Down's syndrome

Question 1

Define DS

Answer 1

A common genetic disorder caused by defect in chromosome 21

Question 2

what is DS aka

Answer 2

Trisomy 21

Question 3

What are the risk factors of DS

Answer 3

Increased age of mother (over 35)
Previous child with DS
Both parents being carriers for the genetic translocation of DS

Question 4

What are the causes of Ds

Answer 4

Most commonly: Non-disjunction - failure of chromosome 21 to separate properly resulting in 3 copies of the chromosome rather than the normal 2

Chromosomal translocation - swapping of part of the chromosome 21 with part of chromosome 14

Question 5

List the signs/symptoms of DS

Answer 5

Small head and neck
Abundant neck skin
Wide hands with short fingers
Protruding, large tongue 
Flat facial profile
Upwards slanting eyes
Flat ears which are positioned lower than normal 
Simian crease (1 crease during flexion)
Growth stunt 
Umbilical hernia
Low muscle tone

Question 6

List some complications of DS

Answer 6

Congenital heart defects e.g. AV or ventricular septal defect
Acute lymphoblastic leukaemia
Hypothyroidism
Hirschsprung’s disease - failure of nerves around anus to develop properly
Duodenal atresia - failure of first part of intestine to develop properly
Alzheimer’s risk
epilepsy risk
infertility (males)

Question 7

List the processes that occur in the first 4 weeks of organogenesis

Answer 7

week 1: fertilisation, cleavage, morula formation, blastocyst formation, blastocyst enters uterine cavity and hatch out of the zone pellucida

Week 2: blastocyst implant on endometrium and implants, bilaminar disc forms as inner cell mass becomes the hypoblast and epiblast layers.

week 3: gastrulation occurs and three germ layers form, notochord, neural tube and heart tube forms

Week 4: 4 limb buds appear, heart begins to beat, neural tube CLOSES

Question 8

List the processes that occur in the first 5-8 weeks of organogenesis

Answer 8

week 5-7: heart separation occurs
week 5-10: physiological umbilical hernia of midgut (out on week 5, back in week 10)

week 6: circulation system appears, clavicle begins to ossify, Sertoli cells appear in gonad, heart and lungs descend into thorax

week 7: limb buds rotate

week 8: bone ossification occurs, foetus looks human, all component of upper and lower limbs are distinct.

Question 9

list the physical changes that occur during pregnancy

Answer 9

Weight gain of around 12.5 kg
Enlargement of the uterus which pushes the intestines, stomach and liver superiorly.
Diaphragm is elevated ad thoracic cavity widens.
Compression of the ureters and urinary bladder = frequent urination
Increased cardiac output (by 40%)
Heart enlarges to accommodate large blood volume
Pituitary gland enlarges (by around 50%)
Thyroid gland increases due to increased activation by hCG

Question 10

During pregnancy, what makes oestrogen and list its roles

Answer 10

First trimester: corpus luteum
Rest of pregnancy: placenta

Enlargement of uterus, breast and mammary glands
Contraction of uterus
Increases blood supply to uterus - provides nutrients
Stimulates growth and development of mammary glands
Improve immune function
Relaxes pelvic ligaments

Question 11

During pregnancy, what makes progesterone and list its roles

Answer 11

First 10 weeks: corpus luteum
Rest of pregnancy: placenta

Inhibits contraction of uterine smooth muscle
Inhibits lactation
Maintains endoemtrial lining
Reduces maternal immune response to allow acceptance of pregnancy
Boosts thyroid function

Question 12

During pregnancy, what makes Human Chorionic gonadotropin hormone and list its roles

Answer 12

Produced by placenta

Prevents involution of corpus luteum to prevent menstruation. (keeps it viable)
Causes corpus luteum to continue secretion of progesterone and oestrogen.

Question 13

List the 3 antenatal screening tests and when they are carried out

Answer 13

10 weeks: BLOOD TEST - sickle cell anaemia, thalassaemia and infections such as HIV, hepatitis B and syphyllis.

11-14 weeks: COMBINED - checks for chromosomal abnormalities e.g. Down’s, Edward’s and Patau’s syndrome.

18-21 weeks: ULTRASOUND – checks for physical abnormalities e.g. Spina Bifida

Question 14

What is the process of checking for Down’s syndrome (what they check for in screening test and what the tests are for diagnostic test)

Answer 14

Screening tests: checks fluid at the back of the baby’s neck to determine the nuchal transparency. iF there are higher levels than normal it is suggestive of DS risk.

Nest step:-
Diagnostic test: 
Chorionic Villus sampling
Amniocentesis
Quadruple test

Question 15

Describe chorionic villus sampling and when it happens

Answer 15

WEEKS 11-14:

Needle is inserted into villus of the chorion and small sample of tissue is taken from placenta.

Question 16

Describe amniocentesis sampling and when it happens

Answer 16

AFTER 15 WEEKS:

needle is inserted and amniotic fluid from amniotic sac is sampled.

Question 17

Describe quadruple SCREENING test - what does it measure ?

Answer 17

THIS IS A SCRENING TEST.
If the combined test was not possible.

Measures levels of alpha fetoprotein and unconjugated estriol (LOW), hCG and inhibin A (HIGH)

Question 18

What supplements should be given to pregnant women, how much and why?

Answer 18

Folic acid: (400 micrograms/day) given to prevent neural tube defects e.g. Spina Bifida

Vitamin D (10 micrograms/day) 
given - regulates calcium and phosphate in the body, which are needed to keep ones and teeth healthy

Question 19

What supplements should be avoided during pregnancy ?

Answer 19

Vitamin A as they can harm the baby

Question 20

what risks do DS diagnostic tests pose?

Answer 20

risk of miscarriage