Mrs Jones' First Consultation Flashcards
List the 7 types of congenital abnormalities and birth defects.
Malformation Disruption Dysplasia Sequence Association Deformation Syndrome
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what is malformation?
- primary structural defect - involves a single organ showing multifactorial inheritance - due to both genetic and environmental factors
what is disruption?
- this is secondary abnormal structure of an organ - caused by ischemia, infection and trauma - it is not geentic but genetic factors can pre dispose to it
what is deformation?
- this is when a mechanical force distorts a structure - occurs is late pregnancy and the prognosis is usually good
what is syndrome?
- this is a consistant pattern of abnormalities with a specific underlying cause - this includes chromosomal abnormalities
what is sequence?
- multiple abnormalities initiated by a primary factor - this could have a genetic component as the initial factor and example is reduced amniotic fluid can lead to the potter sequence this is caused by oligohydraminios which is the reduced volume of amniotic fluid due to failure to produce urine.
an example of sequence?
and example is reduced amniotic fluid can lead to the potter sequence this is caused by oligohydraminios which is the reduced volume of amniotic fluid due to failure to produce urine.
Define dysplasia
Abnormal organisation of cells into tissue - caused by a single gene defect - there is high recurrence in siblings
what is association?
- this is non random occurrence of abnormalities not explained by syndrome
an example of association?
VACTERL association - Vertebral, Anal, Cardiac, Tracheo-Oesophagal, Renal, Limb
What is the most common cause of Sequence e.g. Potter Sequence?
Oligohydramnios – reduced supply of amniotic fluid
What are the 3 types of chromosome?
Metacentric Submetacentric Acrocentric
Describe how chromosome banding works.
Starts at 11 at the centromere – different banding for different stains - the short arm is p and the long arm is q
What are the three different types of chromosomal abnormality?
Aneuploidy Structural Mosaicism
What is mosaicism?
The cells of an individual do not all contain identical chromosomes. There may be two or more genetically different populations of cells. E.g. one cell lineage will be Down Syndrome often the genetic disorder is not fully expressed
what is the definition of autosomal aneuploidy?
- these are numerical abnormalities involving the loss or gain of one or more chromosomes
what is partial aneuploidy?
- these are translocations of certain parts of chromosomes a derivative is a chromosome which looks like it has had a translocation
What is the difference between a balanced and unbalanced translocation?
Unbalanced – there is a loss of genetic material (could result in non viable embryo) balanced - when there is a straight switch of the DNA no genetic material is lost
What could be the potential future issues for someone who has a balanced translocation?
Balanced translocations lead to the formation of quadravalents (rather than bivalents) during meiosis which can lead to strange exchanges in genetic material which can cause disease
List some clinical features of Down Syndrome
- Excess nuchal skin, (neck skin) - sleepy, - severe hypotonia,(less muscle tone) - Single palmar crease, - sandal gap (wide gap between first and second toes) - Upwards slanting eye folds, - macroglossia, (large tongue) - Short stature, - Cardiac abnormalities – ASD and VSD
List three possible causes of Down syndrome.
- Non-disjunction ( failiure to separate) during meiosis I or meiosis II - (4%) Robertsonian translocation –2 acrocentric chromosomes break at the centromere and fuses to form a new chromosome (therefore has additional genetic material) - Mosaicism (1%)
Name two other trisomy disorders
13 – patau syndrome, heart defects cleft lip mental retardation 18 – Edwards heart defects kidney malformation mental retardation
What is monosomy X in females and what are the clinical features?
Turner Syndrome –1/3000 webbed neck, infertile, normal intelligence, Generalised oedema low posterior hairline 80% due to loss of X or Y chromosome in paternal meiosis.
What is polysomy X in males and what are the clinical features?
Kleinfelter’s syndrome – tall, gynaecomastia, (enlargement of breasts) infertile, learning disability - clumsy comes from the X chromosome in either mother or father
How can someone who has sex chromosomes XX be male? chromosome one gender and phenotypically another gender
Due to a translocation - the Y chromosome has the sex determining region on the Y - If there is a translocation of the SRY from the Y to the X you can get an X chromosome with a male determining factor and a Y that has LOST the male determining factor so phenotypically the XX will be male and the XY will be female.
What are genomic disorders?
Disorders in which there is a gain or loss of DNA
Give an examples of two genomic disorders
Deletion – Di George syndrome Duplication – Charcot-Marie-Tooth Disease Type 1A these are micro delation syndrome
what is the human karyotype stained with?
giesma
what is monosomy what is trisomy what is tetrasomy
loss of a single chromosome (always lethal) gain of a one chromosome ( can be tolerated) gain of two chromosomes ( can be tolerated)
what happens when meiosis happens to someone with balanced translocation?
- when someone with balanced translocation undergoes meiosis their chromosomes will form a quadrivalent but it is normally a bivalent
treatment of webbers syndrome?
oestrogen replacement for secondary sexual characteristics and prevention of osteoporosis.
why is gain of chromosomes better tolerated than loss of chromosomes?
- if we lose a chromosome we have lost 50% of the gene pool - if we needed 100% of that chromosome this is very important - loss of an autosomal chromosome is almost always fatal
what are diagnostic features of di- george syndrome?
- cardiac problems - hypoplastic thymus - Hypocalcaemia - lack of calcium in blood stream
what happens in di george syndrome
Micro-deletion of 22q11.2 region containing the gene TBX1 this is delation of transcription factor
what are diagnostic features in charcot marie tooth disease type 1A?
- Muscle weakness - hypotonia - missing reflexes - foot deformities
what happens in charcot marie tooth disease?
- Micro-duplication of PMP22 gene on Chr 17 the deleted gene codes for membrane protein that is a major component of myelin
