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Down Syndrome Flashcards

1
Q

Incidence of Down syndrome

A

1/100 to 1/1000 live births

(Or 1 per 700 live births overall)

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2
Q

Rate of Down syndrome among the children of the US

A

0.15% (= 1.5/1000 = 15/10,000)

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3
Q

What is the most common cause of mental retardation?

A

Down Syndrome

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4
Q

Is it an inherited disease?

A

NO

It is genetic disease, but not inherited

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5
Q

Relation between risk of Down syndrome and maternal age

A

Increasing maternal age >>> Increasing risk of Down syndrome

After 30 years, adding 5years to maternal age = 3times more risk for Down syndrome

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6
Q

Risk of Down syndrome when maternal age 30years

A

1 per 1000 (= incidence of normal population)

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7
Q

Risk of Down syndrome when maternal age 35years

A

1 per 350

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8
Q

Risk of Down syndrome when maternal age 40years

A

1 per 100

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9
Q

Risk of Down syndrome when maternal age 45years

A

1 per 30

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10
Q

Chromosomal abnormality of Down syndrome

A

Trisomy 21

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11
Q

Another name of trisomy 21

A

trisomy G

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12
Q

Meaning of trisomy 21

A

Extra 21st chromosome (fully/partly)

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13
Q

What are the types of Down syndrome?

A

3 types:

1. Trisomy 21 (due to non-dysjunction)- 94%

2. Translocation (due to Robertsonian translocation) 3.5-5%

3. Mosaicism 1-2.5%

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14
Q

Which type of Down syndrome occurs due to Non-dysjunction?

A

Trisomy Down syndrome

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15
Q

Which type of Down syndrome occurs due to Robertsonian translocation?

A

Robertsonian translocation Down syndrome (ROB)

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16
Q

What is the most common mode of cytogenetics in Down syndrome?

A

Non-dysjunction (94%cases)

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17
Q

When does non-dysjunction occur?

A

During meiosis of oogenesis

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18
Q

If a child has non-dysjunction, what is the risk of recurrence in future child?

A

1 per 100 (1%), if mother is less then 35years

(but if trisomy 21 is due to translocation, the risk is higher)

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19
Q

What is the second common mode of cytogenetics in Down syndrome?

A

Robertsonian translocation (2% to 5% cases)

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20
Q

What is Robertsonian translocation?

A

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)

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21
Q

The most common Robertsonian translocation

A

Between chromosome 14 and 21

22
Q

Ratio of new mutation and inheritence from parents of Robertsonian translocation

A

50:50

50% are new, 50% inherited from parents

23
Q

If a child has robertsonian translocation, what are the chances of recurrence in the future?

A

If mother is translocation carrier >>> 10-15%

If father is translocation carrier >>> 2.5%

24
Q

What is the least common mode of cytogenetics in Down syndrome?

A

Mosaichism (1 to 3%)

25
**What is mosaicism**
**Mixture of trisomy 21 and karyotypically normal cells**
26
**Phenotype in mosaicism**
**Milder phenotype**
27
**Down syndrome is characterised by**
**Combination of major and minor differences in structure**
28
**What are the frequent type of presentations?**
often associated with \>\> ## Footnote **Cognitive impairment** **Physical growth impairment** **Particular set of facial characteristics**
29
**How can Down syndrome be identified in a foetus?**
**Amniocentesis during pregnancy**
30
**How can Down syndrome be identified in a baby?**
**At birth, by clinical features**
31
**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**
32
**Learning in Down's syndrome**
**Moderate learning disability**
33
**Features of Down syndrome in the limbs**
**Single palmar crease** **Curvature of 5th finger (= Clinodactyly)** **Pronounced sandal gap between first and second toes** **Hypotonia**
34
**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%**
35
**What is the most common cardiac defect in Down syndrome?**
**Endocardial cushion defect** **= AKA, Atrio-ventricular septal cancal defect (AVSD)** **in 40%cases**
36
**What is the 2nd common cardiac defect in Down syndrome?**
**VSD (Ventricular septal defect)** **30%cases**
37
**What is the 3rd common cardiac defect in Down syndrome?**
**ASD (Atrial septal defect) Secumdum**
38
**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**
39
**Down syndrome + cyanosis \>\> D/D?**
**TOF (Tetralogy of Fallot)**
40
**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**
41
**Gastrointestinal features of Down syndrome**
**Duodenal atresia** **Hirschsprung's disease**
42
**Gonadal feature of female with Down syndrome**
**Subfertility**
43
**Gonadal feature of male with Down syndrome**
**Infertility**
44
**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**
45
**Later reproductive complications of a female with Down syndrome?**
**High incidence of problems with pregnancy and labour**
46
**Body structure complication lately in Down syndrome**
**Short stature** **Atlanto-axial instability**
47
**Hormonal/Endocrine complication of Down syndrome**
**Hypothyroidism**
48
**Complication of brain function lately in Down syndrome**
**Learning difficulties** **Alzheimer's disease (in most by age 50years)**
49
**Haematological disorder in Down syndrome**
**ALL (Acute lymphoblastic leukaemia)** **Also,** **AML (Acute myeloblastic leukaemia)** **Transient leukaemias**
50
**Which type of systemic infection is more common in Down's syndrome?**
**Respiratory infections (repeatedly)**
51
**How does hearing impairment develop in Down syndrome?**
**Repeated respiratory infections \>\>\> glue ear \>\>\> hearing impairment**
52
**Similarity between Down syndrome and Alzheimer's disease**
**In Autopsy,** **Brain of Alzheimer's disease has similarity with brain of Down's**

Genetics (28 decks)

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