Osteochondrodysplasia in Scottish Fold cats - sundust cats
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Clinical
Osteochondrodysplasia in Scottish Fold cats
R MALIKa, GS ALLANa, CR HOWLETTb, DE THOMPSONc, G JAMESd, C McWHIRTERe and K KENDALLf
Objective To better characterise the bone and joint problems which can develop in Scottish Fold cats.
Design Retrospective study of cases seen in five veterinary clinics and radiographic survey of cats in a cattery.
Results Six Scottish Fold cats (four castrated males, two spayed females) aged between 5 months and 6 years were
presented for signs of skeletal disease including lameness, reluctance to jump, a stiff stilted gait, short misshapen distal
limbs, swelling of plantar tarsometatarsal regions and short thick inflexible tails. A further four cases (one male, three
females, 15 months to 11 years) were identified by radiographic screening of a cattery. A diagnosis of osteochondrodys-
plasia was based on characteristic radiological findings including irregularity in the size and shape of tarsal, carpal,
metatarsal and metacarpal bones, phalanges and caudal vertebrae, narrowed joint spaces, and progressive new bone
formation around joints of distal limbs with diffuse osteopenia of adjacent bone. A plantar exostosis caudal to the calca-
neus was present in advanced cases. In all nine cases where pedigree information was available, affected cats
allegedly originated from the mating of a Scottish Fold to a cat with normal ears. The severity and time of onset of phys-
ical signs, and rate of progression and extent of radiographic abnormalities, varied from case to case. Limited histolog-
ical observations suggested the underlying problem may be an osteochondrodysplasia, related to inadequate cartilage
maturation. Clinical signs were ameliorated by administration of pentosan subcutaneously in two of three cats in which it
was trialled, and one of these also benefited from an oral glycosaminoglycan preparation.
Conclusions Clinical and radiological findings were ascribed to defective maturation and function of cartilage, partic-
ularly in the distal limbs, ears and tail. As all Scottish Fold cats suffered from osteochondrodysplasia of some degree,
the best solution would be to avoid using fold-eared cats for breeding and instead use Scottish shorthairs.
Aust Vet J 1999;77:85-92
Key words: Cat, Scottish Fold, osteochondrodysplasia, osteodystrophy, chondrodysplasia, cartilage, autosomal dominant, lameness.
Fold Scottish Fold
PO Orally
SFOCD Scottish Fold osteochondrodysplasia
SC Subcutaneously
Although fold-eared cats were first (prick, pert or upright) ears from this
T
he Scottish Fold is one of the
rarest purebred cats in Australia. bred in 1961 and registered in 1966, type of mating are known as ‘Scottish
The defining feature of the breed there was no mention of any skeletal shorthairs’ in North America and
is its ears, which fold forward (Figure 1). deformities until 1971 when progressive Australia (synonym: Scottish Fold S/E
The ear fold is not present at birth but bony abnormalities and a crippling [straight ear], Scottish Fold variant; J
develops at 3 to 4 weeks of age. The lameness were recognised.1,4 Inheritance Sternbeck personal communication).
