| 
Andrea
Harvey, FAB Lecturer at the University of Bristol Veterinary
School explains more about this inherited disease and how
we can tackle it
PYRUVATE
KINASE (PK) DEFICIENCY is an inherited disease occasionally
encountered in Abyssinian and Somali cats, and also reported
in the domestic shorthair cat. Pyruvate kinase is an enzyme
found within red blood cells which enables them to produce
energy to survive. If this enzyme is lacking, the lifespan
of the red blood cells is significantly reduced, resulting
in a reduction in the number of red blood cells in the circulation
(anaemia).
What
signs does it cause?
The
main consequence of the disease is the development of anaemia.
However since the body can quickly manufacture new red blood
cells the anaemia is usually only intermittently detectable.
Most of the time the anaemia is either only mild, or occurs
gradually, enabling the cat to adapt to the anaemia and not
show any obvious signs. Anaemia often results in only vague
signs such as lethargy and lack of appetite. However, a rapid
severe life-threatening anaemia can also develop. Although
PK deficiency is hereditary, the anaemia is usually mild and
clinical signs may not be obvious, and thus may not be noticed
until the cat is quite old.
 How
is PK deficiency inherited?
The
disease is inherited as an autosomal recessive trait (see
box
1). This means that a
cat can be carrying the defective gene (heterozygous) without
having any symptoms of the disease at all. Affected cats (homozygous)
arise when two carrier cats are mated with each other. Since
carrier cats remain healthy, and the anaemia of affected cats
may not be detected until they are a few years of age, the
potential exists for carrier cats and affected cats to have
had significant numbers of offspring before the disease is
identified. However, the positive side of this is that it
also means if carrier cats are identified they can still be
used for breeding as long as we ensure that they are NOT mated
with another carrier. Mating a carrier with a non-carrier
will not produce any offspring that will suffer from PK deficiency,
and 50 per cent of the offspring will be free of the defective
gene. As long as the offspring are also tested, even carriers
can be bred from again as long as it is ensured that they
are only mated with a non-carrier cat. In this way, controlled
breeding programmes can be implemented so that important lines
can be retained within the gene pool.
What
tests are available and can carrier cats be detected?
Fortunately
a reliable test does exist for PK deficiency. It comprises
a DNA test that is performed on either a blood sample or cheek
swab. Only one laboratory, the Josephine Deubler Genetic Disease
Testing Laboratory at University
of Pennsylvania
in the US
, is able to do this
test. Affected cats as well as carrier cats can be identified
with the test. However the test is expensive ($75 per cat;
approximately ?43) and additional costs of taking samples
and shipping them to the US
further increase the
cost.
Why
worry about PK deficiency?
PK
deficiency is inherited and although predominately a problem
in the US
it is being reported increasingly in cats throughout Australia,
New Zealand
and Europe,
including the UK.
Approximately 2500 cats have been tested at Pennsylvania
since 1998, and around
15 per cent of those have been found to carry the defective
gene (personal communication, Giger U, 2005).
- As
described above, the clinical signs that develop can be
serious and life threatening.
- Because
initial clinical signs can be mild or go unnoticed, affected
cats may not be identified until after they have had large
numbers of offspring.
- Carrier
cats do not show any clinical signs at all. The disease
occurs when two carrier cats are mated with each other.
This is important because a large number of carrier cats
can arise in a population before PK deficiency is even noticed.
- With
any genetic disease, by the time the disease becomes an
obvious problem within a population it is much more difficult
to control and involves a lot more expense and heartbreak.
The
good news!
Although
we know that the disease is already present in the UK, affected
cats do not yet appear to be very prevalent in the UK. Identifying
carrier cats NOW could stop PK deficiency becoming a prevalent
disease in the UK.
- We
can reliably test for affected cats, including identifying
asymptomatic carriers.
- With
help from all Abyssinian and Somali owners, breeders and
breed clubs we can identify the prevalence of PK deficiency
in the UK
(see below project details).
- If
carrier cats are identified they can still be used for breeding
(and must be still used to retain a diverse gene pool) as
long as we ensure that they are NOT mated with another carrier.
How
can we tackle this disease together before it becomes a problem
in the UK?
- We
know that there are some affected cats in the UK
already, but we do
not know how many cats are affected or are carriers. It
is possible that there could be a large number of carriers.
