Hypertrophic Cardiomyopathy in a Monozygotic Twin Pair

A 70-year-old female patient was admitted to our hospital because of atypical chest pain and fatigue. No relevant diseases were recorded in her previous medical history. During the physical examination, she presented with a mild systolic murmur. Her 12-lead ECG indicated right bundle branch block (Figure 1A), and blood pressure was normal. Initial blood test showed normal hs-Troponin T and D-dimer levels. Transthoracic echocardiography (TTE) revealed mild concentric left ventricular (LV) hypertrophy (end-diastolic interventricular septal thickness 14 mm; LV mass index, 96 g/m) with septal bulging and mild aortic stenosis (transaortic mean gradient 18 mm Hg, calculated aortic valve area 1.8 cm) because of valve calcification (Figure 2A; Video I in the Data Supplement). In addition, TTE showed a good LV and right ventricular systolic function, impaired LV relaxation, and minimal mitral and tricuspidal regurgitation (Video II in the Data Supplement). To rule out obstructive coronary artery disease, we performed coronary artery calcium score scan and prospectively ECG-triggered coronary computed tomography angiography using a 256-slice multidetector-row computed tomography. The total coronary artery calcium score was 340; the calcium score of the aortic valve was 731 (Figure 3A). The coronary computed tomography angiography depicted a left dominant coronary system (Figure 4A) and several calcified and partially calcified atherosclerotic plaques along the left anterior descending coronary artery, causing moderate stenosis and partially calcified plaques in the left circumflex coronary artery, causing mild stenosis. The patient was discharged with optimized medications. However, the patient had a monozygotic twin pair, who was diagnosed with aortic valve stenosis several years ago. Therefore, the sibling (second-born twin B) was asked to visit our hospital for further investigation. She was symptom-free, while presenting a moderate systolic murmur intensifying at the late systolic phase on auscultation. Her ECG showed LV strain pattern (Figure 1B). The TTE examination of twin B revealed a typical pattern of hypertrophic obstructive cardiomyopathy: marked LV hypertrophy (end-diastolic interventricular septal thickness 18 mm; LV mass index, 123 g/ m) with systolic anterior motion of the mitral valve with subsequent significant dynamic LV outflow tract obstruction (peak gradient 91 mm Hg) and mitral regurgitation (vena contracta width 7 mm; Figure 2B; Videos III and IV in the Data Supplement). Furthermore, the aortic valve was heavily calcified, suggesting a severe valvular stenosis (aortic valve area 0.6 cm by planimetry). Mild aortic and tricuspid regurgitation was also present beside good LV and right ventricular systolic function and pseudonormal LV filling pattern. The twin pair underwent cardiac magnetic resonance imaging to confirm the diagnosis of hypertrophic cardiomyopathy (HCM) in twin B and, possibly, in twin A (Figure 5). Cardiac magnetic resonance imaging examination of twin B showed LV hypertrophy with septal predominance (LV mass index 141 g/m, maximal end-diastolic wall thickness 27 mm; Figure 5F). Systolic magnetic resonance jet formation of the LV outflow tract was observed, and mitral regurgitation was detected in consequence of the systolic anterior motion phenomenon (Figure 5D and 5E). Aortic valve area was measured 0.7 cm. Interestingly, patchy midmyocardial late gadolinium enhancement was visible in the basal inferolateral segment. In twin A, cardiac magnetic resonance imaging confirmed a marked septal hypertrophy in the basal segments as well (LV mass index 134 g/m, maximal end-diastolic wall thickness 19 mm; Figure 5A). The midmyocardial contrast enhancement was also present in the basal inferolateral segment of the LV (Figure 5C). The presence of basal inferolateral late gadolinium enhancement is a rare coincidence with HCM; however, this late gadolinium enhancement pattern is often associated with rare diseases causing LV hypertrophy (ie, AndersonFabry, Danon disease).