One specific type of aneuploidy is polyploidy.
Diagnosing chromosomal abnormalities
Karyotyping is used to diagnose chromosomal abnormalities. A karyotype is a lab test used to visualize chromosomes, and provides information on the size, shape, number, and structure of chromosomes. Chromosomes are stained and arranged in pairs by length, to allow for better visualization and analysis. Karyotyping can be used to identify aneuploidy as well as structural changes in chromosomes (Figure 2).
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Effects of chromosomal mutations and examples
Chromosomal mutations can be serious. The potential consequences of these mutations range from none or minimal to severe. Chromosomal mutations often have severe consequences, including death of the affected organism. Aneuploidy of autosomal chromosomes is usually lethal.4 Fetal chromosomal abnormalities, especially aneuploidy, are responsible for half of miscarriages.5 Monosomy and trisomy of larger chromosomes are lethal but trisomy of smaller chromosomes (e.g., 13, 15, 18, 21, or 22) results in offspring that can survive from weeks to years4, although offspring will have abnormalities.
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The effects of structural changes to chromosomes, and their severity, depends on the type of change, the impacted genes, and the number of genes or amount of genetic material affected.
Down syndrome
Down syndrome, or trisomy 21, occurs when an individual has an extra copy of chromosome 21. The additional genetic material disrupts normal development, resulting in the physical problems and intellectual disabilities associated with Down syndrome7. Features of Down syndrome include intellectual disability, facial features such as slanting eyes, increased risk of dementia, and lower life expectancy7. More rarely, Down syndrome can also occur when a section of chromosome 21 is translocated to another chromosome. The patient then has two copies of the full 21 chromosome, but also an extra section of that chromosome present on a different chromosome. I.e. there is a triple copy of a particular section of chromsome 21.
Cri-du-chat syndrome
Cri-du-chat, French for “cry of the cat,” is the result of the deletion of the end of the short arm of chromosome 5.8 The syndrome’s name is due to the cry that infants often have, a high-pitched cry that sounds like the cry of a cat.8 The syndrome is characterized by intellectual disability, developmental delays, and distinctive facial features, with larger deletions associated with more severe disability and delays.8
Klinfelter syndrome
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