G6- Chromosomal abnormalities and syndromes Flashcards
How common are chromosomal diseases?
Mostly rare. No clear pattern of inheritance. Usually low risk to relatives
why is staining used on genes?
used to obtain complex banding patterns that allow precise identification of each chromosome and recognition of small additions or deletions
what is the short arm of a chromosome?
p
what is the long arm of the chromosome?
q
what chromosomes are abnormalities found on?
- trisomies 13,18,21
- extra sex chromosomes
what are the types of chromosomal abnormalities?
Structural: translocations, deletions and duplications
How does age affect the number of incidences?
incidences increase with maternal age
what syndrome is trisomy 21?
Downs sydrome (1 in 800)
what are phenotypes of downs syndrome?
- Upslanting palpebral fissures
- Middle third hypoplasia
- Flat nasal bridge
- Open mouth posture
- Protruding fissured tongue
- Low set ears
- Short stature
what syndrome is trisomy 13?
Patau syndrome (1 in 5000)
what are phenotypes of patau syndrome?
convergence of left and right side of the brain
- small eyes or Cyclops
- cleft lip/palate
- simian crease (hand)
what syndrome is trisomy 18?
Edwards syndrome (1 in 3000)
what are phenotypes of Edwards syndrome?
Narrowpelvis • Small jaw • Clenched hands with overlapping digits • Congenital heart defects • Cleft palate - Many die before the age of 1
Why is there only trisomies in 13,18,21?
trisomies in other chromosomes result in spontaneous abortions
what is a syndrome of a single X chromosome?
Turner syndrome (1 in 5000)
what is the phenotype of turners syndrome?
- Normal external vaginal organs
- Uterus and fallopian tubes present
- Neither ovaries (nor testes)
- Growth retardation / Webbed neck
- Bone and heart problems
- infertility
what is SRY?
-Some species (including humans) have a gene SRYon the Y chromosome that determines maleness (produces TDF)
• Human sex is determined by containing SRY or not
• When SRY is activated, cells create testosterone to turn the genderless sex organs into male
• SRY-reliant species can have conditions such as XXY and still viable (but may display features of both sexes)
• SRY and sex determination e.g. was once used in Olympic games
Name a syndrome that affects sex of humans.
Kleinfelters (XXY) (<2 per 1000)
name a syndrome as a result of chromosomal deletion.
Velocardiofacial syndrome
what are problems with Velocardiofacial syndrome?
Developmental delays Speech problems
Cardiac problems
Cleft palate
Mental Health
what are general clinical features that commonly occur in patients with chromosomal abnormalities?
- Developmental delay (physical / mental)
- Short stature
- IQ / cognition / speech
- Congenital heart problems
- Cleft palate
name congenital abnormalities.
- Malformations
- Disruptions
- Deformations
- Syndromes
what is malformation?
primary structural defect occurring during development of an organ or tissue e.g. CP, CL(P)
what is aetiology?
single gene, multifactorial, environmental, teratogen or unknown
what is a syndrome?
The presence of multiple anomalies simultaneously in the same individual giving a pattern of malformation
- Implies a common cause for all the anomalies
Describe disruption : hemifacial microsomia.
Destruction of part of a foetus that had initially developed normally
(Foetus is genetically normal and risk of recurrence is low)
What are examples of Disruption: Hemifacial microsomia?
-atypical facial clefts, digit or limb
amputations caused by amniotic bands.
-Hemifacial microsomia caused by
-haemorrhage/haematoma at the stapedial artery
what is deformation due to?
Due to abnormal intra-uterine moulding in either a healthy or malformed foetus
what are the 2 categories of mental retardation in down syndrome?
(a) Profound - institutionalised (b) Mild - community dwelling
what can down’s syndrome result in?
- Cardiac abnormalities (50%)
- Resistance to infection
- Leukaemia (more prevalent)
what are dental problems of downs syndrome?
-Dental caries - resistant
• Periodontal disease - susceptible
• Malocclusion - common
• Dental anomalies - hypodontia, microdontia, delayed eruption
How does downs syndrome affect dental management?
-Communication problems • Anxiety/Restlessness /Stubborness • Access/macroglossia/Salivation • Cross infection - ? Hep B • Susceptibility to infection • Antibiotic cover • Poor G.A. risk
