Cycstic fibrosis

Question 1

How is cycstic fibrosis inherited

Answer 1

Autosomal recessive

One of the most common autosomal recessive in caucasion population

Question 2

Describe a referal form for cyctic fibrosis

Answer 2

6 yr old girl
High amount of salt in sweat
Recurrent chest infections
Had fetal echogenic bowel
Genetic testing please

Question 3

How many people does CF affect?

Answer 3

CF affects 1 in 2500 live births (carrier frequency of 1 in 25)

Question 4

Whats the life expectancy of CF patients?

Answer 4

Life expectancy ~42 years
Increase from 31 years (15 years ago)
Expected that children born today with CF will live to 50 years

Question 5

What is the gene that causes CF

Answer 5

CFTR gene
Cystic fibrosis transmembrane conductance regulator

Question 6

What is the role of CFTR gene?

Answer 6

Forms chloride channel in membrane of secretory epithelial cells

These cells produce mucus, sweat, saliva, tears, & digestive enzymes

Transports negatively chloride ions into and out of cells

Helps control the movement of water in tissues

Necessary for production of thin, freely flowing mucus

Lubricates & protects the lining of the airways, digestive system, reproductive system, & others

Question 7

What do mutations of CFTR gene cause?

Answer 7

Result is defective chloride transport - don’t get good control of movement of water as you should

Mutations in CFTR gene 🡪 defective chloride transport

Abnormally thick mucus in epithelia of organs 🡪 Multi-organ effects

Question 8

How is CF a multisystem disorder?

Answer 8

Pulmonary

Pancreatic

Gastro-intestinal

Reproductive (males)

Question 9

Describe the pulmonary features

Answer 9

Responsible for at least 80% of CF-related deaths
Thick mucus blocks airways 🡪 chronic obstructive airway disease
Leads to bronchiectasis - Persistent and progressive dilation of bronchi or bronchioles in lungs
Increased susceptibility to chronic respiratory infections,

Question 10

Describe the reproductive features

Answer 10

> 95% males with CF are infertile

Obstructive azoospermia (no sperm in semen)

Congenital absence of the vas deferens (CBAVD) – tubes that carry sperm out of testes

Can be seen as an isolated feature (CFTR spectrum)

Females are fertile, though some evidence of abnormal cervical mucus contributing to infertility

Represents 1.2-1.7% of male infertility

Question 11

Diagnostic tests for cystic fibrosis

Answer 11

Sweat (chloride) test

Question 12

Sweat (chloride) test

Answer 12

CF patients have high amount of salt in sweat
Uses Quantitative pilocarpine iontophoresis
(pilocarpine stimulates sweating, collect sweat using filter paper, measure chloride)
Positive = increased Chlorine in sweat
Done in Biochemistry departments
24hr result
An old diagnostic test for CF - but still used!

Question 13

CF referralls for CF for genetic testing: Diagnostic

Answer 13

Diagnostic Recurrent chest infection
Failure to Thrive
Chronic pancreatitis
Fetal echogenic bowel
Meconium ileus

Question 14

CF referralls for CF for genetic testing: : Family

Answer 14

Carrier and predictive testing
Prenatal

Question 15

CF referralls for CF for genetic testing: Infertility

Answer 15

Azoospermia / Oligospermia / OATS
Gamete donors

Question 16

CF referralls for CF for genetic testing: Newborn screening

Answer 16

Raised IRT on NBS bloodspots

Question 17

Describe CFTR gene

Answer 17

Autosomal recessive
CFTR gene located at 7q31
>2000 mutations, throughout 24 exons

Question 18

Describe CF genetics

Answer 18

Most CFTR variants are missenses & small deletions

deltaF508 or F508 is most common variant (70% of variants)

More correctly called p.Phe508del

A 3 nucleotide deletion causing loss of a phenylalanine (Phe or F) amino acid in exon 10

c.1521_1523delCTT

Mutation types and frequencies also vary between populations

Question 19

Why such a high frequency of CFTR heterozygotes?

