Genetics Flashcards
Mechanism of Prader-Willi
70% deletion of paternal 15q11
25% uniparental disomy chromosome 15 (from mum)
Mechanism of Angelmans
70% deletion maternal 15q12
5-10% UBE3A mutation
5% paternal UPD ch15
What gestation for chorionic villus sampling, and risk of miscarriage?
> 11/40
1-2%
Gestation for amniocentesis and miscarriage risk
> 16/40
0.5-1%
Imprinting means:
Allele from a particular parent is switched off
Trisomy 21 is
Down’s
Trisomy 13 is
Patau
Trisomy 18 is
Edward
First trimester screen includes what tests
bHCG, PAPP-A, nuchal translucency
Trisomies - elevated bHCG and NTS, low PAPP-A
Klinefelters =
Extra X chromosome (47XXY most common), more X’s = worse disease
Central issue in Klinefelters
Androgen deficiency
Disease associations in Klinefelters
VTE, metabolic syndrome, cancer
Cause of DiGeorge syndrome?
Del22q11.2
Manifestations of DiGeorge
CATCH22 Cardiac (TOF/VSD) Abnormal face Thymus hypoplasia (T def) Hypocalc, hypoPTH
Diagnosis of DiGeorge
FISH
Huntington’s disease mode of inheritance
AD
Genetic basis of Huntington’s
CAG trinucleotide repeat disorder
Full penetrance of HD at which number of repeats
40
Juvenile onset HD at which number of repeats
60
HD worse from which parent
Father, instability of CAG triplet in spermatogenesis
Spinocerebellar ataxia mode of inheritance
AD
Age of onset SCA
30-40
How many forms of spinocerebellar ataxia
> 40
Gene implicated in myotonic dystrophy
Dystrophin myotonica protein kinase
Mode of inheritance myotonic dystrophy
AD
Genetic basic of myotonic dystrophy
CTG trinucleotide repeat
Penetrance of myotonic dystrophy
100%
Myotonic dystrophy worse from which parent
Mother
Average life expectancy of classical myotonic dystrophy
48-60, usually 50-1000 repeats
Gene implicated in Duchenne’s
Dystrophin
Mode of inheritance Duchenne’s
XLR
Genetic mechanism for Duchenne’s
Frameshift/nonsense –> truncated/absent protein
Normal function of dystrophin protein
Link actin and cell membrane, stability
CK in Duchenne’s usually..
10x normal
Cardiac involvement in Duchenne’s?
DCM by 18 years old
Female carriers of Duchenne’s need surveillance for…
Heart failure
Becker’s genetic mechanism
Missense mutation of dystrophin, protein present but altered
CK in Becker’s usually
5x normal
Cause of death in Becker’s
DCM in 40s
Marfan’s gene and inheritance
FBN1
AD
Diagnosis of Marfan’s
First degree relative FBN-1 gene mutation Systemic score >7 AOrtic score >2 Ectopia lentis
DDx Marfan’s
Loeys Dietz - similar skeletal features but no ectopia lentis
Gene: TGFbR1/2
Annual surveillance in Marfan’s
Eye exam, TTE
Intervene in aortic aneurysms in Marfans
> 5cm
Increasing >0.5-1cm/y
Gene and inheritance of Noonan’s
PTPN11, AD
Cardiac manifestations of Noonan’s
PV stenosis most common
HCM, ASD< VSD
Neurofibromatosis type 1 inheritance
AD but 30-50% de novo, mutation in NF1 gene
Normal role of neurofibromin
Negative regulator of RAS
Risks of NF1
Optic pathway glioma, breast Ca, malignant nerve sheath tumour, phaeo
Diagnostic criteria NF1
> /=6 cafe au lait patches
/=2 neurofibromas or one plexiform neurofibroma
Axillary or groin freckling
Lisch nodules (iris hamartomas)
Optic pathway glioma
FHx (1 x FDR)
Distinctive osseous lesion (sphenoid wing dysplasia, thinning of long bone cortex +/- pseudoarthrosis)
Gene and inheritance NF2
NF2 gene, AD, up to 50% de novo
NF2 gene encodes for…
Merlin - links between membrane proteins/cell cytoskeleton
Diagnostic criteria NF2
1 of:
- Bilaterla vestibular schwannoma
- 1 x FDR with NF2 and unilat vest schwann OR any two of meningioma, schwann, glioma, neurofibroma, posterior subcapsular lenticular opacities
- Multiple meningiomas AND unilat vest schwann, any two of schwann, glioma, neurofibroma, posterior subcapsular lenticular opacities
Tuberous sclerosis genes are negative regulator of which pathway
mTOR pathway
TSC1 gene codes for
Hamartin
TSC2 gene codes for
Tuberin, tuberous sclerosis type 2
Mode of inheritance tuberous sclerosis
AD
Tumour locations tuberous sclerosis
Brain, heart, lungs, kidneys, skin
Lung associated condition with tuberous sclerosis
LAM
Main organ manifestations of tuberous sclerosis
CNS with epilepsy
Neuropsych
Intellectual disability
Autism
HCM mainly involves the…
Sarcomere
Main genes in HCM
Myosin binding protein C and beta-myosin heavy chain = 70%
Most common gene implicated in DCM
Titin gene
Which genetic cause of DCM is also very pro arrhythmic
LMNA
ARVD cellular site of defect
Desmosomes
Most common gene responsible for ARVD
PKP2
What is Anderson-Tawil syndrome?
LQTS7 - LQTS + period paralysis
CPVT gene…
RYR2
Brudaga gene
SCN5A loss of function