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Genetic counseling - Down syndrome

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Down syndrome is a genetic disability that usually happens spontaneously. It is more likely in older mothers.

Introduction[]

  • What have you been told about why you are here today?
  • We want to discus the triple screen results and what they really mean
  • We want to get a family history to assess for any other risks related to pregnancy
  • We want to talk about the different testing options available to you.

Family history update (at beginning depending on level of anxiety)[]

  • Who in the family has been diagnosed with PKD?
  • What age were they diagnosed?
  • Do any of your family members have high blood pressure?
  • Do any other people in your family have kidney problems?

Medical History (related to PKD)[]

  • Do you see a doctor regularly?
  • Are you currently on any medication?
  • Have you had a renal ultrasound or CT scan?
  • Have you experienced any urinary tract infections?
  • Have you had high blood pressure?
  • Have you experienced any pain in your stomach or back?

Pregnancy History[]

  • Verify dates
  • Any exposures?
  • Any cig/alcohol/drug use?
  • Any increase in blood pressure?
  • Any ultrasounds so far? When is the next one scheduled?

Triple screen info.[]

  • The test itself
    • Best results at 16-18 weeks gestation (can be done from 15-22 weeks)
    • Tests mother's blood
    • NOT diagnostic...simply an indication for additional testing
    • Uses three markers to determine indicators for certain fetal problems
  • The three markers
    • produced by the fetus and the placenta
    • Alpha feto protein(AFP)
    • Human chorionic gonadotrophin (HcG)
      • Most sensitive risk factor for DS
      • Greater than 2.5 MOM indicated risk for DS
    • Estriol
      • Median of 0.5 MOM in Trisomy 18

Interpreting Results[]

  • Certain combinations of levels give us an indication for possible chromosomal abnormalities
  • Standard results AFP =1.0, hCG =1.0, uE3 =1.0
  • High AFP >2.0 or 2.5 MoM indicates ONTD ( see above)
  • High hCG >2.5 MoM indicates Down Syndrome(see above)
  • Low uE3 >0.8 MoM indicates Trisomy 18(see above)
  • Low AFP, high hCG, low uE3 indicates Down Syndrome
  • Low AFP(>0.75 MoM), low hCG(<0.55 MoM), low uE3(<0.60 MoM) indicates Trisomy 18

Patient's results[]

  • AFP = , HcG= , UE3=
  • Increased risk for Down syndrome

Explain chromosomes and what Down syndrome is[]

  • Trisomy 21 (usually - every cell of body)
  • Characteristics
    • intellectual disability (mild to moderate)
    • heart difficulties
    • ear infections
    • Do everything a regular kid can…ride a bike, walk, talk
    • Slower to reach milestones
    • Facial features
  • There is no cure

Calculating odds of Down Syndrome (explain how they determine num.)[]

  • Look at maternal age + AFP MoM + hCG MoM + uE3 MoM = Down Syndrome Risk
  • Risk ³ 1/270 is considered screen positive
    • This is equal to the midtrimester DSR for 35 year-old women
    • AMA woman's risk may be made less by the triple screen results, but it is still considered a test positive because of her age.

Recommendations for abnormal tests[]

  • Ultrasound for examination of physical abnormalities
    • Down Syndrome
      • Nuchal fold (2nd trimester)
        • detects 34%
      • Nuchal translucency (1st trimester)
        • detects 77%
      • Short femur/humerus (detects 80-90% when combined with one of the following two)
      • Echogenic bowel
      • Short ear
  • Amniocentesis
    • Explain procedure
    • 1/200 risk for complications
    • Can't detect all problems with the baby BUT will determine chromosome status
    • Fetal karyotype
      • Down Syndrome
      • Triploidy
      • Trisomies 13, 18
      • Other chromosomal abnormalities

The Basics of PKD[]

  • Definition
    • Multiple cysts in the kidney leading to kidney dysfunction
  • Prevalance = 1/400 - 1/1000
  • Characteristics
    • 90% penetrant
    • initial signs = high blood pressure, blood in urine (50%), pain in side, back or abdomen, UTI, kidney stones (20-30%)
    • Final stage = renal failure (60%) after age 40
    • Mitral valve prolaspse (26% compared to gen pop 2-3%)
    • aneurysms (5-10%) - occurs in familial clusters
    • liver cysts are possible
  • Diagnosis/medical management
    • renal ultrasounds
      • only after age 30 is a negative ultrasound = 5% risk of disease
    • computed tomography (CT) - to detect aneurysm
    • MRI
  • Prevention
    • Diet control = avoid red meat, eat low protein diet, less salt, fresh fruits and veggies, drink lots of water, avoid caffeine
  • Treatment
    • For pain
      • acetaminophren may help
      • laparoscopic surgery to "unroof" cysts
    • For renal failure
      • dialysis
      • renal transplant (75-80% of kidneys work for 5 years)
  • Inheritance (dominant more commonly - recessive is RARE)
    • Description of autosomal dominant and why this is the type
    • Chance of recurrence if the mother has it = 50% chance
    • Chance of recurrence if the mother doesn't have it same as population risk= <1%???? approximately 10% of the PKD patient community became infected through spontaneous mutation, and not through inheritance.
  • Genetics
    • Two genes identified (a third suspected)
    • PKD1 - 16p (90% of PKD) DX is earlier, progresses more rapidly, more likely to be hypertensive
    • PKD2 - chromosome 4
    • Testing is done through linkage

Her options[]

  • A amniocentesis for chromosome risk
  • A renal ultrasound for herself (PKD surveillance)
    • If it is negative and she is 30+, chance of having PKD is <5%
  • Testing by linkage analysis for herself and family
    • Costs approx. $2200 per family
    • >95% accurate in families
  • Prenatal determination (preferably after linkage has been established)
    • CVS testing for linkage studies (9-15 weeks)
    • Amniocentesis for linkage studies (15+ weeks)

Psychosocial issues[]

  • How her brothers illness has affected her
  • Scared about the possibility of having PKD?
  • Worried about PKD for baby?
  • Would a diagnosis of PKD influence a pregnancy decision?
  • How would having a child with DS feel?
  • Support and resources at home?
  • Would the dx of DS influence pregnancy planning?

Resources for patient[]

Notes[]

The information in this outline has not been updated since 2003.


Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling

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