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Cardiac Screening Programs

Key Points

• Effective screening programs have the ability to identify disease, or the risk of a familial disease, and can provide
recommendations on how to use the information provided.
• Hypertrophic cardiomyopathy is the most commonly requested disease for screening, and screening strategies may include
both annual echocardiography and mutation screening, depending on the breed.

INTRODUCTION mutation. Evaluation of pedigrees of affected cats should
show that the disease appears to “skip” a generation
Effective use of, and institution of, screening programs (parents do not show the trait) and males and females
is dependent on two important elements. The first is should equally show the phenotype. Mating two cats
accurate diagnosis of the affected state. The second is that appear normal will produce approximately 25% of
that guidelines are present to make specific recommen- offspring with the affected trait and 75% that do not
dations once the affected status of the breeding animal demonstrate the trait. This suggests that the two parents
has been determined. are silent carriers of a recessive trait. If both parents
show the trait, all offspring should show the trait.
Modes of Inheritance X-linked traits are caused by a mutation in a gene
Cardiac disease (e.g., hypertrophic cardiomyopathy) carried on the X chromosome (i.e., not autosomal).
in the cat is most often inherited in an autosomal domi- They are most commonly recessive. Therefore, males
nant fashion, but other modes of inheritance including will almost always show the affected trait because they
autosomal and X-linked recessive are possible. only have one X chromosome. Because females have
An autosomal dominant trait is one in which the two X chromosomes, they may be silent carriers if they
disease is carried on an autosomal chromosome and have the mutant copy of the gene on only one of their
typically causes clinically evident changes even with only X chromosomes. They will show the phenotype if both
one gene copy of the mutation. Evaluation of pedigrees X chromosomes have the mutant copy of the gene.
of an affected animal should demonstrate that males Evaluation of pedigrees of affected animals should
and females are equally affected and that every affected show more affected males than females and an affected
cat has at least one affected parent. Animals that show male crossed with a normal female should produce
the phenotype (clinical presentation) can be either het- silent carrier (normal phenotype, no clinical evidence of
erozygous (one copy of the mutation) or homozygous disease) females.
(two copies of the mutation). Genetic diseases are also impacted by a phenomenon
Autosomal recessive traits are those carried on an referred to as genetic penetrance. Genetic penetrance
autosomal chromosome as well but since they are reces- determines how much of a trait is demonstrated in the
sive the cat will not demonstrate the clinical presenta- individual. If a trait has incomplete or varied penetrance
tion unless both copies of the individual’s gene have the (feline hypertrophic cardiomyopathy, for example), not

Feline Cardiology, First Edition. Etienne Côté, Kristin A. MacDonald, Kathryn M. Meurs, Meg M. Sleeper.
© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

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