Page 149 - Feline Cardiology

148 Section D: Cardiomyopathies

Genetic Screening Test (see Chapter 28) present and whether treatment is indicated. The
MYBPC3 mutation analysis is performed at the North
Carolina State University College of Veterinary
Key Points Medicine’s Veterinary Cardiac Genetics Laboratory
(www.cvm.ncsu.edu/vhc/csds/vcgl/index.html). A buccal
• Cardiac myosin binding protein C mutations (MYBPC3) mucosal swab using a special test kit provided by the
have been found to cause HCM in some families of laboratory or preferably whole blood (1–1.5 ml) col-
Maine coon cats and Ragdoll cats lected into an EDTA tube can be submitted for mutation
• A genetic screening test for MYBPC3 mutation is analysis. Genetic screening of Maine coon or Ragdoll
commercially available for Maine coon cats and Ragdoll cats related to a cat with confirmed HCM is also recom-
Cardiomyopathies • An echocardiogram is necessary in cats positive for the ation with an echocardiogram.
cats and may be useful for breeding programs. No other
mended, and they may also benefit from further evalu-
breeds have yet to be identified with a causative mutation.
mutation, to evaluate whether there are phenotypic
Circulating Biomarkers (see Chapter 8)
abnormalities or whether the cat is a carrier.
• Purebred cats may develop HCM without possessing the
MYBPC3 mutation, so a negative test does not exclude
the possibility that cat may have HCM. Key Points

• Amino-terminal pro-brain natriuretic peptide (NT-proBNP)
is a sensitive and accurate screening test for detection
of heart failure in cats with cardiomyopathy, and may be
Two sarcomeric mutations of the myosin binding protein
C gene (MYBPC3) have been discovered to cause famil- used to help distinguish whether the dyspnea is caused
by heart failure or primary respiratory disease.
ial HCM in some Maine coon cats and Ragdoll cats. • NT-ProBNP appears to be useful as a screening test to
Each breed has an exclusive mutation, not found in detect cardiomyopathy in asymptomatic cats, but there
other breeds of cats tested. The mutations result in a may be false negatives and false positives.
change in conserved amino acids and altered computed • There are mixed results on the usefulness of cardiac
structure of myosin binding protein C (Meurs et al. troponin I and endothelin-1 for detection of heart
2005). There is an incomplete penetrance of the gene, so disease or heart failure in cats with HCM.
some positive cats may be carriers that do not develop
the abnormal phenotype of concentric left ventricular
hypertrophy. Likewise, some Maine coon cats or Ragdoll
cats have phenotypic evidence of HCM without a posi- Natriuretic peptides
tive genetic screening test, indicating that there are likely The natriuretic peptide family includes atrial, brain (B-
other mutations or factors that cause HCM. The type), and C-type, D-type, and V-type natriuretic peptides.
MYBPC3 mutation screening is recommended for Natriuretic peptides are considered beneficial neuro-
Maine coon cats and Ragdoll cats intended for breeding hormones that counterregulate the renin-angiotensin-
(see Chapter 28). There is a prevalence of 34% of geneti- aldosterone system (RAAS) and endothelin-1. Independent
cally affected asymptomatic Maine coon cats in the of their biological activity, they are produced specifically
general breeding population (Fries et al. 2008). Given by cardiac chambers that are stretched or overfilled, and
this high prevalence, rapid removal of all genotypic as such, they have emerged as useful biomarkers to iden-
positive cats could result in a bottleneck effect with con- tify heart disease in people and animals (Maisel et al.
centration of other abnormalities, so geneticists have 2003; Oyama et al. 2009; Chetboul et al. 2009; Fine et al.
recommended a slower removal through breeding only 2008; Fox et al. 2009; Connolly et al. 2009). In human
negative progeny if possible, or for exceptional cats that medicine, they also serve as negative prognostic indica-
are heterozygous positive and echocardiographically tors for early cardiovascular mortality and levels are often
normal, breeding those cats to negative cats and over a monitored to help tailor heart failure treatment
few generations gradually selecting negative kittens for (Porapakkham et al. 2010; Troughton 2000; Koglin et al.
replacement (see Chapter 28). Any cat testing positive 2001). Likewise, brain natriuretic peptide elevations are
for the mutation should be examined by a cardiologist an independent predictor of cardiovascular mortality in
and an echocardiogram done to assess the clinical status dogs with symptomatic mitral valve degeneration
of the cat. Repeat echocardiograms are recommended (Moonarmart et al. 2010; Serres et al. 2009). Brain natri-
every 6–12 months in asymptomatic genotype positive uretic peptide (BNP or B-type) is normally synthesized
cats to identify whether phenotypic evidence of HCM is in the atria in cats, and there is a novel ventricular synthe-