Genetics and Prenatal Screening

GeneticsEach human cell contains 46 chromosomes made up of DNA.Short segments of DNA are called genesDominant and Recessive GenesWhen one is dominant then that expression trumps the recessive gene.Carriers?Table 3.2- Dark Hair/Blond, Curly/Straight, Dimples/no dimples, double-jointed/normal joints

Chromosome and Gene-linked AbnormalitiesChromosome AbnormalitiesDown syndrome- trisomy 21round face, flattened skull, extra skin over the eyelids, protruding tongue, short limbs, and motor and mental retardation.1/1900 @ 20 years; 1/45 @ 42 years

Chromosome and Gene-linked AbnormalitiesChromosome AbnormalitiesDown syndrome- trisomy 21round face, flattened skull, extra skin over the eyelids, protruding tongue, short limbs, and motor and mental retardation.1/1900 @ 20 years; 1/45 @ 42 years

Fragile X- Problem with the X-chromosome: often breakstypically mental retardationmore frequent in males. Why?1/250 females are carriers vs. 1/800 males

Chromosome and Gene-linked AbnormalitiesGenetic AbnormalitiesPKU- Phenylketonuria- Cannot properly metabolize the substance (phenylalanine).mental retardation and hyperactivity if untreated.Curable -Nature/nurture

Sickle-cell anemia- Deforms the bodys red blood cellscells die causing anemiaEarly death if left untreated.- Penicillin1/400 Af-Am babies born with

Prenatal ScreeningDangerous- Why get it?

Prenatal ScreeningFamily HistoryBlood relatives with disordersHistory of previous miscarriagesChildren with specific genetic disordersMembers of at-risk groupMothers age and Fathers ageBehavior- Do parents use drugs/alcohol

Prenatal detectionHCG-Human Chorionic Gonadotropin- Blood test- similar to a typical pregnancy test Can determine an ectopic pregnancySometimes combined with.

Prenatal DetectionAFP- Alpha-fetoprotein- (also a Blood test) looking for AFP being produced amniotic fluid and mothers blood.Done at 15-20 weeksCan determine if child has Down Syndrome (Decreased Levels)- though only in about 60% of casesCan help determine neural tube defects such as spina bifida (Increased levels)Fetal distress

Prenatal DetectionUltrasound- Standard of CareDone at about 20-22 weeks2-D image using sound wavesConsidered low-risk as long as non-repeated exposure- possible low birth weight

Doppler Ultrasound- 1 hour session- Color- Can look for signs of pre-eclampsia, poor blood flow.

Other ultrasoundshttp://www.youtube.com/watch?v=uo5gOWzgoaY4-D ultrasound

Prenatal DetectionAmniocentesisDone between 16th and 18th week though used to be done at 20th-22nd week. Why the change????Takes two weeks to month to get results.Needle through stomach, uterine wall, and amniotic sac, remove small amt of fluidAvg. range=.3-.5%, but as high as 3-8% fetal lossRisk of loss is greater than risk of birth defects in older momsCan detect several hundred diff birth defects (out of 4000)

Prenatal DetectionCVS- Chorionic Villi SamplingDone at 10-12 weeksResults take less than 10 daysUsing ultrasound, take fetal cells from the chorion (placenta)between a 0.5% and 1% risk of miscarriage Slightly higher risk than amnioPossible birth defects (1/3000)