Trigger 10: Prader-Willi syndrome

Question 1

phenotypes associated with Prader-Willi syndrome

Answer 1

• short stature - hypotonia (poor muscle tone) - small hands and feet - obesity - mild- moderate learning difficulties

Question 2

how common is Prader-Willi

Answer 2

1/15,000

Question 3

Prader-Willi is caused by a defect in an

Answer 3

imprinted gene

Question 4

imprinting

Answer 4

You usually get one copy of genes from your mother and one from your father, in imprinting, one of the genes are silenced. - genes are expressed i an origin specific manner

Question 5

if a gene inherited from the father is imprinted

Answer 5

it is silenced

Question 6

in imprinting you inherit

Answer 6

one working copy

Question 7

if the allele from the father is imprinted …

Answer 7

it is silenced and only the allele forms he mother is expressed

Question 8

if the allele from eh mother is imprinted…

Answer 8

then only the allele from the father is expressed

Question 9

what happens when one gene is imprinted (turned off) and the other is defective

Answer 9

DISEASE e.g. PW

Question 10

imprinting (silencing of genes) is caused by

Answer 10

methylation within germ cells (eggs or sperm)

Question 11

abnormality in which chromosome causes PW

Answer 11

15

Question 12

Why will the phenotype of the offspring be normal

Answer 12

although the maternal gene is impritted (switched off by DNA methylation in the egg), only one copy of the functional gene is needed to be normal

Question 13

Why will this individual have PW?

Answer 13

Only need one copy of the gene to have a normal pehnotyep. however here deletiosn within the chromsome has caused the paternal copy to be defected = gene deleted

Question 14

In PW which allele is imprinted

Answer 14

maternal

Question 15

rare geentic disorders cannot

Answer 15

explain popualtion variation in BMI

• down to a mixture of enironment and genes

Question 16

when letpin is mutated

Answer 16

cant bind to its receptor on the orexigenic or anorexigenic pathway

–> therefore always seems low level-> causes activation of AGPR

Question 17

when leptin recepor mutated

Answer 17

wont bind leptin

• increase hunger due to leptin decreasing hunger at high level

Question 18

MC4R

Answer 18

chidlren get larger and talller

• more hungy
• more food absorbed and less excreted
• high fasting isnulin

Question 19

POMC

Answer 19

when mutated it stops satition signals from being sent

• oxregigenic pathway stays stimulated

Question 20

which part of the brain controls hunger

Answer 20

hypothalic arcuate nuceleus

Question 21

obese patients are

Answer 21

leptin resistant

Question 22

decrease in fat- e.g. when hungry

Answer 22

decrease in leptin

• less leptin bounds to its leptin receptor
• stimulates release of particular NT e.g. AgPR
• AgPR stimulates the orexigenic pathway
• leptin also inhibts POMC receptors- reducing amount of MSH released
• Inhibiting MSH release keeps us from feeling full

Question 23

increase in fat after meal

Answer 23

• increase in leptin
• stimulates anorexigenic pathway
• when leptin receptor not stimulated, AgRP not released, inhibiting appetite
• increase i leptin stimulates POMC neurones, increasing the amount of MSH released- tells us we are full