Chorea
AD trinucleotide (CAG) repeat
GeneHTT CAG expansion · 4p16.3
PenetranceCAG ≥40 fully penetrant
ImagingCaudate atrophy — boxcar ventricles
Chorea RxVMAT2 inhibitors
Chorea + psychiatric decline + family history? CAG ≥40 is fully penetrant Huntington.
Huntington vs acquired chorea
| Huntington (genetic) | Acquired chorea | |
|---|---|---|
| Cause | AD HTT CAG expansion (4p16.3) | Sydenham (post-strep), hemiballism (STN), non-ketotic hyperglycemia |
| Onset / clues | Psychiatric precedes motor; anticipation (paternal); Westphal juvenile <20, >60 repeats, rigidity/dystonia | Child post-strep chorea; acute unilateral flinging; diabetic hyperglycemia |
| Key test | HTT CAG: <27 nl · 27–35 interm · 36–39 reduced · ≥40 full | ASO / anti-DNase B + echo; MRI (STN / T1-bright putamen); glucose |
| Treatment | VMAT2 inhibitors (tetrabenazine, deutetrabenazine, valbenazine) | Valproate (Sydenham) + penicillin ppx; correct glucose |
◆ Signature clue
Progressive chorea + psychiatric decline + AD family history → Huntington; CAG ≥40 is fully penetrant. In any chorea patient <50, always exclude Wilson.
Diagnosis
HTT CAG testing; caudate atrophy → boxcar ventricles. Westphal juvenile onset <20, >60 repeats, paternal, rigidity/dystonia. Exclude Wilson <50 (ceruloplasmin, 24-hr urine copper, KF rings).
Management
VMAT2 inhibitors (tetrabenazine, deutetrabenazine, valbenazine) for bothersome chorea — black-box depression/suicidality warning, so psychiatric comorbidity may favor an antipsychotic strategy.