breed was developed in Scotland by studies were based on three different A limited description of SFOCD was
mating a queen, affected by a natural types of matings: skeletally normal Folds given initially by Jackson,5 and more
mutation, to local farm cats and British to skeletally normal Folds, affected Folds details for a single case were reported
Shorthairs.1 Preliminary genetic analyses to skeletally normal Folds, and affected recently.6 The earliest and most consis-
suggested that the defining genetic Folds to normal cats. Kittens with radio- tent finding is a tail with an abnormally
abnormality, which causes the auricular logical lesions were only produced from thick and inflexible base. The feet are
cartilage to fold, is inherited as a simple Fold-to-Fold matings.5 It was inferred short, and the underlying skeletal
autosomal dominant trait, and the fold- that affected kittens are homozygous for changes result in reduced ability to
ear allele is designated Fd.2,3 the Fd gene: thus normal cats are fdfd, support weight, an abnormal gait and
skeletally normal Scottish Folds are ultimately lameness. In affected
Fdfd, and Scottish Folds with osteodys- homozygous individuals, joint lesions
aDepartment of Veterinary Clinical Sciences, The
trophy are FdFd. It has been suggested progress until the cats are unable to
University of Sydney, New South Wales 2006
bSchool of Pathology, The University of New that breeding of fold-eared cats should walk. Lesions are evident radiographi-
South Wales, Kensington, New South Wales 2052 be limited, and if used at all, they should cally in kittens aged 7 weeks.5 The meta-
cKu-Ring-Gai Veterinary Hospital, 290 Bobbin
be mated only to normal-eared cats.5 physes of metatarsal and metacarpal
Head Road, Turramurra North, New South Wales
The breed was banned in England in bones are distorted with widened
2074
dSylvania Veterinary Hospital, 335 Princes 1974, but continued to evolve in the physes, and similar but less marked
Highway, Sylvania Heights, New South Wales USA where initial imports from the UK changes are evident in phalanges. This
2224 were outcrossed to numerous other results in decreased length and abnormal
eChatswood Veterinary Clinic, 80 Sydney Street,
Willoughby, New South Wales 2068
breeds.1,4,5 Fold-to-Fold matings were shape of these bones and shortening of
fEast Chatswood Cat Clinic, 346 Penshurst Street, avoided, so only about 50% of offspring distal limbs. The caudal vertebrae are
Willoughby, New South Wales 2068 had folded ears. Kittens with normal reduced in length, with widened
Aust Vet J Vol 77, No 2, February 1999 85Clinical
endplates. After age 6 months, gross what small (1.3 kg) for her age (14 become arched and bilateral palpable
plantar exostoses of tarsal and metatarsal weeks). It was presented for evaluation swellings of the tarsi became obvious to
bones become clinically and radiograph- of left hindlimb lameness 5 weeks later, the owner. Radiographs demonstrated
ically evident. Histologically, tissues weighing 1.8 kg. Lameness was thought changes consistent with SFOCD, and
from affected kittens show defective to be worse in the mornings. The distal the cat was euthanased at its owners’
bone formation at growth plates, with hindlimbs were abnormally short and request. Necropsy was not permitted.
disordered chondroblast proliferation misshapen, with excessively curved
and irregular groups of cells arranged toenails. Radiographs of the distal Case 3
haphazardly. Physes are grossly extremities and tail at 21 weeks showed A 16-month-old male Fold (4.0 kg)
expanded with deficient ossification, changes consistent with SFOCD, was presented for right forelimb lame-
irregular mineralisation, defective including marked malformation of ness of 3 weeks duration. It had been
remodelling and supernumerary centres metatarsal and metacarpal bones, considered normal when vaccinated at
of ossification. phalanges and caudal vertebrae. The 14 weeks (1.8 kg), and castrated 6 weeks
The original observations on SFOCD proximal tail was thickened and inflex- later. The affected paw was painful on
were published in a journal not widely ible (Figure 2). No treatment was palpation. Radiographs under general
available outside the UK. Subsequent prescribed and the kitten was spayed. anaesthesia demonstrated changes in the
accounts paraphrase these observations, Radiographs at 6 and 11 months limbs consistent with SFOCD,
but consider the problem as a chon- showed progression of skeletal abnor- including malformed metacarpal and
drodysplasia.7 However, it was noted malities, with development of periartic- metatarsal bones and periarticular new
that problems may occur later in life in ular new bone, narrowed joint spaces bone formation. The cat was treated
some Folds, in which radiographic signs and apparent loss of bone density in with pentosan polysulphate (3 mg/kg
are initially absent,1 and that heterozy- distal limbs. At this time the cat was said SC once weekly for 4 weeks), which
gotes may develop skeletal disease that is to ‘seize up’ during play. Pentosan poly- produced some reduction in lameness.
much milder than observed in homozy- sulphate (3 mg/kg SC every week for 4 The cat died after a traffic accident 1
gous Folds.4 weeks) was prescribed. According to the year later and was submitted for
This article concerns six cats that owners, this reduced signs of dysfunction. necropsy. Tissues were collected for
developed signs of SFOCD. At least five Current therapy is a complex glyco- histopathological examination. Inspec-
of them were allegedly the progeny of saminoglycan preparation (Cartiflex, tion at necropsy showed foreshortening
mating a Fold to a non-Fold. A radio- Pharmedica, 2 g PO daily for 30 days, of the distal limbs.
