Neonatal Screening Flashcards
What is the definition of screening?
the process of identifying apparently healthy individuals who may be at increased risk of a disease or condition
What is the purpose of screening?
by identifying people at an increased risk of a condition, they can be offered information, further tests and/or treatment to reduce their risks and/or complications
What is meant by screening never being 100% sensitive or specific?
sometimes there are false positives/negatives not every person with a condition is identified and sometimes they are identified incorrectly
What criteria are screening programmes based on?
Wilson and Jungner criteria
What are the 5 principles introduced in the Wilson and Jungner Criteria?
- disease must be sufficiently common 2. natural history must be known 3. early therapeutic intervention must be beneficial 4. screening test must be acceptable and affordable 5. there must be a diagnostic confirmatory test
When are babies in the UK screened?
5 days after birth (5 to 8 days in exceptional circumstances)
What details on the neonatal screening card allow the card to be booked in correctly?
- NHS number 2. name 3. address 4. date of birth 5. GP details 6. mother’s details
What details on the neonatal screening card ensure that accurate results are reported?
- date of birth 2. date of sample 3. gestation (premature?) 4. transfusion status 5. hospital status 6. repeat status
Why is hospital status included on a neonatal screening card?
it allows you to find the child if a repeat test is needed
How is a neonatal screening test performed?
blood spots are collected and 3mm discs are punched from the spots usually 4 samples are taken
Why are these examples of poor quality spots?
- too small
- many small spots have been dropped to make a larger spot
- not fully penetrated onto the other side of the paper
Why are these examples of good quality spots?
they have fully permeated through to the other side of the paper and they fill the entire circle
What are the screening standards relating to being timely?
- timely collection of samples
- timely collection of repeats
- timely processing of samples and reporting data
What are the other 2 screening standards that define best practcie?
- all positive cases to be on treatment with referral within 3 days and by a set time frame
- all babies to be tested, including those identified as missed or coming into the country, up to one year of age
What are the 5 conditions on the UK screening programme that have been screened for for a long time?
- phenylketonuria (PKU)
- congenital hypothyroidism
- sickle cell and Hb disorders
- cystic fibrosis (CF)
- Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD)
What are the 4 expanded screening conditions on the UK neonatal screening programme?
- maple syrup urine disease (MSUD)
- isovaleric acidemia (IVA)
- homocystinuria
- Glutaric aciduria type 1 (GA1)
How many births are affected by phenylketonuria?
What happens if it is left untreated?
1 in 10,000 caucasian births
it leads to severe intellectual disability if untreated, but there is an excellent prognosis if treated from birth
What is the screening test for phenylketonuria?
bloodspot phenylalanine
How is a diagnosis of phenylketonuria confirmed?
through plasma phenylalanine measurements
(there is no need to measure enzyme or DNA)
What are the 5 main symptoms involved in the natural history of untreated PKU?
- severe intellectual disability
- seizures and tremors
- spasticity
- behavioural problems and irritability
- eczema in childhood
What is the main treatment for PKU?
low phenylalanine diet with careful monitoring
What are the risks with a low phenylalanine diet?
- risk of tyrosine insufficiency
- risk of vitamin and trace element deficiencies
Why might biopterin in the form of saproterin be given to patient’s with PKU?
biopterin is the cofactor for phenylalanine hydroxylase (the deficient enzyme)
if there is any residual enzyme activity left, this will stimulate enzyme activity and increase the amount of protein that the patient can eat
What types of amino acids need to be supplemented in PKU?
large neutral amino acids involved in brain development
Val, Leu, Ileu
What is the eventual IQ outcome of someome with PKU?
eventual IQ outcome correlates with blood Phe levels
the neurological damage is not reversible
What causes PKU?
it is an inborn error of metabolism where phenylalanine cannot be metabolised properly
How many births are affected by congential hypothyroidism?
What happens if it is left untreated?
1 in 1,500 UK births
severe developmental delay if it is left untreated but excellent prognosis if treated from birth
What is the screening test for congenital hypothyroidism?
bloodspot TSH
How is a diagnosis of congenital hypothyroidism confirmed?
plasma thyroid function tests
there is no need to measure enzyme or DNA
What is the treatment for congenital hypothyroidism?
carefully monitored treatment with thyroxine
the requirements for thyroxine change as the child gets older
How many births are affected by cystic fibrosis?
1 in 2,500
Why is cystic fibrosis known as the “most controversial” screened for condition?
- not all cases are detected by IRT-DNA protocol
- doubts about clinical benefits of early treatment
- difficult to know whether to treat individuals with less severe variants
- carriers are identifed as a consequence of the test
What are the early treatments for cystic fibrosis?
physiotherapy and prophylactic antibiotics
How is cystic fibrosis screened for?
Through measuring blood spot immunoreactive trypsin
If this is high, DNA analysis is conducted
Initially 4 common mutations are looked for
What is the main haemoglobinopathy that is screened for?
How many people are affected?
sickle cell disease affects 1 in 2,000 babies
this can be up to 1 in 300 in certain areas
What other haemoglobinopathy is detected in neonatal screening?
ß-thalassaemia major
it detects carriers and compound heterozygotes with HbC/DPunjab/E/OArab/ß-thal
What is the major benefit of screening for sickle cell disease in newborns?
20% of children with undiagnosed sickle cell disease die during the first 2 years of life
If sickle cell disease is undiagnosed, how do the children often die?
- acute infection
- acute splenic sequestration
- cerebrovascular accident - stroke
How does screening for sickle cell disease provide improved outcomes?
prophylactic penicillin can be initiated
parents can be educated on what an infection may look like, allowing them to get appropriate help
What types of disorders are detected by biochemical screening by TMS?
it has the potential to detect up to 50 IEMs
The main ones are:
- amino acid disorders
- fatty acid oxidation defects
- organic acidaemias
What causes maple syrup urine disease?
a defect in branched chain 2-keto acid dehydrogenase complex
it is an organic acidaemia which makes the urine smell sweet
What are the clinical effects of maple syrup urine disease?
75-80% of neonates have the classical disease and present during the neonatal period
- encephalopathy
- cerebral oedema
- poor feeding
- ketoacidosis
- seizures
What is the target when screening for maple syrup urine disease?
leucine
this shoule be raised
What causes homocystinuria?
What are the 2 types?
it is caused by a defect ß-cystathionine synthase
it is either pyridoxine responsive or pyridoxie unresponsive
What are the screening and secondary targets for homocystinuria?
the screening target it methionine
the secondary target is total homocysteine
What are the clinical effects of homocystinuria?
When does a child typically present with symptoms?
usually healthy at birth and a diagnosis is made in the first 2-3- years of life
- myopia followed by dislocation of the lens
- osteoporosis
- thinning and lengthening of the long bones
- mental retardation
- thromboembolism
Without treatment, how do most people with homocystinuria die?
25% of patients die before the age of 30, usually due to thromboembolism
What biochemical pathway is affected in homocystinuria?
Homocystinuria is a disorder of methionine metabolism, leading to an abnormal accumulation of homocysteine and its metabolites in blood and urine
What is the deficiency present in glutaric aciduria Type 1?
it is a deficiency of glutaryl-CoA dehydrogenase
the body is unable to completely break down the amino acids lysine, hydroxylysine and tryptophan
What is the screening target for glutaric aciduria type 1?
glutaryl carnitine (C5DC)
What are the clinical effects of glutaric aciduria Type 1?
When do infants tend to present with symptoms?
70% of patients have an encephalopathic crisis, most commonly around 9 months of age
90% have had an encephalopathic crisis by 2 years of age, often precipitated by a non-specific intercurrent illness, GI infection of penumonia
What is the eventual result of glutaric aciduria Type 1 after an encephalopathic crisis?
dystonia and dyskinesia
dystonia - uncontrollable contraction of the muscles
dyskinesia - abnormality or impairment of voluntary movement
What % of patients with glutaric aciduria type 1 die before the age of 25?
50%
the survivors usually have severe handicap
What causes isovaleric acidaemia?
a deficiency in isovaleryl-CoA dehydrogenase
this means that people are unable to break down leucine
What is the screening target for isovaleric acidaemia?
isovaleryl carnitine (C5)
What are the clinical effects of isovaleric acidaemia when it presents in neonates?
acute neonatal presentations occur in the first 2 weeks of life
infants are initially well then develop vomiting and lethargy
this progresses into a coma
What are the other 2 ways in which isovaleric acidaemia can present in later life?
acute presentations at a later age are usually precipitated by infection
chronic intermittent presentations may occur within the first year - this involves developmental delay and/or failure to thrive
What other conditions may be picked up on screening via the PKU pathway?
galactosaemia and tyrosinaemia
if there is raised phenylalanine and tyrosine, this is NOT PKU
What other condition may be picked up through screening, due to raised acylcarnitines?
GA2 - Glutaric acidemia type II
this affects the body’s ability to break down proteins and fats to produce energy
