Severe Combined Immunodeficiency Terrier Type (SCID)
Severe Combined Immunodeficiency Terrier Type (SCID) is a genetic immunodeficiency disorder that affects the Jack Russel Terrier breed. SCID leads to an early mortality rate in young Jack Russel Terrier puppies as a result of impaired immune response to infections. Generally, SCID is an inherited disorder affecting humans, mice, horses, and dogs. In humans, SCID is colloquially known as ”bubble boy” disease, since the patients require complete clinical isolation in aim to avoid any contact with environmental microbes and infections. Among dogs, except in Jack Russel Terriers, it has been diagnosed among Frisian Water Dogs, Basset Hounds, and Cardigan Welsh Corgies, but each is caused by a distinct causative mutation, and some are inherited in a different inheritance pattern.
Characteristics and Symptoms
SCID affected puppies are unable to develop their own antibodies and have a very low number of lymphocytic white blood cells. For this reason, affected dogs are not able to fight infections. A complete absence of IgM antibodies in serum was measured. The development of the lymphoid tissue appears to be incomplete and the affected dogs are highly susceptible to recurrent infections. General clinical signs include immunodeficiency, lymphopenia, and lymphoid hypoplasia. Other symptoms may be retarded growth, inability to gain weight or weight loss, diarrhea, vomiting, lethargy, lack of palpable lymph nodes, respiratory, and skin, eye and ear infections. Once the maternal antibodies fade away, affected puppies usually die due to an infection.
Severe Combined Immunodeficiency Terrier Type is caused by a mutation in the PRKDC gene. The mutation causes synthesis of impaired DNA-dependent protein kinase catalytic subunit (DNA-PKcs), which is needed for proper V(D)J recombination during antibody synthesis.
SCID terrier type is inherited in an autosomal recessive pattern. Healthy parents of affected puppy are obligate heterozygotes and therefore carry one mutant allele. Heterozygotes have no symptoms. Dogs homozygous for the mutation will display the symptoms of the SCID. At conception, when mating two carrier dogs, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
Meek, K., Kienker, L., Dallas, C., Wang, Wei, Dark, M.J, Venta, P. J., Huie, M. L, Hirschhorn, R., Bell, T. (2001) SCID in Jack Russell Terriers: A New Animal Model of DNA-PKcs Deficiency. J Immunol August 15, 2001, 167 (4) 2142-2150; DOI: https://doi.org/10.4049/jimmunol.167.4.2142