Flashcards in More Stories from the Genetics Clinic Deck (23):
What happens if the full genome of an embryo derives from one parent and what is the significance of this finding?
Paternal – hydatidiform mole
Maternal – ovarian teratoma
Shows that the origin of the parental DNA is important
What is the mechanism of imprinting?
Which base gets methylated?
5’ position on the pyrimidine ring of the cytosine
What is the general effect of methylation on the gene promoter?
Repressed gene transcription
The loss of function of a gene on which chromosome causes Prader-Willi and Angelman Syndrome?
State some symptoms of Prader-Willi Syndrome
State some symptoms of Angelman Syndrome.
-Developmental delay and speech impairment
-Movement disorder (gait ataxia)
-Behavioral uniqueness: happy demeanor; excitable, short attention span
What are the three possible causes of Prader-Willi and Angelman Syndrome?
Deletion of the PWS/AS critical region on chromosome 15
Other mechanisms e.g. translocations
Describe how uniparental isodisomy can lead to Prader-Willi and Angelman Syndrome.
Non-disjunction in meiosis 2 makes a gamete that has two copies of chromosome 15 resulting in a zygote with three copies of chromosome 15. Failure to remove the duplicated chromosome results in the zygote having two copies of chromosome 15 from the same parent.
How is PWS and AS diagnosed? Which genes near/in the PWS/AS critical region are used?
FISH – fluorescence in situ hybridisation
OR methylation specific PCR
PML (promyelocytic leukaemia) gene is just outside the PWS/AS critical region snRNP (small nuclear ribonucleoprotein) gene is inside the PWS/AS critical region
What phenomenon determines the severity of mitochondrial disease?
State two examples of mitochondrial disease
MELAS and LHON
State some symptoms of MELAS.
Mitochondrial encephalomyopathy (muscle weakness)
Lactic Acidosis (vomiting, diarrhoea)
Episodic seizures, headache, hemiparesis
What mutations cause MELAS?
MTTL1 – tRNA translated codon as Phenylalanine instead of leucine
MTND1 and MTND5 – NADH Dehydrogenase subunits 1 and 5
State some symptoms of LHON
Painless bilateral loss of central vision leading to blindness
Mutations in what genes cause LHON?
MTND1, 4,5 and 6 – NADH Dehydrogenase subunits 1, 4, 5 and 6
MTCYB – cytochrome B
Give two examples of inborn errors of metabolism.
Phenylketonuria and MCAD deficiency
State some symptoms of Phenylketonuria
Blonde hair/blue eyes
How is phenylketonuria detected?
Elevated levels of phenylalanine in the blood
What is the treatment for PKU?
Remove phenylalanine from the diet
What is a common feature of MCAD Deficiency?
Episodic Hypoketotic Hypoglycaemia
A mutation in which gene causes MCAD Deficiency?