Spider lamb syndrome, also known as spider syndrome and more formally as ovine hereditary chondrodysplasia, is a

homozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...

recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

disorder affecting the growth of cartilage and

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticated ...

. The name derives from the limbs of afflicted animals being thin, elongated, and "spider-like". It is a semilethal trait,Spider Lamb Syndrome: Introduction
at

UC Davis School of Veterinary Medicine The University of California, Davis, School of Veterinary Medicine is the largest veterinary school in the United States. Established in 1948, the school is the primary health resource for California's various animal populations. In 2020, the schoo ...

; retrieved July 19, 2012 which is thought to have been first observed in the 1970s, and is most common in sheep of the Suffolk and

Hampshire Hampshire (, ; abbreviated to Hants) is a ceremonial and non-metropolitan county in western South East England on the coast of the English Channel. Home to two major English cities on its south coast, Southampton and Portsmouth, Hampshire ...

breeds. These are both black-faced breeds of sheep; the syndrome has never been detected in white-faced breeds. The syndrome was an economically significant issue for sheep breeders in the 1980s, but with strict testing and breeding programs it has become less common. The mutation which causes spider lamb syndrome is found on ovine chromosome 6, and involves the inactivation of

fibroblast growth factor receptor 3 Fibroblast growth factor receptor 3 is a protein that in humans is encoded by the ''FGFR3'' gene. FGFR3 has also been designated as CD333 (cluster of differentiation 333). The gene, which is located on chromosome 4, location q16.3, is expressed in ...

.Enhanced skeletal growth of sheep heterozygous for an inactivated fibroblast growth factor receptor 3
''Journal of Animal Science'', vol. 84 no. 11 2942-2949; by L. B. Smith, M. R. Dally, R. D. Sainz, K. L. Rodrigue and A. M. Oberbauer It has been compared to dwarfism in beef cattle. Afflicted animals may be visibly deformed at birth and unable to stand, or seemingly normal for the first 4 to 6 weeks of their lives.

Symptoms

Symptoms have been observed on fetal lambs as early as by the completion of the second gestational trimester.Developmental progression of the Spider Lamb Syndrome
by A.M. Oberbauer, N.E. East, R. Pool, J.D. Rowe, and R.H. BonDurant; in ''Small Ruminant Research''; Volume 18, Issue 2, October 1995, Pages 179-184 Under normal production circumstances, the lambs usually do not survive past the neonatal period. For this reason, the disease is considered semi-lethal. The disease typically affects the musculo-skeletal system. The clinical signs can include: skeletal abnormalities, twisted or humped spines, facial defects, bent legs, abnormally long legs, flat ribs, and underdeveloped muscles. Due to these symptoms, lambs cannot stand to nurse. Spider lamb syndrome is untreatable, and in almost all cases, the lambs must be euthanized.

Causes

Spider lamb syndrome is caused by a mutation to the gene for

(FGFR3), on ovine chromosome 6. FGFR3 is in the tyrosine kinase receptor family and its function is to restrict the proliferation of cartilage at the

growth plate The epiphyseal plate (or epiphysial plate, physis, or growth plate) is a hyaline cartilage plate in the metaphysis at each end of a long bone. It is the part of a long bone where new bone growth takes place; that is, the whole bone is alive, wit ...

s of the long bones: regulating ossification (the conversion of cartilage into bone), limiting skeletal elongation, and thereby ensuring that the limbs are the right length.

References

{{reflist Sheep and goat diseases Syndromes in mammals