT1L (NM_032482) | c.3959G>A:p.G1320E | ADHD, dyslexia, DCD | Father, sibling | Paternal dyslexia | Likely pathogenic |
| AD6 | DIP2C (NM_014974) | c.2404C>T:p.R802C | ADHD | Mother; maternal grandmother, aunt, uncle | Maternal ADHD; paternal OCD | Likely pathogenic |
| AD31 | DIP2C (NM_014974) | c.1648C>T:p.H550Y | ADHD, DCD | Father | None | Likely pathogenic |
| AD24 | KDM2A (NM_001256405) | c.1616G>A:p.G539E | ADHD, dyslexia | Mother | None | VUS |
| AD143 | KDM1A (NM_015013) | c.1327G>T:p.E443X | ADHD, dyslexia, developmental delay, learning disorder | Father | Paternal ADHD | Likely pathogenic |
| AD242 | KMT2B (NM_014727) | c.4496A>G:p.K1499R | ADHD | Father, sibling | Paternal ADHD, dyslexia | VUS |
| AD256 | KMT2B (NM_014727) | c.5729C>G:p.P1910R | ADHD | Mother | Maternal ID | VUS |
| AD261 | KMT2B (NM_014727) | c.2599C>T:p.R867C | ADHD | NDa | None | VUS |
| AD262 | KMT2C (NM_170606) | c.12401C>T:p.P4134L | ADHD | Father | None | VUS |
| AD17 | KMT2E (NM_018682) | c.4824dupT:p.H1608fs | ADHD, unspecified learning disorder | Father | None | Pathogenic |
| AD11 | SETD1B (NM_001353345) | c.5303G>A:p.R1768H | ADHD | Father, sibling | None | Likely pathogenic |
| AD9 | SETD1B (NM_001353345) | c.1868C>T:p.P623L | ADHD, dyslexia | Father, sibling | Paternal ADHD | Likely pathogenic |
| AD207 | SETDB1 (NM_001145415) | c.2758T>G:p.S920A | ADHD, dyslexia | Mother, sibling | None | VUS |
| AD16 | PRDM10 (NM_199439) | c.2275A>G:p.M759V | ADHD, dyslexia | De novo | Paternal dyslexia | VUS |
| AD205 | SLC22A23 (NM_015482) | c.1106G>A:p.W369X | ADHD | De novo | None | Likely pathogenic |
| AD13 | SPTBN1 (NM_003128) | c.4873C>T:p.Q1625X | ADHD, dyslexia, DCD | De novo | None | Pathogenic |
| AD255 | COL4A3BP (NM_001130105) | c.264delC:p.P88fs | ADHD | De novo | Maternal dyslexia | Likely pathogenic |
| AD8 | AHNAK (NM_001346445) | c.16995delA:p.K5665fs | ADHD | Father, sibling | None | Likely pathogenic |
| AD238 | CUX2 (NM_015267) | c.1050 + 1G>A | ADHD, dyslexia | Mother | None | Likely pathogenic |
| AD15 | SYNGAP1 (NM_006772) | c.1193C>T:p.P398L | ADHD | Father | None | VUS |
| AD258 | SPTBN1 (NM_178313) | c.5203G>A:p.G1735R | ADHD | NDa | None | Likely pathogenic |
| AD12 | SLC6A8 (NM_005629) | c.263-98G>T | ADHD, dyslexia, DCD | Mother, sibling | Paternal ADHD | VUS |
| AD26 | MICAL3 (NM_015241) | c.5632G>A:p.A1878T | ADHD, dyslexia | Mother, sibling | Maternal ADHD; paternal ADHD | VUS |
| AD19 | DET1 (NM_001144074) | c.1063C>T:p.R355X | ADHD | Mother | Maternal OCD | VUS |
| AD22 | GRIN3A (NM_133445) | c.1643C>T:p.T548I | ADHD, dyslexia | Father, sibling | Paternal ADHD | VUS |
| AD32 | PLPPR4 (NM_014839) | c.1723C>T:p.R575X | ADHD, dyslexia | De novo | Paternal ADHD | VUS |
| AD210 | STARD7 (NM_020151) | c.415C>T:p.Q139X | ADHD, dyslexia, expressive language disorder | Mother | Paternal dyslexia | VUS |
Abbreviations: ADHD, attention-deficit/hyperactivity disorder; DCD, developmental coordination disorder; ID, intellectual disability; ND, not determined; NDD, neurodevelopmental disorder; OCD, obsessive compulsive disorder; VUS, variants of uncertain significance.
Unable to determine de novo status because of missing parental data; de novo variants were confirmed using biological parents.
De novo variants occurred more frequently in probands from simplex families (1 affected child; n = 22), accounting for 7 diagnoses (31%; odds ratio [OR], 4.20; 95% CI, 1.13-15.61; P = .03) (Figure); 80% of diagnoses were attributable to damaging missense variants and/or involved NDD-associated genes (OR, 4.60; 95% CI, 1.15-18.22; P = .03). No significant enrichment for de novo variants was observed in multiplex families (multiple affected children; OR, 1.57; 95% CI, 0.24-10.45; P = .64).
Figure. Rates of Predicted Damaging Rare De Novo Sequence Variations in Individuals With Attention-Deficit/Hyperactivity Disorder (ADHD).
Constrained genes are those with known association with neurodevelopmental disorders.
Rare inherited loss-of-function variants were enriched in probands from multiplex families and/or a family history of ADHD (rate, 1.90) vs controls (1.54) (P = .03), accounting for diagnoses in 17 families (36%). Inherited variants were enriched in genes with variation constraints6 and/or genes with prior association with NDDs (OR, 17.41; 95% CI, 4.14-73.20; P < .001). No significant excess was detected for inherited missense variants.
Discussion
We found that 52% of pediatric ADHD cases were explained by rare de novo or inherited variants. Unlike prior investigations,3,4,5 we increased statistical power to identify candidate variants by stratifying cases by family history of ADHD and narrowing the proband phenotype to confirmed primary ADHD diagnosis (without comorbid ASD or ID). We found excesses of de novo and inherited variants in simplex and familial ADHD cases, respectively. Limitations include small cohort size and lack of unrelated controls. Our results challenge the prior consensus that ADHD is strictly a polygenic disorder1 and suggest that single gene variants account for a significant portion of the genomic architecture underlying ADHD, similar to described rates for ASD.5 We found support for the hypothesis that atypical methylation is associated with ADHD status in that 4 of the genes with variants in multiple families are involved in methylation pathways.
Data Sharing Statement
References
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