Genetic testing
Def: Genetic testing identifies changes in chromosomes, genes, or proteins.
Importance: can confirm or rule out a suspected genetic condition or help determine a person’s chance of developing or passing on a genetic disorder.
More than 1,000 genetic tests are currently in use, and more are being developed.
Knowledge of the test result could lead to emotional and social problems in the child, altering both relationships within a family and expectation for the future in a variety of areas such as education, employment, and relationships.
For many types of genetic analysis, a negative test result must be interpreted with caution in case it is a false negative, i.e a genetic abnormality is actually present but was not detected by the test.
Pathological significance of detected genetic alteration may be unclear due to missense mutation and variable expression.
When preforming genetic testing, it is important to be aware that the diagnosis of a genetic disease will not only have implications for the affected individual but may have ramifications for the other family members, who may be at risk of being affected or of being carriers for the condition.
Several methods can be used for genetic testing:
· Molecular genetic tests (or gene tests): study single genes or short lengths of DNA to identify variations or mutations that lead to a genetic disorder, it depends on base sequences on chromosome.
ü Southern blot analysis
ü The polymerase chain reaction (PCR)
ü DNA sequencing
ü Next generation sequencing (NextGen).
· Cytogenetics: concerned with how the chromosomes relate to cell behavior, particularly to their behavior during mitosis and meiosis include: Karyotyping
· Molecular cytogenetics: involves the combination of molecular biology and cytogenetics
ü Fluorescent in situ hybridization (FISH)
ü Comparative genomic hybridization (CGH).
ü Array comparative genomic hybridization (also microarray-based comparative genomic hybridization, matrix CGH, array CGH, aCGH)
· Biochemical genetic tests study the amount or activity level of proteins; abnormalities in either can indicate changes to the DNA that result in a genetic disorder.
The chromosomes could be sampled from:
˗ Peripheral blood lymphocytes - Bone marrow cells
˗ Skin fibroblast - Solid tissue cells
˗ Amniotic fluid cells
Medical applications (indications of genetic testing, karyotyping, chromosomal culture, analysis) :
1. Multiple congenital anomalies:
Birth defects > one developmental regions of the body
A. Confirmation of a clinical diagnosis
B. Estimate recurrence risk of future sibling