Preventive measures and therapeutic interventions are not restricted to metabolic disorders. Identification of familial forms of long QT syndrome, associated with ventricular arrhythmias, allows early electrocardiographic testing and the use of prophylactic antiarrhythmic therapy, overdrive pacemakers, or defibrillators (Chap. 226). Individuals with familial hypertrophic cardiomyopathy can be screened by ultrasound, treated with beta blockers or other drugs, and counseled about the importance of avoiding strenuous exercise and dehydration (Chap. 231). Likewise, individuals with Marfan syndrome can be treated with beta blockers and monitored for the development of aortic aneurysms (Chap. 242). . | Chapter 064. The Practice of Genetics in Clinical Medicine Part 8 Preventive measures and therapeutic interventions are not restricted to metabolic disorders. Identification of familial forms of long QT syndrome associated with ventricular arrhythmias allows early electrocardiographic testing and the use of prophylactic antiarrhythmic therapy overdrive pacemakers or defibrillators Chap. 226 . Individuals with familial hypertrophic cardiomyopathy can be screened by ultrasound treated with beta blockers or other drugs and counseled about the importance of avoiding strenuous exercise and dehydration Chap. 231 . Likewise individuals with Marfan syndrome can be treated with beta blockers and monitored for the development of aortic aneurysms Chap. 242 . Individuals with a1 antitrypsin deficiency can be strongly counseled to avoid cigarette smoking and exposure to environmental pulmonary and hepatotoxins. Various host genes influence the pathogenesis of certain infectious diseases in humans including HIV Chap. 182 . The factor V Leiden allele increases risk of thrombosis Chap. 59 . Approximately 3 of the worldwide population is heterozygous for this mutation. Moreover it is found in up to 25 of patients with recurrent deep-vein thrombosis or pulmonary embolism. Women who are heterozygous or homozygous for this allele should therefore avoid the use of oral contraceptives and receive heparin prophylaxis after surgery or trauma. The field of pharmacogenomics seeks to identify genes that alter drug metabolism or confer susceptibility to toxic drug reactions. Pharmacogenomics permits individualized drug therapy resulting in improved treatment outcomes reduced toxicities and more cost-effective pharmaceutical care. Examples include succinylcholine sensitivity thiopurine methyltransferase TPMT deficiency malignant hyperthermia dihydropyrimidine dehydrogenase deficiency the porphyrias and glucose-6-phosphase dehydrogenase G6PD deficiency. As noted above the identification of .
