Changes

==Description==

==Description==

Severe combined immunodeficiency disease (SCID) of horses is an autosomal, recessive hereditary disease occurring in 2-3% of Arab or cross-bred Arab foals. It is characterised by a complete absence of functional B and T lymphocytes and affected (homozygous) foals fail to produce antigen-specific immune responses.

Severe combined immunodeficiency disease (SCID) of horses is an autosomal, recessive hereditary disease occurring in 2-3% of Arab or cross-bred Arab foals. It is characterised by a complete absence of functional B and T lymphocytes and affected (homozygous) foals fail to produce antigen-specific immune responses. The disease results in the absence of a functional immune system and affected foals are unable to resist or recover from infections.  

==Signalment==

==Signalment==

Only Arab or cross-bred Arabs are affected.  

Only Arab or cross-bred Arabs are affected.  

*Defect in DNA-dependent protein kinase gene

 

**Gene codes for a DNA repair enzyme involved in V(D)J recombination for antigen receptors of [[Lymphocytes - Introduction|lymphocytes]] (e.g. Ig and TCR)

SCID occurs due to a mutation in the allele encoding for DNA-dependent protein kinase (DNA-PK) that is involved in V(D)J lymphocyte recombination. V(D)J recombination is required for antigenic receptor expression on B and T lymphocytes. Without these receptors, differentiation of B and T lymphocytes does not occur and lymphoid tissue fails to develop. The result of this mutation is a complete is a severe immunodeficiency.

*Foals develop infections (usually around 8 weeks of age as maternal [[Immunoglobulins|antibody]] in [[Materno-Fetal Immunity - Introduction#Passive transfer via colostrum|colostrum]] wanes around this time)

 

 

Affected foals are clinically normal at birth and usually develop infections at around two to three months of age due to declining maternal antibodies in the colostrum. The most common clinical signs relate to infections of the respiratory tract such as nasal discharge, cough, dyspnoea or increased respiratory sounds.

*Foals usually die from bronchopneumonia

*Foals usually die from bronchopneumonia

[[Category:Primary Adaptive Immunity Deficiencies]]

[[Category:Primary Adaptive Immunity Deficiencies]]

[[Category:To Do - Blood]][[Category:To Do - SophieIgnarski]]

[[Category:To Do - Blood]][[Category:To Do - SophieIgnarski]]

[[Category:Horse]]

[[Category:Horse]]