Aneuploidy is a change in the number of chromosomes that can lead to a chromosomal disorder. The most recognized forms of aneuploidy are the trisomy diseases of Down syndrome and Edwards syndrome. Trisomy may not necessarily be present in all cells in an individual. It may be detected in just a specific tissue or within different cells in a tissue. When the presence of chromosomal abnormalities occurs differentially within an individual, it is called chromosomal mosaicism. In general, as we would expect, individuals who are mosaic for a chromosome change tend to have a less severe form of the syndrome present than full trisomy individuals. Critical examples of mosaicism are found in leukemia cases, specifically; chronic lymphocytic leukemia (CLL) which is a trisomy of chromosome 12 and acute myeloid leukemia (AML) prognosis which is a trisomy of chromosome 8. Aneuploidy is common in cancerous cells. The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or disease. ... The International Statistical Classification of Diseases and Related Health Problems 10th Revision (ICD-10) is a coding of diseases and signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or diseases, as classified by the World Health Organization (WHO). ... // Q00-Q99 - Congenital malformations, deformations and chromosomal abnormalities (Q00-Q07) Congenital malformations of the nervous system (Q00) Anencephaly and similar malformations (Q01) Encephalocele (Q02) Microcephaly (Q03) Congenital hydrocephalus (Q04) Other congenital malformations of brain (Q05) Spina bifida (Q06) Other congenital malformations of spinal cord (Q07) Other congenital malformations of nervous... // Q00-Q99 - Congenital malformations, deformations and chromosomal abnormalities (Q00-Q07) Congenital malformations of the nervous system (Q00) Anencephaly and similar malformations (Q01) Encephalocele (Q02) Microcephaly (Q03) Congenital hydrocephalus (Q04) Other congenital malformations of brain (Q05) Spina bifida (Q06) Other congenital malformations of spinal cord (Q07) Other congenital malformations of nervous... The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or disease. ... The following is a list of codes for International Statistical Classification of Diseases and Related Health Problems. ... A genetic disorder is a condition caused by abnormalities in genes or chromosomes. ... Trisomy 18 or Edwards Syndrome (named after John H. Edwards, who first described the syndrome in 1960) is a genetic disorder. ... Mosaicism In medicine (genetics), a mosaic or mosaicism denotes the presence of two populations of cells with different genotypes in one patient, where usually one of the two is affected by a genetic disorder. ... Chronic lymphocytic leukemia (also known as chronic lymphoid leukemia or CLL), is a type of leukemia, or cancer of the white blood cells (lymphocytes). ... Acute myeloid leukemia (AML), also known as acute myelogenous leukemia, is a cancer of the myeloid line of white blood cells, characterized by the rapid proliferation of abnormal cells which accumulate in the bone marrow and interfere with the production of normal blood cells. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ...

Commonly observed forms

Monosomy

Monosomy is the presence of only one chromosome from a pair in a cell's nucleus. Partial ====Human monosomy==== Human genetic disorders arising from monosomy arefemale, also known as Turner syndrome A scheme of a condensed (metaphase) chromosome. ... In cell biology, the nucleus is an organelle, found in most eukaryotic cells, which contains most of the cells genetic material. ...

• Cri du chat syndrome -- (French for "cry of the cat" after the distinctive noise by affected persons' malformed [[
• 1p36 Deletion Syndrome -- a partial monosomy caused by a deletion at the end of the short p arm of chromosome 1

Cri du chat syndrome (French for Cry or call of the cat), also called deletion 5p syndrome,5p minus or Le Jeune’s syndrome, is a rare genetic disorder due to a missing portion of chromosome 5. ... 1p36 deletion syndrome is a congenital genetic disorder characterized by moderate to severe intellectual disability, delayed growth, hypotonia, seizures, limited speech ability, malformations,caesiatomi, hearing and vision impairment, and distinct facial features. ... Chromosome 1 is, by convention, the designation for the largest human chromosome. ...

