Down's sydnrome Flashcards
What is a trisomy?
An extra chomocomy
What is trisomy 21? Trisomy 13? Trisomy 18?
Trisomy 21 - Down’s
Trisomy Eighteen - Edwards
Trisomy Thirteen - PaTau’s
What are clinical features of down’s syndrome?
Facial features Flat occiput Single palmar crease Incurved fifth finger Wide sandal gap Hypotonia Short neck
PROBLEMS Palpebral fissure upslanting Round face Occipital nasal flattening Brushfield spots (pigmented on iris) Low set small ears Epicanthic folds Mouth open, protruding tongue Strabismus Sandle Gap Single palmar crease
How can diagnosis of Down’s be confirmed?
Inform parent of Down’s syndrome test
Blood sent for analysis using real-time PCR or rapid FISH
Discuss long term implications, how and why condition has arisen, risk of recurrence, possibility of antenatal diagnosis in future
What congenital malformations are common in Down’s syndrome?
AVSD
Tetralogy of Fallot
Duodenal atresia
Hirschprung’s
What mechanisms lead to the extra chromosome 21?
Meiotic nondisjunction
- Chromosome 21 pairs fail to separate at meiosis so one gamete has 2 chromosome 21s and one has none
- Fertilisationof gamete with two chromosome 21s gives rise to zygote with trisomy 21
Translocation (5%)
Extra chromosome 21 is joined onto another chromosome (Robertsonian translocation)
- Set of 46 chromosomes but with three copies of C21 material
- Parental chromosomal analysis is recommended because one parent may well carry translocation in balanced form
Mosaicism (1%)
Some of the cells are normal and some have trisomy 21
Usually arises after formation of chormosmally normal zygote by non-disjunction at mitosis
What increases the risk of down’s syndrome?
Increased maternal age
Previous Down’s child in mother under age of 35
Describe Down’s syndrome screening
Nuchal translucency on US at 11-13+6 weeks
Combined testL
NT+serum BhCG + PAPPA
If later - triple or quadruple test offered between 15-20 weeks
AFP + unconjugated estriol + hCG + inhibin A
All low except hCG and inhibin A –> Down’s
If increased risk of Down’s identified, amniocentesis to check fetal karyoteype
OR
Noninvasive prenatal testing
Cell-free fetal DNA analysed from maternal blood
Facial appearance in Down’s syndrome?
Round face Flat nasal bridge Upslanted palpebral fissures Epicanthic folds (fold of skin running across inner edge of palpebral fissure) Brushfield spots in iris (pigmented) Small mouth and protruding tongue Small ears Flat occiput Third fontanelle
What later medical problems occur in Down’s syndrome?
Delayed motor milestones Learning difficulties Short stature Increased susceptibility to infections Hearing impairment from secondary otitis media Cataracts Squints Myopia Increased risk of leukaemia Acquired hip dislocation Obstructive sleep apnoea Hypothyroidism Coeliac disease Epilepsy Early onset Alzheimer's
What are clinical features of trisomy 18?
Edward’s syndrome
Low birthweight Prominent occiput Small mouth and chin - micrognathia Short stenum Flexed overlapping fingers Rocker-bottom feet Cardiac and renal malformations
What re clinical features of trisomy 13?
Patau’s
Microcephaly Small eyes - microphthalmia Cleft lip/palate Polydactyly Scalp lesions Cardiac and renal malformations
