ABSTRACT
The large group of haemoglobin disorders, of great importance in many parts of the world, contains perhaps the best understood disorders that exist. Sickle cell disease, caused by homozygosity for a glutamic acid to valine substitution at amino acid number 6 in ß-globin, is exceptionally common in some regions, and the heterozygote frequency reaches and can even exceed 1 in 8 in some parts of Africa. A variety of disease associations have been described with the ABO blood group system but are too weak to be of use in genetic counselling. Fetal blood sampling will often allow prenatal detection of both immune deficiencies and blood cell disorders but has largely been replaced by molecular analysis of chorion villus samples, as the specific genes have been identified. Haemophilia represents a major genetic counselling problem, particularly since most haemophiliac males reach adult life with only moderate disability, and frequently reproduce.