Disomy

A disomy is the presence of a pair of chromosomes. For diploid organisms, such as humans, it is the normal condition. For organisms that are normally triploid or above, disomy is an aneuploidy. It can also refer to cells that are normally haploid, such as gametes.

Uniparental disomy, the disomy refers to two copies of the chromosome from one of the parents (with no contribution from the other parent). Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or part of a chromosome, from one parent and no copies from the other parent. ...

Trisomy

A trisomy is the presence of three, instead of the normal two, chromosomes of a particular numbered type in an organism. Thus the presence of an extra chromosome 21 is called trisomy 21. A scheme of a condensed (metaphase) chromosome. ... Chromosome 21 is one of the 23 pairs of chromosomes in humans. ...

Full trisomy of an individual occurs due to non-disjunction during meiosis I or meiosis II of gametogenesis resulting in 24 vice 23 chromosomes in a reproductive cell (sperm or egg). Thus, after fertilization, the resulting fetus has 47 chromosomes vice the typical 46. The most common forms of autosomal trisomy are trisomy of chromosome 21 which results in Down syndrome and trisomy of chromosome 18 which results in Edwards syndrome. In rare cases, a fetus with trisomy of chromosome 13 can survive. Trisomy 13 is called Patau syndrome. Autosomal trisomy is frequently associated with severe congenital abnormalities, mental retardation and shortened life expectancy. Nondisjunction is the homologous chromosomes to properly segregate during meiotic or mitotic anaphase, resulting in daughter cells with abnormal numbers of chromosomes. ... For the figure of speech, see meiosis (figure of speech). ... Gametogenesis is the creation of gametes by meiotic division of gametocytes into various gametes. ... Trisomy 18 or Edwards Syndrome (named after John H. Edwards, who first described the syndrome in 1960) is a genetic disorder. ... Patau syndrome, also known as trisomy 13, is a chromosomal abnormality, a syndrome in which a patient has an additional chromosome 13 due to a non-disjunction of chromosomes during meiosis. ...

A partial trisomy occurs when part of an extra chromosome is attached to one of the other chromosomes, or if one of the chromosomes has two copies of part of its chromosome. A mosaic trisomy is a condition where extra chromosomal material exists in only some of the organism's cells.

Human trisomy

A trisomy can occur with any chromosome. Most trisomies, like most other abnormalities in chromosome number, result in distinctive and serious birth defects. Mostly, the causes are autosomal and sex chromosomal nondisjunction. Most trisomies result in spontaneous abortion; the most common types that survive to birth in humans are: Nondisjunction is the failure of the chromosomes to properly segregate during meiotic or mitotic anaphase, resulting in daughter cells with abnormal numbers of chromosomes. ...

Autosomal nondisjunction

• Trisomy 21 (Down syndrome)
• Trisomy 18 (Edwards syndrome)
• Trisomy 13 (Patau syndrome)
• Trisomy 12 (A prognostic indicator of Chronic Lymphocytic Leukemia)
• Trisomy 9
• Trisomy 8 (Warkany syndrome 2)

Trisomy 16 is the most common trisomy in humans, occurring in more than 1% of pregnancies. This condition, however, usually results in spontaneous miscarriage in the first trimester. The most common trisomy in viable births is Trisomy 21. Trisomy 18 or Edwards Syndrome (named after John H. Edwards, who first described the syndrome in 1960) is a genetic disorder. ... Patau syndrome, also known as trisomy 13, is a chromosomal abnormality, a syndrome in which a patient has an additional chromosome 13 due to a non-disjunction of chromosomes during meiosis. ... Chronic lymphocytic leukemia (also known as chronic lymphoid leukemia or CLL), is a type of leukemia, or cancer of the white blood cells (lymphocytes). ... Trisomy 9 is a chromosomal disorder caused by having three copies (trisomy) of chromosome number 9. ... Warkany syndrome 2, also known as trisomy 8, is a chromosomal disease that has severe effects on the unborne child, as complete trisomy 8 is a frequent cause of early abortion. ... Miscarriage or spontaneous abortion is the natural or spontaneous end of a pregnancy at a stage where the embryo or the fetus is incapable of surviving, generally defined in humans at a gestation of prior to 20 weeks. ...

