1. Down Syndrome (Trisomy 21( Trisomy 13 & 18
Dr Pupak Derakhshandeh, PhD
Ass Prof Medical Science of Tehran University

2. What are chromosomes?
Chromosomes are the structures that hold our genes
Genes are the individual instructions that tell our bodies how to develop and function
They govern our physical and medical characteristics, such as hair color, blood type and susceptability to disease.
Each chromosome has a p and q arm; p is the shorter arm and q is the longer arm.
The arms are separated by a pinched region known as the centromere

4. How many chromosomes do humans have?
The typical number of chromosomes in a human cell is 46 - two pairs of 22 + XX/XY
Holding an estimated 30,000 to 35,000 genes.
One set of 23 chromosomes is inherited from the biological mother (from the egg), and the other set is inherited from the biological father (from the sperm).

5. study of the chromosomes
with a microscope , then Stainning
The chromosomes look like strings with light and dark "bands"
A picture, or chromosome map, of all 46 chromosomes is called a karyotype
The karyotype can help identify chromosome abnormalities that are evident in either the structure or the number of chromosomes.

6. The pairs have been numbered from 1 to 22, with the 23rd pair labeled "X" and "Y."
In addition, each chromosome arm is defined further by numbering the bands that appear after staining
The higher the number, the further that area is from the centromere.
The first 22 pairs of chromosomes are called "autosomes"
Final pair is called the "sex chromosomes."
The sex chromosomes an individual has determines that person's gender; females have two X chromosomes (XX), and males have an X and a Y chromosome (XY).

8. Karyotype 46), Xy)

10. How Chromosome Abnormalities Happen?
Meiosis
Mitosis
Maternal Age
Environment

11. Meiosis Chromosome abnormalities :
happen as a result of an error in cell division. “Meiosis” is the name used to describe the cell division that the egg and sperm go through when they are developing.
Normally, meiosis causes a halving of chromosome material, so that each parent gives 23 chromosomes to a pregnancy

12. Meiosis

13. Meiosis

14. Chromosome abnormalities
Abnormality of chromosome number or structure:
Numerical Abnormalities
Structural Abnormalities

15. Numerical Abnormalities
When an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy).
An example: Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two).

16. Numerical Abnormalities
Kleinfelter Syndrome is an example of trisomy the individual is born with three sex chromosome, XXY.
Turner Syndrome is an example of monosomy the individual is born with only one sex chromosome, an X.

18. Down Syndrome (Trisomy 21(

19. Down Syndrome (Trisomy 21(

20. Down syndrom) Trisomy 21, 47)
critical region:
A region on the long (q) arm of chromosome 21
Down syndrome causes mental retardation
a characteristic facial appearance
multiple malformations

21. critical region: Associated with a major risk for heart malformations
a small but still significant risk of acute leukemia
3 copies of chromosome number 21

22. incidence of 1 in 660 and is by far the most common chromosomal abnormality Slight flattening of the face
A low bridge of the nose (lower than the usually flat nasal bridge of the normal newborn)
An epicanthal fold (a fold of skin over top of the inner corner of the eye, which can also be seen less frequently in normal babies)
A ring of tiny harmless white spots around the iris
mental retardation

23. Down Syndrome: Prenatal Risk
The risk of trisomy 21 is directly related to maternal age
Patients who will be 35 years or older on their due date should be offered chorionic villus sampling or second-trimester amniocentesis

24. Women younger than 35 years should be offered maternal serum screening at 16 to 18 weeks of gestation
The maternal serum markers used to screen for trisomy 21 are alpha-fetoprotein, unconjugated estriol and human chorionic gonadotropin

25. The use of ultrasound to estimate gestational age improves the sensitivity and specificity of maternal serum screening. (Am Fam Physician 2000;62:825-32,837-8.)

26. Etiology and Clinical Manifestations
Trisomy 21 is present in 95 percent of persons with Down syndrome.
Mosaicism, a mixture of normal diploid and trisomy 21 cells, occurs in 2 percent.

27. Etiology and Clinical Manifestations
The remaining 3 percent have a Robertsonian translocation in which all or part of an extra chromosome 21 is fused with another chromosome.

28. Robertsonian translocation
The reciprocal transfer of the long arms of two of the acrocentric chromosomes: 13, 14, 15, 21 or 22
On rare occasions, other non-acrocentric chromosomes undergo Robertsonian translocation

29. Robertsonian translocation
a reciprocal transfer of the whole long or short arms close to the centromere
A relatively common Robertsonian translocation is between chromosome 14 and chromosome 21
In meiosis, a trivalent is formed.

30. Robertsonian translocation

33. TRANSLOCATIONS

34. Balanced reciprocal translocation

36. Frequency of Dysmorphic Signs in Neonates with Trisomy 21
Dysmorphic sign Frequency (%)
Flat facial profile
Poor Moro reflex
Hypotonia
Hyperflexibility of large joints 80
Loose skin on back of neck
Slanted palpebral fissures 80

37. Frequency of Dysmorphic Signs in Neonates with Trisomy 21
Dysmorphic sign Frequency (%)
Dysmorphic pelvis on radiograph 70
Small round ears
Hypoplasia of small finger,
middle phalanx
Single palmar crease

39. Persons with Down syndrome usually have mild to moderate mental retardation
School-aged children with Down syndrome often have difficulty with language, communication
Adults with Down syndrome have a high prevalence of early Alzheimer's disease

40. Down Syndrome

41. Incidence of Some Associated Medical Complications in Persons with Down Syndrome Disorder Incidence (%)
Mental retardation >95
Growth retardation >95
Early Alzheimer's disease %
by age 60
Congenital heart defects
(atrioventricular canal defect,
ventricular septal defect, atrial septal
defect

