2.15 Flashcards
(20 cards)
The same allele can have a different effect, depending on which parent it was
inherited from
Prader-Willi syndrome is a genetic condition that affects
1 in every 12000-15000 people
Prader-Willi affects both sexes and all
ethnic groups
Prader-Willi is caused by
deletion of some of the genetic material on chromosome 15
A child only develops Prader-Willi syndrome if the defective chromosome 15 is inherited from the
father
12 main features of a child born with Prader-Willi:
- characteristic facial features (e.g. almond-shaped eyes, down-turned mouth, eyes close together, eyes pointing in different directions, thin upper lip)
- development delay including mild-moderate learning difficulties
- feeding problems in infancy leading to low weight gain
- underdevelopment of the sex organs and delayed puberty
- poor muscle tone
- rapid weight gain between 1-6years, can lead to serious obesity if no steps are taken to reduce this
- extreme hunger and obsession with food
- infants and children are usually happy and loving, with few behaviour problems, older children and adults may show behaviour problems, including temper tantrums and violent outbursts
- obsessive/compulsive behaviour (stealing and lying)
- usually short in stature, with small hands and feet
–often fair skin and light-coloured hair
-may have speech problems
No cure for PWS but many of the symptoms can be
managed
A key priority for PWS is to manage the person’s
weight
Parents of children with PWS need to give the child a
balanced, low-energy diet with plenty of vitamins and minerals
The use of growth hormone helps the child to
grow taller
gain more muscle mass
Sex hormones may be used to
encourage more normal sexual development at puberty
Advice is given about
behavioural management
Speech and language therapy will help if there are
speech disorders
Special educational programmes can assist the child to develop to their
full potential
During gametogenesis certain genes in both sperm and oocytes are modified by the addition of
methyl (-CH3) groups
The addition of methyl (-CH3) groups is called
epigenetic imprinting
Epigenetics is used to describe
inherited changes in the DNA that do not involve a change in the DNA base sequence
As a result of epigenetic imprinting, the chromosome is ‘labelled’ as
maternal or paternal and this means that they have different effects on the developing embryo
The process must be
reversible - father to daughter = paternal, daughter to her child = maternal
Epigenetic changes may be brought about by the environment, e.g. some heavy metals and pesticides can cause changes in DNA methylation - this also decreases as
cells age
