Page 105 - Feline Cardiology

104 Section D: Cardiomyopathies

INTRODUCTION stenosis, hyperthyroidism, or acromegaly. HCM is a
primary myocardial disorder, indicating that the myo-
cardial abnormality is due to a defect most often within
Key Points the sarcomere (i.e., individual contractile element within
the heart) of the cardiomyocytes, and not secondary to
• Hypertrophic cardiomyopathy (HCM) is a primary other causes (Figure 11.1). Approximately two-thirds of
myocardial defect diagnosed by presence of increased people who develop HCM have an autosomal dominant
left ventricular wall thickness, in the absence of heritable defect (with incomplete penetrance pattern) in
secondary causes of concentric hypertrophy. one of 11 sarcomeric proteins. Currently there are hun-
• HCM is the most common heart disease of cats and is dreds of mutations in dozens of genes, and this number
the most common form of feline cardiomyopathy.
Cardiomyopathies • HCM is inherited in Maine coon cats and Ragdoll novel mutations (for updated information, access the
is expected to expand with discoveries of additional
cats as an autosomal dominant trait with incomplete
human gene mutation database at hgmd.cf.ac.uk). Often
penetrance. This means that HCM affects all individuals
individual families have novel mutations, which makes
that have the mutation, but to varying degrees. For
widespread genetic screening difficult, even in human
example, homozygous affected cats typically show
obvious phenotypic abnormalities, and heterozygous
described in cats, and is caused by mutations in myosin
affected cats have much more variability in penetrance medicine (Marian et al. 2001). Familial HCM has been
and may demonstrate only mild phenotypic binding protein C in Maine coon cats and Ragdoll cats
abnormalities. (Meurs et al. 2005, 2007). The etiology of HCM in other
• Hypertrophic obstructive cardiomyopathy (HOCM) cats remains unknown and may be caused by unrecog-
indicates that there is dynamic systolic anterior motion nized mutations.
of the mitral valve (SAM) accompanying HCM. Initial veterinary reports in the 1960s and 1970s often
named HCM as idiopathic cardiomyopathy, primary
myocardial disease, or feline cardiomyopathy. At that
Hypertrophic cardiomyopathy (HCM) is the most time, the similarities between feline and human HCM
common cardiac disease in cats, and is defined as con- in clinical features and pathology were beginning to be
centric hypertrophy of the left ventricle (i.e., thick ven- recognized, and feline HCM was identified as a model
tricular wall) in the absence of other causes of concentric for human disease (Tilley et al. 1977). The term “hyper-
hypertrophy including systemic hypertension, aortic trophic cardiomyopathy” became more prevalent in the

Troponin T a-Tropomyosin Troponin C Troponin I Myosin-binding Actin
(~15%) (<5%) protein C
(~15%)

Myosin b-Myosin Myosin Myosin
light chain heavy chain rod head
(<1%) (~35%)

Figure 11.1. Sarcomeric proteins found to have mutations that cause familial hypertrophic cardiomyopathy in people. HCM is a pri-
mary myocardial disease caused by mutations in sarcomeric proteins within the cardiomyocytes. Mutations of all sarcomeric proteins
displayed in the figure, as well as titin (not shown), have been shown to cause familial HCM in humans. Two missense mutations of
myosin binding protein C (the blue protein in the figure) have been found to cause familial HCM in Maine coon cats and Ragdoll cats,
and a screening test is now available. Obtained with permission; Spirito et al. N Eng J Med 336:776, 1997.