Downs syndrome

Question 1

What are risk factors for down syndrome?

Answer 1

• increasing maternal age
• previous child with down syndrome

Question 2

Describe the clinical features of down syndrome

Answer 2

• clinical heart defects
• Mental retardation (IQ 30-60), higher risk of alzheimers
• Increased risk of Leukemia
• Middle phalange of the 5th finger is shorter than normal, causing fifh finger clinodactyly (curvature basically)
• Flat face
• Protruding tungue

Question 3

What is the life expectancy of someone with down syndrome?

Answer 3

50 years

Question 4

Are people with down syndrome infertile?

Answer 4

Sometimes. Women with down syndrome give birth to children with down syndrome 40% of the time.

Question 5

A downs syndrome screening can be slightly different depending on how far along the pregnancy is. One is before 14 weeks, whilst the other can be between 14-20 weeks. State what each test consists of.

Answer 5

< Week 14: Blood test and Nuchal Translucency scan

Weeks 14-20: Blood test

Question 6

Explain what the Nuchal translusency test is for downs syndrome screening

Answer 6

• Ultrasound scan
• Measures the translusency of the collection of fluid under the skin at the back of the fetus’ neck

Question 7

Describe what blood tests are measuring in downs syndrome screening

Answer 7

• PAPP-A (Pregnancy assoicated plasma protein A) - this is typically lowered in downs syndrome children
• Free levels of HCG being increased is possible marker of downs syndrome

Question 8

Screening tests can only indicate the likelyhood or chances that a mother is carrying a baby with Down syndrome. What are they main diagnostic tests for down syndrome?

Answer 8

Chorionic Villus sampling

Amniocentesis

Question 9

Describe amniocentesis

Answer 9

• Sampe of fluid that bathes the fetus is withdrawn through a needle inserted in through the mother’s abdominal wall then into the uterus
• Sample is then used to analyse the chromosome of the fetus
• Low risk of miscariage

Question 10

Describe chrionic villus sampling

Answer 10

A catheter is guided through the vagina, cervix and then advanced to the chorionic villi (which contain the fetal capillaries under ultrasound guidance)Tissue is taken to test for chromosomal abnormalities.

Question 11

Explain the pathogenesis of Down syndrome

Answer 11

• 3 copies of chromosome 21
• Failure of separation of chromosmes (during meiosis I of gametogenesis) - this is called nondisjunction (94%)
• translocation of the long arm of chromosome 21 to another chromosome such as 14 accounts for 5% of cases
• Mosaicism - failure of chromosome separation during MITOSIS