Cystic Fibrosis Flashcards
New born screening process
Heel prick at 1-2 days of age
20+ metabolic disorders tested
45 babies per year have a disorder
Your new born baby’s blood test
-The New Born Metabolic Screening Programme
Given to every mother before testing
- Abbreviated facts about the disorders looked for
- frequency of disorder
www. nsu.govt.nz
Cystic Fibrosis
Genetic Disorder
Gene codes for protein which forms CL channel
(Gene –> Protein –> Chloride Transport Channel)
Cl cannot be pumped out of cell - Na+ stays with the Cl- –> water stays with both (due to high osmolarity)
So all secretions in the airways of ducts are thick and sticky
Cystic Fibrosis the Abnormality
Gene --> Protein --> Cl Transport Channel CFTR gene (DNA) --Transcription--> mRNA message --Translation--> Chain of 1480 a/acids --Protein folding + transport to membrane --> CFTR protein in cell membrane allowing Cl flow Intra --> Extra cellular space
Functioning CFTR channel
Cl pumped out Na+ triples across (balanced) Water also balanced across cell membrane -Thin Watery mucus -Hydrated enviro to allow Cilia to work -Bugs and dust settle on this flow, going up the respiratory tract and is cleared
Abnormal CFTR channel
Cl cannot be pumped out of cell - Na+ stays with the Cl- –> water stays with both (due to high osmolarity)
So all secretions in the airways of ducts are thick and sticky
-dehydrated
Newborn Screen for CF
Thick secretions block the fine pancreatic duct – enzymes cannot move into GI tract -but continues to make enzymes, arent secreted naturally into the duck = overflow/ --> Enzymes are then absorbed into the bloodstream The screening measures: 1. Blood trypsin (pancreatic enzyme) 2. If high → 3 common CF genes
The Family
Christine and Rob have their first child Zak – things have been going well
Lead Maternity Carer gets a notification letter
The screening test for cystic
fibrosis on this baby was POSITIVE.
The positive test means baby either
has CF or is a carrier for CF.
We suggest referral to the regional
CF paediatrician.
What do you think the family want to know?
What information would you like to be able to give them?
Does Zak have CF Cystic Fibrosis or is he a carrier? What does a positive screen mean? What is his chance of having CF ? How will he show if he has got CF ? Has there been a mistake?
Cystic Fibrosis From Book
Caused by: a defective gene and its protein product, leading to thick, sticky mucous
Can lead to: poor growth, chest infections and shortened life
Treated by: high calorie diet, medicines and physiotherapy to keep the lungs healthy
Occurs in: about 8 babies every year
What would the family want to know if Zak does have CF Cystic Fibrosis?
What is CF? What will happen to him? Can it be treated? What can they do to help him? Will he die? How long will he live? Can he have children? What about other family members?
Steps after being Positive on the New born Screen Test to see if Zak has CF or is a carrier
- Sweat Test
- Sodium and Chloride production in sweat - Genetics from Zak
- to check for mistakes
- test for 31 mutations - Stool samples for (pancreatic) enzymes
- look for trypsin in gut
- if not present, would start enzymes regardless for waiting or other tests, as baby wont be able to grow if cannot break down food
What does it mean for Zak : Most common
- Recurrent pneumonias → progressive lung disease
- Failure to thrive/poor growth
-inability of pancreatic enzymes to functioning normally breaking down food
Normal Neurology, Normal Development
Other Possible issues for Zac over time
-all essentially re thick sticky secretions blocking something Nasal polyps Sinusitis Diabetes -enzymes still made, damage pancreas becuase arent released, enough Islet cells damaged to cause diabetes Liver disease Gallstones Portal hypertension Distal intestinal obstructive syndrome, constipation Vitamin deficiencies -absorbption Bone disease Fertility concerns
Management of CF: Regular Review
- History
- Growth (height, weight)
- Physical signs
-Finger clubbing (swollen)
-chest deformity
-Cough
-Auscultation
-Abdominal examination
(seen more in late teens and early adults, due to management being more intensive)
Investigations of CF (Respiratory Testing)
Check for infection - Cough swabs (tonsils) - Sputum - Bronchoscopy & lavage (thick secretions plug the airways- free this) Oxygen Saturation monitoring Lung function tests (when children older) X-rays Radiology: CXRs, CT scans, Ultrasounds -regularily reviewed
Ausculation
- Normal: Inspiratory longer
- Asthma
- hyperinflated X-ray
- prolonged expiration
- very tight and wheezy - Crackles
- Hyperinflated + Patchy consolidation throughout (areas of fibrosis and bronchixis)
- air going through mucus or popping open of alveoli - Wides spread changes with Atelectasis, bronchial wall thickening, bronchieclasis, fibrosis
Prevalance of Respiratory Microorganisms by Age Cohort
Infection changes with time
Common early: Staphylococcus Aureus + H influenza.
