Genetics Flashcards
What is Down’s Syndrome
Down’s Syndrome is caused by three copies of chromosome 21. It is also called trisomy 21. It gives characteristic dysmorphic features and is associated with a number of associated conditions. Th
Down’s Syndrome
Dysmorphic Features
- Hypotonia (reduced muscle tone)
- Brachycephaly (small head with a flat back)
- Short neck
- Short stature
- Flattened face and nose
- Prominent epicanthic folds
- Upward sloping palpebral fissures
- Single palmar crease
What are Epicanthic folds and palpebral fissures
Epicanthic folds are folds of skin covering the medial portion of the eye and eyelid. The palpebral fissures are the gaps between the lower and upper eyelid.
Complications of Down syndrome
- Learning disability
- Recurrent otitis media
- Deafness. Eustachian tube abnormalities lead to glue ear and conductive hearing loss.
- Visual problems such myopia, strabismus and cataracts
- Hypothyroidism occurs in 10 – 20%
- Cardiac defects affect 1 in 3, particularly ASD, VSD, patent ductus arteriosus and tetralogy of Fallot
- Atlantoaxial instability
What are Antenatal Screening for Down’s Syndrome
Combined Test
Triple Test
Quadruple Test
What is Combined Test
The combined test is the first line, most accurate and test of choice where possible. This test is performed between 11 and 14 weeks gestation. It involves combining results from ultrasound and maternal blood tests.
Ultrasound measures nuchal translucency, which is the thickness of the back of the neck of the fetus. Down’s syndrome is one cause of a nuchal thickness over 6mm.
Maternal blood tests:
- Beta‑human chorionic gonadotrophin (beta-HCG). A higher result indicates a greater risk.
- Pregnancy‑associated plasma protein‑A (PAPPA). A lower result indicates a greater risk.
What is Triple Test
The triple test is performed between 14 and 20 weeks gestation. It only involves maternal blood test results:
- Beta-HCG. A higher result indicates greater risk.
- Alpha-fetoprotein (AFP). A lower result indicates a greater risk.
- Serum oestriol (female sex hormone). A lower result indicates a greater risk.
What is Quadruple Test
The quadruple test is performed between 14 and 20 weeks gestation. It is identical to the triple test but also includes maternal blood for inhibin-A. A higher inhibin-A indicates a greater risk
The screening tests provide a risk score for the fetus having Down’s syndrome. When the risk of Down’s is greater than 1 in 150 (this result occurs in around 5% of tested women) the woman is offered________ or ______ _______ ______
The screening tests provide a risk score for the fetus having Down’s syndrome. When the risk of Down’s is greater than 1 in 150 (this result occurs in around 5% of tested women) the woman is offered amniocentesis or chorionic villus sampling.
WHat is Chorionic villus sampling (CVS) and Amniocentesis
- Chorionic villus sampling (CVS) involves an ultrasound guided biopsy of the placental tissue. This is used when testing is done earlier in pregnancy (before 15 weeks).
- Amniocentesis involves ultrasound guided aspiration of some amniotic fluid using a needle and syringe. This is later in pregnancy once there is enough amniotic fluid to make it safer to take a sample.
What is Non-Invasive Prenatal Testing
Non-invasive prenatal testing (NIPT) is a relatively new test for detecting abnormalities in the fetus during pregnancy. It involves a simple blood test from the mother. The blood will contain fragments of DNA, some of which will come from the placental tissue and represent the fetal DNA. These fragments can be analysed and detect conditions such as Down’s.
Management for down syndrome
Management involves supportive care from the multidisciplinary team to help them meet their needs:
- Occupational therapy
- Speech and language therapy
- Physiotherapy
- Dietician
- Paediatrician
- GP
- Health visitors
- Cardiologist for congenital heart disease
- ENT specialist for ear problems
- Audiologist for hearing aids
- Optician for glasses
- Social services for social care and benefits
- Additional support with educational needs
- Charities such as the Down’s Syndrome Association
TOM TIP: When asked by an examiner about the management of a complex multi system disorder such as Down’s syndrome, always start your answer with
“management would involve members of the multidisciplinary team”
What is Klinefelter syndrome
Klinefelter syndrome occurs when a male has an additional X chromosome, making them 47 XXY. Under normal circumstances males have XY sex chromosomes and females have XX sex chromosomes.
Rarely people with Klinefelter syndrome can have even more X chromosomes, such as 48 XXXY or 49 XXXXY. This is associated with more severe features.
Features of Klinefelter syndrome
Usually patients with Kleinfelter syndrome appear as normal males until puberty. At puberty can develop features suggestive of the condition:
- Taller height
- Wider hips
- Gynaecomastia
- Weaker muscles
- Small testicles
- Reduced libido
- Shyness
- Infertility
- Subtle learning difficulties (particularly affecting speech and language)
There is no way to treat the underlying genetic cause of Klinefelter syndrome. Treatment aims to help with the features of the condition:
- Testosterone injections improve many of the symptoms
- Advanced IVF techniques have the potential to allow fertility
- Breast reduction surgery for cosmetic purposes
Multidisciplinary team input:
- Speech and language therapy to improve speech and language
- Occupational therapy to assist in day to day tasks
- Physiotherapy to strengthen muscles and joints
- Educational support where required for dyslexia and other learning difficulties
Klinefelter Syndrome
There is a slight increased risk of what diseases:
Breast cancer compared with other males (but still less than females)
Osteoporosis
Diabetes
Anxiety and depression
