Genetics

Question 1

What is the mode of inheritance of Huntington’s Disease?
~ What is the repeated gene?

Explain what anticipation is:

List some symptoms/ signs of huntingtons: (4)

What type of penetrance does the disease have? - What does this mean for family members with the gene?

Answer 1

Autosomal dominant
~ CAG gene repeats

Anticipation: Successive generations inherit more CAG repeats in the gene → earlier onset & increased severity of the disease

• Chorea (involuntary, abnormal movements)
• Dementia (poor memory/ cognitive function)
• Personality change
• Depression/ psychosis etc

Full penetrant - all family members with the gene will develop the disease at some point

Question 2

Amyotrophic lateral sclerosis is a type of what disease?

List some features of this condition: (4)

What gene mutation is associated with this condition?

What is the treatment of this condition?

What type of penetrance does the disease have? - What does this mean for family members with the gene?

Answer 2

Motor neurone disease

ONLY motor symptoms!!!!!!
• Progressive muscle weakness (LMN)
• Muscle wasting (LMN)
• Hyper-reflexia (UMN)
• Spasticity (UMN)

SOD gene

NO TREATMENT

Incomplete penetrance:
~ People with the gene don’t always develop the disease so offspring may/ may not be affected
~ Environmental factors ‘switch’ the gene on - nobody knows how/ why

Question 3

Germline mutations:
• occur in what cells?
• can mutations be passed on to offspring?

Somatic mutations (non-germline):
• occur in what cells?
• can mutations be passed on to offspring?

Answer 3

Germline:
• mutations occur in egg/ sperm
• mutations are passed to offspring - offspring will have the mutation in every cell within their body!

Somatic:
• mutations occur in any cell of the body except egg/ sperm
• mutations are not passed to offspring

Question 4

Lynch syndrome (HNPCC) is caused by mutations in what?

What mode of inheritance is seen in Lynch syndrome?

What are the 3 commonest cancers associated with the condition?

Answer 4

DNA mismatch repair genes

Autosomal dominant

** Colon cancer ** - commonest in distal colon
• Endometrial
• Ovarian

Question 5

Tuberous Sclerosis is a genetic condition in which hamartomas form throughout the body (benign tumours composed of multiple cell types).
What is the mode of inheritance?

What are the classic triad of features seen in Tuberous Sclerosis?

List some skin lesions seen in this condition: (3)

Answer 5

Autosomal dominant

• Epilepsy
• Learning difficulties
• Skin lesions
• Ash leaf spots
• Shagreen patches
• Angiofibromas (looks like acne on nose, cheeks, chin)

Question 6

What is Neurofibromatosis Type 1 (NF1)?

What mode of inheritance is seen in NF1?

List some common symptoms/ signs of NF1: (5)

Answer 6

A genetic condition that causes cancers to grow along the nerves (often benign but can turn malignant)

Autosomal dominant

• Cafe au lait spots (coffee colour patches on the skin) - see below
• Axilliary freckling
• Neurofibromas (small nodular tumours on the skin)
• Brown patches on the iris
• Learning difficulties/ epilepsy

Question 7

What is the mode of inheritance of Myotonic dystrophy?
~ What is the repeated gene?

Explain what anticipation is:

List some symptoms/ signs of Myotonic dystophy: (6)

Answer 7

Autosomal dominant
~ CTG repeats

Anticipation: Successive generations inherit more CTG repeats in the gene → earlier onset & increased severity of the disease

• Distal muscle weakness/ stiffness (diaphragm/ face)
• Saggy face (due to muscle weakness)
• Bilateral ptosis
• Bilateral cataracts
• Frontal balding
• Difficulty letting go after shaking someones hand