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Flashcards in More Stories from the Genetics Clinic Deck (23):
1

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

2

What is the mechanism of imprinting?

DNA Methylation

3

Which base gets methylated?

5’ position on the pyrimidine ring of the cytosine

4

What is the general effect of methylation on the gene promoter?

Repressed gene transcription

5

The loss of function of a gene on which chromosome causes Prader-Willi and Angelman Syndrome?

Chromosome 15

6

State some symptoms of Prader-Willi Syndrome

Hyperphagia
Obesity
Mental Retardedness
Short Stature
Hypotonia
Infertility

7

State some symptoms of Angelman Syndrome.

-Developmental delay and speech impairment
-Movement disorder (gait ataxia)
-Behavioral uniqueness: happy demeanor; excitable, short attention span

8

What are the three possible causes of Prader-Willi and Angelman Syndrome?

Deletion of the PWS/AS critical region on chromosome 15
Uniparental isodisomy
Other mechanisms e.g. translocations

9

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.

10

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

11

What phenomenon determines the severity of mitochondrial disease?

Heteroplasmy

12

State two examples of mitochondrial disease

MELAS and LHON

13

State some symptoms of MELAS.

Mitochondrial encephalomyopathy (muscle weakness)
Lactic Acidosis (vomiting, diarrhoea)
Stroke
Episodic seizures, headache, hemiparesis

14

What mutations cause MELAS?

MTTL1 – tRNA translated codon as Phenylalanine instead of leucine
MTND1 and MTND5 – NADH Dehydrogenase subunits 1 and 5

15

State some symptoms of LHON

Painless bilateral loss of central vision leading to blindness

16

Mutations in what genes cause LHON?

MTND1, 4,5 and 6 – NADH Dehydrogenase subunits 1, 4, 5 and 6
MTCYB – cytochrome B

17

Give two examples of inborn errors of metabolism.

Phenylketonuria and MCAD deficiency

18

State some symptoms of Phenylketonuria

Mental retardation
Blonde hair/blue eyes
Eczema

19

How is phenylketonuria detected?

Elevated levels of phenylalanine in the blood

20

What is the treatment for PKU?

Remove phenylalanine from the diet

21

What is a common feature of MCAD Deficiency?

Episodic Hypoketotic Hypoglycaemia

22

A mutation in which gene causes MCAD Deficiency?

ACADM

23

What is the treatment for MCAD Deficiency?

Maintain adequate calorie intake to prevent the body from switching to beta-oxidation.