Answer 19

Genetic defects leading to reduced CFTR protein expression or chloride transport capacity lead to cystic fibrosis

Conversely…

Overstimulation of CFTR in intestinal epithelial cells by bacterial toxins leads to secretory diarrhoea

Having less CFTR may provide a selective advantage

Toxins (such as cholera) activate the protein kinases responsible for “priming” the CFTR channel

• Much larger world health problem: 3 million deaths per year of children the age of 5

Question 20

GENETIC TESTING

Answer 20

1. Sequence whole gene

Or

2. Test for specific most common variants?
   And
   Follow up whole gene sequnece if needed?

Elucigene CF-EU2v1 assay
Fluorescent ARMS PCR (amplification refractory mutation system)
50 mutations panel

Question 21

CF-EU2V1 ASSAY

Answer 21

Primer sequence specific for variant
If variant not present, primer doesn’t bind
No PCR product
Variant present – primer binds – PCR product#
Also primer for wildtype

Question 22

Look at slides for CF-EU2V1 assay results

Question 23

P.(ARG117HIS)(;)(PHE508DEL) COMPOUND HETEROZYGOUS

What does this mean for the patient?

Answer 23

Positive for two CFTR mutations:
Arg117His
Phe508del
Confirms diagnosis of Cystic Fibrosis
Are they are the same or different allele?
Recommend carrier status of parents be checked

Question 24

What does autosomal recessive mean?

Answer 24

If both parents are carriers

25% risk of affected child

50% risk of carrier child

Question 25

How has there been significant improvement in life expectancy over last 20 years

Answer 25

Mainly due to: -
Centralisation of care at cystic fibrosis centres (MDT)
Aggressive proactive treatment of symptoms

Question 26

Treatment for respiratory symtpoms

Answer 26

Respiratory
– Physiotherapy
– Oral, inhaled or IV antibiotics
– Bronchodilators
– Mucolytic agents to reduce
mucus viscosity
– Anti-inflammatory agents
– Home oxygen therapy
– Lung or heart-lung transplantation
– Lifestyle (exercise)

Question 27

Treatment for GI symptoms

Answer 27

GI
– High calorie, high fat diet
– Supplemental feeding
– Oral pancreatic enzyme replacement therapy
– Tube feeding

Question 28

Treatment for infertility

Answer 28

CABVD
– ART (microscopic epydidymal sperm aspiration (MESA) and intracytoplasmic sperm injection (ICSI)

Question 29

Molecular therapies

Answer 29

Personalised medicines that are designed to work with specific CFTR mutations
Four drugs have been licenced for use in the UK: Symkevi, Kalydeco, Orkambi and Kaftrio

Question 30

Symkevi

Answer 30

Combination of ivacaftor and tezacaftor – effective for those homozygous for F508del and those compound heterozygous for p.(Phe508del) and another residual function mutation Licenced for those over 12 years of age.

Question 31

Kalydeco

Answer 31

Ivacaftor only. effective in anyone with at least one of the following nine gating mutations: G551D, G178R, S549N, S549R, G551S, G1244E, S1251N, S1255P or G139D, or those with the R117H mutation, which around 5% of the population of people with CF in the UK have. Licenced for those over 6 months of age, and to those aged 18 or older who have R117H.

Question 32

Orkambi

Answer 32

Combination drug made up from ivacaftor and lumacaftor –
Effective for people homozygous for F508del (50% of people with CF in the UK).
It is licensed for people over the age of 2.
Slows decline of lung function by 42%.

Video explaining how Orkambi works
https://www.orkambi.com/how-orkambi-works

Question 33

Kaftrio

Answer 33

New
Combination therapy: ivacaftor, tezacaftor and elexacaftor
Effective for people homozygous for F508del (50% of people with CF in the UK).
It is licensed for people over the age of 12.
Increases lung function by 10-14%.