Paediatric genetics Flashcards
When does Turner’s syndrome occur?
when a female has a single X chromosome, making them 45 XO
What is the life expectancy of someone with Turner’s syndrome?
close to normal
What are the three main features of Turner’s syndrome to look out for in exams?
short stature, webbed neck and widely spaced nipples.
Apart from short stature, webbed neck and widely spaced nipples, what other features do you see in Turner’s syndrome?
High arching palate
Downward sloping eyes with ptosis
Cubitus valgus
Underdeveloped ovaries with reduced function
Late or incomplete puberty
Most women are infertile
What is cubitus valgus?
abnormal feature of the elbow. When the arm is extended downwards with the palms facing forward, the angle of the forearm at the elbow is exaggerated, angled away from the body
What conditions are associated with Turner’s syndrome?
Recurrent otitis media
Recurrent urinary tract infections
Coarctation of the aorta
Hypothyroidism
Hypertension
Obesity
Diabetes
Osteoporosis
Various specific learning disabilities
How do you help prevent short stature in Turner’s syndrome?
Growth hormone therapy
How can you help establish female secondary sex characteristics, regulate the menstrual cycle and prevent osteoporosis in females with Turner’s syndrome?
Oestrogen and progesterone
How can you increase the chance of a woman with Turner’s syndrome of becoming pregnant?
Fertility treatment
What is the most common cause of Primary Amenorrhoea?
Turner’s syndrome
What is Down’s syndrome also known as?
Trisomy 21
Why is Down’s syndrome also known as Trisomy 21?
Because it is caused by three copies of chromosome 21.
What dysmorphic features are seen in Down’s syndrome?
Hypotonia (reduced muscle tone)
Brachycephaly (small head with a flat back)
Short neck
Short stature
Flattened face and nose
Prominent epicanthic folds
Upward sloping palpebral fissures
Single palmar crease
Low set ears
What are epicanthic folds?
folds of skin covering the medial portion of the eye and eyelid
What are palpebral fissures?
gaps between the lower and upper eyelid
What are the complications of Down’s syndrome?
Learning disability
Recurrent otitis media
Deafness. Eustachian tube abnormalities lead to glue ear and conductive hearing loss.
Visual problems such myopia, strabismus and cataracts
Hypothyroidism
Cardiac defects
Atlantoaxial instability
Leukaemia is more common in children with Down’s
Dementia is more common in adults with Down’s
What cardiac defects are most common in those with Down’s syndrome?
ASD, VSD, patent ductus arteriosus and tetralogy of Fallot
What are the three tests for Down’s syndrome?
Combined test, triple test and quadruple test
What is the first line and most accurate test for Down’s syndrome?
The combined test- combines ultrasound and maternal blood tests
When is the Down’s combined test performed?
Between 11-14 weeks of gestation
What does the ultrasound measure in the combined test for Down’s syndrome?
Measures nuchal translucency, which is the thickness of the back of the neck of the foetus. (thickened in Down’s)
What thickness is the nuchal translucency in Down’s?
Over 6mm
What in the maternal blood will indicate that a child will have a higher risk of Down’s in the combined test?
A higher level of Beta‑human chorionic gonadotrophin (beta-HCG) or a lower level of Pregnancy‑associated plasma protein‑A (PAPPA)
When is the triple test for Down’s performed?
14-20 weeks of gestation- just maternal blood tests
What in the maternal blood will indicate that a child will have a higher risk of Down’s in the triple test?
Beta-HCG. A higher result indicates greater risk.
Alpha-fetoprotein (AFP). A lower result indicates a greater risk.
Serum oestriol (female sex hormone). A lower result indicates a greater risk.
When is the quadruple test for Down’s performed?
Between 14 and 20 weeks of gestation
What is included in the quadruple test for Down’s that isn’t in the triple test?
Inhibin-A
Does a higher or lower level of inhibin A indicate a higher risk for Down’s?
Higher
What procedure is a woman offered in their child has a greater than 5% chance of having Down’s?
amniocentesis or chorionic villus sampling
What does chronic villus sampling involve?
an ultrasound guided biopsy of the placental tissue. This is used when testing is done earlier in pregnancy (before 15 weeks).
What does amniocentesis involve?
ultrasound guided aspiration of some amniotic fluid using a needle and syringe. This is later in pregnancy once there is enough amniotic fluid to make it safer to take a sample.
What is the relatively new test for detecting abnormalities in the fetus during pregnancy?
Non-invasive prenatal testing (NIPT)
What are the regular follow up investigations that are important for children with Down’s?
Regular thyroid checks (2 yearly)
Echocardiogram to diagnose cardiac defects
Regular audiometry for hearing impairment
Regular eye checks
What does the combined test for Down’s include?
Ultrasound, beta-HCG and PAPPA
What is included in the triple test for Down’s?
Beta-HCG (raised), AFP (low), Serum oestriol (low)
What is included in the quadruple test for Down’s?
Beta-HCG, AFP, serum oestriol and inhibin-A (high)
What is the average life expectancy of someone with Down’s?
60 years
What is fragile X syndrome?
a mutation in the FMR1 (fragile X mental retardation 1) gene on the X chromosome
What does the FMR1 gene code for?
the fragile X mental retardation protein, which plays a role in cognitive development in the brain
Is fragile X x-linked and is it dominant or recessive?
X linked but we don’t know if it is dominant or recessive
Which gender is affected by Fragile X syndrome?
Males are always affected, females vary in how much they are affected
What are the features of Fragile X syndrome?
Delay in speech and language development. Other features are:
Intellectual disability
Long, narrow face
Large ears
Large testicles after puberty
Hypermobile joints (particularly in the hands)
Attention deficit hyperactivity disorder (ADHD)
Autism
Seizures
What is the life expectancy of someone with Fragile X syndrome?
Similar to general population depending on disabilities and complications
Is CF dominant or recessive?
Recessive
What is CF caused by?
a genetic mutation of the cystic fibrosis transmembrane conductance regulatory gene on chromosome 7
What is the most common variant of CF?
delta-F508
What is delta-F508 for?
cellular channels, particularly a type of chloride channel
What percentage of people are carriers of CF?
1 in 25
What percentage of children have CF?
1 in 2500