2005 WESTIE EDUCATION SEMINAR
Genetics, Pediatrics, Fading Puppy Syndrome - Part 1 of 2
Editor’s note: This is the handout that accompanied the very informative lecture given by Margret Casal at the WFA
dinner and seminar during the WHWTCA Specialty weekend. This newsletter features the Genetics portion of the lecture.
Pediatrics and Fading Puppy Syndrome will be covered in the winter edition of the WFA NEWS.
By Margret Casal, Dr med vet, PhD, Dipl ECAR (Reproduction)
Ryan Veterinary Hospital of the University of Pennsylvania
Fall 2005, NEWS
A. GENETICS
MODES OF INHERITANCE
Keywords
Gene: Basic element of heredity
that determines traits. A gene is
transmitted from parents to
offspring.
Allele: Alternative version of a
given gene
Locus: Location on a chromosome
where a gene with a specific
function resides.
Homozygote: Pairs of alleles of a
given gene are the same.
Heterozygote: Pairs of alleles of a
given gene are different.
Genotype: Genetic make-up (blue
print).
Phenotype: Observable properties
as determined by the genotype
(i.e. what the animal actually
looks like).
In a simple analogy, the genotype
can be described as the architectural
blueprint and the phenotype
as the building that is built
from the blueprint In the following
handout you will find information
on modes of inheritance,
an overview of genetic tests, and
a list of the most common or well
described genetic diseases in the
West Highland White Terrier.
Mendelian Genetics
(Simple genetic traits)
Autosomal dominant
inheritance
One allele of a given gene is
enough to determine the phenotype
(trait/disease allele D with d
being normal) and since the gene
is located on an autosome (not sex
determining chromosome) the
risk to males and females is equal.
Affected individuals are usually
heterozygotes (Dd). At least on
parent is affected, unless the
condition is the result of a new
mutation.
A.) Affected x normal matings
produce 50% affected offspring.
50% of the animals are normal
(phenotype) and are homozygous
in the normal allele (dd) and 50%
of the animals are phenotypically
affected and are heterozygous for
a normal and a trait determining
allele (Dd).
B.) Affected x affected matings
(rare) produce 75% affected
offspring. Only 25% of the offspring
are normal (dd), but 75%
are phenotypically affected but
genotypically different; 50% are
heterozygote (Dd) und 25% are
homozygotes (DD). Double doses
of dominant traits often lead to a
more severe phenotype that can
lead to early morbidity and mortality.
In autosomal dominant disorders
that are either severely deleterious
or that would be selected
against by breeders, most of the
cases observed in a population
will represent new mutations.
These will occur as rare sporadic
cases with no prior evidence of
their occurrence in related animals.
Autosomal recessive inheritance
An animal has to have two trait
determining (disease) alleles to
express the phenotype or be
affected (rr). Again both female as
well as male animals are equally
affected. An animal that has one
disease allele is phenotypically
normal but is called a carrier (for
the disease allele; Rr). The normal
individual has the “RR”
genotype.
A.) Carrier x normal mating produces
50% carrier offspring. 100%
of the animals are of a normal
phenotype. However, 50% of
these are homozygous in the
normal allele (RR) and 50 % of the
animals are carriers (Rr) and thus
heterozygous for a normal and a
trait determining allele.
B.) Carrier x Carrier matings
produce 75% phenotypically
normal offspring. However, 2/3
of these are carriers (Rr, Rr, RR).
Without specific tests it is often
impossible to distinguish the
normals from the carriers. 25% of
the offspring are affected (rr).
Autosomal recessive inherited
diseases are by far the most
common class of single gene
disorders in domestic animals. In
affected families, most affected
animals are born to clinically
normal parents that are carriers of
a mutant allele that has been
inherited from an ancestor that is
common to the sire and the dam
(some degree of inbreeding is
present).
X-chromosomal recessive inheritance
The gene of interest is located on
the X-chromosome: Therefore
two copies of the trait determining
(disease) allele are necessary
in females but only one copy is
needed in males for the phenotype
to be expressed.
