Human genetics: genetic testing

genetic counseling

• assesses reproductive risks

• process of communication that deals with occurrence or risk of genetic disorder in a family

what can be used to determine risk?

• prenatal screening

• cytogenic or biochemical tests

• pedigree analysis

types of testing and screening

• newborn screening: 48-772 hours after birth

• carrier testing: done on family members with history of genetic disorder

• pre-natal testing: fetus or genetic disorder

• pre-symptomatic: late onset disorder

criteria for testing

• severe phenotype

• mutations must be known

• high penetrance

chronic villus testing

• insert catheter into chorion of uterus to collect fetal cells

• diagnoses biochemical and cytogenaeic defects

• performed in eighth or ninth week

amniocentesis

• remove amniotic fluid containing fetal cells

• used to diagnose genetic and developmental disorders

• performed in 16th week

chronic villus sampling vs. amniocentesis

• chronic villi sampling: remove cells from chorion, done earlier in pregnancy, detects genetic abnormalities

• amniocentesis: remove cells from amniotic fluid, neural tube defects, birth defects

free fetal DNA testing

• alternative to amniocentesis

pre-implantation genetic diagnosis

• removing cell from 3 day embryo

• can also be used to analyze polar bodies

• can be used for selective traits

why is genetic testing not always possible?

• because there can be multiple mutations for same disease

• ex. cystic fibrosis has 25 mutations

newborn screening

• not DNA test, enzyme test

• detects issues with metabolism

gene therapy

transfer of cloned genes into somatic cells to treat genetic disorder

somatic gene therapy

• only form of gene therapy used to date

• gene transfer to somatic target cells

therapies not in use due to ethical issues

• germ-line gene therapy

• mitochondrial replacement therapy

• enhancement gene therapy