L. Wylie, A. Ramage, D. C. MacLeod
Department of Medicine, Queen Margaret Hospital, Dunfermline
Correspondence to: Dr D.C. MacLeod, Consultant Cardiologist, Queen Margaret Hospital, Whitefield Road, Dunfermline, Fife KY12 0SU
Tel. 01383 623 623 ext 2208 Fax. 01383 627 028
email donnie.macleod@faht.scot.nhs.uk
We report the case of identical twin sisters, both with hypertrophic cardiomyopathy, and both found to have similar echocardiographic appearances in the form of asymmetric septal hypertrophy. This is unusual, in that published reports commonly describe the heterogeneous expression of this condition in twins.
Key words: Hypertrophic cardiomyopathy, identical twins, echocardiography
The diagnosis of
hypertrophic cardiomyopathy (HCM) is
conventionally supported by the echocardiographic demonstration of left
ventricular hypertrophy in the absence of any other condition associated with
increased left ventricular wall thickness. Pedigree studies indicate autosomal
dominant transmission with variable penetrance and expression. Up to 75% of
first degree relatives of those with HCM do not appear to have acquired the
condition, whilst approximately 50% of cases may be considered sporadic.1-5 In
identical twins, it might be assumed that HCM would be identically or similarly
expressed, but the prevailing feature of reports to date is heterogeneity, the
condition being present in one twin but not the other.6-8 Indeed, on this basis,
an early hypothesis proposed a recessive mode of inheritance in certain cases.9
We describe the near identical morphologic expression of HCM in a pair of monozygotic twins.
Case report
Twin 1
A woman of 62 years was found to have a mid-systolic murmur when admitted with anaemia secondary to upper gastrointestinal blood loss. She was free of cardiac symptoms, was not hypertensive, and there was no family history of cardiac disease or sudden death. An electrocardiogram was normal. Echocardiography demonstrated HCM in the form of asymmetric septal hypertrophy (Figure 1). The interventricular septum measured 25 mm in systole (normal 13 ± 2 mm).
Twin 2
The second twin was offered clinical assessment and echocardiographic screening in view of the diagnosis of HCM in a first degree relative. There were no cardiac symptoms. Examination revealed a mid-systolic murmur, and she was normotensive. The electrocardiogram was normal, and the echocardiographic appearances were similar in nature to those of her sister, the systolic dimension of the interventricular septum being 22 mm.
Descendants
The offspring of both women have also been screened, without any evidence of transmission.
As discussed in the detailed study of Epstein et al,7 genetic pleiotropy is the most plausible explanation for the apparent absence of HCM in the twins and first degree relatives of those affected. Interestingly, Epstein et al report that the absence of echocardiographic evidence of hypertrophy in relatives does not necessarily exclude electrophysiological abnormalities, with potential liability to ventricular rhythm disturbance.
This case report demonstrates that HCM may indeed have similar structural consequences in identical twins, and is a reminder of the role of echocardiographic screening.
Acknowledgement: The expert technical assistance of Mr N. McMullan with the figure is gratefully acknowledged.
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8 Ko YL, Tang TK, Chen JJ, Hshieh YY, Wu CW, Lien WP. Idiopathic hypertrophic cardiomyopathy in identical twins. Morphological heterogeneity of the left ventricle. Chest 1992;102:783-785
9 Littler WA. Twin studies in hypertrophic cardiomyopathy. Br Heart J 1972;34:1147-1151