Sex-chromosomal nondisjunction

Aneuploidy of sex chromosomes can also occur. The presence of extra X chromosome(s) causes Klinefelter syndrome in men and Triple X syndrome in women, while monosomy X (45, X) gives rise to women with Turner syndrome.

• XXX (Triple X syndrome)
• XXY (Klinefelter's syndrome)
• XYY (XYY syndrome)

Triple X syndrome is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female. ... Not to be confused with XXX syndrome. ... Not to be confused with XXY syndrome. ...

Tetrasomy and pentasomy

A tetrasomy and a pentasomy are the presence of a respectively four or five copies of a chromosome. Although very rare, reported examples of tetrasomy and pentasomy in humans include the karyotypes XXXX (XXXX syndrome), XXXY, XXYY, XYYY, XXXXX (XXXXX_syndrome), XXXXY, XXXYY, XXYYY and XYYYY.^{[citation needed]} XXXX syndrome (also called tetrasomy X, quadruple X, or 48, XXXX) is a rare chromosomal disorder caused by the presence of four X chromosomes instead of two X chromosomes, which are normally found in females. ... XXXXX syndrome (also called pentasomy X) is the presence of three additional X chromosomes. ...

Detection

Example of Trisomy 21 Detected via qPCR Short Tandem Repeat assay

Several prenatal tests can be performed on an expectant mother to detect aneuploidy in the fetus. Fetal cells from the amniotic fluid or chorionic villus are collected and analyzed by one of several techniques which include Fluorescence In Situ Hybridization (FISH) karyotyping, Quantitative Polymerase Chain Reaction (PCR) of Short Tandem Repeats, Quantitative Fluorescence PCR (QF-PCR), Quantitative Real-time PCR (RT-PCR) dosage analysis, Quantitative Mass Spectrometry of Single Nucleotide Polymorphisms, and Comparative Genomic Hybridization (CGH). A program for detecting aneuploidy by short tandem repeat fragments is SoftGenetics GeneMarker® software. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The amniotic sac is a tough but thin transparent pair of membranes which holds a developing embryo (and later fetus) until shortly before birth. ... The chorion undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo. ... A metaphase cell positive for the bcr/abl rearrangement using FISH. The chromosomes can be seen in blue. ... Quantitative polymerase chain reaction (qPCR) is a modification of the polymerase chain reaction used to rapidly measure the quantity of DNA, complementary DNA or ribonucleic acid present in a sample. ... A short tandem repeat (STR) in DNA is a class of polymorphisms that occurs when a pattern of two or more nucleotides are repeated and the repeated sequences are directly adjacent to each other. ... Real-Time PCR, also called quantitative (real-time) PCR, is a method of simultaneous DNA quantification and amplification. ... Comparative genomic hybridization (CGH) is a molecular-cytogenetic method for the analysis of regional changes in the DNA content of tumor cells. ...

Pregnant women over the age of 35 are screened for trisomy caused syndromes in the fetus because the risk of these syndromes increases as the mother ages. During the procedure whereby cells are collected for analysis, maternal cells can be mixed in with fetal cells. This phenomenon is called Maternal Cell Contamination (MCC).

Sources

• This article incorporates public domain text from The U.S. National Library of Medicine.
• Sex chromosome tetrasomy and pentasomy. PMID 7567329

See also

• Ploidy
• Polyploidy
• Chromosome abnormalities

Ploidy is the number of homologous sets of chromosomes in a biological cell. ... Polyploidy refers to cells or organisms that contain more than two copies of each of their chromosomes. ... A chromosome abnormality reflects an abnormality of chromosome number or structure. ...

External links

• SoftGenetics GeneMarker® fragment analysis software
• Aneuploidy Testing
• Aneuploidy FAQ
• Genetics of Aneuploids
• Aneuploidy: Trisomy and Monosomy
• Chromosomal Chaos and Cancer - Peter Duesberg, Scientific Amercan, May 2007