Canine Leukocyte Adhesion Deficiency Type I (Irish Setter Type)

Test Overview:

Canine leucocyte adhesion deficiency (CLAD) is an autosomal recessive disorder that has been documented in Irish setters and a few Irish setter crosses. It is a rare disease that is similar to LAD in humans, and is caused by a defect of the white blood cells (or leucocytes) of the immune system. The white blood cells lack a certain surface protein or receptor called CD18, which means that when there is an infection in the body somewhere these white blood cells cannot respond properly. They are unable to interact in a cell-to-cell or cell-to-matrix manner, so cannot migrate from the blood vessels to the site of infection, or fight infection at the site. This condition is caused by a mutation in the ITGB2 gene, which encodes the integrin beta 2 subunit (CD18). Carriers who have one copy of the mutation show no clinical signs, while dogs with two copies of the mutation (affected) develop clinical disease and generally die by the age of six months. A genetic test is available to screen breeding animals for this devastating disease. Clinical signs are seen in young puppies, often at less than 12 weeks of age. The average age of presentation to a veterinarian is 13.5 weeks. Signs include recurrent infections, including umbilical infections, fever, inappetance, poor growth, impaired wound healing and enlarged lymph nodes. Superficial infection of the gums with salivation is common, and as the disease progresses the jaw bone can become thickened. Lameness and swelling of the distal limb bones can also be seen. A characteristic sign is skin infections without purulent exudates. Infections initially respond to antibiotics, but recur once medication finishes. Antibiotics become less effective as time goes on. Puppies generally succumb by the age of six months. Pathology testing will show that the white cell count is high, because the bone marrow is still producing white blood cells but because they cannot move into tissue to fight infections there are higher than normal numbers in the blood, and a neutrophilia with left shift is common. Treatment with gene therapy (i.e. stem cell therapy to introduce stem cells infused with normal CD18-producing capability) has shown success, with clinical signs resolving in treated puppies. Limited availability and high cost of such treatment means it is rarely used at the present time, but shows great promise for the future.