Polysomy is when a person has an extra chromosome, which can occur during cell division or genetic material exchange. Down syndrome and Kleinfelter syndrome are examples. Polysomy can cause physical and developmental issues, and increase the risk of certain cancers.
People with polysomy have an extra copy of a chromosome. The problem can arise during meiosis, the cell division that produces sperm and egg cells, when a pair of chromosomes fails to separate completely, resulting in cells with more or fewer chromosomes than normal. Translocation, or the exchange of genetic material, between chromosomes can also be a cause. Down syndrome is a widely known disease, which occurs due to an extra chromosome. Kleinfelter syndrome is another form of polysomy, in which males have an extra X sex chromosome in addition to X and Y.
Children with Down syndrome have a third chromosome linked to the 21st pair, making the total chromosome number 47 rather than the normal 46. Healthcare professionals also refer to the syndrome as trisomy 21. Children born with this type of polysomy tend to to have a flat nose, small ears and mouths, and almond-shaped eyes. They are often slow learners and suffer from various medical conditions. Studies suggest that as many as half of babies born with trisomy 21 have heart conditions that include defects in the wall, or septum, that divides the heart.
Male babies born with Kleinfelter syndrome have three sex chromosomes, XXY, instead of the normal pair of sex chromosomes, XY. Babies may or may not develop symptoms from this abnormality, but they tend to have weaker muscles, which prevents them from sitting up, crawling or walking as quickly as other children of a similar age. During puberty, these males grow taller, but with leaner and less defined muscles than other males. Adolescents with Kleinfelter may have less body and facial hair, develop wider hips, and be deficient in testosterone production. Testosterone replacement can ease difficulties during adulthood which include diabetes and osteoporosis.
Females may have a congenital abnormality known as triple X syndrome, in which three or more X sex chromosomes are present. The physical characteristics of the condition include long legs and torsos resulting in increased height. Girls with this form of polysomy often have learning disabilities and act in ways that are emotionally inappropriate for their age. Many XXX females, however, mature to adulthood without social difficulties. The more X chromosomes a child has, the more likely they are to experience symptoms.
Researchers have found that individuals who show polysomy on chromosomes 3, 17 and 31 may have an increased risk of developing certain types of bladder, breast, lung and skin cancers. Women with polysomy 17, in particular, may have an increased number of human epidermal growth factor receptor 2 (HER-2) sites, which may increase the incidence of breast cancer. Tumors resulting from this congenital disorder respond well to anthracyclines as part of the chemotherapy regimen.
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