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Chromosome Aneuploidies

Chromosome aneuploidy is the presence of an abnormal number of chromosomes in a cell. For instance, a normal human cell has 23 pairs chromosomes, or a total of 46 chromosomes. The body cells of a patient with chromosome aneuploidy, however, may have 45 or 47 chromosomes. An extra or missing chromosome is usually associated with some genetic disorders. Most embryos cannot survive with a missing or extra chromosome and are spontaneously aborted. About 60% of the miscarriages are due to chromosomal abnormalities.




Example of chromosome aneuploidy – The karyotype of a person with Down syndrome (Trisomy 21), showing the characteristic three copies of chromosome 21

The most common aneuploidy that embryo can survive to birth is trisomy 21, which is found in Down Syndrome patient and about 1 in every 800 newborns is affected by this genetic condition. Trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome) are also common genetic disorders that affect 1 in 5,000 and 1 in 16,000 newborns respectively. The likelihood that a pregnancy will result in an embryo with chromosomal aneuploidy increases with a woman’s age, particularly above 40 years old.



Reference

  • U.S. Department of Energy Human Genome Program 2006
  • Griffiths AJ et al. 2000, ‘An Introduction to Genetic Analysis’ (7 ed.). pp. Chapter 18
  • JK, Morris et al. 2002, "Revised estimates of the maternal age specific live birth prevalence of Down's syndrome", Journal of Medical Screening. 9 (1): 2–6.
  • Ontaio Health Technology Assessment series 2019, ‘Noninvasive Prenatal Testing for Trisomies 21, 18, and 13, Sex Chromosome Aneuploidies, and Microdeletions: A Health Technology Assessment’, Health Quality Ontario, 9(4);1-166