Trisomy 21

Question 1

What is Down syndrome also known as?

Answer 1

Down syndrome is also known as Trisomy 21.

Question 2

What is the incidence of Down syndrome in live births?

Answer 2

The incidence is approximately 1:800 - 1:1000 live births.

Question 3

How does the risk of Down syndrome correlate with maternal age?

Answer 3

The incidence is approximately 1:800 - 1:1000 live births.

Question 4

How does the risk of Down syndrome correlate with maternal age?

Answer 4

The risk increases with increasing maternal age, with a risk of 1:400 at 35 years and 1:60 at 42 years.

Question 5

Despite the increased risk with maternal age, who gives birth to most infants with Down syndrome?

Answer 5

Despite the increased risk with maternal age, most infants with Down syndrome are born to mothers under 30 years old.

Question 6

What is the primary genetic mechanism responsible for Down syndrome?

Answer 6

Non-disjunction, which accounts for 95% of cases.

Question 7

What is the percentage of Down syndrome cases caused by translocation?

Answer 7

Translocation accounts for approximately 4% of Down syndrome cases.

Question 8

How might translocation influence the risk of Down syndrome in future pregnancies?

Answer 8

Translocation can be heritable and may influence the risk of Down syndrome in future pregnancies.

Question 9

What is the percentage of Down syndrome cases caused by mosaicism?

Answer 9

Mosaicism accounts for about 1% of Down syndrome cases.

Question 10

Genetics

Answer 10

Non- dysfunction
Translocation
Mosaicism

Question 11

Clinical features most commonly found in newborn infants

Answer 11

• Hypotonia.
• Upslanting palpable fissures.
• Flat nasal bridge.
• Brachcephaly (short, wide head).
• Short neck.
• Protruding tongue.
• Single palmer crease.
• Clinodactyly (incurved fifth finger).
• Sandle gap.

Question 12

Cardiac complications

Answer 12

40-50% have cardiac abnormalities of which AVSD and VSD are the
most common

Question 13

GIT complications

Answer 13

: Duodenal atresia (double bubble on AXR) is the most common.

Question 14

Endocrine complications

Answer 14

Hypothyroidism can be present but is more common later in childhood.

Question 15

All infants with suspected Down syndrome should have
the following

Answer 15

• Full karyotype (unless done antenatally).
• Thyroid test (unless cord thyroid done).
• Cardiac evaluation (even if asymptomatic).
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  138 Down Syndrome (Trisomy 21)
• Follow-up for development, vision, hearing etc.
• Counselling for parents.

Question 16

Trisomy 13 (Patau) and Trisomy 18 (Edward) are the other two syndromes with an
extra chromosome, but these infants are usually born with multiple abnormalities
and seldom survive longer than a few months.

Answer 16

Trisomy 13, also known as Patau syndrome, and Trisomy 18, also known as Edwards syndrome.

Question 17

How do infants with Trisomy 13 and Trisomy 18 typically present?

Answer 17

These infants are usually born with multiple abnormalities.

Question 18

What is the typical prognosis for infants with Trisomy 13 and Trisomy 18?

Answer 18

Infants with Trisomy 13 and Trisomy 18 seldom survive longer than a few months.