graphic survey in a cattery suggested then 2 g twice weekly) that also appears
that, contrary to contemporary wisdom, to reduce the cat’s discomfort. Case 4
this was likely a widespread problem in An 11-month-old male Fold was
this breed. Case 2 presented for limping. The cat had been
A 6-month-old castrated Fold was considered normal when vaccinated at
Case reports presented for an abnormal gait which 18 weeks and castrated at 8 months. It
Case 1 had become noticeable over the had been lame for several weeks, and
A female Fold (Figure 1) brought in preceding 3 weeks. The cat’s movements appeared to avoid jumping from any
for vaccination was considered some- had become stiff and stilted, its back had height. Hard, symmetrical, non-painful
Figure 1. The cat in case 1. Note the forward-folding ears. Figure 2. The thickened, shortened, inflexible tail of the cat in case
86 Aust Vet J Vol 77, No 2, February 1999Clinical
swellings were palpable around hindclaws need regular trimming as they originated from the mating of a Fold to
tarsometatarsal regions and similar but tend to grow abnormally. a cat with normal ears, this being a
less prominent swellings were evident Scottish shorthair in seven instances,
around carpometacarpal regions. Mild Further cases and a British Shorthair in one. In six
bilateral patellar luxation, worse on the To further assess the prevalence of cases the queen was a Fold, while in
left, was present. Hindlimb radiographs SFOCD, distal limbs and tails of three cases the tom was a Fold. Thus
demonstrated changes consistent with ‘asymptomatic’ breeding stock from a none resulted from a Fold-to-Fold
SFOCD, including abnormalities in commercial cattery were screened radio- mating. Several of the cats were closely
shape and size of metatarsal bones, with graphically. Five cats were examined, related: cats in cases 2 and 3 and one of
milder changes in the distal forelimbs. four Folds (three females of 4, 5 and 11 the cats from the cattery had the same
Samples of synovial fluid from carpus years; one male of 15 months of age) parents, while cats in cases 4 and 5 and
and tarsus showed no abnormalities. and a Scottish Shorthair (male, 9 years). another cat from the cattery were the
The cat was re-presented 10 months All Folds had radiographic changes product of another parent set. Of the
later because of worsening signs. The indicative of SFOCD, ranging from very remaining three cats, two came from
owners considered the cat to be in pain, mild (15-month-old male) to severe (4- entirely different lines.
particularly on cold mornings. It could year-old female), but no abnormalities
not jump, and movement was difficult were detected in the Scottish Shorthair. Radiographic findings
even after it had ‘warmed up’. Radiog- The changes observed in the worse Radiographs provided the basis for
raphy demonstrated progression of affected 4-year-old female Fold were confirming a diagnosis of SFOCD.
skeletal lesions, with periarticular new more extensive and severe than those of Changes were similar in all cats, and the
bone formation resulting in ankylosis of the 11-year-old female. The tail was two cats subjected to serial radiography
distal joints. The owners requested affected in all Folds except the 5-year- showed progressive disease. The rate of
euthanasia of the cat. Tissues for old female. progression differed between cats, as did
histopathological examination were the age of apparent onset of clinical
collected at necropsy. Mating data signs. Arbitrarily, we divided the radio-
Pedigrees were obtained for nine Folds graphic changes into two components.
Case 5 with SFOCD: cases 1 to 5 and the four Firstly, there were skeletal deformities
A 1-year-old spayed Fold was affected Folds in the cattery. All cats which were thought to result from
presented for right forelimb lameness of
a few days duration. During physical
examination, pain was detected on
palpation of the forelimbs. Radiographs
demonstrated changes consistent with
SFOCD, with shortening and outward
bowing of metacarpals two and five, but
little periarticular new bone formation.
Similar changes were noted also in the
hindlimbs. The tail was unremarkable
radiographically.
Case 6
A 6-year-old castrated Fold was
presented for investigation of a loco-
motor problem. The cat had been
recently rehoused, and its new owner
noted the cat had a stiff, short and some-
what immobile tail, and misshapen and
splayed claws. The cat’s gait was
abnormal, it limped occasionally and
flinched and vocalised when picked up.
