genetics Flashcards
how do you do a DNA test on baby in utero?
take tissue from-
placenta = chorionic villus biopsy
skin/urine ells = amniocentesis
also fetal DNA from maternal serum
describe confined placental mosaicism
placenta has abnormal number of chromosomes but foetus does not e.g. can have trisomy 21 but baby doesn’t
what can you look for in invasive foetal testing?
chromosome abnormalities using micorarray
single gene changes using PCR/sequencing, NGS
what are the pros and cons of chromosome microarray?
pros- high resolution, technically easier, quick
cons- finds polymorphisms, can make incidental findings
when do you use chromosome microarray?
high risk of chromosomal trisomy
foetal abnormality on screening
parent has balanced chromosomal rearrangement
what are the differential diagnoses of a floppy baby?
Central(most common)
Hypoxic ischaemic encephalopathy
Intracranial haemorrhage
Cerebral malformations
Chromosomal abnormalities (e.g.Trisomy 21, Prader-Willi syndrome)
Congenital infections (TORCH)
Acquired infections
Peroxisomal disorders
Drug effects (e.g. benzodiazepines)
also abnormalities in Spinal cord, anterior horn cell, neuromuscular junction, muscle, peripheral nerves or metabolic myopathies
what are the next steps when you have a floppy baby?
do bloods (genetic, metabolic, infection, CK), imaging (cranial USS & MRI), neurology review, neurology review, early intervention & regular review
what things do you test floppy babies for rapidly?
myotonic dystrophy, PWS, spinal muscular atrophy
what is hypochondroplasia?
form of skeletal dysplasia less severe than achondroplasia
caused by specific activating mutations in FGFR3 gene
causes short stature and can cause temporal lobe epilepsy
what is is russell silver syndrome?
growth disorder characterised by slow growth before and after birth
can cause ‘elfin features’
poor weight gain
what causes russell silver syndrome?
abnormality of gene methylation
what is the treatment for russell silver syndrome?
growth hormone
when is growth hormone recommended?
small for gestational age without catch up growth by the age of 4
(growth hormone deficiency, turners syndrome, russell silver etc. also PWS)
why would you give growth hormone in PWS?
to help with muscle tone and encourage exercise to prevent T2DM
what happens when x chromosome forms a ring?
produces similar symptoms to turner’s syndrome- treat as such
investigations: IGF1, TFTs, coeliac screen, bone age x-ray
treatment: growth hormone, puberty induction, renal & cardiac follow up, bp monitoring, annual bloods, thyroid and coeliac screening
