Prescreening of Genetic Diseases (It’s worth & potential)

1. Prescreening of Genetic Diseases (It’s worth & potential) Dr PupakDerakhshandeh, PhD Ass Prof of Medical Science of Tehran University

2. Prescreening for • Down syndrome and trisomy 13 & 18 • Breast cancer (BRCA1 AND BRCA2 GENES) • Colorectal cancer • SMA carrier testing • Factor V Leiden • Cardiovascular risk with C-reactive protein • and Apolipoprotein E

3. Prescreening for Down syndrome and trisomy 21, 13 & 18

4. Down Syndrome (Trisomy 21(

5. Down Syndrome (Trisomy 21( Trisomy 2(

6. First trimester screening for Down syndrome and trisomy 13 & 18(up to12W) • The availability and acceptability of early invasive diagnostic methods (eg, chorionic villus sampling, CVS) • The continued need for second trimester screening for open fetal neural tube defects

7. Women with singleton pregnancies: first-trimester combined screening • measurement of Nuchal translucency • pregnancy-associated plasma protein A [PAPP-A] • The free beta subunit of human chorionic gonadotropin (HCG) at 10 weeks 3 days through 13 weeks 6 days of gestation

8. Nuchal translucency screening involves the measurement by ultrasound of the skin thickness at the back of the neck of a first trimester fetus

9. Identification about 85-90% of affected fetuses in the first-trimester • maternal age was combined with fetal NT • and maternal serum biochemistry (free β-HCG and pregnancy-associated plasma protein (PAPP-A)

11. Second-trimester (13-24W) quadruple screening • measurement of: • alpha-fetoprotein • total human chorionic gonadotropin (HCG) • unconjugated estriol • inhibin A at 15 through 18 weeks of gestation

12. Maternal serum alpha-fetoprotein (MSAFP) • fetus has two major blood proteins: • albumin and alpha-fetoprotein (AFP) • Since adults typically have only albumin in their blood • the MSAFP test can be utilized to determine the levels of AFP from the fetus

13. MSAFP • the gestational age must be known with certainty • the amount of MSAFPincreases with gestational age • Neural tube defect

14. Neural tube defect (NTD) • in the fetus: • from failure of part of the embryologic neural tube to close • there is a means for escape of more AFP into the amniotic fluid !

15. Note! • the MSAFP can be elevated for a variety of reasons • which are not related to fetal neural tube or abdominal wall defects, so this test is not 100% specific

16. Neural tube defect

17. Maternal blood sampling for fetal blood cells • This is a new technique • use of the phenomenon of fetal blood cells gaining access to maternal circulation through the placental villi • only a very small number of fetal cells enter the maternal circulation in this fashion

18. Prenatal screening and diagnosis of neural tube defects • Neural tube defects (NTD): second most prevalent congenital anomaly in the United States • Two factors have played a significant role in the prevention of this disorder in developed countries: • Sonographic imaging combined withamniocentesis for diagnosis of affected fetuses • folic acid supplements for prevention of the disorder

19. Anencephaly (failure of closure at the cranial end of the neural tube)

20. Spina bifida (failure of closure at the caudal end of the neural tube)

21. Environmental factors • The frequency of NTDs is increased with exposure to certain environmental factors: • drugs (valproic acid, carbamazepine, Folic acid deficiency) • diabetes mellitus • Obesity • Adequate folate is critical for cell division due to its essential role in the synthesis of: • nucleic • certain amino acids

22. Genetic factors the observations that NTDs have a high rate: • in monozygotic twins • more frequent among first degree relatives • more common in females than males • The risk of recurrence for NTDs: approximately 2 to 4 percent when there is one affected sibling • With two affected siblings, the risk is approximately: 10 percent • to be higher in countries such as Ireland where the prevalence if NTDs is high

23. NOTE: • The genetic polymorphisms : • mutations in the methylene tetrahydrofolate reductase gene • may increase the risk for NTDs • Folate is a cofactor for this enzyme • which is part of the pathway of homocysteine metabolism in cells • The C677T and the A1298C mutations are associated with elevated maternal homocysteine concentrations and an increased risk for NTDs in fetuses

24. Prevention of neural tube defects • can be accomplished by supplementation of the maternal diet with only 4 mg of folic acid per day • but this vitamin supplement must be taken a month before conception and through the first trimester

25. Maternal serum beta-HCG • the beta-HCG can be used in conjunction with the MSAFP to screen for chromosomal abnormalities, and Down syndrome in particular • An elevated beta-HCG coupled with a decreased MSAFP suggests Downsyndrome

26. Maternal serum estriol • made by the fetal adrenal glands • Estriol tends to be lower when Down syndrome is present

27. Inhibin-A • An increased level of inhibin-A is associated with an increased risk for trisomy 21 • A high inhibin-A may be associated with a risk for preterm delivery

28. Trisomy 21 MSAFP / beta-HCG estriol / inhibin-A

29. overlapping are typical for trisomy 18

30. PrescreeningBRCA1 AND BRCA2 GENES

31. BRCA1 AND BRCA2 GENES • Breast cancer develops in about 12 percent of women who live to age 90 • a positive family history is reported by 15 to 20 percent of women with breast cancer • They are associated with an inherited gene mutation

32. Two major susceptibility genes for breast cancer, BRCA1 and BRCA2 • Testing for mutations in these genes, is available • Clinicians and patients must decide when it is appropriate to screen for their presence

33. BRCA mutations • The reason why BRCA mutations predispose mainly to breast and ovarian cancers is unclear • intact BRCA1 represents a barrier to transcriptional activation of the estrogen receptor • that functional inactivation could lead to altered hormonal regulation of mammary and ovarian epithelial proliferation

34. BRCA1 or / and BRCA2 gene abnormalities • Cancer risk with a high penetrance • women who have inherited mutations • the lifetime risk of breast cancer is between 65 and 85 percent by age 70

35. Ovarian cancer • Ovarian cancer is also linked to the presence of BRCA mutations • the lifetime risk of ovarian cancer: • between 45 and 50 percent in women who have a deleterious BRCA1 mutation • and 15 to 25 percent for those with a BRCA2 mutation

36. BRCA2-associated cancers • prostate cancer • male breast cancer • pancreatic cancer • Although the risk of male breast cancer and pancreatic cancer may be under 10 percent • the risk of prostate cancer in BRCA2 carriers may be as high as 35 to 40 percent

38. BRCA 1 • The gene Locus for BRCA1: 17q21 • a large gene • 24 exons • encoding a 220 kD • 1863 amino acids • Two recognizable motifs

39. BRCA2 • BRCA2 (13q12.3) • was identified by Wooster et al. in 1995 • It encodes for 384 kD nuclear protein • 3418 amino acids • BRCA2 bears no homology to any known tumour supressor genes • contains 27 exons • spread over 70 kb of genomicDNA

40. BRCA1 Gene

41. BRCA2 Gene

42. SSCP single strand conformation polymorphism • simplicity • clearly by heteroduplex analysis (HA)

43. Pedigree of a selected family with breast cancer

44. SSCP AnalysisBRCA1 Exon 15, 4650delCA

45. Pedigree of a selected family with breast cancer

46. SSCP AnalysisBRCA1, Exon 20,Nt 5382

47. SSCP AnalysisExon 11pi BRCA1 MS R1347G

48. Breast Cancer Families

49. Significance of family history • Degree of relatedness to affected relatives • Number of affected relatives • The age of the relative (s) when breast cancer occurred • Whether there is a family history of ovarian cancer

50. Mutations in BRCA1/2 gene