Spider Lamb Syndrome

Ovine hereditary chondrodysplasia

What is the disease? How does it present? Is it lethal?

Spider Lamb Syndrome is a semi-lethal autosomal recessive disorder found most often in Suffolk and Hampshsire breeds of sheep. This progressive disease was first observed in black-faced lambs during the mid-1970s. It has since been identified with a mutation within the gene for fibroblast grown factor receptor 3 (FGFR3) on the distal end of ovine Chromosome 6.

Because the disease is characterized as simple autosomal recessive and all lambs afflicted by the disease will never reach sexual/breeding maturity, the only way this disease can be passed on is if both ram and ewe are carriers. In other words, both parents may have a "normal" phenotype but if both have a heterozygous (Ss) genotype, there is a 1/4 (25%) offspring will be homozygous recessive (ss) with spider lamb syndrome phenotype.

Diagnosis:
1) Lambs are abnormal at birth, unlikely to ever stand; OR
2) Although lambs appear normal at birth, structural abnormalities gradually appear between 2-6 weeks.

Structural Abnormalities:
  • facial defects, e.g. roman nose
  • humped/twisted spines
  • abnormally long legs, often twisted or splayed (hence "spider legs")
  • flattened ribs
  • underdeveloped musculator

Treatment/Outcome

At this time there is no treatment. Individuals afflicted with this syndrome are homozygous recessive and rarely survive; therefore SLS lambs have no breeding value and are an economic liability. Due to the progressive malformation of the skeletal and musculatory systems, animals with SLS must eventually be destroyed.


Check out the video below for a heart-melting look at Gitta, the precocious spider lamb!

Meet Gitta: Spider Lamb Syndrome

Is Spider Lamb Syndrome Preventable?

YES! The transmission of this syndrome is entirely preventable through selective breeding and genetic testing. If homozygous dominant (SS) rams are used, there is no chance of transmission regardless of the ewe's genotype. If a ram is a known carrier (Ss), then the ewes should also be tested. In the event both potential parents are carriers (Ss), breeding should not be pursued.

If genetic testing is not an option for breeders, breeding records (including progeny information) and pedigrees can be used to lessen the incidence of mating two carriers.
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Fun Facts!

  • Mutation probably first occured in the late 1960s and was proliferated in breeding stock that was popular for its production and show-ring performance.
  • Structural abnormalities are thought to be the result of highly disorganized, nonparallel coumns of chondrocytes in the growth plates.
  • Although suspected carriers are actively culled from flocks, frequency of SLS remains relatively high.
  • Researchers are studying positional cloning of the gene responsible for SLS with the goal of fully eliminating the recessive allele.
  • Not all lamb structural deformities are due to SLS. This is why it's important to perform postmordem evaluations and test breeding stock.
  • SLS has a human chromosomal equivalent at the 4p16.3 location.

Discussion Questions:

1) Do you think it is more humane to immediately euthanize a lamb born with Spider Lamb Syndrome or allow them to experience life (& hopefully flourish like Gitta the playful lamb)?

2) Suppose you had a flock of sheep and year after year a significant percentage of lambs are born with spider lamb syndrome. What steps would you need to take to prevent future instances of the disease?

3) Currently spider lamb syndrome has been observed in several breeds of sheep in the US, Canada and Australia--but not Europe. Is it possible for European shepards to prevent spider lamb syndrome from even occuring in their flocks? Why or why not? What steps would need to be taken?

References

References

References were found using academic library subscription service therefore hyperlinks cannot be provided:

N.E. Cockett, T.L. Shay, J.E. Beever, D. Nielsen, J. Albretsen, M. Georges, K. Peterson, A. Stephens, W. Vernon,O. Timofeevskaia, S. South, J. Mork, A. Maciulis, T.D. Bunch (1999)

Localization of the locus causing Spider Lamb Syndrome to the distal end of ovine Chromosome 6, Mammalian Genome, 10:1, 35-38


SJ O'Brien, M Menotti-Raymond, WJ Murphy, WG Nash, J Wienberg, R Stanyon, NG Copeland, NA Jenkins, JE Womack, JA Marshall Graves (1999) The Promise of Comparitive Genomies in Mammals, Science, New Series, 286:5439, 458-462 + 479-481

KG Thompson, HT Blair, LE Linney, DM West & T Byrne (2005) Inherited chondrodysplasia in Texel Sheep, New Zealand Veterinary Journal, 53:3, 208-212

Linked references available below: