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Chromosomal Abnormalities in Developmental Disorders

Explore the impact of chromosomal abnormalities on human development, covering topics from haploid and diploid cells to syndromes like Down syndrome and Turner syndrome. Learn about trisomies, triploidy, and genetic imprints affecting cognitive and physical health. Discover conditions such as Fragile X syndrome and Angelman syndrome, and understand the complexities of genetic imprinting. Gain insights into clinical manifestations and management of chromosomal-linked disorders.

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Chromosomal Abnormalities in Developmental Disorders

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  1. Developmental Chromosomal abnormalitiesLecture 7

  2. introduction • Normal human cells contain 23 pairs of chromosomes • This includes one pair of sex chromosome XX or XY • During cell division we can identify chromosomes • Lymphocytes incubated for 2-3 days or uncultured bone marrow in 4-24 hours

  3. continue • Haploid: set of 23 chromosomes • Diploid: normal number of 46 chromosomes • Aneuploidy: less than an even multiple of 23 usually is 45 or 47 and rarely 48,49 • Triploidy: 69 chromosomes • Mosaicism • Abnormal in deletion and translocation(balanced and unbalanced)Balanced

  4. Incidence • The earlier the abortion the more likely to be chromosomal • 50% of spontanous abortion are chromosomal abnormal • Mostly triploidy. 45 XO, trisomy 16 • 98% of fetus with turner abort • Generally 6/1000 the incidence of chromosomal abnormalities

  5. When to suspect it • Unexplained infertility/ balanced translocation • Multiple abortion >2 • Prior case of defective baby

  6. When to suspect it…continue • Presence of congenital anomalies • 45% have minor single anomalies • 9% 3 minor anomalies • 1.5% HAVE major anomaly • 2 or more major anomalies may represent genetic syndrome or chromosomal abnormalities(10%).

  7. Down Syndrome • Incidence 1/700 • 2/3 of down fetus spontaneously abort • Clinical diagnosis depend on gestalt • Trisomy 21 in 94% of cases with extra chromosome from mother mostly(95%) • Risk correlate with maternal age • <25 y/o 1/1600 • >40 y/0 1/80 • 2% are mosaic

  8. Other Clinical features • Hypotonia without weakness • Clinodactaly protruded tongue,small ears,brachycephaly,small up turned nose, depressed nasal bridge. • Mental retardation, socially do better with good environment (Happy children)

  9. Clinical issues • Cardiac and GI • Hypothyriodism • Transient leukemoid reaction • Alzheimer’s disease up to 25% over 40 y/o • Early death relate to cardiac dysfunction

  10. Trisomy 18 • Incidence 1/8000 • Overlaps with trisomy 13 • Sever Mental retardation • >90% dead in 1st year

  11. Trisomy 18 • Small face with prominant occiput • Small sternum and pelvis • Flexion deformity of the finger • VSD and horseshoe kidney

  12. triploidy • Complete extra set of chromosomes • Mostly miscarriages • Fetal wastage skeleton more than cephalic, 2% survive to be recognized • Large hydatidiform placenta • VSD, ASD, Syndactaly • Genital and CNS abnormalities

  13. Trisomy 13 • Sever developmetal retardation • Incidence 1/20000 • 90% dead in the 1st year

  14. Trisomy 13 • Midline brain defect • Malformed ear • Microophalmos and coloboma • Scalp defect

  15. Turner syndrome • Most common abnormality in early abortion • Female, short stature, primary amenorrhea, sterility, spares hair and underdeveloped breast • Neonatal: wide spaced nipple, lymphedema , shield chest, • Coarctation of the aorta

  16. Continue turner syndrome • Normal IQ scale with difficulty in spatial orientation such as map • Present with short stature or delay sex maturation • Hormonal therapy

  17. continue • Mosaisim (15%), remove gonads • Recurrent risk is 1-2% • Noonan syndrom AD, fresh mutation • Pulmonary stenosis, nl stature, microceph, mental retardation

  18. Klinefelter syndrome • 20% of aspermic adult male (blocked spermatogenesis • 47 XXY in 80% and mosaic in 20% • IQ is 98 (normal) with mild decrease in verbal IQ • Scoliosis, decrease libido may improve with testesterone, gynecomastia

  19. Fragile X Syndrome • Moderate to sever mental retardation • Speech delay, short attention, hyperactivity • Poor motor coordination and mouthing objects • Poor socialization, temper tantrum • Mood disorder (bipolar), schizophrenia

  20. Fragile X syndrome • Long protruding ears • Long face and prominent jaw • Flattened nasal bridge • High arch palate • Macroorchidism • Genetic is complex, 80% penetration in male and 30% penetration in female

  21. Genetic imprinting • Means: as genomes pass through miosis it is normal for part of it to change. • During miosis inactive X chromosome become active and changes on fragiloe X gene (imprinting) make it malignant

  22. Angelman syndrome • Sever mental retardation • Inappropriate laughter • Decrease pigmentation of choroid or iris (pale blue eyes) • Ataxia and jerky eye movement • Sever speech proplem • Deletion of b15q11q13, maternal in origin • Paternal uniparental disomy

  23. Prader-willi syndrome • (A fat red faced boy in state of somnolency) Charles Diickens • Early hypotonia • Obesity • Short stature as adult • Almond shaped blue eyes • Mental retardation (mild to moderate) • Narrow hands

  24. Chromosomal linked disorder • Smith Lemli opitz syndrome • Low cholesterol • High 7 dehydrocholesterol • Like trsomy 18 • CHARGE • Coloboma • Heart • Atresia of choanae • Retarded • Genitalia hypoplasia • Ear anomalies • VATER

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