Genetics Flashcards
What are chromosome disorders?
- structural abnormalities
- extra abnormal portion
- abnormal number
of chromosomes.
What are deletion disorders?
A portion of the chromosome is missing.
What are translocation disorders?
One portion of one chromosome is directly swapped with a portion of another chromosome.
What is trisomy?
A person has an extra copy of a chromosome, meaning they have a total of 47 chromosomes.
What is mosaicism?
A chromosomal abnormality that occurs after conception, meaning there is an anomaly in a portion of cells in the body and not in others.
Principles of mitochondrial inheritance.
At the time of conception, the sperm carrying the father’s genetic material enters the oocyte and the DNA in the nucleus of both cells combine.
As mitochondrial DNA is located in the tail of the sperm, which does not enter the oocyte, the mitochondrial DNA of the zygote is of maternal origin.
What is karyotyping?
Looking at the number of chromosomes, their size and basic structure.
Pathophysiology of Down’s syndrome.
Three copies of chromosome 21 (trisomy 21), gives dysmorphic features.
Dysmorphic features of Down’s syndrome.
- hypotonia
- brachycephaly
- short neck
- short stature
- flattened face and nose
- single palmar crease
- prominent epicanthic folds
- upward sloping palpebral fissure
Complications of Down’s syndrome.
- learning disability
- recurrent otitis media
- deafness
- visual problems
- hypothyroidism
- cardiac defects (e.g. ASD, VSD, tetralogy of Fallot)
- leukaemia
- dementia
What is the combined test for Down’s syndrome?
Antenatal screening at weeks 11-14 gestation:
1) Ultrasound showing nuchal thickness
2) Bloods showing elevated b-hCG and low PAPPA
What is the triple test for Down’s syndrome?
Antenatal screening at weeks 14-20 gestation:
1) Raised b-hCG
2) Low AFP
3) Low serum oestriol
How is Down’s syndrome antenatally tested for?
Combined / triple test for screening.
If screening results significant, a sample of fetal cells can be taken and sent for karyotyping:
- amniocentesis
- chorionic villus sampling
Management of Down’s syndrome.
Supportive care from the multidisciplinary team:
- occupational therapy
- SALT
- physiotherapy
- dietician
- paediatrician
- GP
- health visitors
- cardiologist
- ENT specialist
- optician
- social services
- support with educational needs
- Down’s syndrome association
Routine investigations in Down’s syndrome.
- thyroid checks every 2 years
- echocardiogram to diagnose cardiac defects
- regular audiometry for hearing impairment
- regular eye checks for visual impairment
Prognosis of Down’s syndrome.
Depending on severity of associated complications - mean life expectancy is 60 years.
Aetiology of Klinefelter syndrome.
Male has an additional X chromosome (47 XXY)