• A pediatrician evaluates a child with multiple congenital malformations and orders a high-resolution genomic test for submicroscopic chromosomal deletions or duplications that are below the level of resolution of routine chromosome analysis (Case 32).

• A genetic counselor specializing in hereditary breast cancer offers education, testing, interpretation, and support to a young woman with a family history of hereditary breast and ovarian cancer (Case 7).

• An obstetrician sends a chorionic villus sample taken from a 38-year-old pregnant woman to a cytogenetics laboratory for confirmation of abnormalities in the number or structure of the fetal chromosomes, following a positive screening result from a non-invasive prenatal blood test (see Chapter 17).

• A hematologist combines family and medical history with gene testing of a young adult with deep venous thrombosis to assess the benefits and risks of initiating and maintaining anticoagulant therapy (Case 46).

• A surgeon uses gene expression array analysis of a lung tumor sample to determine prognosis and to guide therapeutic decision making (see Chapter 15).

• A pediatric oncologist tests her patients for genetic variations that can predict a good response or an adverse reaction to a chemotherapeutic agent (Case 45).

• A neurologist and genetic counselor provide APOE gene testing for Alzheimer disease susceptibility for a woman with a strong family history of the disease so she can make appropriate long-term financial plans (Case 4).

• A forensic pathologist uses databases of genetic polymorphisms in his analysis of DNA samples obtained from victims’ personal items and surviving relatives to identify remains from an airline crash.

• A gastroenterologist orders genome sequence analysis for a child with a multiyear history of life-threatening and intractable inflammatory bowel disease. Sequencing reveals a mutation in a previously unsuspected gene, clarifying the clinical diagnosis and altering treatment for the patient (see Chapter 16).

• Scientists in the pharmaceutical industry sequence cancer cell DNA to identify specific changes in oncogenic signaling pathways inappropriately activated by a somatic mutation, leading to the development of specific inhibitors that reliably induce remissions of the cancers in patients (Case 10).