The role of genetic counseling in the management of prenatally detected congenital heart defects.

Genetic counseling should be used in the context of prenatal diagnosis of congenital heart defects for several reasons. The insight gathered through the family history, review of ultrasound findings, and chromosome analysis may help to determine the origin of the defect, such that more precise information about prognosis and recurrence risks can be given. This information should be used by the patient to consider options for the current pregnancy and management of future ones. The difficult and emotionally charged decisions that come with prenatal diagnosis of congenital heart defects demand that the psychosocial burden be explored with the patient. Genetic counseling should facilitate the decision-making process and address patient needs. Genetic counselors have the training, experience, and time to focus on these elements. The role of genetic counseling in congenital heart defects is likely to increase as advances in understanding the underlying genetic causes are made and incorporated into patient care and counseling. Genetic counseling for this indication will become more common as prenatal detection improves and as more affected individuals live to reproductive age.

Specific binding by EcoRV endonuclease to its DNA recognition site GATATC.

Restriction endonuclease EcoRV has been reported to be unable to distinguish its specific DNA site, GATATC, from non-specific DNA sites in the absence of the catalytic cofactor Mg2+, and thus to exercise sequence specificity solely in the catalytic step. In contrast, we show here that under appropriate conditions of pH and salt concentration, specific complexes with oligonucleotides containing the GATATC site can be detected by either filter-binding or gel-retardation. Equilibrium binding constants (K(A)) are easily measured by both direct equilibrium and equilibrium-competition methods. The preference for "specific" over "non-specific" binding at pH 7 in the absence of divalent cations is about 1000-fold (per mole of oligonucleotide) or 12,000-fold (per mole of binding sites). Ethylation-interference footprinting shows that the "specific" complex includes strong contacts to the phosphate groups GpApTpApTC. Specific DNA binding is strongly pH-dependent, decreasing about 15-fold for each increase of one pH unit above pH 6, but non-specific binding is not; thus, binding specificity decreases with increasing pH. Gel retardation and filter-binding at pH < or = 7 yield essentially identical values of K(A) for specific-site binding, but at pH > 7 gel retardation significantly underestimates K(A). Specific-site binding is stimulated about 700-fold by Ca2+ (not a cofactor for cleavage), but with non-cleavable 3'-phosphorothiolate and 4'-thiodeoxyribose derivatives whose response to Ca2+ is similar to that of the parent oligonucleotide, Mg2+ stimulates binding only fourfold and twofold, respectively. Thus, binding specificity is not dramatically enhanced by Mg2+. Taking into account discrimination in binding and in the first-order rate constant for phosphodiester bond scission, the overall discrimination exercised against the incorrect site GTTATC is about 10(7)-fold. EcoRV endonuclease is thus not a "new paradigm" for site-specific interaction without binding specificity, but like other type II restriction endonucleases achieves sequence specificity by discriminating both in DNA binding and in catalysis.