The human heart is divided into four chambers. One of the four chambers, the left
ventricle, is the chamber mainly responsible for pumping blood out of the heart into the
circulation. There is an inherited condition affecting the heart, passed on through
genetics, hypertrophic cardiomyopathy (HCM). HCM causes the left ventricle to become
abnormally enlarged (left ventricular hypertrophy LVH).
Some patients with the abnormal genes that may cause HCM do not have the characteristic LVH.
Approximately 20 - 40% of patients with the genetic abnormality (missense mutation of genes
encoding for sarcomeric protein) actually have an enlarged left ventricle. Because of this,
researchers believe there may be other factors, along with the genetic abnormality that
contribute to the development of HCM. Researchers are interested in learning more about
several factors they suspect may play a role in the development of HCM.
Specifically, researchers plan to study levels of a hormone and the protein it attaches to,
which may contribute to the development of an abnormally enlarged heart. Insulin-like
growth factor (IGF-1) and insulin-like growth factor binding protein (IGFBP) work together
with growth hormone (GH) in the development and maturation of many organ systems. Previous
studies have suggested that these hormones affect the development and function of the heart.
Patients participating in this study will undergo a variety of tests including collection of
blood samples, echocardiogram of the heart, treadmill exercise test, and continuous
electrical monitoring of heart activity (Holter monitor).
Hypertrophic cardiomyopathy (HCM) is a genetic disease with an autosomal dominant pattern of
inheritance which is characterized by left ventricular hypertrophy (LVH). HCM is often
caused by missense mutations of genes that encode for sarcomeric proteins. The LVH varies
markedly in patients with identical sarcomeric gene mutations, and notably, 20 to 40% of
subjects with disease mutation do not have LVH as assessed by echocardiography. These
findings suggest that other factors affect LV wall thickness in HCM. We wish (1) to
investigate the potential role of IGF-I and its binding protein, IGFBP3, in determining
increased LV mass in HCM caused by sarcomeric mutations; and (2) to assess myocardial
ultrasound backscatter, exercise tolerance, and propensity to arrhythmias, in subjects who
have inherited sarcomeric mutations but who do not have LVH.
HCM subjects 5 years or older, with distinct sarcomeric gene mutations and LV wall
thickness greater than 15 mm in subjects older than 18 years, and greater than 2 SDs in
subjects 18 years of age or younger, as assessed by MRI.
Age- and gender-matched blood relatives with sarcomeric gene mutations but without LVH.
Age- and gender-matched blood relatives without sarcomeric gene mutations.
History of hypertension (basal systolic and diastolic pressures above 170 mm Hg and 95 mm
Hg, respectively) or another systemic or cardiac disease that may cause cardiac
History of recent acute illness or other chronic illness that might affect plasma levels
of IGF-I and IGFBP3.
History of thyrotoxicosis, diabetes mellitus or abnormally elevated fasting blood sugar.
Any conditions which would exclude patients from undergoing MRI scan.