Monocephalus dipygus parapagus: A suspected case of complete caudal duplication in a British Blue kitten

A conjoined twin British Blue kitten was born alive by unassisted vaginal delivery to a 28-month-old pedigree queen. The queen had been vaccinated several months before oestrus, fed a commercial dry diet with raw fit-for-human consumption steak and was regularly dewormed. The gestation occurred over the summer period but the weather pattern was particularly mild and cool. The sole medication the cat received from the current owner was an application of Revolution (Selamectin; Pfizer) before, and in the first month of, pregnancy for treatment of a flea burden. Immunisation with an unknown vaccine had occurred months previously. The queen and one other cat lived in an outdoor, standard cattery separate from the main house. The queen suffered no illness during the pregnancy and gave birth naturally to five live kittens including the conjoined twin.

Grossly, the kitten demonstrated a small bifurcation in the lower mandible and an extensive cleft palate. The upper body as far as the last rib appeared normal but the bifurcation of the body then occurred, resulting in two identically paired hind limbs and tail sections, each facing the other rather than in parallel. Any placental tissue had been ingested by the queen by the time the breeder discovered the kitten. All four of its lower limbs and both tails were observed to move quite actively but the upper body and head appeared to move sluggishly by comparison. The breeder had the kitten euthanased after 20 min of life. The body was not made available for post mortem or radiographic examination.

Conjoined twinnings consist of the union of two more or less developed organisms by a partially duplicated body or by a duplication of the body axis. ¹ Dipygus (double buttocks) denotes conjoined twins with the head and thorax completely merged and the pelvis and lower extremities duplicated; when the duplications of the lower parts are symmetrical it is additionally called duplicitas posterior, as is in this case. True cephalic parapagia is classified as a monocephalus dipygus where the duplication occurs in the posterior region ^2,3 and is known as parapagus if the parts are united laterally or parapagia if the union is parallel. ⁴

The degree of dipygus can vary from very minor to the more complete form seen here where there appears to be complete duplication of pelvic and lower limbs, tails and external genital openings. As in complete dipygus where the two small pelves are situated side-by-side and the person or animal has active control over all four legs – this kitten had been seen to employ coordinated movements of the hind limbs. This movement of the paired hind limbs makes it highly suspicious that the vertebral column was thus divided in the area of the first or second lumbar vertebra with duplication of the spinal cord. Each of the supernumerary limbs of this kitten was equally developed with no abnormal or missing digits or nails on any of the limbs (Fig 1).

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Fig 1.

Ventral view showing complete caudal limb duplication and bifurcation of rostral mandible.

Complete dipygus is also reported to have a tendency to throw cleft palate, as was additionally seen in this case. ³

Caudal duplications though extremely rare, have been described and published in both the human and veterinary literature since the 17th century. ⁵ Embryonic duplications are important because they are usually associated with dystocia and reproductive wastage. ⁶ Conjoined twinning in humans is expected to occur if the embryonic disc divides later than the 13th day post fertilisation as this results in an incomplete division. ⁷

The majority of congenital malformations are triggered by genetic or environmental ⁸ factors. In this instance, no other similar presentations had been seen by using this genetic line of cats by the original Breeder who owned the registered closed cattery that was clear of feline immunodeficiency virus, feline leukaemia virus and feline infectious peritonitis at the time of sale of this queen.

No excessive environmental climatic conditions occurred immediately before or during the pregnancy whilst in the care of the current breeder and the cat was/is virus and disease free in the year since purchase.

The sole medication the cat received from the current owner was an application of Revolution (Selamectin; Pfizer) before, and in the first month of pregnancy, for treatment of a flea burden. Immunisation with an unknown vaccine had occurred months previously. The queen and one other cat live in an outdoor standard cattery separate from the main house.

There remains the possibility that the cat was exposed to unknown teratogens during pregnancy. Excessive inline breeding was evident in the pedigree of the female cat. The same recurrent ancestor appears in the stud's pedigree. The co-efficient of inbreeding of the queen is 8.6% with a 98.9% rate of inbreeding. Forty-six ancestors were found of which 24 are unique, of 22 are duplicate and 11 are common ancestors. The dam's paternal grandfather is from an aunt-to-nephew mating and her maternal grandfather is from an half-sibling-to-half-sibling mating. The co-efficiency of the sire is 0% with 38 ancestors found, 10 of which are duplicated. Additionally, the sire's paternal grandfather is from a mother-to-son mating and the maternal grandfather is from a father-to-daughter mating. This same grandfather is also an half-uncle to the queen. The monocephalic kitten had a co-efficient of 3% and a 99.6% rate of inbreeding. Eighty-six ancestors were found of which 49 are unique, 37 are duplicates and five are common.

Whilst no pregnancy is without some risk, given the previous result, however rare it may be, and in view of the risk of potential loss of progeny, harm to the queen and financial loss, the breeder is ethically opposed to repeating this pairing. The remaining progeny were also not suitable show-quality stock further increasing the owner's reluctance to repeat the combination. The breeder intends to only breed the cat once more before desexing. The breeder has been advised to consider out-breeding both the queen and stud male to a recent unrelated overseas imported stud male and queen.

The veterinary literature contains reports of monocephalus dipygus in cattle, ⁹ buffalo, ¹⁰ sheep, ¹¹ goats ³ and most recently in the dog of an incomplete parapagia form and a craniothoracopagus form in the dog respectively. ^12,13 To the best of this author's knowledge, this would appear to be the first reported monocephalic dipygus case exhibiting a complete caudal and/or a parapagus duplication variant in cats.