Affected males are hemizygotes
(they only have one X chromosome).
Most affected offspring
are males, born of matings between
carrier females and normal
males.
In such matings, 50% of the sons
are affected and 50% of the
daughters are carriers.
Affected females only occur as
the result of matings between
affected males and carrier or
affected females. When the male
is the only affected parent, male
to male transmission of the
condition is never observed.
A.) Carrier female x normal male
matings result in 50% of the males
being affected (XcY). 100% of the
females and 50% of the males are
of a normal phenotype but half of
the females are carriers(XXc).
B.) Carrier female x affected male
matings (rare) produce 50% affected
offspring. Half of all males
are affected (XcY) and the other
half normal (XY); whereas half of
all females are carriers (XXc) and
the other half affected (XcXc).
In domestic animals, an important
feature of X-linked recessive
disorders is that in matings of
carrier females to normal males,
one half of the male offspring will
be affected, regardless of whether
the male is related to the female.
Thus, inbreeding is not a prominent
feature in X-linked recessive
disorders. This is in contrast to
autosomal recessive inheritance,
in which inbreeding is often
present, the parents of affected
offspring having inherited the
mutant gene from ancestors
which they share.
Complex Modes of Inheritance
(e.g. Polygenic traits)
Many diseases that are of great
concern to both breeders and
veterinarians are caused not by a
single gene but by the interactions
of several genes. To make matters
more difficult for the breeder and
the geneticist, the phenotype (or
the appearance of the trait or
disease) can often be modified by
environmental influences such as
nutrition or exercise. Examples
include hip dysplasia, elbow
dysplasia, heart disease and
epilepsy.
GENETIC TESTS
Test Mating - If, as is the case with
many genetic disorders, there is
no available laboratory test for the
carrier state, the only method by
(Continued from page 3)
which carriers can be detected is
test mating. The animal to be
tested is hypothesized to be a
carrier and is usually mated to an
animal known to be a carrier or
affected. If any affected offspring
are produced, we know that the
tested animal is a carrier and the
hypothesis is shown to be correct.
If, however enough normal
offspring and no affecteds are
produced, we can reject the carrier
hypothesis with some degree of
statistical assurance.
Biochemical testing - For some
genetic diseases, carriers are
identifiable by biochemical testing
(e.g., enzyme defects, clotting
factor defects). These assays can
be very useful and have been all
that has been available for a
number of years. However,
compared with the possibility of
DNA-based tests (see below), they
have a number of disadvantages,
including:
- Normal and carrier levels of
the enzyme/substrate often
overlap.
- A biochemical test may not be
possible for a specific disease
because the in vitro assay
(laboratory test) results do not
reflect the in vivo (real-life)
conditions.
- A test may be possible but is
not available because of expense.
- The enzyme or substrate may
be unstable and would not
survive shipment.
- Age matched controls are
necessary.
- There may be lab to lab variation
in the assay.
- The tissue needed for the assay
may be difficult to obtain.
Molecular Genetic (DNA-Based)
Tests for Affected and Carrier
Animals -
DNA-based genetic tests identify
differences in DNA sequences and
are of two different varieties. One
type of test, referred to as a mutation-
based test, recognizes disease-
causing mutations while a
second type of test, the linkedpolymorphism
test, recognizes
DNA differences that are near the
disease-causing gene and are used
to track normal and mutant alleles
of that gene through pedigrees.
While there are significant differences
between how these two
types of tests are developed and
how they are used, they both
involve the same basic techniques.
Essentially all DNA-based genetic
tests are based on the polymerase
chain reaction, and consequently
can be performed using a very
small amount of DNA from the
animal of interest. DNA-based
genetic tests have the advantage
(over biochemical assays) that
DNA is very easy to obtain by
fairly non-invasive techniques
and is very stable. Common
sources of DNA include: blood,
hair follicles, cheek swabs, semen,
and skin biopsies.
USES OF GENETIC TESTING
The more accurate the test, the
quicker a disease can be eliminated
from the breeding stock.
The parents and relatives can be
tested and their use as a breeder
established if they are not carriers
for the disease. Alternatively, if
we know that a champion dog is a
carrier of a specific disease but the
dog has all the best qualities for
its breed, then we are able to not
only test the bitch he is to be bred
to ensuring that she is not a
carrier, but we can also test the
offspring and retain only those for
future breeding that are not
carriers. Thus, we do not have to
loose the desired traits in the
champion dog.
The practicality of a genetic
screening program depends on
the following requisites:
Disease must occur in a defined
population (family, herd, breed)
with sufficient frequency to be of
economic or social importance.
The test for the heterozygote is
accurate and affordable. Removal
of heterozygotes (carriers) does
not deplete key genetic resources.
Test and control program should
be acceptable to breeders (precede
by educational and public relations
programs). Genetic counseling
is available to breeders. Breed
society has rules to insure control
is based on test results (registries).
GENETIC COUNSELING: IS IT
A GENETIC DISEASE?
This is probably the most common
question posed to the veterinarian
by the conscientious
breeder when confronted with a
puppy with an unusual illness.
What are the chances of it happening
again? What can be done
about it? First, it is most important
to make an accurate diagnosis.
Second, one needs to know if
the same disease has been seen in
related animals, in the same breed
or is known to be a genetic disease
in other species. If any of
these statements are true, then
one is most likely dealing with a
genetic disease. Or, to quote the
“father” of small animal genetics,
Dr. Donald Patterson, “Everything
is inherited until proven
otherwise!” Alternatively, if the
same disease has never been seen
in the breed and is not known to
be inherited in other species, then
one may be dealing with a developmental
disorder that may have
occurred during pregnancy as a
result from toxins, malnutrition,
medications, and such.
In summary, a disease has been
seen in the breed before or occurs
as a genetic disease in another
species, it is likely to be genetic in
the animal presented to the
veterinarian. If one needs to
make an educated guess as to the
mode of inheritance, then it is
helps to have an idea of the
biochemical cause of disease.
Most enzyme deficiencies are
autosomal recessive and most
structural defects are dominant.
These are just rules of thumb,
there are exceptions!
Editor’s note: This is the part two of the handout that accompanied the very informative lecture given by Margret Casal at
the WFA dinner and seminar during the 2005 WHWTCA Specialty weekend. This newsletter features the Pediatrics and
Fading Puppy Syndrome portion of the lecture.
Genetics, Pediatrics, Fading Puppy Syndrome - Part 2 of 2
By Margret Casal, Dr med vet, PhD, Dipl ECAR (Reproduction)
Ryan Veterinary Hospital of the University of Pennsylvania
Winter 2006, NEWS
B. PEDIATRICS IN A
NUTSHELL
Pediatrics is defined as the
study and treatment of children
in health and disease. Childhood
is defined as the period of life
between infancy and puberty. In
humans, there are volumes of
books with tables, graphs, and
guidelines such as the ¡°Denver
scores¡± which one can refer to for
assessment of growth and development
in a pediatric patient.
Unfortunately, we can only rely
on very few tables, our own
experience and the breeders¡¯
observations and thus may not be
completely aware of the diversity
present in the many different
breeds of dogs and cats. This
chapter deals with outward,
physical characteristics that are
common within the cat or dog
population and that can be used
either to simply determine the
age of stray animal or to assess if
a developmental delay is present
due to congenital or acquired
diseases.
History
Because of the unusual or nonspecific
clinical signs, it is of great
importance to obtain a comprehensive
history not only of the
patient himself, but also of the
littermates, parents and other
relatives. The history should
include number of ill animals, the
method by which they were
raised, their normal environment,
behavior of each puppy within
the litter, body weight curves,
duration and type of clinical
signs, and medications given.
