Jamie R. Listokin
Attention-Deficit/Hyperactivity Disorder (ADHD) is characterized by symptoms of inattention, hyperactivity, and/or impulsivity (American Psychological Association, 2000).Three types of presentations:
ADHD children may suffer from deficits in overall self-control, leading to classic symptoms of hyperactivity and poor emotion regulation (Kofler, Rapport, Sarver, Raiker, Orban, Friedman & Kolomeyer, 2013).
- Predominantly hyperactive/impulsive presentation
- Predominantly inattentive presentation
- Combined presentation
- Pooled results from 20 twin studies indicate the heritability of ADHD is 76% (Faraone et al., 2005).
- Findings from longitudinal twin studies suggest that the continuity of ADHD symptoms from childhood to adolescence is associated with genetic influences (Kuntsi et al., 2005).
- Genetic studies of quantitative ADHD symptom scores in children further support the idea that genetic factors may related to symptom severity (Anttila et al., 2018).
Previous GWAS Study
A previous genome-wide association study (GWAS) (Demontis et al., 2018) on 20,183 individuals with ADHD and 35,191 controls were collected from 12 European, North American, and Chinese cohorts.
Two of the SNP variants occur in the SEMA6D and SORCS3 genes.
- In total, 304 genetic variants have been associated with ADHD. Of those, 12 variants surpassed the threshold for genome-wide significance (P < 5×10−8).
- The SEMA6D gene was significantly associated with increased risk for ADHD and putamen volume (Hawi, 2018).
- The SORCS3 gene has been to be a risk factor for both ADHD (Lesch, 2008). and bipolar disorder (Ollila, 2009).
The goal of the current study was to develop an assay for the presence for a SNP in selected genes.
- Primers were designed for:
- rs281324 in the SEMA6D gene
- rs11591402 in the SORCS3 gene
A PCR reaction was performed.
Products were visualized on 1% agarose gels, purified and sent out for sequencing.
We sequenced the region including the SNPs. This was a proof of principle; therefore, we did this on 10 de-identified participants.
Figure 1. Gel Electrophoresis Results of SEMA6D PCR
- Five participants were homozygous for the T allele
- Three participants were homozygous for the C allele.
- One participant was heterozygous for the T and C alleles
- "Normal" sequence and SNP associated with ADHD.
Figure 2. Chromatogram of heterozygous rs281324 SNP
Figure 3. Gel Electrophoresis Results of SORCS3 PCRThere were long stretches of repeat nucleotides in this PCR product.
- As a result of using Taq, it is very difficult to interpret the sequencing.
Figure 4. Chromatogram of SORCS3 results
DiscussionIn the SEMA6D gene, we were successfully able to amplify the region where the SNP is. Normal and ADHD-associated SNPs were detected. The analysis sets the stage for a larger sample in a targeted population.
In the SORCS3 gene, we were unsuccessful in generating readable sequences of the region of the SNP.
- If this was to be conducted on a larger scale, we would do a more efficient analyses method, such as Taqman or Allelle Specific Analyses.
- More stringent sequencing methodology needs to be applied in order to sequence this region.
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