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Updated: May 18 2021

Chromosomal Diseases

Images
https://upload.medbullets.com/topic/102035/images/william_syndrome.jpg
https://upload.medbullets.com/topic/102035/images/down_syndrome.jpg
  • 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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