Autosomal Trisomy - definiton

Autosomal Trisomy - definiton

Autosomal Trisomy is a chromosomal disorder in which there are three instead of the normal two copies of an AUTOSOME (nonsex chromosome). An autosomal trisomy may be complete (affect all cells) or mosaic (affect only some cells). The most commonly occurring complete autosomal trisomies that are survivable are those involving chromosomes 21, 18, and 13, which result in the chromosomal disorders DOWN SYNDROME (trisomy 21), EDWARDS SYNDROME (trisomy 18), and PATAU’S SYNDROME (trisomy 13). These trisomy disorders may also occur as a mosaic. Mosaic autosomal trisomies typically produce less severe, though still significant, physical and mental impairments. Complete autosomal trisomies affecting other chromosomes are often lethal, nearly always causing death early in development and well before birth.

Though the risk for autosomal trisomy disorders increases with a woman’s age at the time she becomes pregnant, most autosomal trisomy disorders occur in pregnancies in younger women because the rate of CONCEPTION is significantly higher among younger women. The risk is highest for women who have previously given birth to a child with a trisomy disorder. Obstetricians can detect fetal trisomy disorders generally within the first and early part of the second trimesters of PREGNANCY with prenatal tests. The diagnostic path usually incorporates a combination procedures including

  • BLOOD tests that look at the levels of proteins the FETUS and placenta are making
  • ULTRASOUND, which shows physical anomalies that suggest a chromosomal disorder
  • CHORIONIC VILLI SAMPLING (CVS) and AMNIOCENTESIS, which permit examination of fetal cells

See also BIRTH DEFECTS; CHROMOSOMAL DISORDERS; CONGENITAL ANOMALY; GENETIC COUNSELING; GENETIC TESTING; MOSAICISM; PREGNANCY.

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Genetics and Molecular Medicine

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