2.  Chromosomes are the structures that hold our genesgenes  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 centromerecentromere

4.  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.  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 karyotypekaryotype  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"autosomes  Final pair is called the "sex chromosomes."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. Meiosis Mitosis Maternal Age Environment

11.  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.  Abnormality of chromosome number or structure: ◦ Numerical Abnormalities ◦ Structural Abnormalities

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

16.  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. Trisomy 2( Down Syndrome (Trisomy 21(

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

21.  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.  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.  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.  The remaining 3 percent have a Robertsonian translocation in which all or part of an extra chromosome 21 is fused with another chromosome.

28.  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.  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

35. 

36. Dysmorphic sign Frequency (%) Flat facial profile 90 Poor Moro reflex 85 Hypotonia 80 Hyperflexibility of large joints 80 Loose skin on back of neck 80 Slanted palpebral fissures 80

37. Dysmorphic sign Frequency (%) Dysmorphic pelvis on radiograph70 Small round ears 60 Hypoplasia of small finger, middle phalanx 60 Single palmar crease 45

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

41. Mental retardation >95 Growth retardation >95 Early Alzheimer's disease 75% by age 60 Congenital heart defects (atrioventricular canal defect, ventricular septal defect, atrial septal defect 40

42. Hearing loss 40 to 75 Ophthalmic disorders (congenital cataracts, glaucoma( 60 Epilepsy 5 to 10 Gastrointestinal malformations (duodenal atresia, Hirschsprung disease)5 Hypothyroidism 5 Leukemia 5

43. Increased susceptibility to infection (pneumonia, otitis media, sinusitis, pharyngitis(1-6 Infertility>99% in men anovulation in 30% of women

44. . Maternal Serum Screening 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.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

45.  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.  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.  Maternal serum screening (multiple-marker screening) can allow the detection of trisomy 21 pregnancies in women in this younger age group.

48.  Alpha-fetoprotein (AFP)  unconjugated estriol  human chorionic gonadotropin (hCG)  the serum markers most widely used to screen for Down syndrome

49.  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.  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.  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.  In women older than 35 years, the triple test fails to detect 10 to 15 percent of pregnancies affected by trisomy 21.

53. 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. 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 %

57.  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.  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.  chromosomes 18 (aqua), X (green), and Y (red). chromosomes 13 (green), and 21 (red) chromosomes 13 (green), and 21 (red)

62. 2:1 ratio (Down's Syndrome) 1:1 ratio (normal fetus)

63. Trisomy 18, 47 Ch.

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

71. Kleinefelter XXY

72. Kleinefelter/47XXY