PMC9453449_01
(A) Dysmorphology pictures of the boy included mandibular hypoplasia, single palmar crease, and long bone over hyperextension. (B) Genetic testing of our patient identified a heterozygous missense mutation named c.652C > T (p.R218W) in the coding region of KCNJ2. His parents were tested as wild types without mutations, so our patient carried a de novo mutation.
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F1
The physical examination revealed dysmorphology, including mandibular hypoplasia, single palmar crease, and long bone over hyperextension (Figure 1A). Figure 1). Furthermore, frequent PVCs (38% of total beats) in bigeminy and recurrent asymptomatic non-sustained bidirectional or polymorphic ventricular tachycardia (bVT/pVT, 2,659 times VT) were shown in 24-h Holter recording (GE MARS) (Supplementary Figure 2). T (p.R218W, NM_00891, Figure 1B) in the C-terminal interaction domain of KCNJ2. The mutation was a hot spot that caused loss of function and resulted in a dominant-negative effect on Kir2.1. His parents were tested as wild types without mutations (Figure 1B).
Electrocardiogram (ECG) of the local hospital demonstrated sinus rhythm with frequent PVCs. Enlarged U waves (U wave is considered enlarged if its amplitude is >= 0.15 mV and its duration is >= 210 ms, indicated by red arrows) in leads II, III, aVF, V1-V2, and wide T-U junction (Tp-Up, 240 ms) were shown in ECGs. He had QTc of 380 ms and QUc of 671 ms.
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F2
Enlarged U waves (U wave is defined as an early diastolic deflection after the end of the T wave and is considered enlarged if its amplitude is >= 0.15 mV and its duration is >= 210 ms, indicated by red arrows in Figure 2) in leads II, III, aVF, V1-V2, and wide T-U junction (T peak-U peak 240 ms) were shown in ECGs. Figure 1). Furthermore, frequent PVCs (38% of total beats) in bigeminy and recurrent asymptomatic non-sustained bidirectional or polymorphic ventricular tachycardia (bVT/pVT, 2,659 times VT) were shown in 24-h Holter recording (GE MARS) (Supplementary Figure 2).
Frequency of ventricular arrhythmia in 24-h Holter recording before and after taking mexiletine 3 days, kinds of ventricular arrhythmias (isolated PVCs, bigeminy PVCs, couplet PVCs, and non-sustained ventricular tachycardia) were suppressed.
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F3
A 24-h Holter was performed after the treatment showed decreased PVC burden from 38 to 3% of total beats (Figure 3) and absence of ventricular tachycardia. The test results revealed a QUc 730 ms at the baseline heart rate 78 bpm and 590 ms during exercise with a heart rate of 121 bpm, a U wave infusion with the P wave, and a "U on P" sign (U-wave masquerading P-wave) at peak heart rate 144 bpm (Supplementary Figure 3).