Polysomy
Polysomy is an aneuploid condition with extra chromosome copies.
Polysomy is a form of aneuploidy in which an organism possesses at least one extra chromosome beyond the usual diploid complement, resulting in three or more copies of a particular chromosome. It is most often caused by nondisjunction during meiosis, though translocation mutations can also be responsible. Polysomy is notable for its association with various diseases, including Down syndrome in humans, where trisomy of chromosome 21 occurs.
In mammals
Polysomy is observed in several canine cancers, including leukemia, hemangiopericytomas, and thyroid tumors. Abnormalities of chromosome 13 appear in canine osteoid chondrosarcoma and lymphosarcoma; dogs with lymphosarcoma and trisomy 13 tend to have longer first remission and survival durations and respond well to chemotherapy. Polysomy of chromosome 13, often resulting from centric fusions, is significant in prostate cancer development, and because canine chromosome 13 resembles human chromosome 8q, research may inform human prostate cancer treatment. Chromosomes 1, 2, 4, 5, and 25 are also frequently involved in canine tumors, and chromosome 1 may harbor a gene that promotes tumor development and karyotypic changes such as centric fusions. Aneuploidy from nondisjunction is common in tumor cells. Sex chromosome polysomies are rare; 49,XXXXY occurs in 1 per 85,000 newborn males, and other X polysomies are even rarer. Polysomy Y affects 1 in 975 males and can cause psychiatric, social, and somatic abnormalities. Polysomy X may lead to mental and developmental retardation and physical malformation. Klinefelter syndrome (47,XXY) is a human X polysomy. X chromosome polysomies can be inherited from either parent, and sex chromosome polysomies arise from successive nondisjunctions in meiosis I and II. Tetrasomy and hexasomy 8 are rare compared to trisomy 8, the most common karyotypic finding in acute myeloid leukemia and myelodysplastic syndromes. Polysomy 8 syndrome is associated with a high incidence of secondary diseases and a six-month survival rate.
In insects
In a population of male grasshoppers (Chorthippus binotatus) from the Sierra Nevada in Spain, polysomic mosaics possess an extra E group chromosome in their testicles, but this abnormality is not passed to offspring. Male grasshoppers (Atractomorpha similis) from Australia carry between one and ten extra copies of chromosome A9, with one extra copy being most common; most polysomic males produce normal sperm, though polysomy can be transmitted through both sexes via nondisjunction. Heterochromic polysomy occurs in mole crickets with 23 chromosomes and may contribute to evolution within Gryllotalpa gryllotalpa, along with environmental and mating factors. In Drosophila, metafemales with three X chromosomes rarely survive, possibly because the extra X chromosome decreases gene expression.
In fungi
Polysomy hasn't been studied in many fungi, possibly because their chromosome counts are low, as pulsed field gel electrophoresis shows. In Saccharomyces cerevisiae Flor strains, polysomy of chromosome 13 occurs. This chromosome holds the ADH2 and ADH3 loci, which code for alcohol dehydrogenase isozymes key to wine aging through ethanol oxidation. Disrupting the yeast RNA1 gene with LEU2 sequences encourages this polysomy.
Diagnostic tools
Fluorescence in situ hybridization (FISH) is a cytogenetic technique useful for diagnosing polysomy, including common autosomal trisomies (13, 18, 21) and sex chromosome polysomies. Testing for chromosomal aneuploidy with FISH can increase cytology sensitivity and improve cancer diagnosis accuracy; the Cervical Cancer TERC FISH test detects amplification of the human telomerase RNA component gene and/or polysomy of chromosome 3. Spectral karyotyping (SKY) assigns a color to each chromosome and is typically performed after conventional cytogenetics detects an abnormality, with FISH confirming the chromosome identity. Giemsa banding (G-banded karyotyping) allows detection of polysomies by counting stained chromosomes, and several cells must be analyzed to detect mosaicism. Chromosomal microarray analysis, including SNP arrays and comparative genomic hybridization (CGH), can identify submicroscopic abnormalities; CGH has been used to detect polysomy 17 in breast cancer and, when combined with ultrasound findings, may aid clinical diagnosis.
More in Chromosomal Abnormalities
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced