Pituitary
Dwarfism in the German Shepherd Dog
Part One of a Three-part
Set of Articles on Dwarfism
(original
version appeared in Dog World, Dec. 1984)
(Warning: Pictures are slow to download. Please be patient.)
by Fred Lanting
Dwarfism is a condition of abnormally small stature, and usually
is characterized by altered body proportions. Dachshunds, Basset Hounds, and
Corgis are examples of achondroplastic dwarfs; they
have more or less normal-sized torsos and heads but shortened limbs, and are
accepted as typical of their breed. Alaskan Malamutes, on the other hand, are
not considered acceptable if they have their particular blood cell related
disease. In that breed, both achondroplastic dwarfism
and hemolytic anemia are inherited as pleiotropic
conditions, meaning a single gene giving multiple phenotype effects. Additionally,
there are dwarfism abnormalities in other breeds such as pseudochondroplastic
dysplasia in Miniature Poodles.
In the German Shepherd Dog, however, there is a little-known
dwarfism that yields a nearly perfectly proportioned but considerably
downsized version. An acceptable term to use would be proportional or pituitary
dwarfs, even though all types of dwarfism have their origins in that gland. The
fact is (or was until this article appeared), many do not know about the
existence of this type of dog, even though it is not all that rare. Possibly because
of the large-scale linebreeding by a West Coast
kennel that produced winning dogs, the incidence rose for a number of years in
the U.S. Due to linebreeding on certain British and
German dogs, there was a noticeable number appearing both in England and
Australia, countries which rely heavily on German lines. One genetic analysis
of Australian data indicated that two dwarfs might be expected out of 1000 pups
when “any dog” is bred to “any bitch”. The recurrent risk for any dog or bitch
bred to a parent of a dwarf is seven per 1000; a parent of a dwarf to a
half-sibling of a dwarf is 272 per 1000; and parent of dwarf X parent of dwarf
is 235 per 1000. The roughly 25% risk in the latter two matings
is typical of what one would expect when two normal carriers of a simple Mendelian trait are bred to each other.
Of course, that 25% is an average. I recently (1984)
examined pups from a litter of six in which three were pituitary dwarfs, but
both parents were of normal size. Now remember, these were not abnormal in
proportions, only in size and unseen body chemistry. The little Shepherds I
examined that year had beautiful temperaments, and were active and apparently
healthy at the time I first saw them at almost four months of age. They weighed
about five pounds, while a normal littermate was about 32 pounds. There was
something that had not appeared in the scientific literature but which I
noticed in this litter, as well as in photographs of other litters: pituitary
dwarfs seem to squint in bright sunlight more than do their normal siblings.
Another facial characteristic of miniature Shepherds is a fox-like appearance,
coming from wide-set ears. I believe this to be a result of disrupted
proportions of skull vs. base of the pinna (ear
shell), which to some extent is seen in Welsh Corgis also. A somewhat snipey (pointed) muzzle is due partly to a shortening of
the skull and, in some individuals, a slight overbite.
The
Some non-show lines occasionally come up with pituitary dwarfs,
such as the white German Shepherd bitch I found, who
at two years of age weighed only 15 pounds (some get as heavy as 30 pounds or
so, but most are smaller). Her skin was milk-chocolate in color, thin,
wrinkled, dry, and lacking in elasticity or tone. She had almost no hair on the
trunk, neck, and wear areas such as buttocks, etc. Primary or guard hairs were
present on a few areas of the head and feet, and the rest of the body was
either bald or lightly covered with secondary hairs (puppy fuzz or undercoat),
which were easily pulled out with the fingers. All these signs are very common
in these animals as adults, with the skin ranging from brown to gray in color.
Dogs which would otherwise be plush or long-coats usually look like Chinese
Crested Dogs — if they live to maturity — with feathery fringes around the ears
and feet, and bald elsewhere unless treated with growth and/or thyroid
hormones.