Radiographs showed changes consistent
with SFOCD; there was little bony
deformity, but periarticular new bone
was prominent and had resulted in Figure 3. (A) Dorsopalmar radiograph of the distal forelimb of the cat in case 3 at 16
ankylosis of intertarsal and months. The metacarpal bones and phalanges are shortened somewhat, the distal radial
tarsometatarsal joints. The cat was and ulnar growth plates are of an abnormal shape, and there is ‘mushrooming’ of the
treated with pentosan polysulphate (3 distal radial metaphysis. There is also extensive periarticular new bone formation around
mg/kg SC once weekly for 4 weeks) carpal and proximal metacarpal bones that has resulted in bony ankylosis. Intercarpal
without discernible improvement. Signs and carpometacarpal joint spaces appear almost completely obliterated. A dorsopalmar
were unchanged 1 year later. The cat’s radiograph of a normal cat’s metacarpals is provided in (B) for comparison; note the
difference in the length of the metacarpal bones and phalanges.
Aust Vet J Vol 77, No 2, February 1999 87Clinical
abnormal bone growth during develop-
ment, and corresponded to the anatom-
ical finding of shortened distal extremi-
ties. These changes were conspicuous in
cases 1, 3 and 4, although similar but
more subtle changes could be discerned
in all other cases. In case 3, for example,
the metacarpal bones were shorter than
normal, of abnormal shape (proximal
and distal ends disproportionately large)
and of inconsistent length (metacarpals
three and four disproportionately
shorter) (Figure 3A). Similarly, the
phalanges were of abnormal size and
shape. Deformities of the distal appen-
dicular skeleton were even more promi-
nent in case 1: all metatarsal and
metacarpal bones were shortened and
malformed, some having a bent shape
with swollen proximal and distal ends,
while phalanges were similarly affected
(Figures 4 and 5). Radiographs of the
tail were not performed routinely, but
cats with a short thick tail invariably had Figure 4. Dorsopalmar radiograph of the
caudal vertebrae that were shorter and distal hindlimb of the cat in case 1 at 6
wider than normal (Figure 6). Interest- months. The metatarsal bones are shorter
ingly, the tail was unaffected in case 4 than normal, misshapen asymmetrically,
and one of the cattery cats despite severe with swelling of the proximal and distal
progressive appendicular disease. ends and bending of shafts. Intertarsal
Secondly, there were additional bone and tarsometatarsal joint spaces seem
changes evident in sequential radio- normal, and periarticular new bone forma-
graphs that suggested a progressive tion is not apparent.
ankylosing polyarthropathy affecting Figure 5. Lateral radiograph of the distal
distal limb joints. Changes of this type hindlimb of the cat in case 1 at 6 months.
were present in all cases, but developed The metatarsal bones are shorter than
more rapidly in cats with distal limb normal, asymmetrically misshapen, with
shortening (Figures 3 and 7) than in enlargement of proximal and distal ends
cases with normally proportioned limbs and bending of shafts. Intertarsal and
(Figure 8). Pelvic limbs tended to be tarsometatarsal joint spaces are of rela-
earlier and more affected. Periarticular tively normal appearance, and periartic-
ular new bone formation is not apparent.
new bone formation, the most conspic-
uous change, was typically first detected
along proximal metatarsals, where it
extended and merged with new bone
formed on the distal tarsal bones
(Figures 7 and 8). These changes were
progressive, occurred circumferentially
around the tarsometatarsal joint, and
eventually resulted in tarsometatarsal
and intertarsal ankylosis (Figures 7 and
8). The periarticular new bone was typi-
cally smooth, although the extensive
new bone that formed plantar to the
calcaneus and eventually extended into
adjacent soft tissues as an exostoses was
more irregular. Intertarsal and
tarsometatarsal joint spaces became Figure 6. Radiograph of the thickened shortened inflexible tail of the cat in case 1 at 11
irregular, indistinct and progressively months. Several caudal vertebrae are shorter than normal, with enlarged bony vertebral
narrowed, and the corresponding joints endplates, reduced intervertebral spaces and new bone formation tending towards anky-
in the forelimbs eventually became simi- losis of adjacent vertebrae.
