Genetic Material Flashcards
How common is chromosomal conditions in miscarriages
50%
Aneuploidy
More or fewer chromosomes than normal
Deletion
Whe part of chromosome is missing or part of dna code is missing
Inversion
A chromosome breaks and the piece of it turns around and reattaches itself
What is a ring chromosome
Where the ends are attached to itself to form a ring
Translocation
A chromosome segment rearranges from one location to another. It can happen either with in he same chromosome or move to another chromosome
Mosaicism
2 or more sets of chromosome in the cells with different genetic material
What is trisomy
Presence of extra chromosome
How does trisomy occur
Asa result of non disjunction - the paired chromosomes fail to move to opposite poles during meiosis so do not divide evenly
This leaves 1 chromosome in one cell and three in the other cel rather than. 2 and 2
Alll are fatal in utero apart from. Trisomy of chromosome 21 (downs),18 (Edward’s) and 13 (Patau)
What are the screening choices
No screening
Only downs
Only Edward’s and pataus
Downs edwards and pataus
What is combined screening for trisomy conditions
Ultrasound and blood test
When does combined screening happen
Between 11-14 week
What does the ultrasound do in combined screening
Measures the fluid on he back of the fetal neck - nucal translucency
What is measured in the blood test for screening test
PAPP-A and hCG levels
What is correlated with a foetus with trisomy condition
High measurement of nuchal fold
Low measurement of PAPP-A
High levels of hCG
Results from the tests are collated with maternal age to give individualism chance for foetus having downs
What is a high risk of downs
1;150 or less
What is low risk of downs
1:151 or more
Quadruple screening for downs
Blood test only takes place betweeen 14-20 weeks
Tests for alpha- fetal protein (AFP), human chlorionic gonadrotropin (hCG), estriol and inhibin A.- four markers
Less accurate than combined test - 5% false positive
What is the NIPT
Non invasive prenatal testing is a folllow up screening test for a high chance result from imbibed or quadruple test
Takes sample of maternal blood and screens piece of DNA some of which are fetal from the placenta.it screens for more than expected levels of DNA from chromosomes 13,18 and 21
42 per 100,000 results will be a false productive
Whe are autosomal dominant conditions screened an why
Under specific circumstances - family history
More likely to be known bout by the family so special screening can be offered
Whe are autosomal recessive conditions screened and why
Offered routinely to pregnant women
Occurs less frequently in the family pedigree
What is sickle cell diease
Red blood cells are sickle shaped rather than biconcave
They dump together abusing them to get stuck in small blood vessels
Can cause inflammatory diseases
Causes anaemia severe pain and life threatening infections.
Mainly affects people of Friday or Caribbean origin
What is thalassaemia
Red blood cells produce no or little amounts of haemoglobin
It causes severe anaemia requiring frequent blood transfusion and medications
Who does thalasseamia affect most
Mainly affects people of Mediterranean, south Asian southeast Asian and Middle Eastern origin
How is screening for sickle cell and thalasseamia performed
Thalasseamia offfered to all
Screening for SCD offered to all who live in area of hig prevalence where greater then 1.5 per 10000 pregnancies affected by this condition
Blood test is performed before 10 weeks
If pregnant women is found to be a carrier the biological father of the unborn baby will be offered screening too
If both are carries the women will be offered diagnostic testing to see if the feus is affected by the condition
How do you diagnostically test for fetal genetic conditions
Chorionic villus sampling
Amniocentesis
PCR
Microarray
Karyotyping
Chlorionic villus sampling
Local anaesthetic used to numb the abdomen
Fine edge inserted intro abdominal to obtain a sample of placental tissue to test fetal dna
Ultrasound scan is used to guide the needle
Performed between 11-14 weeks but can be done later
Risk of miscarriage approx 0.5% following procedure
Amniocentesis
Local anaesthetic used to numb abdomen
Fine needle inserted and sample of amniotic fluid is O’Brien’s
Ultrasound scan is used to guide the needle
Fetal dna in the amniotic fluid is tested for genetic conditions
Performed between 15 - 20 weeks but can be done later
PCR
Heat and enzymes - polymerase - used to multiply, deconstructed then reconstruct dna so equipment can detect genetic variations
Results ina few days
Targets specific genetic changes
Microarray
Lab tool used to detect the expression of thousands of genes at the same time
DNA microarrays are microscopic slides that are inter with thousands of tiny spot in defined positions with each spot contain a known dna sequence or gene
Sample compared with a reference sample o detect genetic differences
Karyotyping
Pairing and ordering all the chromosome providing a genome - wide snapshot of an individuals chromosome
Staining used to reveal the structural feature on. Glass slide under a microscope
What s neural tube defects
The neural tube develops to form the spinal ord, brain and spine
With a defect the spinal cord does not fs instead it remains open
Multi factorial condition cause by multiple genetic and multiple environment factors. Sub clinic a genetic mutation is exposed to aggravating conditions - including folate deficiency, maternal diabetes, anti-convulsant mdcation, smoking an obesity
Varies in severity from spinal bifilar - affects exposure of spinal cord - -to anencephaly - affects exposure/ absence of brain
Neural tube defects are primarily screened for at the 18-20 week anomaly ultrasound scan
Who is involved in clinical genetics
Collaboration between
Family
Clinical genetics sevice
Cytogenetic laboratories molecular
Genetics laboratories
Other medical departments
Lay support groups
What do clinical genetics do
Diagnose/confirm a genetic condition
Assess referred patients and relatives level of risk of a genetic condition
Provide required info
Provide psychological support
Make recommendations
Make referrals
What are the aim of geneti counselling
Help the individuals and families to.
Understand he medical facts
Appreciate the way heredity contributes to the disorder and reoccur acne
Understand the options for dealing itch recurrence
Choose the course of action hichseems appropriate them
Make the best possible adjustment to the disorder
What are the core principles of genetic counselling
Autonmy of individual
Patients right. Full and complete information ina Orem they understand
Preservation of confidentiality
Aimed at. Facultative decision making with time to explore all options
What at the referra; pathways for clinical genetics
Patient contacts clinical genetics directly - self referral
Via g, midwife
Secondary care practioners
Clinical laboratories
Who is offered a referral for genetic counselling
People who suspect they have genetic condition
People itch family history of genetic condition
Pregnancy people with genetic issues
People with a sting family family history of cancer
Infants and children suspected of having a genetic conditioon
Role of midwife
Simplify terms
Gain consent
Provide support
Reassurance
Non judgmental,
No bias
Educate and inform