Older: Pseudomonas Aeruginosa increase (sensitive and drug resistance.)
-use different antibodies
Treatment for CF
- Respiratory
- Nutrition
- Other
Respiratory aspect of CF Treatment
Chest physiotherapy
-daily (multiple), percussion, devises to increase resistnace so huff and sputum up, vibrational vest
-children get very tired of it, so switch around
Exercise
-enjoyable way to clear lungs
Antibiotics
-oral (mainly)
-nebulised (allows high levels in lung and systemic absorption)
-intravenous (porton for child having repeated pneumonia)
Nutrition aspect of Treatment
Enzyme replacement
-immediate
-in apple purree as cannot swallow capsules until 5/6yrs
Vitamin supplementation
-mainly fat soluble (they struggle to absorb)
High calorie diet
Supplemental feeding via gastrostomy
-cannot eat enough. Additional feeding via tube going straight into stomach overnight
-regular weekly tablets (14yrs spend 2 hrs a day doing treatment)
Lung function over time
With each decade –
lung function over time
decreasing more slowly
-Other complications now evolving:
How long will Zak live?
In 2014 – current life expectancy - 39.3 years
- improving, so expect life expectancy to increase
- but requires a lot of input from family
2012 National Data registry
2012 National Data registry
- shows relative data in NZ and internationally
- and improvements/how things are changing over time
The future for the family
- The family would like to have more children
- can it happen again?
- can it be prevented? - Their own siblings are also having children
- What advice should be give to the wider family members?
False Positives
20%
-if child cannot gain weight = very high likelihood
CF Inheritance
Autosomal Recessive -has to come from both parents -both parents carriers generally Both grandparents 1/2 risk of being carrier. atleast 1 is a carrier, sometimes both. -Risk for next child: 1/4
Things to consider as a Clinical geneticist
Genetic Testing
-May inadvertently reveal family relationships (non-paternity) (dad isnt dad)
-see which mutation is coming from which side
-“De Novo” mutation that happened within egg/sperm - extremely rare
-Ability to give consent for testing
a) Informed
b) For children need to demonstrate a direct benefit
c) Who can have access to results (informed and confirmation)
Distress with new diagnosis/loss of “perfect” child
-not known in the family
Feelings of guilt
Options for the future
-when is the right time to discuss these things
GC Appointment
Reviewing diagnosis
-typically know that both parents are autosomal recessive, but checking
Answering questions
Can it happen again?
-Parents would like to have more children.
What about the rest of the family?
-Both have siblings wanting to have families.
Arrange testing
Checking to see how they are managing
-come back later? family positions change over time
Referrals
Family Planning
Can be difficult and distressing decisions
(guilt. importance of having to take care of CF child, tension would be more spread, potential for cross infection)
Options
-Not having further children
-Having children with no testing (3/4 chances not going to have another CF child)
-Sperm donor
-Prenatal testing for information or TOP
-Pre-implantation genetic diagnosis with IVF
Decisions influenced by ethical, religious beliefs, views on sickness and disability, treatment availability and efficacy, availability of social and financial support for the family
Prenatal testing CVS
11-13 wks Testing placental tissue -Only done at MFM units -Need for maternal sample -Placental placement -Placental mosaicism Results 1-2 wks 1/500 risk of miscarriage Reveals karyotype and gender
Prenatal testing Amnio
15 wks on Testing amniotic fluid Results in ~2 wks 1/1000 risk for miscarriage Reveals karyotype and gender
Preimplantation Genetic Diagnosis
Couples who are eligible can access up to 2 publically funded cycles
-has to be SEVERE
Eligibility criteria
-female partner under 40y
-non-smoker
-BMI under 32.
