Hypertrophic cardiomyopathy in identical twins: a case report with mismatch between genotype and phenotype

Figures

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  Figure 1. Electrocardiogram showing Twin A sinus rhythm, heart rate of 60 b.p.m., cardiac axis +60°, and no evidence of left ventricular hypertrophy according to the Sokolow–Lyon criteria (A) and Twin B sinus rhythm, heart rate of 68 b.p.m., cardiac axis +30°, evidence of left ventricular hypertrophy according to the Sokolow–Lyon criteria and T wave inversion in precordial lateral leads, DII and aVF, suggestive of apical hypertrophic cardiomyopathy (B).

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  Figure 2. Two-dimensional transthoracic echocardiographic images corresponding to Twin A (Video 1). Arrows indicate septal hypertrophy of the left ventricle in the parasternal long-axis (A), apical four-chamber (B), short-axis (C), and M-mode (D) views. Colour M-mode demonstrates systolic anterior motion of the mitral valve (asterisk in E) and the acceleration it produces in the left ventricular outflow tract and the resulting mitral regurgitation (arrow in E). Continuous-wave Doppler showing a typical late peaking appearance of the Doppler velocity profile, with a resting left ventricular outflow tract gradient of 30 mmHg (F).

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  Figure 3. Three-chamber (A), four-chamber (B), apical (E), medium (F), and basal (G) short-axis cine steady-state free precession (SSFP) images of Twin A with corresponding delayed enhancement images (K–M) showing basal anteroseptal hypertrophy (yellow arrows in A, B, F, and G) with replacement fibrosis (yellow arrows in L and M) in the same areas. Three-chamber (C), four-chamber (D), apical (H), medium (I), and basal (J) short-axis cine SSFP images of Twin B with corresponding delayed enhancement images (N–P) showing medium apical hypertrophy (green arrows in C, D, H, and I) with replacement fibrosis (green arrows in N and O) in the same location.

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  Figure 4. The stress test of Twin A shows sinus tachycardia (A) at the beginning and 1-min ventricular tachycardia (B).

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  Figure 5. Captured subcutaneous electrocardiogram report showing the detection of ventricular fibrillation at approximately 36.0 s and receives an appropriate shock (represented by a lightning bolt), followed by a pause and returning to sinus rhythm. S, detection; •, dismiss; T, tachycardia detection; C, charging start; N, noise.

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  Figure 6. Two-dimensional transthoracic echocardiographic images corresponding to Twin B (Video 2). Arrows indicate mid-apical hypertrophy in the apical four-chamber (A), apical two-chamber (B), and parasternal short-axis (C) views. M-mode demonstrates the normal thickness of the interventricular septum (D) and a slight systolic anterior motion of the mitral valve (asterisk in D). Continuous-wave Doppler showing a maximum resting left ventricular outflow tract gradient of 13 mmHg without significant obstruction (E). The global longitudinal strain of the left ventricle decreased to −14.5% (F), with greater involvement at the apical level in all its segments and medial, especially in the anterior and inferolateral segments.

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  Figure 7. Pedigree: Family history and genetic testing reveal no familial background of apical or septal cardiomyopathy, and the pathogenic variant does not segregate within the family. Neither the twins nor the father exhibits clinical signs that would justify investigation for any form of mucopolysaccharidosis.