Evaluation of a screening programme for identification of mannosidosis heterozygotes in angus cattle

Abstract

Extract

Diseases inherited as simple recessives frequently reflect simple anomalies of structural or enzymic proteins. Many such inherited diseases of humans have now been defined in biochemical terms (McKusick, 1971) but relatively few have been described adequately in domestic animals. When the biochemical anomaly is known, then it is frequently possible to develop screening programmes to detect diseased young before the disease is manifest clinically. Such programmes may involve families or small populations at risk, or be developed as mass screening programmes for the entire neonatal population of an area or country. In many biochemically defined diseases inherited as recessives, the heterozygous statecan also be recognized. This is either through detection of a mutant structural protein in the otherwise phenotypically normal individual — e.g., the “S” haemoglobin in carriers of sickle-cell anaemia (Lehmann and Huntsman, 1972) — or where an enzyme deficiency is known, by the gene dosage phenomenon — i.e., heterozygotes having approximately half the normal amount of the enzyme (Engel, 1972). Where these phenomena are recognized, screening programmes for heterozygotes can be undertaken, particularly within families related to a case of the disease. A number of such tests are currently available or are being developed in human medicine. Mass screenings of large populations for carriers of specific genetics defects are less common, and to date, only two have been developed. One of these concerns Tay Sachsdisease of Ashkenazi Jews and is operative in several North American cities (Kaback and Zeiger, 1972). The otherconcerns mannosidosis of Angus cattle and is operative, in New Zealand (Jolly et al., 1974b).