88 Aust Vet J Vol 77, No 2, February 1999Clinical
larly affected (Figure 3). As well, tarsal changes, typically with a small number
and metatarsal bones became less radio- of fibrous synovial villi and a minimal
dense, with irregular punctate areas of cellular response. The predominant
osteolucency giving the tarsal bones a proliferative cell in the villus was the
moth-eaten appearance (Figure 7). synovial membrane cell, although occa-
The proximal limb joints, long bones sionally mononuclear cells were present
of the limbs and the vertebral column, also. The fibrocartilage at tendo-osseous
except for the tail, appeared unaffected. junctions appeared distorted without an
ordered junctional array. Mature bone in
Histopathological findings nodules and spicules was evident in peri-
Tissues from cases 3 and 4 were fixed articular dense connective tissue of liga-
for 2 to 3 months in buffered formalin ments and joint capsules, forming
(pH 7.2) and decalcified using a rapid osseous projections (enthesophytes).
decalcification procedure for 2 days This bone appeared to be forming as a
followed by a further 5 days in 5% result of an intermembranous process.
formic acid. The tissues were then In case 3 the distal radial and ulnar
routinely dehydrated and embedded in growth plates were present but function-
paraffin. Sections cut at 4 and 7 µm were ally closed. Growth plate cartilage chon-
stained with haematoxylin and eosin. drocytes were small, eosinophilic, but
Similar histological changes were somewhat clustered, and each separated
observed at the articular surfaces of the by considerable matrix. The chondro-
phalanges, metatarsal and metacarpal cytic morphological features of the
bones. Some interphalangeal joints physis were more like that of the
sectioned were distorted and subluxated. resting/proliferating chondrocytic zone
Some bones in the distal limbs had and these cells seemed not to have
abnormal articular cartilage. The hyaline entered the hypertrophic stage of matu-
cartilage was thicker in places: here ration. Remodelling of cartilage
necrotic cartilaginous foci were evident appeared disturbed as a result of inade-
although the cartilage maintained its quate chondrocytic maturation.
microscopic structure, but with chon-
drocytes failing to take up stain. Nearby Discussion
cells stained correctly and, on the edge The defining phenotypic feature
of this thicker articular cartilage, prolif- which identifies a cat as a Scottish Fold Figure 7. Lateral radiograph of the distal
erating chondrocytes appeared to grow suggests a developmental cartilage hindlimb of the cat in case 2 at 6 months.
from the margins towards the centre of defect, the most obvious manifestation The distal tibia and fibula, tarsal and
the articular cartilage (Figure 9). Where of which is forward folding of the ears. metatarsal bones and phalanges are not
articular cartilage was thicker it appeared This presumably results from the carti- markedly deformed, although the
to be inadequately resorbed, and the lage of the pinna lacking sufficient metatarsal bones are shorter than normal,
underlying junction between cartilage resilience to support the ear against the with metatarsal bones 2 and 5 being
and bone had a transitional zone with effect of gravity. It is hardly surprising splayed outward. Smooth new bone
either a discontinuous tide mark or a then that some cats with this genetic formation is evident around the tarsus
‘stuttered’ layered tide mark. Large defect have other abnormalities referable and proximal portion of the metatarsus
isolated islands of hyaline cartilage were to defective cartilage function. and has resulted in bony ankylosis of the
tarsometatarsal and intertarsal joints. The
observed in some places, extending from In order to fully describe the osteo-
intertarsal and tarsometatarsal joint
the articular cartilage into epiphyseal chondrodysplasia encountered in Scot-
spaces appear indistinct and may be
bone (Figures 10 and 11), and in other tish Folds it would be necessary to
narrowed irregularly, and tarsal bones
places microscopic foci of apparently observe and sample representative tissues
have a moth-eaten appearance, perhaps
viable cartilage were enclosed in during skeletal development, to more contributed to by overlying periarticular
subchondral bone. These findings closely follow the process of endochon- bone.
suggested that remodelling of cartilage dral ossification in distal extremities
was slowed, perhaps due to delayed or radiographically and microscopically.
