A 16-year-old girl presents with recurrent syncope triggered by emotional stress and loud noises during school. ECG shows QTc prolongation of 485 ms with low-amplitude notched T-waves. Genetic testing confirms a heterozygous mutation in KCNH2. The inheritance pattern marked **B** in the pedigree diagram represents the mode of transmission in this family. Which of the following clinical features is MOST consistent with this inheritance pattern and genotype?
A. Syncope triggered by exercise and swimming, with broad-based T-waves; best managed with beta-blockers and sport restriction
B. Syncope triggered by auditory stimuli and emotional stress, with bifid T-waves; excellent response to beta-blockers and avoidance of QT-prolonging drugs
C. Congenital sensorineural deafness with QT prolongation; autosomal recessive inheritance requiring biallelic mutations
D. Syncope during rest and sleep with long isoelectric ST segment; requires mexiletine in addition to beta-blockers
Explanation
Why option 1 is correct
The patient's clinical presentation (syncope triggered by auditory stimuli and emotional stress, low-amplitude notched/bifid T-waves, KCNH2 mutation) is pathognomonic for LQT2, which is inherited as autosomal dominant (Romano-Ward syndrome) — the inheritance pattern marked B in the pedigree. LQT2 arises from loss-of-function mutations in KCNH2 (chromosome 7q36), encoding the α-subunit of the rapid delayed-rectifier IKr current. Heterozygous carriers manifest the full phenotype. Management focuses on beta-blockers (first-line), avoidance of QT-prolonging drugs, and correction of electrolytes — particularly hypokalemia, to which LQT2 is exquisitely sensitive (HRS/EHRA 2022, ESC VA 2022).
Why each distractor is wrong
Option 2: Describes LQT1 (KCNQ1 mutation), characterized by exercise/swimming-triggered syncope and broad-based T-waves. This is also autosomal dominant but the clinical phenotype and trigger profile do not match this patient's auditory and emotional stress triggers.
Option 3: Describes LQT3 (SCN5A mutation), with rest/sleep-triggered syncope and long isoelectric ST. Although autosomal dominant, the clinical presentation and T-wave morphology are inconsistent with this patient's findings.
Option 4: Describes Jervell and Lange-Nielsen syndrome (autosomal recessive, pattern A in the pedigree), which requires biallelic mutations and includes congenital sensorineural deafness — neither of which is present in this patient.
High-YieldNEET PG
LQT2 (KCNH2) = auditory/emotional triggers + bifid T-waves + autosomal dominant (Romano-Ward) + exquisite sensitivity to hypokalemia and QT-prolonging drugs.
HRS/EHRA Inherited Arrhythmia Consensus 2022; ESC VA 2022
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