Genetic kidney disease - Polycystic kidney disease

Question 1

What are types of genetic differences that make you more susceptible to a disease?

Answer 1

Family history

Race

Question 2

What is a characteristic of an autosomal dominant condition?

Answer 2

Men and women are affected equally

Question 3

What is a characteristic of a X linked condition?

Answer 3

Affects males in a family

Inherited from mother

No affected offspring with only father affected

Question 4

What is a characteristic of an autosomal recessive condition?

Answer 4

Affected siblings have healthy parents

Question 5

What are the 4 mechanisms by which an autosomal dominant disease is expressed in the body

Answer 5

1. Haploinsufficiency - not enough protein made
2. Gain-of-function - mutant protein causes disease
3. Dominant negative - mutant protein inhibits wild type by interacting with it
4. Somatic second hit

Question 6

Describe the process by which somatic second hit leads to condition

Answer 6

When cell divides, it may experience a mutation as we age

In normal people - asymptomatic, still have one more copy of the healthy gene

If this happens a second time = no more of the protein is encoded. If this is an oncogene => cancer

In patients with only one normal copy of the gene = somatic second hit (mutation when dividing) is catastrophic

Question 7

What type of genetic condition is somatic second hit?

Answer 7

Inheritance = dominant

Cellularly = recessive, need somatic second hit to be expressed

Question 8

What conditions are characterised for being somatic second hit?

Answer 8

BRCA - ovarian and breast cancer

Polycystic kidney disease

Question 9

What two genes are linked to polycystic kidney disease?

Answer 9

PKD1 and PKD2

Not possible to distinguish in an individual which gene is defective

Question 10

What percentage of patients with kidney transplants do ADPKD sufferers represent?

Answer 10

10% - most common Mendelian condition in the UK

Question 11

What is the pathophysiology of ADPKD?

Answer 11

1. Cysts accumulate in the kidney and liver at random
2. Grow over course of a person’s life
3. High blood pressure develops
4. Renal function gradually deteriorates

Question 12

What is the median age of kidney failure in ADPKD patients?

Answer 12

55-65 years

Question 13

How is ADPKD diagnosed?

Answer 13

Family history

Flank pain or blood in urine

Scan for another reason

May present with kidney failure of high BP

Question 14

What does CT scan of ADPKD sufferers show?

Answer 14

Enlarged, cystic architecture of the kidney

Circular, non enhancing, homogenous lesions that surround and abliterate normal parenchyma

Question 15

What is a nephroctomy?

Answer 15

Removal of the kidney

Done in patients with extremely enlarged kidneys

Question 16

What are the extrarenal manifestations of ADPKD?

Answer 16

Increased risk of brain aneurysm

Liver cysts - commonly asymptomatic as don’t cause functional problems

Question 17

What are treatment options for ADPKD sufferers?

Answer 17

1. Control of BP - protect kidney function
2. Avoid dehydration - ADH released from posterior pituitary activates cAMP in cells lining the cysts = causes them to enlarhe
3. Drugs - Tolvaptan blocks V2 receptors and reduces rate of growth of cysts/ progression of kidney failure
4. Treat urine infection - if infection gets into cysts = difficult to treat since blood supply is removed

Question 18

Why do ADPKD sufferers have increased dialysis survival rates compared to sufferers of other renal conditions?

Answer 18

ADPKD is mainly a renal condition

Other conditions = multisystemic

Question 19

Why is there a smaller transplant pool amongst ADPKD sufferers?

Answer 19

Genetic condition -> family members are likely to have it

Question 20

Treatment for extrarenal manifestations of ADPKD

Answer 20

Aneurysms - screening

Liver cysts - rarely need transplant (1%)

Octreotide - agonist for somatostatin receptor, reduces cAMP levels in cyst cells