cause of down syndrome
meiotic non disjunction most common during oogenesis (94%)
maternal nondisjunction is cause in 88%
47XX/XY + 21
unbalanced robertsonian translocation (5%) -> family history
what are the screening bloods tests offered for downs syndrome
10-14 weeks: beta hcg + pregnancy associated plasma protein + ultrasound scan +maternal age
= gives estimated risk of downs syndrome (picks up 84%)
14-20 weeks: beta hcg, alpha fetoprotein, inhibin A and unconjugated oestradiol
calculates risk of downs with maternal age
if risk of downs more than 1 in 150 -> offered diagnostic test -> CVS (10-13 weeks gestation) or amniocentesis (16 -20 weeks). both have 1% risk of miscarriage
dysmorphic features of downs syndrome
Other features and conditions associated with downs syndrome
How to test for downs syndrome
QF-PCR for chromosome 21 ** + karyotype
what are the features of edwards syndrome (trisomy 18)
What are the features of patau syndrome (trisomy 13)
how do you diagnose turners sydnrome
Karyotype
what are the physical features of turners syndrome
which conditions is Turners syndrome associated with?
How can you manage Turners syndrome?
what is the cause of Klinefelters syndrome
47 XXY
non disjunction in stage 1 of meiosis causes additional Y chromosome and forms barrs body
How do Klinefelters syndrome present at puberty?
Which conditions is Klinefelters syndrome associated with?
breast cancer
hypothyroid
mitral valve prolapse
osteoporosis
autoimmune disease
leukaemias
management of Klinefelters
testosterone
Genetic mutation in William syndrome
microdeletion of chromosome 7 (7q11.23)
diagnosis of william syndrome
FISH or chromosomal miroarray
features of william syndrome
genetic cause of DiGeorge syndrome?
22q11 microdeletion syndrome (reduction in T box transcription factor 1) and disrupts development in the 3rd and 4th pharyngeal arch
defect in neural crest cells
clinical features of DiGeorge syndrome
C - cardiac - ToF, interrupted aortic arch
A- abnormal facies e.g. narrow palpebral fissures, high broad nasal bridge, short philtrum
T- thymic aplasia - immunodeficiency
C- cleft palate
H- hypocalcaemia and hypoparathyroidism
22
inheritance of noonan syndrome
autosomal dominant
genetic cause of noonan syndrome
mutation in PTPN11 gene on chromosome 12 ** or mutation in SOl1 gene on chromosome 2
clinical features of noonan syndrome
genetic cause of Tay sachs
frameshift mutation in HEXA gene on 15q23-q24 causing failure to break down GM2-GANGLIOSIDE - which then accumulates in neurones and causes neurodegeneration
decreased lysosomal hydrolysis