module 16 - genetic counseling

define genetic screening

a tool to ID ppl at higher risk of developing or are carrying specific disorders

what are the three reasons for genetic screening?

• detect disease before symptoms appear for early intervention

• ID ppl carrying genetic mutations - aid reproductive decision

• tract disease incidence

describe carrier screening

• blood, saliva, tissue sample is taken from the parent most likely to be a carrier first.

• if (-), no further testing

• if (+), test other parent

• typically looking for recessive disorders

what disorders ad diseases are looked for in carrier screening?

• cystic fibrosis

• fragile X syndrome

• sickle cell anemia

• tay-sachs disease

describe prenatal genetic screening

• not completely accurate

• blood tests (maternal alpha-fetoprotein), US, DNA tests in first/second trimester

how does heredity and environment play a role in diseases?

epigenetics → family Hx of a disease may turn on in an individual due to environmental stressors

what are the three criteria the ACMG uses to determine which disorders should be screened for in newborns?

• disease is detectable in 24-48 jrs of birth before symptoms occur

• follow up accurate Dx test

• proven benefits of early detection and Tx

chromosome disorders

change in structure of number of a chromosome due to duplication or loss of material

euploidy

addition of chromosome to all original pairs

trisomy

additional chromosome

monosomy

one chromosome deletion (incompatible with life)

trisomy 21 (down’s syndrome)

extra chromosome 21 that is unattached

risk increases with maternal age

mosaic down syndrome

some cells have 47 chromosomes while others have the usual 46

trisomy 18 (edward’s syndrome)

severe cognitive impairment and physical abnormalities - has short life span

trisomy 13 (patau syndrome)

greater gene imbalance and short life span

aneuploidy

the total number of chromosomes is not a multiple of the haploid (23) (ex. trisomies)

describe sex chromosome aneuploidies and provide examples

• decreased intelligence/learning disabilities

• ex. klinefelter syndrome, turner syndrome

describe x-linked recessive inheritance

• affects males

• males are not carriers

• female carriers are not affected

intrauterine environment disorders

• teratogens

• inborn errors of metabolisms

• metabolic pathway disruption

• PKU

• galactosemia

• molecular Dx techniques

what are indications for prenatal testing?

• maternal age >/=35 (>/=31 if twins)

• abn maternal serum screen

• previous child defect

• FHx of genetic condition

• maternal disease/teratogen exposure

• infections (rubella, CMV, toxoplasmosis)

• ethnic-based risks