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Y1 - MCD > Genetics 4-5 > Flashcards

Genetics 4-5 Flashcards

1
Q

What is a silent mutation?

A

Change in the third nucleotide but does not cause a change in the amino acid translated.

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2
Q

What is a driver mutation?

A

The first mutation that causes the cell to change from normal to a mutated cancerous cell.

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3
Q

What is a tumour-suppressor gene?

A

Acts as a cell cycle regulator and as the stop signal. Controls mitosis so it does not lead to uncontrolled growth.

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4
Q

What are photo-oncogenes?

A

Opposite of tumour suppressor genes. Promote growth and proliferation. Normally growth factors, transcription factors or tyrosine kinases.

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5
Q

What does Knudson’s two-hit hypothesis state?

A

That mutations in both alleles of a gene are needed to cause a disease. Hit 1 is normally a point mutation whereas hit 2 is normally a deletion, causing total loss of transcription and giving rise to malignancy potential.

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6
Q

What is retinoblastoma?

A

A checkpoint protein between G1 and S phase which normally binds to E2F (transcription factor) to prevent growth factor release.

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7
Q

What happens in the case of mutant retinoblastoma?

A

Retinoblastoma can’t properly bind to E2F so growth signals are produced, possibly causing malignancy.

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8
Q

What mutations can cause inherited breast cancer?

A

BRCA1 and BRCA2 germline (less common)

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9
Q

What are healthy BRCA genes responsible for?

A

Normally are tumour suppressor genes but when mutated they lose the ability to stop the cell cycle.

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10
Q

What does the BRCA mutations also predispose an individual to?

A

Ovarian cancer

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11
Q

How does the BRCA mutations change risk to breast cancer?

A

Increases lifetime risk up to 60% of developing breast cancer before the age of 90.

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12
Q

What conditions can predispose an individual to colorectal cancer?

A

Adenomatous polyposis and Lynch syndrome

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13
Q

What is the risk of developing colorectal cancer if they have predisposing conditions?

A

Almost 100% lifetime risk

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14
Q

What is pharmacogenomics?

A

Branch of pharmacology which deals with the influence of genetic variation on drug response. Allows personalisation of drug treatment.

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15
Q

When is a nuchal scan performed?

A

Between the 10th and 14th week.

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16
Q

What does a nuchal scan measure and detect?

A

Thickness of the fluid at the back of the foetus’ head. Increased thickness can indicate chromosomal abnormalities (Down syndrome), birth defects and skeletal dysplasia

17
Q

What are the two prenatal scanning methods used?

A

Ultrasound and foetal MRI

18
Q

When is a foetal MRI performed and what does it measure?

A

After 20 weeks. Measures nasal bone (another test for Down syndrome and cardiac defects)

19
Q

When can an ultrasound be performed?

A

From 5 weeks but best after 9 weeks.

20
Q

What are the two non-invasive prenatal tests used?

A

Maternal blood test and cell-free foetal DNA.

21
Q

How does the maternal blood test work?

A

Markers in the blood detect an increased risk of foetal trisomy 21, 18 and neural tube defects

22
Q

How does cell-free foetal DNA work?

A

Analyses the DNA fragments in the blood. 10-20% of this comes from the placenta which is representative of the unborn foetus.

23
Q

Which test determines the gender of the baby?

A

Cell-free foetal DNA

24
Q

What is cell-free foetal DNA used for?

A

Determines the sex of the baby and can be used to investigate X-linked recessive disorders.

25
Q

What are the two invasive prenatal tests used?

A

Chorionic villus sampling (CVS) and an amniocentesis

26
Q

How does CVS work?

A

Done either trans-abdominally or trans-vaginally. Takes a sample of the chorionic villus (developing part of the placenta) which carries the same DNA as the foetus.

27
Q

When can CVS and amniocentesis be performed?

A

CVS - 11-14 weeks

Amnio - 16 weeks onwards

28
Q

How does an amniocentesis work?

A

Takes a sample of the amniotic fluid through the abdomen which contain foetal cells.

29
Q

What are the risks associated with CVS and an amniocentesis?

A

CVS - 1-2% chance of miscarriage

Amnio - 1% chance of miscarriage and risk to infection is increased

30
Q

What is PGD?

A

Pre-implantation genetic diagnosis. A genetic test carried out on IVF embryos before implantation to make sure they are free of certain genetic conditions that the parents are at risk of passing on to their offspring.

31
Q

What is the criteria for PGD?

A
  • Female partner younger than 40
  • Female partner bMI between 19 and 30
  • Both non-smokers
  • Have no living unaffected children from relationship
  • Known risk of child having serious genetic condition
    Eligible couples are given three rounds of PGD.
32
Q

What are the five main neonatal screening tests in the UK?

A
  • Sickle cell disease
  • Cystic fibrosis
  • Phenylketouria
  • MCAD deficiency
  • Congenital hypothyroidism
33
Q

What are the symptoms/signs of phenylketonuria?

A
  • Severe mental retardation
  • Eczema
  • Tyrosine deficiency (decreased melanin) so blonde hair and blue eyes
  • Phenylalanine hydroxylase deficiency
    Phenylalanine accumulates (causing brain damage) and is covered to phenylpyruvate and excreted in the urine.
34
Q

How is phenylketonuria diagnosed and treated?

A
  • Early detection is required
  • Screen for increased phenylalanine in the blood
  • Treated by removing excess phenylalanine from diet
35
Q

What does MCAD stand for?

A

Medium-chain Acyl-CoA dehydrogenase

36
Q

What are the signs/symptoms of MCAD?

A
  • Coma
  • Metabolic acidosis
  • Episodic hypoketonic hypoglycaemia
  • Encephalopathy
  • Sudden death (SIDS)
    Any fat that is absorbed is not useful as beta oxidation cannot be performed due to a deficiency in MCAD enzyme.
37
Q

What is a common cause of monogenic obesity?

A

Unresponsive to leptin. Leptin is a hormone produced by adipose tissue working on the brain. Obese people produce more leptin and sometimes the receptors can become immune to it, resulting in uncontrolled appetite and consequent obesity.

38
Q

What gene is thought to be the most common cause monogenic diabetes?

A

MC4R dominant allele

Y1 - MCD (38 decks)

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