Topic 20: Genetic Testing and Gene Therapy

genetic testing

testing for single gene disorders and chromosomal disorders

diagnostic testing

performed when an individual is suffering a set of symptoms and their physician suspects that it may be a particular genetic disease

predictive and pre-symptomatic genetic testing

performed on an individual who is a risk of having a genetic disease but does not (yet) show symptoms

carrier testing

performed to determine if a phenotypically unaffected person is heterozygous for a recessive disease-associated allele

prenatal testing

find out if a fetus has a chromosomal abnormality or a Mendelian genetic disorder

pre-implantation genetic testing

performed on embryos produced by in vitro fertilization to test them for Mendelian genetic disorders, aneuploidy, or chromosomal rearrangements

newborn screening

performed on a population level to determine if they have been born with any of a select list of genetic disorders

pharmacogenetic testing

performed to identify people who may have adverse reactions or insensitivity to a drug due to their genotype

cytogenetic testing

use microscopy to examine a subject’s karyotype to look for chromosomal rearrangements or aneuploidy

biochemical testing

genetic disorder is detected by an abnormal level of a substance in the blood

cffDNA testing

uses the fragments of fetal DNA that are present in a mother’s bloodstream during pregnancy

allele specific probes

detects a specific, known complementary DNA sequence

DNA sequencing

determine the nucleotide sequence of the relevant gene in the patient and search the DNA sequence data for pathogenic variants

compound heterozygote

a recessive genetic disorder is due to being homozygous for loss of function mutations in which the two alleles are different specific sequence changes

expanded carrier screening panel

an individual can be tested for a panel of a few hundred genetic disorders, regardless of family history or any other risk factors

incidental finding

finding a pathogenic variant for a disorder you had not expected

ex vivo gene therapy

collect target cells from the patient, culture them and administer the therapy, and then reintroduce them to the patient’s body

in vivo gene therapy

therapeutic material is introduced into the patient’s system, for example by injection, and it then finds and enters the target cells

gene addition

introduce a therapeutic gene to provide what the patient is lacking due to their pathogenic genotype

gene inactivation / inhibition

directly undoes the causative gene variant

gene editing

make a change in the patient’s DNA using targeted mutagenesis

viral vector

engineered to infect a cell and deliver its DNA, but not to reproduce

nonviral vector

contain the therapeutic genetic material and introduce it into the cell by fusing with the cell membrane

lipid nanoparticle

deliver the therapy to a specific organ or tissue due to specific proteins on the outer layer

packaging cell

mammalian cells grown in culture in which the enzymes and structural proteins encoded by the helper virus make copies of the viral vector and package them into viral particles which are released

helper virus

derivative of a virus that has genes for the enzymes needed to replicate and package viruses but lacks the DNA sequences needed to get replicated or integrated