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Human Genetic Disorder - Abnormalies of Autosomes

   Abnormalies of Autosomes 
Edward’s syndrome
  • 18- Trisomy
  • It was described by Edward in 1960
  • Syndrome is due to an extra chromosome number 18
  • Total number of chromosomes is 47.
  • It occurs more often in females than males
  • Frequency: 1 per 8000 live births
  • Symptoms: Small jaws, deformed ears, small mouth, nose and fingers, small sternum and pelvis.
Patau’s Syndrome
  • 13-Trisomy or D-Trisomy
  • The common anomalies of D-trisomy include hare-lip, cleft-palate, sloping forehead with relatively small head and brain and defective eye development.
Down Syndrome
  • First autosomal aneuploidy, described by John Longdon Down (1866) under the name of mongoloid idiocy or mongolism.
  • 21-Trisomy
  • 47 chromosomes instead of 46 with three copies of chromosome 21 instead of of usual two.
  • Karyotype: XXY (reason: Non-disjunction of chromosome of pair during meiosis)
  • The frequency of non-disjunction of chromosome pair 21 increases with mother age.
  • The frequency of abnormality is 1in 600 live births.
  • Clinical symptoms : Male with slowly degenerating testes, enlarged breasts.
Cri du syndrome (Cat cry syndrome)
  • The affected newborn cries like mewing of a cat, hence it is named a Cri du chat (cat cry)
  • Is due to a deletion in the short arm of the chromosome number 5
  • Symptoms: Person has a small head widely spaced eyes, moon like face , cry like kitten, and congenital heart disease.
21-monosomy
  • Caused by the complete loss of one chromosome of the 21st chromosome pair.
  • 45 chromosomes only
  • Symptoms: Nose is prominent and distance between the eyes is less than normal, ears are large and muscles are contracted.
Myelogenous leukemia
  • Caused by the deletion of some portion of long arm of chromosome 22 and its addition to chromosome 9 (Reciprocal translocation)



Philadelphia chromosome

  • It brings about change in the conformation of C-Abl protein and activates a latent oncogenic potential causing production of excess of granular leuckocytes and hence called chronic granulytic leukemia . This 22 nd chromosome whose a little segment from long arm is deleted , is called Philadelphia chromosome, as it was first reported in the city of Philadelphia in 1959.
Alzheimer's disease
  • Neuro-degenerative disease of brain is caused by the accumulation of Amyloid protein plaques in the brain resulting in the degeneration of neurons.
  • The protein involved, Amyloid β peptide is produced and processed in a number of ways in the brain.
  • This disease is due to ageing and involvement of two defective alleles, one on the chromosome -21 and other on chromosome 19.

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