inadequate maturation. Some bones Though our histological observations bone in these regions have a transition
displayed subarticular osseous erosions are limited, it seems that the cartilage in from chondrocytes to osteocytes and this
consisting of areas of osteoclasis, accom- bones of distal limbs is replaced slowly, morphological appearance is encoun-
plished by mostly mononuclear osteo- possibly reflecting inappropriate chon- tered in conditions such as avian
clasts, marginated by subperiosteal bone drocytic maturation. The presence of dyschondroplasia8 and dyschon-
formation. large islands of epiphyseal cartilage droplastic lesions seen in fast-growing
Flaking and fibrillation of the articular attached to articular cartilage suggests large and giant breeds of dogs.9 If similar
cartilage was sometimes evident. defective endochondral osteogenesis. changes occur in physeal cartilages
Chronic synovitis accompanied these The junctions between cartilage and during development, there would be
Aust Vet J Vol 77, No 2, February 1999 89Clinical Figure 8. Dorsopalmar (A) and lateral (B) radiographs of the distal pelvic limb of the cat in case 6 at the age of 6 years. Smooth periarticular new bone formation is evident around the tarsus and proximal portion of the metatarsus and has resulted in bony ankylosis of the tarsometatarsal and intertarsal joints. A large enthesophyte is present on the calcaneus, although this is hard to discern in the photo- graph. The intertarsal and tarsometatarsal joint spaces are indistinct and narrowed. Note that the metatarsal bones are nearly ‘normal’ in length. Similar changes are evident in the lateral radiograph (C) of the distal thoracic limb. delayed and dysplastic osteogenesis in new bone formation at insertions of joints; this may reflect abnormal stresses certain bones, such as metacarpal and tendons and joint capsules, as well as about affected joints and/or be a more metatarsal bones, which would result in degenerative joint disease and synovitis. direct result of the abnormal fibrocarti- malformation. Thus the abnormalities Deficiencies in the function of articular lage architecture observed in these in size and shape of bones in cats with cartilage, which normally provides a fric- regions. Less severely affected cats have SFOCD might occur because of defec- tionless intra-articular surface, may little developmental bone malformation tive endochondral ossification in distal contribute to premature and accelerated and tend to present at an older age, extremities. degenerative joint disease. The severe when periarticular new bone formation Later in life, malformation and periarticular new bone formation at and allied changes have moved towards resulting abnormal mechanical forces distal extremities of affected cats corre- ankylosis of distal joints. presumably take their toll, resulting in sponds to new bone formed in the The danger of producing cats subarticular osteoclasis and periarticular tendons and joint capsules of distal homozygous for the Fd gene from Fold- 90 Aust Vet J Vol 77, No 2, February 1999
Clinical
Figure 9. Photomicrograph of articular cartilage from a tarsal Figure 11. A higher power photomicrograph of the section in
bone from the cat in case 3. There is variability in the staining of Figure 10 displaying an irregular chondro-osseous junction. The
the chondrocytes at the centre of the articular cartilage: some cartilaginous matrix (C) has different staining characteristics
(small arrows) stain conspicuously with haematoxylin, whereas with eosinophilic foci (E) having similarities to that of nearby
others (curved arrows) stain faintly suggesting karyolysis, while osseous matrix (B). An erosion site at the bone-cartilage junc-
some chondrocytic lacunae appear empty (arrowhead). The tion is filled by plump mesenchymal cells (arrow). Haematoxylin
osteochondral junction is represented by a dense haematoxylin and eosin x 75.
line (H). The subchondral bone is absent in one area, resorbed
by osteoclasts (large arrows) and replaced by mononuclear
mesenchymal cells. Haematoxylin and eosin x 75.
Clearly there is considerable variation in the severity of
changes and rate of progression, as the cat in case 6 had rela-
tively mild disease at 6 years, whereas cats in cases 2 and 4
were sufficiently affected for owners to opt for euthanasia at
ages 6 and 21 months.
We suspect subclinical or mild involvement may be present
in nearly all mature heterozygous Folds. The natural course of
this disease in affected individuals needs to be established.
Such studies could be performed readily, because radiological
examination of the distal limbs should provide a sensitive and
specific screening tool for cats in which physical signs, such as
lameness, a short immobile tail, and plantar tarsal exostoses,
are absent. Further information concerning the changes in the
bones and joints could be obtained non-invasively using serial
computed tomography or magnetic resonance imaging of
affected distal extremities.
Figure 10. The section displays an irregular mass of cartilage (C) It could be argued that some of the cats described here orig-
extending from the articular surface (A) of the tarsal bone into inated from matings other than those recorded on their regis-
the bone (B) and, although a rim of bone separates cartilage tration papers, but the possibility that this was the case for all
from the large central intra-osseous fatty marrow tissue (Fa), this nine cats for which pedigrees were available seems remote.