- The
first step should be to try and establish the prevalence
of the disease within the UK
.
- In
order to do this we need to test as many Abyssinian and
Somali cats (breeding and neuter cats of all ages) as possible.
- Once
we know the prevalence of the disease in the UK
we can establish effective
breeding programmes to prevent carrier cats being mated
with each other, in order to eradicate PK deficiency from
UK Abyssinian and Somali cats, while maintaining the desired
qualities in these breeds.
- It
is extremely important that carrier cats ARE still bred
from (but in a controlled way) since if they are all neutered,
the gene pool will be significantly reduced which will increase
the risks of other genetic problems arising.
NB.
It is important that we recognise and tackle this problem
now to ensure that PK deficiency does not become a problem
in UK cats. However, we do not want to unduly worry owners
of Abyssinian and Somali cats, as to date, the disease has
been rarely recognised in the UK and many breeders are already
testing for the disease.
Current
project
We
have begun a project to try and determine the prevalence of
PK deficiency in UK Abyssinian and Somali cats. This is being
done in collaboration with Urs Giger from the Josephine Deubler
Genetic Disease Testing Laboratory at University of Pennsylvania,
whereby they will perform the testing for a much reduced cost
of $30 (approx ?16.50) per cat if we send them large
numbers of DNA samples in batches. In addition to performing
the actual testing, there are also several other steps involved
which further increase the cost of testing including the cost
of swabs, taking the cheek swabs from cats, extracting the
DNA from the swabs and sending the DNA to the US. We had applied
for a grant to enable all of these costs to be covered so
that there would not be any costs involved for owners. Unfortunately
we were not awarded this grant. However, the University
of Bristol
has raised funds to
cover the costs of the swabs, travel/taking the swabs, DNA
extraction (?10 per sample)
and postage, which just leaves ?16.50 per cat to be
raised to enable the project to go forward.
The
main problem we are currently encountering is that while most
breeders are willing to pay this reduced cost to test their
own breeding cats, not many people are willing to pay to test
neutered or retired breeding cats as it is of no significance
to breeding programmes whether these cats are carriers or
not. However, it is very important that we also test neutered
pet cats and cats of all ages, in order to obtain enough samples
to give us meaningful results regarding the prevalence of
the defective gene in the UK.
Furthermore since the numbers of breeding cats is relatively
small, it is unlikely we will be able to offer the low cost
of testing if we are only testing breeding cats.
We
therefore are unable to offer this reduced cost to enable
testing of specific individual cats, but are instead looking
to raise enough funds through donations towards the study
to enable us to test at least 150 Abyssinian and Somali cats
in the UK,
to include breeding and neutered cats of all ages. Although
we have already begun sampling some cats (we sampled approx
40 Somalis at the Somali show in March, and will be sampling
Abyssinians at the Abyssinian show in June) and have received
correspondence from a number of owners with approx 70
cats being offered for sampling), we are unable to process
these samples or take further samples until we have raised
sufficient funds. We are hoping that owners that were willing
to pay for their cat
to be tested will still contribute the same amount of money
to the project, but please be aware that this will be partly
used to help test other neutered and retired breeding cats.
We are hoping that the remainder of the required funds will
be donated by the breed clubs and other individuals.
Any
additional funds raised will be used to test additional cats
in the future and/or put into a fund to help with the treatment
of any cats suffering from PK deficiency.
Please
note that samples submitted for this study will be tested
in batches once the target number of samples has been taken,
as this is the only way that we can cover the costs for the
study. We can therefore not guarantee how long it will take
before results are obtained, as this will depend on how long
it takes us to raise the necessary funds and obtain all the
samples. We can only offer this reduced cost for testing for
samples submitted for the purposes of this study. Owners who
require test results more urgently will need to have their
cats tested by the conventional route (ie, sending samples
directly to University
of Pennsylvania,
cost $75 per cat).
If
you would like any further information regarding the study
or would like to make a donation towards this study or would
be willing to have your Abyssinian or Somali cat sampled,
please contact Andrea Harvey at The Feline Centre, University
of Bristol Veterinary School, tel. 0117 928 9558, fax 0117
928 9559, email: a.m.harvey@bristol.ac.uk
Please
send donations to Andrea at the above address. Cheques should
be made payable to The University of Bristol, but please include
a note stating that it is a donation for the feline PK deficiency
study. | 
