Primary, severe, combined immunodeficiency disease of Arabian foals.

Set in a context of immunodeficiency diseases in general this paper provides a brief, illustrated review of a primary, severe, combined immunodeficiency (PSCID) disease of Arabian foals. Affected foals are clinically normal at birth but beginning at about 10 days of age they develop a range of clinical signs particularly bronchopneumonia and diarrhoea with which adenoviruses are peculiarly associated. Despite intensive therapy foals invariably die by about 3 months of age. Affected foals are profoundly lymphopagenic (greater than 1000 lymphcoytes per mm3). There is thymic and lymph node hypoplasia and all lymphoid tissues are profoundly depleted of both T and B lymphocytes. The depletion of both T and B lymphocytes suggests that the primary defect is at the level of bone marrow stem cells which are the precursor cells for both lymphocyte populations. PSCID of Arabian foals is inherited as a simple, autosomal, recessive gene. Some 2 to 3% of all such foals may be born with PSCID, this frequency corresponds to a gene frequency of about 30% in parents. The syndrome is, therefore, an important cause of economic wastage. It also represents the only occurrence of the syndrome in an animal species other than man and as such has considerable comparative interest.