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Timothy Syndrome — EECC MCQ

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HardArrhythmia & ElectrophysiologyTimothy SyndromeEECC

A 50-year-old man with Timothy syndrome (LQT8, CACNA1C mutation) presents with bradycardia, syndactyly, and intermittent 2:1 AV block. What distinguishes Timothy syndrome from other long QT subtypes?

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Correct answer: B — Timothy syndrome is an ultra-rare multi-system channelopathy caused by CACNA1C (L-type calcium channel) mutations characterised by extreme QT prolongation, 2:1 AV block, syndactyly, cardiac structural abnormalities, immune deficiency, and autism spectrum disorder — it has the highest mortality among LQTS subtypes

Timothy syndrome (TS) is one of the rarest and most severe forms of LQTS, caused by gain-of-function mutations in CACNA1C (encoding the alpha-1C subunit of the L-type calcium channel). The phenotype is multi-system: (1) Cardiac: extreme QT prolongation (QTc often >550 ms), functional 2:1 AV block, lethal ventricular arrhythmias (VT/VF), structural abnormalities (PDA, PFO, VSD, TOF, HCM); (2) Extracardiac: syndactyly (fused fingers/toes — pathognomonic), autism spectrum disorder, immune deficiency, hypoglycaemia, hypothermia, cognitive impairment. The 2022 ESC VA/SCD Guidelines classify TS among the highest-risk channelopathies. Treatment: beta-blockers, mexiletine, ICD for survivors of cardiac arrest. Prognosis is poor — median survival approximately 2.5 years without intensive management. Syndactyly + prolonged QT should always raise suspicion for TS.

Reference: ESC (2022): VA/SCD Guidelines