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Downs syndrome


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Downs syndrome

  1. 1. Down’s Syndrome<br />
  2. 2. What is Down’s syndrome?<br />Down syndrome or down’s syndrome( named in UK) is a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome{additional chromosome, as a result total chromosome number becomes 47(45A+XX/XY) instead of 46(44A+XX/XY)}.<br />The average IQ of children with down’s syndrome is around 50 compared to normal children with an IQ of 100.<br />J.L Down<br /><ul><li>It is named after John Langdon Down,a Brtish physician who described the Syndrome in 1866.
  3. 3. The disorder was identified as a chromosome 21 trisomy by Jerome Lejeune in 1959.
  4. 4. It is an Autosomal recessive disorder.</li></li></ul><li>Signs & Symptoms.<br />Individiuals with Down’s syndrome have following symptoms:-<br /><ul><li>Mental retardation.
  5. 5. Half moon face.
  6. 6. Puffy cheeks.
  7. 7. Small eyes.
  8. 8. Mongolian type face.
  9. 9. Microgenia(abnormally small chin).
  10. 10. Macroglossia(enlarged tongue near the tonsils).
  11. 11. Brushfield spots(white spots on Iris).
  12. 12. Speech, motor skills delay.
  13. 13. Short stature(149cm women,157cm men)
  14. 14. Obesity.</li></li></ul><li>Complications.<br />Individuals with Down syndrome have a higher risk for many conditions:-<br /><ul><li>Congenital Heart disease(mainly atrio-ventricular septal canal defects).
  15. 15. Hematological Malignancies(such as Leukemia).
  16. 16. Thyroid disorders(hypothyroidism due to dysfunction of thyroid gland).
  17. 17. Infertility.
  18. 18. Gastrointestinal Problems(duodenal atresia,annular pancres etc).
  19. 19. Opthalmology(cataracts,glaucoma,refractive errors brushfield spots).</li></ul>Health benefits-<br />Down syndrome patients experiences reduced incidences of many cancers except leukemia as a direct result of Tumor-suppressor genes on chromosome 21.<br />
  20. 20. Genetics<br /> Trisomy of 21st chromosome<br />
  21. 21. Cause of the Disease.<br /> Down syndrome is developed due to Trisomy of 21st chromosome.<br />What is Trisomy?<br />Autosomal Trisomy(as in case of Down syndrome) is a genetic abnormality in which there are 3 copies, instead of the normal 2 of a particular chromosome.It is a type of aneuploidy(an abnormal number of chromosome).<br /><ul><li>When a particular organism has one extra chromosome,in addition to normal diploid number(2n+1),it is called Trisomic.It is formed by fusion of “n” and “n+1” gamete during Meiosis.</li></li></ul><li>Cause of Trisomy<br />Trisomy develops due to Non-disjunction of 21st chromosome during oogenesis.Thus the ovum consists of 24 chromosomes.If such ovum is fertilised by a normal spermatozoan, The 21st chromosome becomes Trisomic and the zygote contains 47 chromosomes. <br /><ul><li>Normal ovum consists of 23 chromosomes(22+X).
  22. 22. Abnormal ovum in this case consists of 24 chromosomes(23+X).</li></li></ul><li>What is Non-disjunction?<br />Non-disjunction may be defined as a failure of the two chromosomes of a particular homologous pair to separate at the time of meiosis.<br /><ul><li>Non-disjunction is the cause of Trisomy.</li></ul>Non-disjunction arises from a failure of homologous chromosomes to separate in Meiosis-I,or the failure of sister chromatids to separate during Meiosis-II or mitosis.<br />