The short version
A good family history is one of the cheapest, most useful things you can give a clinician. It tells them which inheritance pattern to look for and which tests are worth requesting. ADHD clusters in families but does not follow a simple single-gene pattern. Some rare movement conditions do.
The usual mix-up
"Nobody else in my family has it, so it cannot be genetic." Not so. A variant can arise for the first time in you (de novo), sit silently in both parents (recessive), or show up weakly or not at all in relatives (reduced penetrance). Relatives may also be undiagnosed, especially in older generations.
Inheritance patterns in plain English
| Pattern | What it looks like in a family | Example in this series |
|---|---|---|
| Autosomal dominant | One changed copy is enough. Can appear in every generation | Dominant GCH1 deficiency, the commonest dopa-responsive dystonia form [1] |
| Autosomal recessive | Two changed copies needed. Parents usually unaffected carriers. Often skips generations | Recessive GCH1 deficiency [2]; most reported SPG7-related disease (not yet verified) |
| X-linked | Passed on the X chromosome. Affects males more obviously | Not a main pattern in this series |
| De novo | New in the affected person, absent in both parents | Rare damaging variants in ADHD [3] |
| Polygenic (many small effects) | Clusters in families with no clean pattern | Typical ADHD [4] |
Two ideas that explain "missing" family history
- Reduced penetrance. Some carriers never develop symptoms. In the dominant GCH1 form, symptoms are more common in females, and most asymptomatic adult carriers were male [1]. A parent can carry the variant while seeming unaffected.
- Variable expressivity. Carriers of the same variant can be mildly or severely affected, or affected in different ways.
How to collect a useful family history
Aim for three generations: you, parents, siblings, grandparents, aunts, uncles, cousins and children. For each person, note the following.
| Question | Why it helps |
|---|---|
| Relationship and age, or age at death | Places them on the tree |
| Any diagnosed condition, and at what age it started | Age of onset separates inheritance patterns |
| Walking, stiffness, tremor, falls, "clumsy" or "tight" legs; symptoms that vary through the day | Flags movement disorders, including dopa-responsive types |
| ADHD, autism, dyslexia, learning difficulties, or "never diagnosed but obviously" | Shows neurodevelopmental clustering |
| Any genetic tests and their results | Avoids repeating work |
| Parents who are blood relatives, or shared ancestry or region | Raises the chance of recessive conditions |
| Response to medicines (what helped, what made things worse) | Can echo across relatives |
| Early deaths, and causes | May reveal undiagnosed conditions |
Keep it factual. Record what is known and mark guesses as guesses. A clinician can work with "uncle, walked stiffly from his thirties, never diagnosed".
What a negative family history does and does not mean
It lowers the odds of some dominant conditions but does not exclude recessive, de novo or reduced-penetrance conditions, nor relatives' undiagnosed disease. Clinicians weigh it alongside examination and tests.
Limits
- This page explains patterns; it does not say what pattern any family has.
- The reduced-penetrance statement applies to dominant GCH1 deficiency as reported in the MDSGene review [1]. Other conditions differ.
- ADHD is not inherited like a single-gene condition [4].
Sources
Bibliographic details checked against PubMed.
- Weissbach A et al. Relationship of genotype, phenotype, and treatment in dopa-responsive dystonia: MDSGene review. Mov Disord 2022;37(2):237-252. DOI · PMID 34908184
- Novelli M et al. Mov Disord Clin Pract 2024;11(9):1072-1084. DOI · PMID 39001623
- Olfson E et al. Nat Commun 2024;15:5870. DOI · PMID 38997333
- Faraone SV, Larsson H. Mol Psychiatry 2019;24(4):562-575. DOI · PMID 29892054