The short version
- ADHD runs in families. Twin studies put heritability at about 74% (Tier B).
- There is no single "ADHD gene". The picture is thousands of common variants that each nudge risk a tiny amount, plus rarer variants with bigger effects, plus chance and environment (Tier B).
- Genes describe risk. They are not a diagnostic test and they do not tell a clinician which medication to use (Tier B).
- Some rare single-gene conditions affect the same dopamine pathways and can produce movement symptoms. That is a differential diagnosis question for specialists, not proof that ADHD is caused by those genes (Tier A for the conditions, Tier D for any link to ADHD).
The usual mix-up
"It's genetic" gets heard as "one faulty gene". The real finding is closer to "many small dials and a few large switches". Keeping those two pictures apart is the whole point of this series.
Reading order
| # | Article | Read it when you want to know |
|---|---|---|
| GEN-01 | ADHD and genes: what the evidence shows | The headline numbers and what they do and do not mean |
| GEN-02 | How to read a genetic claim | Whether a claim you have seen is strong, weak or oversold |
| GEN-03 | The dopamine supply chain in plain English | Which step does what, and which genes sit where |
| GEN-04 | Common variants, rare variants and the heritability gap | Why "74%" and "about a third" are both true |
| GEN-05 | Polygenic scores: what they can and cannot do | Whether a DNA score can diagnose ADHD |
| GEN-06 | When movement symptoms and ADHD traits overlap | Which single-gene conditions clinicians consider |
| GEN-07 in preparation | Genes and medication | What pharmacogenomics does and does not cover |
| GEN-08 in preparation | Genetic testing on the NHS | What to ask for, what results can mean |
| GEN-09 | Family history and inheritance patterns | How to collect a family history that helps a clinician |
| GEN-10 | Autism genetics in brief | Heritability, overlap with ADHD, and why it matters for care |
| GEN-11 | Glossary | Any term you hit and do not recognise |
How every article in the series is built
- Short version
- The usual mix-up
- The plain-English layer
- The deeper layer (optional to read)
- Limits (what this does not claim)
- Sources
Evidence tiers used in this series
| Tier | Meaning | How it is written |
|---|---|---|
| A | Established biology, in textbooks and guidelines | Stated plainly |
| B | Robust ADHD evidence: large, replicated, or consensus reviews | Stated plainly, source named |
| C | Preliminary, peripheral (e.g. blood cells), small or unreplicated | "One small study found..." |
| D | Open hypothesis | "One working idea is... It has not been tested in..." |
Limits
This series explains the science. It does not diagnose, and it does not replace a clinician or a genetics service. Population findings describe groups; they do not predict one person.
Sources
See each article. Bibliographic details for papers cited in this series were checked against PubMed.