A two-locus genetic interaction between LPHN3 and 11q predicts ADHD severity and long-term outcome

Abstract

The severity of attention-deficit/hyperactivity disorder (ADHD) symptoms is a major predictor of long-term ADHD outcome. To investigate if two-locus interactions might predict ADHD severity, we studied a sample of 1341 individuals from families clustering ADHD, using the Vanderbilt Assessment Scale for Parents. Latent class cluster analysis was used to construct symptom profiles and classify ADHD severity. Single nucleotide polymorphisms (SNPs) spanning ADHD-linked chromosomal regions on chromosomes 4, 5, 10, 11, 12 and 17 were genotyped. SNPs associated with ADHD severity were identified and potential two-locus genetic interactions were tested. We found that SNPs within the LPHN3 gene interact with SNPs spanning the 11q region that contains DRD2 and NCAM1 not only to increase the risk of developing ADHD but also to increase ADHD severity. All these genes are identified to have a major role in shaping both brain development and function. These findings demonstrate that genetic interactions may predict the severity of ADHD, which in turn may predict long-term ADHD outcome.

Figure 1

Profile plots derived using latent class cluster analysis applied to attention-deficit and hyperactivity disorder symptoms as measured by the Vanderbilt Assessment Scale for Parents (VAS-P) questionnaire. For each domain, VAS-P symptoms profiles within clusters are shown in a scale from 1 to 4 (1=never, 2=occasionally, 3=often and 4=very often). Demographic characteristics for each cluster are shown in a scale from 0 to 1, representing the proportion of individuals from the population with such characteristics. (a) Inattention (Q1–Q9): Q1: careless, inattentive; Q2: sustains attention poorly; Q3: appears to not listen; Q4: poor follow through; Q5: disorganized; Q6: avoids/dislikes sustained mental effort; Q7: loses needed objects; Q8: easily distracted; and Q9: often forgetful. (b) Hyperactivity/impulsivity items ( Q10–Q18): Q10: fidgets or squirms; Q11: cannot stay seated; Q12 restless; Q13: loud; noisy; Q14: always ‘on the go' Q15: talks excessively; Q16: blurts out; Q17: impatient; and Q18: intrusive. (c) Oppositional defiant disorder (ODD; Q19–Q26): Q19: loses temper; Q20: argues with adults; Q21: defies adults' rules; Q22: annoys others; Q23: shifts blames to others; Q24: touchy; Q25: angry/resentful; and Q26: vindictive. (d) Anxiety and depression (Q41–Q47): Q41: fearful, worried; Q42: fear of making mistakes; Q43: feels useless; Q44: blames self; Q45; feels unloved; Q46: sad; and Q47: embarrassed.

Figure 2

Genotypic frequency distribution for pairs of single nucleotide polymorphisms (SNPs) contributing to interaction effects and assessed by the Cochran–Mantel–Haenszel test. Significant interaction effects involve markers in the LPHN3 gene and a region in 11q that harbors the NCAM1 and DRD2 genes. Epistatic effects are depicted by changes in color that represent significant differences in genotypic distribution among severe (cases) vs not severe (controls) individuals. In there, the genotypes for one marker are held fixed whereas genotypes on the other marker vary. Inattention: (a) markers rs1947275 harbored in LPHN3 and rs17596017, in NCAM1, contribute to the severity of symptoms in this domain (M²=33.163, FDR-corrected P-value <0.001); (b) markers rs1947275 harbored in LPHN3 and rs12799083, in DRD2, produce a significant interacting effect contributing to the severity of symptoms (M²=28.456, FDR-corrected P-value <0.005). H/I: (c) markers rs35106420, in LPHN3, and rs620291, in NCAM1, produce an interacting effect contributing to the severity of symptoms (M²=20.497, FDR-corrected^* P-value <0.05). ODD: (d) markers rs995447, in LPHN3, and rs11214505, in NCAM1, interact to modify the severity of symptoms (M²=41.379, FDR-corrected P-value <0.0001); (e) rs734644, in LPHN3, and rs4938006 produce an epistatic effect contributing to the severity of symptoms (M²=26.795, FDR-corrected P-value <0.01). A/D: (f) markers rs1510920, in LPHN3, and rs4938006 localized closest to NCAM1 in an intragenic region of chromosome 11q, interact to modify the severity of symptoms (M²=41.379, FDR-corrected P-value <0.0001). ^*FDR-corrected P-values calculated on the basis of 567 independent tests, corresponding to the maximum number of SNP pairs for each of the four domains of the VAS-P questionnaire from which the severity of symptoms was derived. Abbreviations as in Figure 1.