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Chromosomal Abnormalities (i) - Coggle Diagram
Chromosomal Abnormalities (i)
Causes of genetically determined diseases
chromo abnormalities
either numerical or structural
common cause of early spontaneous miscarriage
incidence in liveborns = 1 in 150
usually multiple congenital anomalies + cognitive difficulties
single gene defect (Mendelian disorders)
other genetic mechanisms
interaction of genetic + environmental factors (polygenic, multifactorial)
Down Syndrome (trisomy 21)
most common autosomal trisomy
most common genetic cause of severe learning difficulties
incidence in liveborns = 1 in 650
clinical features
hypotonia
flat occiput
single palmar creases
incurved 5th finger
sandal gap
CHD in 30% (esp AVSD)
round face
flat nasal bridge
upslanted palpebral fissues
epicanthic folds
brushfield spots (pigmented spots) in iris
small mouth
protruding tongue
small ears
3rd fontanelle
short neck
duodenal atresia
Hirschsprung disease
delayed motor milestones
moderate-severe learning difficulties
short stature
Dx = FISH
difficult to give long-term prognosis in neonatal period
over 85% survive to 1yr
50% live to over 50
increased risk of other medical problems
hypothyroidism
impaired hearing + vision
atlanto-axial instability
infections
secretory OM
cataracts, squints, myopia
leukaemia
solid tumours
coeliac
epilepsy
Alz
cytogenetics
Meiotic non-disjunction (94%)
error @ meoisis
pair fails to separate
parental chromos don't need to be examined
related to maternal age, but can occur in spermatogenesis
a/w nuchal thickening
amniocentesis to check foetal karyotype
Robertsonian translocation (5%)
usually with chromo 14, 15, 21, or 22
parental chromo analysis recommended
in 25% of cases a parent will carry a balanced translocation
if a parent carries the rare 21:21 translocation all offspring will have Downs
Mosaicism (1%)
some cells normal + some have trisomy 21
non-dysjunction @ mitosis
phenotype sometimes milder
Edwards Syndrome (trisomy 18)
1 in 8000
most die in infancy
dx confirmed by chromo analysis
Many affected foetuses detected on US, confirmed by amniocentesis
Recurrence risk low except when due to parental balanced translocation
features
low birthweight
prominent occiput
small mouth + chin
short sternum
flexed overlapping fingers
rocker-bottom feet
cardiac + renal malformations
Patau Syndrome (trisomy 13)
1 in 14000
most die in infancy
dx confirmed by chromo analysis
Many affected foetuses detected on US, confirmed by amniocentesis
Recurrence risk low except when due to parental balanced translocation
features
structural brain defects
scalp defects
microphthalmia + other eye defects
cleft lip + palate
polydactyly
cardiac + renal malformations