42. Disorder Incidence (%)
Hearing loss to 75
Ophthalmic disorders
(congenital cataracts,
glaucoma(
Epilepsy to 10
Gastrointestinal malformations (duodenal atresia,
Hirschsprung disease) 5
Hypothyroidism
Leukemia

43. Disorder Incidence (%)
Increased susceptibility to
infection (pneumonia, otitis media, sinusitis, pharyngitis( 1-6
Infertility >99% in men
anovulation in % of women

44. Estimated risk of Down syndrome according to maternal age. . .
                                                                                                                             
FIGURE 1. Estimated risk of Down syndrome according to maternal age. Data from reference 8.
                                                                                                                             
FIGURE 1. Estimated risk of Down syndrome according to maternal age. Data from reference 8.
                                                                                                                             
FIGURE 1. Estimated risk of Down syndrome according to maternal age. Data from reference 8.
Estimated risk of Down syndrome according to maternal age
Maternal Serum Screening
Maternal Serum Screening
Maternal Serum Screening

45. The risk of having a child with Down syndrome
1/1,300 for a 25-year-old woman;
at age 35, the risk increases to 1/365
At age 45, the risk of a having a child with Down syndrome increases to 1/30

46. Maternal Serum Screening
If all pregnant women 35 years or older chose to have amniocentesis
about 30 percent of trisomy 21 pregnancies would be detected
Women younger than 35 years give birth to about 70 percent of infants with Down syndrome

47. The risk of having a child with Down syndrome
Maternal serum screening (multiple-marker screening) can allow the detection of trisomy 21 pregnancies in women in this younger age group.

48. Maternal Serum Screening "triple test" or "triple screen" "Multiples of the Median (MoM)"
Alpha-fetoprotein (AFP)
unconjugated estriol
human chorionic gonadotropin (hCG)
the serum markers most widely used to screen for Down syndrome

49. "Multiples of the Median (MoM)"
AFP is produced in the yolk sac and fetal liver.
Unconjugated estriol and hCG are produced by the placenta.
The maternal serum levels of each of these proteins and of steroid hormones vary with the gestational age of the pregnancy.

50. "Multiples of the Median (MoM)"
With trisomy 21, second-trimester maternal serum levels of AFP and unconjugated estriol are about 25 percent lower than normal levels
maternal serum hCG is approximately two times higher than the normal hCG level

51. Maternal Serum Screening "triple test" or "triple screen"
The triple test can detect approximately 60 percent of the pregnancies affected by trisomy 21, with a false-positive rate of about 5 percent.

52. Maternal Serum Screening "triple test" or "triple screen"
In women older than 35 years, the triple test fails to detect 10 to 15 percent of pregnancies affected by trisomy 21.

53. Recurrence Risk and Family History
If a patient has had a trisomy 21 pregnancy in the past, the risk of recurrence in a subsequent pregnancy increases to approximately 1-3
percent above the baseline risk determined by maternal age

54. Diagnosis of a chromosome-21 translocation in the fetus or newborn is an indication for karyotype analysis of both parents
If both parents have normal karyotypes, the recurrence risk is 2 to 3 percent

55. Ultrasonographic Findings Associated with Fetal Down Syndrome
Chorionic villus sampling
10 to 12 weeks 0.5 to 1.5 %
Early amniocentesis
12 to 15 weeks 1.0 to 2.0 %
Second-trimester amniocentesis
15 to 20 weeks 0.5 to 1.0 %

56. a woman having amniocentesis

57. Counseling Aspects
Women who will be 35 years or older on their due date should be offered chorionic villus sampling or second-trimester amniocentesis.
Women younger than 35 years should be offered maternal serum screening at 15 to 18 weeks' gestation.

58. Ultrasound
During the first trimester of the majority of pregnancies, it is possible to measure the size of the fluid area at the back of the fetus’s neck, known as the nuchal translucency or NT The increasing size of the NT indicates a greater risk of the fetus having Down’s syndrome.

59. Ultrasound

60. Fluorescent In Situ Hybridisation techniques

61. female fetus with trisomy-21
chromosomes 18 (aqua), X (green), and Y (red).
chromosomes 13 (green), and 21 (red)

62. Quantitative fluorescent polymerase chain reaction
2:1 ratio (Down's Syndrome)
1:1 ratio (normal fetus)

63. Trisomy 18, 47 Ch.

64. Trisomy 18, 47 Ch. incidence of about 1 in 3,000
There is a 3:1 preponderance of females to males
Thirty percent of affected newborns die within the first month
50% by two months
and 90% by one year.
severe mental retardation
microcephaly
overlapping fingers, and rocker bottom feet
Neurologically they are hypertonic
Other common malformations include congenital heart, kidney, .... abnormalities.

65. Trisomy 18, 47 Ch.

67. Trisomy 13 (XX/XY, 47 Ch) has an incidence of 1 in 5,000
Forty-four percent of affected newborns succumb in the first month of life
and 69% by six months
Only 18% of the babies born with trisomy 13 survive the first year
microcephaly
microophthalmia (small eyes)
cleft lip or cleft palate
polydactyly (extra fingers)
congenital heart defects
urogenital defects
brain malformations
severe to profound mental retardation.

68. Turner Syndrome ( 45, X)
45, X

69. Turner Syndrome (45, X)

70. Turner syndrome Only females One X chromosome
Or has two X chromosomes but one is damaged
Short stature
Delayed growth of the skeleton
Sometimes heart abnormalities
Usually infertile due to ovarian failure
Diagnosis is by blood test (karyotype)
1 out of every 2,500 female live births worldwide
Short neck with a webbed appearance

71. Kleinefelter
XXY

72. Kleinefelter/47XXY