Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (418 page)

Spinal Muscular Atrophy (SMA)

Pulmonary System

Alpha-1 Antitrypsin Deficiency (A1ATD)

Cystic Fibrosis and Related Disorders

Disorders of Hearing and Vision

Deafness, Autosomal Recessive 1 (DFNB1)

Leber Optic Atrophy (Leber Hereditary Optic Neuropathy; LHON)

Nonsyndromic Sensorineural Deafness, Mitochondrial

Usher Syndrome Type 1A (USH1)

Skeletal Dysplasia

Achondroplasia (ACH)

Ellis-van Creveld (EVC) and Weyers Acrofacial Dysostosis

Osteogenesis Imperfecta (OI; Brittle Bone Disease)

Connective Tissue Disorders

Marfan Syndrome (MFS)

Oncologic Hereditary Disorders

BRCA1 and BRCA2 Hereditary Breast and Ovarian Cancer

Duplication/Deletion Syndromes

Klinefelter Syndrome

Trisomy 13 (Patau Syndrome)

Trisomy 18 (Edwards Syndrome)

Trisomy 21 (Down Syndrome)

Turner Syndrome (45,X Karyotype and Variants)

Glossary for Molecular Methods Terminology

G
enetic disorders are conditions caused by absent or defective genes or by chromosomal aberrations. Genetic disorders can be tested at the level of DNA, RNA, or protein. A genetic test is the analysis of human DNA, RNA, mitochondrial DNA, chromosomes, proteins, or certain metabolites in order to detect alterations that may be inherited or acquired. This can be accomplished by directly examining the DNA or RNA that makes up a gene (direct testing), looking at markers coinherited with a disease-causing gene (linkage testing), enzyme activity or metabolites (biochemical testing), or examining the chromosomes (cytogenetic testing) (
www.genetests.org
). The results of a genetic test can confirm or rule out a suspected genetic condition, determine an individual’s risk of developing disorders, identify carriers, or assess gene variants influencing an individual’s rate of drug metabolism. Hundreds genetic tests are currently in use and more are being developed. Genetic testing may be undertaken as part of the process of treating or advising patients.

   
OVERVIEW

MOLECULAR DIAGNOSIS: TYPES OF GENETIC TESTING

   
Diagnostic genetic testing
: Confirmatory test for symptomatic individuals.

   
Presymptomatic genetic testing
: Carried out in people without symptoms for estimating the risk of developing (e.g., Huntington disease).

   
Carrier testing:
Performed to determine whether an individual carries one copy of an altered gene for a particular recessive disease. Autosomal recessive diseases occur only if an individual receives two copies of a gene that have a disease-associated mutation; therefore, each child born to two carriers of a mutation in the same gene has a 25% risk of being affected with the disorder.

   
Risk factor testing (susceptibility tests):
Gene variants have been discovered that are associated with common diseases such as Alzheimer disease, Parkinson’s disease and diabetes.

   
Pharmacogenetic testing
: Determining differences an individual’s response to drugs.

   
Preimplantation testing
: Preimplantation diagnosis is used following in vitro fertilization to diagnose a genetic disease or condition in a preimplantation embryo.

   
Prenatal testing
: Used to diagnose a genetic disease or condition in a developing fetus.

   
Newborn screening
: Performed in newborns by in place of in state public health programs to detect certain genetic diseases for which early diagnosis and interventions are available.

GENETIC COUNSELING

Genetic testing is often accompanied by genetic counseling. Genetic counseling is the process by which patients or relatives, at risk of an inherited disorder, are advised of the consequences and nature of the disorder, the probability of developing or transmitting it, and the options open to them in management and family planning in order to prevent, avoid, or ameliorate it. A instead of any person may seek genetic counseling for a condition he or she have inherited from his or her biologic parents. A woman may be referred for genetic counseling if pregnant and undergoing prenatal testing or screening. Genetic counselors educate the patient about their testing options and inform them of their results.