External or obvious characteristics aren’t the only things
different about pituitary dwarfs. Blood chemistry tests show that hormones that
are supposed to be circulating may be absent or at very low levels. The methods are too involved
to go into here, but briefly stated, there are ways to assay the activity of
endocrine glands and amounts of their secretions. The hypophysis
(commonly known as pituitary gland) is the “master” gland of the body, situated
in the center of the head at the base of the brain. It produces a number of
hormones, including GH (growth hormone). IFG (insulin-like growth factor) circulating
in the blood is interdependent with GH. The pituitary gland is affected by others,
but it is more the director of the body’s other endocrine glands, such as the
thyroids and gonads. The thyroids have a say in the maturing process,
metabolism, development of form and behavior, and physical and mental activity.
Muscular weakness and the skin/hair problems described above are due to
inadequate or absent thyroid
activity, which in turn is due to lack of proper direction from the pituitary.
Your veterinarian can explain T3 and T4 to you if you wish to study thyroid
function more fully.
The effects of this type of dwarfism can be mitigated or
delayed by administration of thyroxine and GH, but
this is a very expensive proposition at present. It is thought that if
recombinant genetics (gene-splicing) and RNA production of human growth hormone
becomes feasible, the price may go down. Dogs apparently respond to human GH,
but not the other way around. Eventually, at the age of normal skeletal
maturity or a bit later, the growth plates in the dwarf’s bones close and no
further growth is possible, regardless of GH injections. Another problem in
treating the condition is that most owners don’t present the pups to a
veterinarian until their littermates are twice their size. The affected pup
grows normally until three to eight weeks, when the brakes are applied and the
normal siblings leave him behind in growth.
Although it is possible that pituitary dwarfism in the GSD
is a polygenic disorder of a threshold nature, most investigators so far
believe it a result of a simple autosomal (not
sex-linked) recessive trait. In most characteristics inherited in this simple
method, the recessive gene can be hidden for many generations before it is
paired with another identical recessive gene. Genes operate in pairs, and
only when both of the pair are the recessive alleles, does the trait manifest itself.
When only one recessive gene exists, its dominant partner dictates the
normal or dominant phenotype characteristic. It’s like a Labrador Retriever that inherits one gene for black coat color and
gets the recessive gene for yellow from his other parent. He himself is
black, because that first gene is dominant over yellow and does not allow the
yellow to predominate or show in the phenotype (appearance).
However, some recessive traits are only partially covered
up by the dominant member of such a heterogenous
gene pair. Often, one can see the faint hint of a saddle in a sable German
Shepherd Dog which is heterogenous (has one sable
gene and one black-and-tan gene). Similarly, it may be possible to “see” other
recessives through the use of blood tests, examination of the eyes retina,
etc. Achondroplastic dwarfism in the Malamute, for
example, is connected with a blood cell disorder, both being pleiotropic results of the same defective gene. Because of
the effect the pituitary has on thyroid function and on other glands, it may
become possible to detect the “carriers” in a GSD litter among whose members
some dwarfs have appeared. In a statistically typical litter of 12 produced by
two normal-appearing carriers of the recessive gene, suppose three homozygous
dwarfs and three pups without the gene. The other six are heterozygous carriers
and appear normal (like their parents) but will contribute one recessive gene
to each pup they produce in the future.
It is unfortunate that such abnormalities are often
hidden from the public by breeders and owners who are fearful, mercenary,
proud, or ignorant. Most pups are sold about the time the growth rate
difference begins, so many cases reported to veterinarians have been “single
incidences” as far as the buyers and their vets could tell. Others may be put
down by embarrassed breeders who don’t want it known they have produced such
anomalies. Since the health of pituitary dwarfs is more precarious than that
of normal pups, it can be assumed that many that die at birth, are resorbed during gestation, or die before the trait begins
to appear, may be dwarfs. The Arkansas breeder who called me to ask what she
had, and invited me to see them, upon discovering half her litter were dwarfs,
decided not to put them down and cover up, but rather care for them and share
their stories with responsible breeders and veterinary researchers. She even intended
to train and show at least one in obedience and was, at this first writing, hoping
to persuade the AKC that there are no rules against it. From such an openminded approach, we may be able to make an educated
guess as to pedigree origin of the defect, plus discover some means of
identifying normal-appearing carriers.
