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Genetics Flashcards

1
Q

Why are people referred to genetics?

A
  • Family history genetic condition in relatives
  • Diagnosis of genetic conditions (known / unknown)
  • Management of genetic conditions
  • Genetic counselling
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2
Q

What do people need to know before undergoing a genetic test?

A
  • What test is for / what’s the point in having it done?
  • How likely is it to be positive
  • What happens if its positive
  • What if its negative
  • What if false positive / false negative
  • Implications for other family members of positive results
  • DNA stored
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3
Q

What types of pregnancy testing/screening are there?

A
  • Targetted

- Whole population

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4
Q

When may someone undergo genetic screening?

A
  • Antenatal
  • Neonatal
  • Child
  • Adult
  • Pre-pregnancy
  • In maturity
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5
Q

What types of genetic testing is available in relation to reproducing?

A
  • Test at birth
  • Chorionic villus sampling
  • Amniocentesis
  • Pre-implantation genetic diagnosis
  • Adoption
  • Gamete donation
  • Non invasive prenatal testing
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6
Q

When can non invasive prenatal testing be performed?

A

Around week 10

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7
Q

What is the inheritance of Duchenne muscular dystrophy?

A

X-linked

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8
Q

What types of genetic testing are associated with Ducehnne muscular dystrophy?

A
  • Carrier testing
  • Prenatal diagnosis
  • Pre-implantation diagnosis
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9
Q

What are the features of autosomal dominant inheritance?

A
  • Each child has 50% chance of inheriting mutation
  • No skipped generations
  • Equally trasmitted
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10
Q

How is Down syndrome screened for?

A
  • Maternal age
  • Triple screening
  • CUBS screening
  • Selection for amniocentesis
  • Free fetal DNA
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11
Q

Give examples of common recessive disorders that raise screening issues.

A
  • N. Europe Cystic Fibrosis
  • Africans Sickle Cell DiseaseS
  • Mediterranean, Asia Thalassaemias
  • Ashkenazi Jews Tay-Sachs disease
  • CF W1282X
  • Breast / ovarian cancer BRCA1
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12
Q

What targeted carrier testing is available in the UK?

A
  • CF mutation analysis 80-90% sensitive
  • Haemoglobinopathy MCV, Hb electrophoresis , sickledex
  • Tay Sachs enzyme activity
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13
Q

What is CF caused by?

A

Defect of cellular chloride transport

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14
Q

How is CF diagnosed?

A
  • Immunoreactive trypsin (first 6 weeks)
  • Sweat test
  • Genotyping
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15
Q

How can CF present?

A
  • Lung infections
  • Meconium ileus
  • Pancreatic insufficiency
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16
Q

What is the prevalence of CF?

A

1 in 2,500

17
Q

What is sickle cell disorder caused by?

A

Abnormal Hb gene

18
Q

What does sickling cause?

A
  • Pain+++
  • Cold, dehydration, infections
  • Jaundice, stroke, leg ulcers, eyes, kidneys
  • Anaesthetic issues
19
Q

What is Tay Sachs disease

A

Progressive, genetic, lysosomal storage disease.

20
Q

What is the cause of Tay Sachs disease?

A

Hexosaminidase A (hex-A) deficiency results in the build up of lipid GM(2) ganglioside, esp. in nerve cells in the brain.

21
Q

How does Tay Sachs disease present?

A
  • Baby usually develops normally until about 6 months of age.
  • Progressive neurological deterioration.
  • Usually fatal by 3-5 years.
22
Q

What is the epidemiology of Tay Sachs disease?

A
  • 1in 25 Ashkenazi Jews are carriers

- 1 in 250 of the general population are carriers.

23
Q

What is involved in new-born screening?

A
  • Clinical examination
  • hearing
  • Blood spot
24
Q

Why do we screen babies?

A
  • To enable early detection of pre-symptomatic babies
  • To enable early treatment to improve health
  • To reduce anxiety caused by uncertainty over symptoms before clinical diagnosis is made
25
Q

What do we screen for in new-borns?

A
  • PKU
  • Congenital hypothyroidism
  • Sickle cell disease
  • Medium chain acyl CoA dehydrogenase deficiency
  • CF
  • Homocysteinuria
  • Isovaleric acidaemia
  • Maple syrup urine disease
  • Glutaric aciduria type 1
26
Q

What is the prevalence of PKU?

A

Affects approximately 1 in 10,000 babies in UK (ie about 80 born each year)

27
Q

What is the inheritance of PKU?

A

Recessive (biochemical screen, carriers not identified)

28
Q

What is PKU?

A

Babies with the condition are unable to break down phenylalanine (amino acid)

29
Q

When should PKU treatment start?

A

By 21 days

30
Q

How does PKU present?

A
  • Untreated babies develop serious, irreversible, mental disability
  • Early treatment with a strictly controlled diet prevents disability
31
Q

What is the epidemiology of congenital hypothyroidism?

A
  • 1 in 4,000 babies UK

- 1 in 10 cases inherited – hormone test

32
Q

When should treatment for congenital hypothyroidism start?

A

By 21 days

33
Q

How does congenital hypothyroidism present?

A
  • Untreated babies -> serious, permanent, physical and mental disability
  • Early treatment with thyroxine tablets prevents disability
34
Q

What is the problem in congenital hypothyroidism?

A

Baby does not have enough thyroxine

35
Q

What is the epidemiology of MCADD?

A

1 in 10,000-20,000 UK babies

36
Q

What is the inheritance of MCADD?

A

Recessive (carriers not identified)

37
Q

What is the problem in MCADD?

A

Babies with MCADD cannot easily break down fat to make energy for the body

38
Q

How do babies with MCADD present?

A
  • Serious life-threatening symptoms can occur quickly in babies not feeding well or unwell
  • Mean age at first presentation is14 months.
  • 25% mortality rate
39
Q

What is the treatment for MCADD?

A
  • Treatment to prevent metabolic crisis: avoid fasting and monitor frequency of meals
  • Emergency regime: glucose polymer (maxijul) and IV dextrose

Reproduction (34 decks)

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