Prenatal diagnosis of hemoglobinopathies by restriction endonuclease analysis: Pregnancies at risk for sickle cell anemia and S-O(Arab) disease

The advantages of prenatal diagnosis by restriction endonuclease analysis of aminocyte DNA are its sensitivity and relative safety. Fetal mortality associated with amniocentesis ranges from <0.5% to 1.5% in various studies in comparison to the 3%-9% mortality associated with fetal blood sampling. The major disadvantage to prenatal diagnosis of sickle cell disease by restriction endonuclease analysis is that the 13.0 kb Hpa I fragment is not invariably associated with the β(s) gene. Based on the information currently available, 30% of individuals with Hb AS, e.g., the father in Family B, and 13%-20% of individuals with Hb SS, e.g., the individual, will not have the 13.0 kb Hpa I fragment. Therefore, to determine if this method is applicable to prenatal diagnosis in a particular family, the restriction endonuclease patterns of both Hb AS parents must be known. Furthermore, to eliminate possible errors introduced by assuming the β(A) and β(S) genes in a specific family are found within the 7.6 and 13.0 kb fragments, respectively, the restriction endonuclease patterns of the parents with Hb AS and a previous child with Hb SS or Hb AA must be known. If such a child is not available, studies of grandparents with Hb AA and Hb AS are then indicated. A second disadvantage to prenatal diagnosis by these methods is the unlikely possibility of culturing some maternal cells from amniotic fluid samples. Because ascertainment of the restriction patterns of both parents and any affected sibs of a fetus at risk for sickle cell anemia is required, restriction enzyme analysis of the DNA of these individuals should be completed before the fourteenth week of pregnancy. This allows sufficient time for an amniocentesis and 3-4 weeks for amniocyte culture in those families in whom the methods are found to be applicable. Alternatively, DNA can be prepared directly from uncultured amniocytes. Should the restriction patterns of the parents indicate that these methods are not applicable, hemoglobin synthetic studies with their higher associated risk can be offered.