The queen¡¯s or the bitch¡¯s history
should include vaccination dates,
estrous cycle (intervals and
duration), breeding practice,
medications or supplements
given during pregnancy, and
problems during pregnancy or
birth. Has the disorder with
which the patient is being presented,
been seen in previous
litters or in any of the relatives? In
certain cases, clients are advised
to bring the whole litter or at least
one healthy littermate including
the mother, so that the patient can
be compared with its
littermate(s). If the patient or its
littermates have not been vaccinated
yet, it may be better to have
them come in the back door, to
avoid exposure to all the infectious
diseases that may linger in
the waiting room.
Physical Examination
The physical examination of
the neonate and the juvenile
patient can be challenging. Owners
as well as littermates that
were brought in for comparison
can be quite distracting. Usually,
one cannot expect cooperation
from the youngest of our patients,
especially those that are already
aware of their surroundings.
They are so distracted by the new
environment that something as
simple as a menace reflex is
difficult to elicit. While everyone
knows how to perform a physical
examination, the following two
paragraphs focus on some of the
differences to adults and are
illustrated with some examples.
The list is not complete, but
comparison with the some of the
developmental landmarks described
below may be helpful in
determining other abnormalities.
For the physical examination of
a neonate, a pediatric stethoscope
with a 2 cm bell is helpful. A
digital thermometer allows rapid
measurement of the body temperature,
without causing great
discomfort. Because the neonate
can have a body temperature
lower than 94°F, a digital thermometer
that measures down to
92°F is practical. Neonates cannot
regulate their body temperature
during the first 2 weeks of life.
Therefore, they should be examined
on a warm, clean surface
rather than the cold metal table.
Checking the oral mucous membranes
(MM) assesses hydration
in the neonate, as their skin turgor
is not developed as in adults.
Moist MM are present in an
adequate state of hydration, but
tacky to dry MM indicate 5-7%
dehydration. At 10% dehydration, the MM are very dry and
there is a noticeable decrease in
skin elasticity. The neonate is
born with hair that covers most of
the body except the ventral
abdominal skin. Lack of hair or a
sparse hair coat may indicate
either a genetic abnormality of the
skin or premature birth. The
neonate normally has non-haired,
dark-pink, ventral abdominal
skin. Bluish or dark red discolorations
are indicative of a neonate
in distress (cyanosis or
sepsis, respectively). Other than
urine and feces, discharge from
any orifice is abnormal in the
neonate. The neonate¡¯s head,
body, limbs, and tail are examined
for symmetry and normal conformation.
The head is specifically
examined for open fontanels, cleft
palates, bulging from behind
closed eyelids, and formation of
the nose and external ears. The
presence of flattening or malformations
of the chest are noted
(e.g. swimmer syndrome, pectus
excavatum), as are bulges in the
neck area (e.g. gas in the esophagus,
ectopic heart, goiter). Neonatal
puppies are mildly pudgy
and should never be bloated,
which would be a sign of distress.
The abdomen and urachus are
especially examined for defects of
the abdominal wall and ventral
urine scalding (e.g. cannibalism
due to an overzealous mother,
ventral closure defects, persistent
urachus). The genitals and the
anus are checked for patency by
stimulating urination and defecation
using a moistened cotton
ball. The presence of hair coat
abnormalities over the dorsum
may indicate the presence of a
spina bifida. The tail is examined
for muscle tone, length, curliness
and kinks. Abnormalities in tone
may be indicators for associated
defects or problems (e.g. abnormal
innervation of the distal
pelvis).
The physical examination of
the older pediatric patient follows
the general guidelines as in
the adult. However, many metabolic
diseases with a genetic basis
begin becoming apparent between
3 - 5 months of age. They
are usually of a progressive,
degenerative nature characterized
by failure to thrive and clinical
signs specific to the disease.
Comparison to littermates is
extremely useful in these cases,
but not always possible. As
above, the whole patient is examined
for symmetry, conformation,
body weight, and stature. The
eyes deserve special attention, as
many disorders especially infectious
and hereditary diseases can
be picked up at a very early age
by a careful fundic examination.