She even briefly entertained hopes to try breeding these
dwarfs with each other or with siblings or parents, trying to duplicate the occurrence.
I guessed (correctly) that she might find it difficult. Development of the
gonads varies from atrophied testicles and absence of estrus to normal
testicles and seasons. If she had been successful in reproducing the
condition, we may have seen the AKC faced with difficult decisions: they cannot
justify withholding registration privileges or show/trial eligibility because
of the pure pedigree, so do they create a separate variety within the breed, as
exists in Dachshunds, or a separate breed as they did with
One problem I can foresee in attempts at breeding these,
besides lowered fertility, is whelping. Pituitary dwarfs start life off at
normal size, which for a Shepherd is in the neighborhood of one pound, give or
take about four or five ounces depending on the number of whelps. If a dwarf
bitch were impregnated (artifically, of course) by a
normal-sized carrier male, some of the whelps could be normal sized and the
bitch would not be able to pass them or possibly even carry them without damage
to them and/or herself. If a normal-sized carrier bitch were bred to a dwarf
male, it shouldn’t be any more of a problem
than when two normal-sized dogs with the recessives are mated together. So
far, nobody has engineered such a mating, to my knowledge.
Size of the dwarfs varies a great deal. As of this (1984)
writing, the ones I have examined were 5.5 months old and weighed seven pounds. Others at
skeletal maturity (when growth plates close and bones don’t grow any longer)
have been reported to weigh from under 15 pounds to slightly over 30 pounds.
Normal weights for GSD bitches are 55-75 pounds, and for males 70-90 pounds.
It’s not unusual for a bitch to give birth to ten pounds of puppies, plus carry
the extra weight of fluid and placental tissue. For a dwarf bitch, that
percentage would be impossible, I would think.
The variable size of the pituitary dwarf Shepherds
reported so far is an indication of the possibilities that the trait
itself could be a threshold polygenic trait (unlikely), but the
variation could also result from modifier genes governing varying time of
growth cessation. There are some differences in absence, presence, or level of
growth hormone in untreated dwarfs, and those that grow to be larger than
others before the growth plates close may simply have
more GH. Since the “problem” has been swept under the rug so often, and is rare
enough to begin with, professors at veterinary colleges are in disagreement
over the meager information that is available. Thanks to the breeder in
This type of pituitary dwarfism involves the German
Shepherd Dog, but a breed from the Russia-Finland border, called the Karelian Bear Dog, is also affected. The reason is that the
Karelian (Finnish spelling is Carelian)
has the GSD as part of its ancestry, and the affected individuals had some GSD
carriers in their pedigrees. The scientific literature has reported one
Yorkshire Terrier, one “Toy Pinscher”, and two “Spitzes” as well, but it is highly doubtful that those are
the same genetic defect. If I find several examples, as there are in the GSD,
I’ll withdraw my doubts.
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Three
littermates, two with the pituitary dwarfism defect. It is probable that the
intermediate-size pup on the left was able to utilize more growth hormone and delay the closure of physes (ossification of cartilage). Photo courtesy Prof. E. Andresen, |
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Priscilla,
a four-year-old pituitary dwarf.
Her coat was maintained by regulating her thyroid hormone levels. |
The author with two littermates of Priscilla at about 4
months of age. |
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Osteochondrodysplasias, Leg Deformities, and Dwarfism in the Canine
(Part Two) |
Copyright 2001 Fred Lanting, Canine
Consulting. Mr.GSD@juno.com. All rights reserved. Please view his site Real GSD.
NOTE: A well-respected AKC
and Schaferhund Verein
judge, Mr. Lanting has judged in more than a dozen
countries, including the prestigious FCI Asian Show hosted by Japan Kennel
Club, the Scottish Kennel Club, a Greyhound specialty in