Genetics Flashcards by Patrick Kilgannon

What are chromosome disorders?

structural abnormalities
extra abnormal portion
abnormal number

of chromosomes.

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What are deletion disorders?

A portion of the chromosome is missing.

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What are translocation disorders?

One portion of one chromosome is directly swapped with a portion of another chromosome.

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What is trisomy?

A person has an extra copy of a chromosome, meaning they have a total of 47 chromosomes.

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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.

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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.

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What is karyotyping?

Looking at the number of chromosomes, their size and basic structure.

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Pathophysiology of Down’s syndrome.

Three copies of chromosome 21 (trisomy 21), gives dysmorphic features.

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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

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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

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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

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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

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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

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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

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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

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Prognosis of Down’s syndrome.

Depending on severity of associated complications - mean life expectancy is 60 years.

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Aetiology of Klinefelter syndrome.

Male has an additional X chromosome (47 XXY)

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Features of Klinefeter syndrome.

Normal development until puberty, then:
- tall
- wide hips
- gynaecomastia
- weak muscles
- small testicles
- reduced libido
- shyness
- infertility
- subtle learning difficulty

Management of Klinefelter syndrome.

testosterone injections for symptomatic improvement
advanced IVF treatment to enable fertility
breast reduction surgery for cosmetic purposes

MDT team involved:
- SALT to improve speech and language
- occupational therapy
- physiotherapy to strengthen muscles and joints
- educational support for learning difficulties

Prognosis of Klinefelter syndrome.

Slight increased risk of:
- breast cancer
- osteoporosis
- diabetes
- anxiety and depression

Life expectancy is close to normal.

Infertility can sometimes be managed with IVF techniques.

Aetiology of Turner syndrome.

Female has a single X chromosome (45XO).

Features of Turner syndrome.

short stature
webbed neck
wide nipples
infertility
late or incomplete puberty

Associations of Turner syndrome.

recurrent otitis media
recurrent UTIs
coarctation of the aorta
hypothyroidism
obesity
diabetes
osteoporosis
learning difficulties

Management of Turner syndrome.

growth hormone therapy to prevent short stature
oestrogen and progesterone replacement to establish secondary sexual characteristics
fertility treatment to increase the chances of becoming pregnant.

Inheritance pattern of Noonan syndrome.

Autosomal dominant

Features of Noonan syndrome.

- short stature - broad forehead - wide space between the eyes - low set ears

Associated conditions to Noonan syndrome.

- congenital heart disease - undescended testes, leading to infertility* - learning disability - bleeding disorders - lymphoedema - increased risk of leukaemia and neuroblastoma

Management of Noonan syndrome.

Supportive management by multidisciplinary team. Main complication is congenital heart disease requiring corrective surgery.

Inheritance pattern of Marfan syndrome.

Autosomal dominant

Pathophysiology of Marfan syndrome.

Genetic condition affecting the gene responsible for creating fibrillin, resulting in abnormal connective tissue.

Features of Marfan syndrome.

- tall stature - long neck - long limbs - long fingers - high arch palate - hypermobility

Conditions associated with Marfan syndrome.

- lens dislocation in the eye - joint dislocation and pain due to hypermobility - scoliosis of the spine - pneumothorax - GORD - mitral valve regurgitation - aortic valve regurgitation - aortic aneurysms

Management of Marfan syndrome.

Greatest risk is from associated cardiac complications: - surgical correction - avoid intense exercise - avoid caffeine - beta blockers or ARBs - carefully consider pregnancy Physiotherapy can be helpful in strengthening joints. Genetic counselling. Yearly echocardiograms and review by opthalmology.

Pathophysiology of Fragile X syndrome.

Mutation in FMR1 gene, which does for the fragile X mental retardation protein. The fragile X mental retardation protein plays a role in cognitive development in the brain.

Inheritance pattern of Fragile X syndrome.

X-linked No evidence to suggest dominant or recessive.

Features of Fragile X syndrome.

- intellectual disability - long, narrow face - large ears - large testicles after puberty - hypermobile joints - ADHD - autism - seizures

Management of Fragile X syndrome.

Multidisciplinary team to manage the condition. Life expectancy is similar to the general population, however may be reduced depending on associated disabilities or complications.

What is Prader-Willi syndrome?

Loss of functional genes on the proximal arm of chromosome 15 inherited from the father: - due to deletion - both copies of chromosome 15 inherited from mother

Features of Prader-Willi syndrome.

- constant hunger, leading to obesity - hypotonia - learning disability - hypogonadism - fair, soft skin - dysmorphic features - narrow forehead - thin upper lip - do

Management of Prader-Willi syndrome.

NICE recommend treatment with growth hormone, to improve muscle development and body composition. Supportive care from MDT: - dieticians - education support - social workers - psychologists or psychiatrists - physiotherapist - occupational therapists

What is William syndrome?

Random deletion of genetic material on one copy of chromosome 7.

Features of William syndrome.

- starburst eyes - flattened nasal bridge - small chin - sociable, trusting personality - mild learning disability

Conditions associated with William syndrome.

- supravalvular aortic stenosis - hypercalcaemia - hypertension - hypercalcaemia

Management of William syndrome.

MDT approach. Echocardiograms and blood pressure monitoring. Low calcium diet - avoid calcium and vitamin D supplements.