Ventro-lateral strabismus (down
and out cross-eyed) may indicate
the presence of a hydrocephalus,
while nystagmus, either horizontal
or vertical, may point towards
inner ear infections, polyps in
cats, trauma or other CNS disorders
(hereditary or infectious).
The neck again is examined for
bulges in the esophagus (e.g. gas
indicating a possible
megesophagus or vascular ring
anomaly; solid swellings indicating
foreign bodies) and soft tissue
lumps in the thyroid area (e.g.
goiter). The limbs are examined
for malformations and especially
pain (e.g. hypertrophic osteodystrophy,
panosteitis, elbow and hip
dysplasia; vaccine reactions;
trauma). Abnormal conformation
of the genitals may indicate
hermaphroditism, intersexes,
cryptorchidism, or future problems
(e.g. skin fold pyoderma in
bitches with a small, tucked-in
vulva). Urine scalding may be
present in animals with chronic
urinary tract infections and/or
incontinence (e.g. immune deficiencies,
bladder diverticulum,
ectopic ureters, hour glass bladders,
kidney malformations).
Vaginal discharge or the presence
of hair stuck together at the
ventral commisure of the vulva in
bitches before their first heat is a
common finding with puppy
vaginitis. Fecal staining may
indicate diarrhea, fecal incontinence,
or the patient's inability to
groom itself due to a more severe
disorder.
Normal Development
During the first week of life
newborn puppies sleep throughout
most of the day (80%), and
nurse vigorously for a short
period of time every 2-4 hours.
As the brain is not completely
developed at birth, neuromuscular
reflexes are missing and the
only motor skills present are
crawling, suckling, rooting,
righting, and distress vocalization.
The neonates only respond
to stimuli such as odor, touch,
and pain. The bitch initiates
urination and defecation by
licking the urogenital area. At
three days of age, puppies should
be able to lift their head, and by
one week crawl in a coordinated
manner. Puppies are unable to
maintain their body temperature
during the first few days of life.
At this time, heat is produced by
brown fat metabolism, which is
under the control of the sympathetic
nervous system (nonshivering
thermogenesis), and the
shiver reflex does not develop
until after the first week of life.
Therefore, their body temperature
at birth (94.5-97.3°F) is lower than
in adults and rises to 93.7-100.1 F
during the first week of life. Heart
and respiratory rates may be
irregular at birth (P=160-200/min,
R=10-20/min) and there is no
abdominal component to their
breathing. During the first week,
the neonates begin to adjust to the
new, extra-uterine physiology
(200-220/ min, R=16-35/min).
The umbilical cord dries out
during the first day of life and
should have fallen off by day 3-4.
The flexor tone present at birth
switches over to extensor tone
after the 4th day of life.
During the second week of
life, puppies begin to crawl and
their body temperature slowly
rises towards normal adult levels.
Puppies will have doubled their
birth weight by 10 – 12 days and
they begin to open their eyes at 10
– 12 days of age. Remnants of
hyaloid artery attached to
posterior lens capsule may be
seen for a few days after the eyes
open. The external ear canals
open at 14 – 16 days of age. The
iris is not very well pigmented,
has a blue-gray color, and the
cornea is slightly cloudy due to
increased water content. By the
end of three weeks of age puppies
should be able to stand and have
good postural reflexes.
At the end of the third,
beginning of the fourth week of
life, the body temperature has
reached 99.3° - 101.5°F. At two to
three weeks of age deciduous
incisors and at 3 weeks deciduous
canines begin erupting in
puppies, respectively (Table 2).
During this time puppies attempt
to walk, and urination and
defecation become voluntary.
They begin to take an interest in
their environment as their
auditory, visual, and motor
functions are developing.
However, their sight is still poor
at this time. By the end of three
weeks of age, the puppies may be
encouraged to eat solid food.
