L2: Down Syndrome Flashcards
Epidemeology of Down Syndrome
Def & Results of Meiosis
Cytogenic Types of Down Syndrome
- Complete Trisomy 21
- Mosaic Down Syndrome
- Translocation Down Syndrome
What Characterizes Complete Trisomy 21?
The Most Common
Complete Trisomy 21
- Karyotyping
47,XX + 21
Incidence of Complete Trisomy 21
What Is Complete Trisomy 21 dependent on?
Maternal Age
Cause of Complete Trisomy 21
- Non-disjunction of chromosome 21 during meiotic division (80 % in maternal meiosis I)
- lt occurs during oogenesis more than spermatogenesis.
Risk of Recurrence in Complete Trisomy 21
1-2% regardless of maternal age
What Characterizes Mosaic Down Syndrome?
The Best Type
Mosaic Down Syndrome
- Karyotyping
47, XX + 21 / 46, XX
Incidence of Mosaic Down Syndrome
1-2% of cases (more with maternal age)
Cause of Mosaic Down Syndrome
- Non-disiunction occurring early in the division of the zygote, which results in two lines of cells (normal & trisomic)
Risk of Recurrence i Mosaic Down Syndrome
Same as Complete
Clinical manifestations in mosaic type are โฆ.. than complete trisomy
Iess
- ln mosaic type, non-disjunction occurs during โฆ. division
- while in complete type, it occurs during โฆ. division
- mitotic
- Meiotic
What Characterizes Translocation Down Syndrome?
The Most Serious Type
Translocation Down Syndrome
- Karyotyping
46,XX, t(14q, 21q)
Incidence of Translocation Down Syndrome
o lncidence 3- 4%
o Common in young age < 25 years
o Robertsonian translocation is the most common type
โฆโฆ. translocation is the most common type
Robertsonian
Cause of Translocation Down Syndrome
Risk of Recurrence in Translocation Down Syndrome
Types of inherited Translocation
- D/21 Translocation
- G/21 Translocation
D/21 Translocation