Dr athal pediatric chromosomal Abnormalities

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Chromosomal Abnormalities

  • Chromosomal abnormalities are either numerical or structural.

  • Chromosomal abnormalities occur in approximately 8% of fertilized ova but only in 0.6% of liveborn infants.

  • 50% of spontaneous abortuses have chromosomal abnormalities.

  • In newborns and older children, many features suggest the presence of a chromosome anomaly, including LBW (SGA), FTT, developmental delay, and the presence of three or more congenital malformations.

  • Acquired chromosomal changes play a significant role in carcinogenesis and tumour progression.

  • The diagnosis is confirmed by chromosome analysis

Down Syndrome (trisomy 21)

  • DS is the most common abnormality of chromosomal number. It occurs in 1 of every 1000 births.

  • DS considered most common genetic cause of moderate intellectual disability and characteristic dysmorphic features.

  • Cytogenetics: the extra chromosome 21 may result from:

    • Nondisjunction.

    • Translocation.

    • Mosaicism.

Non-disjunction (94%):

  • Most cases result from an error at meiosis, the pair of chromosome 21s fails to separate, so that one gamete has two chromosome 21s and one has none.

  • Fertilisation of the gamete with two chromosome 21s gives rise to a zygote with trisomy 21.

  • Parental chromosomes do not need to be examined.

Clinical Features:

Down's syndrome is usually suspected at birth because of the baby's facial appearance.

Typical craniofacial appearance

  • Brachycephaly with flat occiput and third fontanelle

  • Round face and flat nasal bridge.

  • Upslanted palpebral fissures.

  • Epicanthic folds (a fold of skin running across the inner edge of the palpebral fissure).

  • Brushfield spots in iris (pigmented spots).

  • Small mouth and protruding tongue.

  • Small ears.

Other Anomalies

  • Normal BW & length, but hypotonic.

  • Short neck

  • Short broad hand with single palmar creases, incurved fifth finger.

  • Wide 'sandal' gap between 1st & 2nd toes.

  • Congenital heart defects (40%)

  • Duodenal atresia

  • Annular pancreas

  • Imperforated anus.

  • Hirschsprung's disease

Later Medical Problems:

  • Delayed motor milestones.

  • Moderate to severe learning difficulties.

  • Increased susceptibility to infections.

  • Hearing impairment from secretory otitis media.

  • Visual impairment from cataracts, squints, myopia.

  • Increased risk of leukaemia and solid tumours.

  • Risk of atlantoaxial instability.

  • Hypothyroidism and DM.

  • coeliac disease

  • Epilepsy

  • Alzheimer's disease

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