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Diseases Resulting from Autosomal Chromosome Abnormalities
  •  Down syndrome
    • most common chromosomal disorder
    • most common cause of congenital mental retardation
    • causes
      • trisomy 21 
        • nondisjunction (most common cause)
          • occurs during anaphase of meiosis I
        • Robertsonian translocation 
        • mosaicism (least common cause)
    • presentation  
      • appearance
        • short stature
        • hypotonia
        • unique facial structure
          • epicanthic folds, macroglossia, flat profile, depressed nasal bridge
      • simian crease in palm
    • ↑ risk for
      • congenital heart disease
        • combined ASD and VSD
      • AML (< 3 y/o)
      • ALL (> 3 y/o) 
      • Alzheimer's disease
        • by 5th decade
        • due to amyloid precursor protein (APP) gene on 21
      • Hirschsprung's disease, duodenal atresia, congenital heart anamolies
        • atrioventricular canal is most common
        • endocardial cushion defects also very common
    • screening 
      • + quad screen  
        • ↓ α-fetoprotein
        • ↓ estriol
        • ↑ inhibin A
        • ↑ β-hCG
        • remember: high (hCG, inhibin); deficit (estriol, fetoprotein)
      • + ultrasound shows
        • high amount of fluid behind the neck
          • ↑ nuchal translucency
      • can confirm diagnosis with amniocentesis or chorionic villus sampling  
  • Edwards' syndrome 
    • most common trisomy resulting in live birth after Down syndrome
    • cause
      • trisomy 18  
        • nondisjunction
    • presentation
      • mental retardation
      • unique appearance
        • rocker-bottom feet
        • micrognathia
          • small jaw
        • low-set ears
        • clenched hands with overlapping fingers
        • prominent occiput
      • congenital heart disease
        • VSD
    • death < 1 y/o
  • Patau's syndrome
    • cause
      • trisomy 13
        • nondisjunction
    • presentation
      • mental retardation
      • unique appearance
        • microphthalmia
        • microcephaly
        • cleft lip/palate
        • holoprosencephaly
        • polydactyly
      • VSD
      • cystic kidneys
    • death < 1 y/o
  • Cri-du-chat syndrome
    • cause
      • microdeletion of short arm of chromosome 5 
    • presentation
      • high-pitched crying/mewing
        • origin of name: French for cry-of-the-cat
      • microcephaly
      • moderate to severe mental retardation
      • epicanthal folds
      • VSD
  • Williams syndrome
    • cause
      • microdeletion of long arm of chromosome 7
        • region lost includes elastin gene
    • presentation
      • distinctive "elfin" facies
      • mental retardation
      • hypercalcemia
        • ↑ sensitivity to Vitamin D
      • unique behaviors
        • well-developed verbal skills
        • extreme friendliness with strangers
        • musical talent
      • supravalvular aortic stenosis
  • 22q11 microdeletions 
    • cause
      • microdeletion at chromosome 22q11
        • abnormal embryological development of 3rd and 4th pharyngeal pouch
    • variable pressenation
      • CATCH-22 disease
      • cleft palate
      • abnormal facies
      • T-cell deficiency
        • due to thymic aplasia
      • cardiac abnormalities
      • hypocalcemia
        • due to parathyroid aplasia
        • results in tetany
    • specific presentation of 22q11 microdeletions
      • DiGeorge syndrome 
        • defects in
          • thymus
          • parathyroid
          • heart
      • velocardiofacial syndrome
        • defects in
          • palate
          • face
          • heart
        • no abnormalities thymus, parathyroid
 

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