By the end of 4 – 6 weeks of
age, the iris color changes into the
adult color and the mild corneal
clouding disappears leading to
greatly improved vision. By 6
weeks of age the testicles should
be descended in the dog. Puppies
should be able to eat solid food
without encouragement. The
bitch will start weaning the
puppies at 6-10 weeks of age. The
optic disk may still appear
smaller than in adults and has a
different color due to incomplete
myelination but the retinal vessels
look similar to adult vessels. By
the end of 8 weeks, all of the
deciduous teeth have erupted in
both puppies. Because of extreme
breed differences in dogs, puppies
should be compared to litter
mates to assess growth rates and
weight gain.
Examination of the eyes reveals
a blue-gray tapetum until
reaching adult colors at about 4 –7
months of age. By four months of
age most breeds of puppies will
have reached 50% of their
expected adult weight. At this
age, they lose their deciduous
teeth and begin replacing them
with permanent teeth, which is
completed by 6 – 7 months of
age. With a few exceptions (large
breed dogs, Basenjis, sight
hounds) this coincides with puberty.
C. THE FADING PUPPY
SYNDROME
The fading puppy syndrome is
characterized by a pattern of
increasing weakness, failure to
nurse, weight loss, hypothermia,
and death prior to weaning,
usually in the first two weeks of
life. It is actually not a single
disease entity but rather common
clinical signs caused by different
underlying diseases processes.
There are no obvious clinical
signs or pathological findings,
such as poor mothering, mastitis,
neonatal canine herpes infections,
or cleft palate, etc. Fading
puppies usually have a low birth
weight to begin with, are restless,
and cry often beginning shortly
after birth. In studies of purebred
kennels from the 1950’s and 60’s,
it was shown that 20-30% of
puppies died before reaching
weaning age. However, these
studies were performed at a time
where vaccines were not as
readily available and diagnostics
were less detailed. Thus, it is
possible that some of the losses
may be attributed to infectious
diseases or non-recognized
genetic defects. Studies
performed in the 80’s revealed
that of 500 puppies about 30%
had died before weaning
(stillborn puppies were excluded).
In 55% of these puppies, no cause
of death was found even after
careful histopathological and
microbiological examination.
This is consistent with our own
findings in which we lose about
16% of pups before weaning age.
These are dogs that are housed in
a controlled, specific-pathogenfree
environment.
There is a report of surfactant
deficiency in lungs of fading
puppies, but it was not clear if
this was the defect leading to
death or if this was secondary to
the dying state. While the fading
puppy syndrome is not a single
disease entity, there is evidence
that a large proportion of the
neonatal mortality is due to
homozygosity for deleterious
genes. One study examined
differences in mortality between
purebred populations and
outbred populations; that is,
offspring of dogs of one breed
being bred to dogs of another,
unrelated breed. Another study
looked at a colony of purebred
beagles and found that there was
a 26% mortality rate among
puppies with a lower (0.26)
coefficient of inbreeding to 75%
mortality among puppies with a
high (0.67) coefficient of
inbreeding. The most obvious
difference between kitten and
puppy mortality is the biphasic
nature of deaths in kittens; while
most of the fading puppies die at
the time of birth, kittens die at
birth and at the time of weaning.
Despite these differences and in
light of the findings in both
puppies and kittens, every
attempt should be made to obtain
a diagnosis. Unfortunately,
infectious diseases develop too
rapidly in the neonate to obtain
results quick enough to be of
value to the affected individual
but may be useful for litter mates.
Urine metabolic screening and
post mortem examinations should
be performed on “fading”
neonatal and juvenile animals.
Although most cases will not, at
our present level of knowledge,
yield a positive diagnosis even
with the use of microbial cultures and histopathological
examination of fixed tissue, the
performance of the post mortem
examination is essential to
diagnose those conditions which
are recognizable. Also, because of
the evidence that close inbreeding
increases the rate of fading
puppies, matings, which
consistently produce a high
percentage of neonatal deaths,
should be avoided.
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