bone is thin in one region (arrow). Part of the joint surface is Analysis of microsatellites to determine paternity would theo-
lined by fibrovascular tissue (FV). Haematoxylin and eosin x 7.5. retically be able to confirm or refute this possibility,10,11 but
was not attempted. Alternatively, Scottish shorthairs used in
the matings may have been phenotypically ‘normal’ but geno-
typically heterozygous for the Fd gene, due to incomplete
to-Fold matings has been long understood by breeders who penetration of the trait.12 This possibility is compatible with
recognise that severe signs develop early in cats of the FdFd the observation by breeders that some kittens with folded ears
genotype. What is unclear, however, is the extent to which grow to have apparently normal ears.13 Another possibility is
similar but milder changes develop in heterozygous Folds. that inheritance of the Fd gene shows the genetic phenomenon
This report suggests that significant disease can develop in of ‘anticipation’, whereby expression of the defect develops
heterozygous Folds as young as 6 months, and similar conclu- at a progressively earlier age and/or becomes more severe
sions were recently made in a case report from California.6 in succeeding generations. Such phenotypic alterations
Aust Vet J Vol 77, No 2, February 1999 91Clinical
have been described for several human of alleviating tarsal pain in a severely 7. Bennett D. Musculoskeletal system. In: Chan-
dler EA, Gaskell CJ, Gaskell RM, editors. Feline
disorders inherited in an autosomal affected cat,6 while our findings suggest medicine and therapeutics. Blackwell, Oxford,
dominant fashion including myotonic that treatment with pentosan and 1994:174.
dystrophy,14 Huntington’s disease,15 glycosaminoglycans can be helpful. 8. Poulos PW, Reiland S, Elwinger K, Olsson S-E.
autosomal dominant polycystic kidney Nonsteroidal anti-inflammatory agents Skeletal lesions in the broiler, with special refer-
ence to dyschondroplasia (osteochondrosis).
disease,16 and spinocerebellar ataxia type considered to be safe for cats, such as Pathology, frequency, and clinical significance in
1.17 In these disorders, progressive carprofen,18,19 may also have a place. As two strains of birds on high and low energy food.
amplification of DNA-triplet repeats Scottish Shorthairs have the same ‘wide, Acta Radiol 1978;Suppl 358:229-276.
9. Olsson S-E. Osteochondrosis in the dog.
within or adjacent to the disease gene round eyes, sweet expression, soft voice, Pathology, radiographic and clinical diagnosis.
occur in successive generations, and this and fondness for affection’ as Folds,1 a Sven Vet Tidn 1977;29:547-572.
instability of DNA is associated with suitable solution to SFOCD would be 10. Binns MM, Holmes NG, Marti E, Bowen N. Dog
increased disease severity.17 If heritable to abandon using fold-eared cats and parentage testing using canine microsatellites. J
Small Anim Pract 1995, 36:493-497.
unstable DNA was involved in the instead use Scottish Shorthairs, with 11. Fredholm M, Wintero AK. Efficient resolution of
genetic inheritance of SFOCD, the occasional outcrosses to British Short- parentage in dogs by amplification of microsatel-
phenomenon of anticipation would hairs and domestic shorthaired cats to lites. Anim Genet 1996;27:19-23.
12. Nicholas FW. Introduction to veterinary
provide an explanation as to why maintain hybrid vigour. If this policy
genetics. Oxford University Press, Oxford,
heterozygous Folds seem more likely to was adopted, the problem of SFOCD 1996:141-142.
develop clinical signs now than in early could be eliminated in one generation. 13. Maggitti P. Scottish fold cats. Barron’s educa-
studies.5 tional series, Hauppauge, 1993:11-5,77-82.
14. Howeler CJ, Busch HFM, Geraedts et al.
Although more work needs to be Acknowledgments Anticipation in myotonic dystrophy: fact or fiction.
done, the conclusion from this case The authors thank Dr Caroline Brain 1989;112:779-797.
series is that if breeders continue to O’Leary for introducing us to the 15. Ridley RM, Firth CD, Crow TJ, Conneally PM.
produce cats with cartilage insufficiently concept of heritable unstable DNA and Anticipation in Huntington’s disease is inherited
through the male line but may originate in the
strong to support the weight of the ear, anticipation. The cooperation of female. J Med Genet 1991;28:224-231.
some cats will inevitably develop joint Bajimbi cattery in facilitating these 16. Fick GM, Johnson AM, Gabow PA. Is there
and bone problems because of the studies was greatly appreciated. Richard evidence for anticipation in autosomal-dominant
polycystic kidney disease? Kidney Int
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