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Understanding Chromosomal Disorders: Causes, Examples, and Management

Learn about chromosomal disorders, including Down syndrome, Trisomy 21, Trisomy 18, Trisomy 13, Klinefelter syndrome, and Turner syndrome. Explore risk factors, clinical presentations, and management options. Discover how genetic counseling and screening play a crucial role in preventing chromosomal abnormalities.

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Understanding Chromosomal Disorders: Causes, Examples, and Management

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  1. Chromosomal Disorders Fahd Alshehri Ali Almater Abdulrahman Alqahtani Abdullah Alshehri Abdullah Alshahrani

  2. Case scenario • A 36-years old woman, G3P2 with one prenatal visit at 35 weeks but otherwise uneventful prenatal course delivers a 3900g female child. • At birth the infant is noted to have decreased tone, upslanting palpebral fissures and epicanthal folds. • The extremities show single transverse palmar crease

  3. So, • Advanced maternal age • Hypotonia • Dysmorphic features: palpebral fissures epicanthal folds simian crease

  4. What do you think? • Down Syndrome. • What is your next step? • Karyotype

  5. What is the management? • Variable • How to prevent? • Genetic counselling.

  6. Screening? • Should be offered ONLY when termination of pregnancy is acceptable.

  7. What is “chromosomal disorders”? • Any disorder that results in an abnormal chromsomal sets.

  8. EUPLOIDY 46, XY

  9. Numerical chromosomal disorders • Euploidy: = 2n = 46 chromosomes • Aneuploidy: ≠ 2n is the state of not having euploidy Examples: Down syndrome Turner syndrome

  10. Risk factors 1- advanced maternal age: Increases the incidence of meiotic errors (non-disjunction). 2- history of unexplained 1st TM abortions. 3- exposure to irradiations. 4- previous baby with chromosomal disorder.

  11. Aetiology • Non-disjunction • Abnormal separation of chromosomes during cell division. • The result: • Extra chromosome = trisomy • Missing a chromosome = monosomy

  12. Trisomies 3 copies of a particular chromosome

  13. Trisomy 21 • Down syndrome • 47,XX+21 • 47,XY+21 • The MC abnormality of chromosomal number.

  14. Trisomy 21 • 96% non-disjunction • 4% translocation of the long arm of chromosome 21 to chromosome 22

  15. Trisomy 21 • C|P: • Hypotonia: improves with age • Characteristic facial features: • Flattened occiput • Upslanting palpebral fissures. • Epicanthal folds. • Large protruding tongue. • Short broad hands. • Transverse palmar crease. • Wide gap between the first and second toes.

  16. Trisomy 21 • Intellectual disability • 40% congenital heart disease: • The cause of early-life deaths • 10% GI anomalies: • Duodenal atresia

  17. Trisomy 21 • Increase risk of leukemia. • More susceptible to infection. • More risk of cataract. • Early-onset Alzheimer disease.

  18. Trisomy 18 • Edwards syndrome. • 2nd MC. • 47,XX +18 • 47,XY +18 • ˃ 95% aborted. • ˂ 10% survive the 1st year.

  19. Trisomy 18 • C|P: • LBW • MR • Hypertonia • Prominent occiput • Low-set malformed ears • Short stature • Clenched fists.

  20. Trisomy 18 • Microcephaly, micrognathia. • Congenital heart disease. • Rocker-bottom feet, hammer toe. • Omphalocele.

  21. Trisomy 13 • Patau syndrome. • 3rd MC. • 47,XX +13 • 47,XY +13 • ˂ 8% survive the 1st year.

  22. Trisomy 13 • C|P: • LBW • Microcephaly • Midline facial defects • CNS anomalies & MR

  23. Trisomy 13 • Male: Hypospadias & cryptorchidism • Female: Hypoplastic labia minora

  24. Klinefelter syndrome • 47,XXY • MC cause of hypogonadism in males • Caused by non-disjunction

  25. Klinefelter syndrome • C|P: • With puberty: • Presence of Pubic & axillar hair with testis of an infantile volume. • Tall & long limbs. • Slim. • Osteopenia, osteoporosis. • Gynecomastia

  26. Klinefelter syndrome ↑ LH ↓testesterone So, affected individuals are infertile

  27. Monosomies ONLY one copy of a particular chromosome

  28. Monosomies Turner syndrome

  29. Turner syndrome • The ONLYmonosomic viable condition. • 45, X0 • 99% aborted, constituting 13% of all 1st trimester abortions. • 25% mosaic. • Caused by mitoticnon-disjunction (post-conceptus mitotic non-disjunction event). • So, maternal age is not a risk factor.

  30. Turner syndrome • C|P: • Facial characteristics: • Low-set malformed ears. • Triangular face. • Flattened nasal bridge. • Epicanthal folds. • Neck: webbed. • Chest: • Shield-shaped. • Widened inter-nipple distance.

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