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Genetics > Down Syndrome > Flashcards

Down Syndrome Flashcards

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Biology 101 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
Q

What is mosaicism

A

Mixture of trisomy 21 and karyotypically normal cells

26
Q

Phenotype in mosaicism

A

Milder phenotype

27
Q

Down syndrome is characterised by

A

Combination of major and minor differences in structure

28
Q

What are the frequent type of presentations?

A

often associated with >>

Cognitive impairment

Physical growth impairment

Particular set of facial characteristics

29
Q

How can Down syndrome be identified in a foetus?

A

Amniocentesis during pregnancy

30
Q

How can Down syndrome be identified in a baby?

A

At birth, by clinical features

31
Q

Features of Down syndrome in the head and face

A

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
Q

Learning in Down’s syndrome

A

Moderate learning disability

33
Q

Features of Down syndrome in the limbs

A

Single palmar crease

Curvature of 5th finger (= Clinodactyly)

Pronounced sandal gap between first and second toes

Hypotonia

34
Q

Cardiac features/complications of Down syndrome

A

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
Q

What is the most common cardiac defect in Down syndrome?

A

Endocardial cushion defect

= AKA, Atrio-ventricular septal cancal defect (AVSD)

in 40%cases

36
Q

What is the 2nd common cardiac defect in Down syndrome?

A

VSD (Ventricular septal defect)

30%cases

37
Q

What is the 3rd common cardiac defect in Down syndrome?

A

ASD (Atrial septal defect) Secumdum

38
Q

What are the less common cardiac defects in Down syndrome?

A

Tetrallogy of Fallot (TOF) in 5% cases

Isolated patent ductus arteriosus (PDA) in 5% cases

39
Q

Down syndrome + cyanosis >> D/D?

A

TOF (Tetralogy of Fallot)

40
Q

Down syndrome + acyanotic heart disease >>> D/D?

A

1st D/D: Enocardial cushion defect/Atrioventricular septal defect

2nd D/D: Ventricular septal defect

3rd D/D: Atrial septal defect- secundum

41
Q

Gastrointestinal features of Down syndrome

A

Duodenal atresia

Hirschsprung’s disease

42
Q

Gonadal feature of female with Down syndrome

A

Subfertility

43
Q

Gonadal feature of male with Down syndrome

A

Infertility

44
Q

Why males are infertile and females are subfertile in Down syndrome?

A

Down syndrome affects spermatogenesis >>> males are almost always infertile

Female do NOT have spermatogenesis >> remains subferile due to disease

45
Q

Later reproductive complications of a female with Down syndrome?

A

High incidence of problems with pregnancy and labour

46
Q

Body structure complication lately in Down syndrome

A

Short stature

Atlanto-axial instability

47
Q

Hormonal/Endocrine complication of Down syndrome

A

Hypothyroidism

48
Q

Complication of brain function lately in Down syndrome

A

Learning difficulties

Alzheimer’s disease (in most by age 50years)

49
Q

Haematological disorder in Down syndrome

A

ALL (Acute lymphoblastic leukaemia)

Also,

AML (Acute myeloblastic leukaemia)

Transient leukaemias

50
Q

Which type of systemic infection is more common in Down’s syndrome?

A

Respiratory infections (repeatedly)

51
Q

How does hearing impairment develop in Down syndrome?

A

Repeated respiratory infections >>> glue ear >>> hearing impairment

52
Q

Similarity between Down syndrome and Alzheimer’s disease

A

In Autopsy,

Brain of Alzheimer’s disease has similarity with brain of Down’s

Genetics (28 decks)

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