Privately funded PGD costs approximately $20,000 (if dont want to wait on waitlist or if dont meet the criteria)
ICSI
After IVF
when sperm is injected into the egg’s nucleus
-couples followed closely
Embryo biopsy
3-5 days of growth
extract 1-2 cells and send off for testing
embryos frozen during testing (so not growing too fast during testing)
Test takes couple of weeks, done through feasibility study, take samples from parents and grandparents, to make a really good quality test so require only 1-2 cells
Blastocyst
Once found cells that are -ve for condition
=will unfreeze embryos
= whichever ones survive they will implant back
Pregnancy guarrentee
Pregnancy is NOT guaranteed (20-30% pregnancy chance if young and healthy)
No eggs are recovered at the time of egg collection.
No viable embryos for transfer
-Some or even all eggs may fail to fertilise.
-Not every embryo will be suitable for biopsy.
-There may not be a genetic result from every embryo, or the result may be inconclusive (i.e. the test might fail on some embryos). These embryos are generally not transferred.
-There may not be any unaffected embryos.
-Some embryos may not survive the freeze/thaw process
The result is not 100% accurate, prenatal diagnosis is recommended (testing during pregnancy)
Risk of miscarriage, as for any pregnancy.
Does not rule out chromosome abnormalities- e.g downsyndrome
Referrals
- If the couple want PGD
- referral to Northern Regional fertility service
- waitlist (2 yrs) - If the couple gets pregnant naturally
- referral to Maternal Fetal Medicine team
- liaise with molecular genetics laboratory to ensure they are aware of PND
- -maternal DNA sample for MCC studies
- -information about what mutations the parents carry
Its not just the procedure
- Indication – referral-check woman is clear
- Counselling- test and procedure
- Prerequisites-patient and procedural
- Follow up results- who will do this?
- Final outcomes- care and support
Why might we be doing this today?
- Previously affected pregnancy
- Family history-parental carriers
- Abnormality seen on a pregnancy scan
- Possibly parental concern
Why might we be doing this tomorrow?
Non Invasive Prenatal Testing
• parents will know their genotypes or be screened
•**will test in pregnancy, non invasively
• Will there be gene-stem cell therapy for affected fetuses?
Antenatal scan
Meconium Pseudocyst
- Secretions thicken in bowel,
- Meconium becomes thick in the bowel -is ecogenic (bright)
- comes up on the US –> marker/sign for CF
Prenatal Diagnosis allows reproductive choice
For the patients
– Impact on parents and family (95%parents want to have info so know what to do (but only 45% would act upon this info))
– Prevent suffering of baby-child
– Reassurance if baby unaffected
– Options not to continue if baby affected
– Preparations for the new baby
• We can not preempt what the parents will choose to do
• Most parents want to know
Need for DNA
Options
• DNA from tissue- INVASIVE TESTS
Trophoblast – early placenta
Fetal cells- fibroblasts in amniotic fluid
• DNA from maternal plasma NIPT-NIPD
Can get DNA from the embryo at IVF and PGD and maybe media fluid
Trophoblast
• Can extract DNA from chorionic villi obtained by
Chorionic Villus Sampling-CVS
• Advantages
Earlier in pregnancy
Direct DNA extraction (as placental tissue is dividing rapidly)
• Disadvantages:
Technically more difficult than amniocentesis
Maternal cell contamination ~1% of samples
Mosaicism can also occur (placental cells not recognised by mother)
Fetal cells in amniotic fluid
• Obtain these by amniocentesis, culture then DNA extraction
• Advantages
Technically easier
• Disadvantages
Later in pregnancy >14 weeks longer processing time
All invasive procedures have a loss rate ~ 0.4%
Syncytial knots Or
Syncytial nuclear aggregates
Non Invasive Prenatal Testing
Presence of fetal DNA in maternal plasma and serum
10% of DNA in mothers blood is fetal
• Sequencing 10 commonest mutations
• If paternal ≠ maternal - fetus not affected
• If paternal=maternal
• Offer invasive prenatal testing
New Diagnostic approaches
Whether mother carries paternal mutation, and if not she can be reassured
Benefits of NIPT
• No miscarriage risk
• Simpler, less stressful
• Informed TOP decision • Preparation for affected • Earlier result
• (preferred blood test)
How do you date a pregnancy?
Crown Rump Length
- measure from head to tail of baby
- will predict delivery +- 5 days for 40 weeks
- most reliable estimate
An ethical question
Should health care resources be spent on a very expensive way of providing information only, which does not alter care or outcomes?
-95% want to know even though 45% wouldnt act
