Down Syndrome Flashcards
Incidence of Down syndrome
1/100 to 1/1000 live births
(Or 1 per 700 live births overall)
Rate of Down syndrome among the children of the US
0.15% (= 1.5/1000 = 15/10,000)
What is the most common cause of mental retardation?
Down Syndrome
Is it an inherited disease?
NO
It is genetic disease, but not inherited
Relation between risk of Down syndrome and maternal age
Increasing maternal age >>> Increasing risk of Down syndrome
After 30 years, adding 5years to maternal age = 3times more risk for Down syndrome
Risk of Down syndrome when maternal age 30years
1 per 1000 (= incidence of normal population)
Risk of Down syndrome when maternal age 35years
1 per 350
Risk of Down syndrome when maternal age 40years
1 per 100
Risk of Down syndrome when maternal age 45years
1 per 30
Chromosomal abnormality of Down syndrome
Trisomy 21
Another name of trisomy 21
trisomy G
Meaning of trisomy 21
Extra 21st chromosome (fully/partly)
What are the types of Down syndrome?
3 types:
1. Trisomy 21 (due to non-dysjunction)- 94%
2. Translocation (due to Robertsonian translocation) 3.5-5%
3. Mosaicism 1-2.5%
Which type of Down syndrome occurs due to Non-dysjunction?
Trisomy Down syndrome
Which type of Down syndrome occurs due to Robertsonian translocation?
Robertsonian translocation Down syndrome (ROB)
What is the most common mode of cytogenetics in Down syndrome?
Non-dysjunction (94%cases)
When does non-dysjunction occur?
During meiosis of oogenesis
If a child has non-dysjunction, what is the risk of recurrence in future child?
1 per 100 (1%), if mother is less then 35years
(but if trisomy 21 is due to translocation, the risk is higher)
What is the second common mode of cytogenetics in Down syndrome?
Robertsonian translocation (2% to 5% cases)
What is Robertsonian translocation?
Long arm (q) of chromosome 21 breaks and attaches to long arm (q) of chromosome 14 or 21 itself.
results in >>> t(21q:14q) OR t(21q:21q)
The most common is: on 14 = t(21q:14q)
The most common Robertsonian translocation
Between chromosome 14 and 21
Ratio of new mutation and inheritence from parents of Robertsonian translocation
50:50
50% are new, 50% inherited from parents
If a child has robertsonian translocation, what are the chances of recurrence in the future?
If mother is translocation carrier >>> 10-15%
If father is translocation carrier >>> 2.5%
What is the least common mode of cytogenetics in Down syndrome?
Mosaichism (1 to 3%)
What is mosaicism
Mixture of trisomy 21 and karyotypically normal cells
Phenotype in mosaicism
Milder phenotype
Down syndrome is characterised by
Combination of major and minor differences in structure
What are the frequent type of presentations?
often associated with >>
Cognitive impairment
Physical growth impairment
Particular set of facial characteristics
How can Down syndrome be identified in a foetus?
Amniocentesis during pregnancy
How can Down syndrome be identified in a baby?
At birth, by clinical features
Features of Down syndrome in the head and face
Brachycephaly (shorter skull)
Flat occiput
Flat/round face
Upslanting palpebral fissures
Epicanthic folds
Brushfield spots on irish
Cataract (only in 3%)
Small ears
Protruding tongue
Horizontally furrowed tongue
Learning in Down’s syndrome
Moderate learning disability
Features of Down syndrome in the limbs
Single palmar crease
Curvature of 5th finger (= Clinodactyly)
Pronounced sandal gap between first and second toes
Hypotonia
Cardiac features/complications of Down syndrome
Congenital heart defect is present in 40-50% cases
Multiple may be present
1. Endocardial cushion defect ( = AVSD: Atrioventricular septal canal defect) >> in 40% cases
2. Ventricular septal defect >> 30% cases
3. Secundum ASD (Atrial septal defect)) >> 10%
4. Tetrallogy of Fallot (TOF) >> 5%
5. Isolated patent ductus areriosus (PDA) >> 5%
What is the most common cardiac defect in Down syndrome?
Endocardial cushion defect
= AKA, Atrio-ventricular septal cancal defect (AVSD)
in 40%cases
What is the 2nd common cardiac defect in Down syndrome?
VSD (Ventricular septal defect)
30%cases
What is the 3rd common cardiac defect in Down syndrome?
ASD (Atrial septal defect) Secumdum
What are the less common cardiac defects in Down syndrome?
Tetrallogy of Fallot (TOF) in 5% cases
Isolated patent ductus arteriosus (PDA) in 5% cases
Down syndrome + cyanosis >> D/D?
TOF (Tetralogy of Fallot)
Down syndrome + acyanotic heart disease >>> D/D?
1st D/D: Enocardial cushion defect/Atrioventricular septal defect
2nd D/D: Ventricular septal defect
3rd D/D: Atrial septal defect- secundum
Gastrointestinal features of Down syndrome
Duodenal atresia
Hirschsprung’s disease
Gonadal feature of female with Down syndrome
Subfertility
Gonadal feature of male with Down syndrome
Infertility
Why males are infertile and females are subfertile in Down syndrome?
Down syndrome affects spermatogenesis >>> males are almost always infertile
Female do NOT have spermatogenesis >> remains subferile due to disease
Later reproductive complications of a female with Down syndrome?
High incidence of problems with pregnancy and labour
Body structure complication lately in Down syndrome
Short stature
Atlanto-axial instability
Hormonal/Endocrine complication of Down syndrome
Hypothyroidism
Complication of brain function lately in Down syndrome
Learning difficulties
Alzheimer’s disease (in most by age 50years)
Haematological disorder in Down syndrome
ALL (Acute lymphoblastic leukaemia)
Also,
AML (Acute myeloblastic leukaemia)
Transient leukaemias
Which type of systemic infection is more common in Down’s syndrome?
Respiratory infections (repeatedly)
How does hearing impairment develop in Down syndrome?
Repeated respiratory infections >>> glue ear >>> hearing impairment
Similarity between Down syndrome and Alzheimer’s disease
In Autopsy,
Brain of Alzheimer’s disease has similarity with brain of Down’s
