Aneuploidy

Aneuploidy is a genetic condition in which a cell or organism has an incorrect number of chromosomes other than the typical or diploid (2n) set of chromosomes for the species. Normally, human cells contain 46 chromosomes (23 pairs), but in aneuploidy, this number can be altered, which can lead to a variety of genetic disorders and medical conditions.

Examples of aneuploidy include:

1. Down syndrome (trisomy 21): In this case, a person has an extra copy of the 21st chromosome, resulting in various physical and mental disabilities.
2. Edwards syndrome (trisomy 18): This condition is associated with an extra copy of the 18th chromosome and often leads to serious medical problems.
3. Pato syndrome (trisomy X): Women with this syndrome have an extra copy of the X chromosome, which can cause physical and mental disabilities.
4. Klinefelter syndrome (XXY): Men with this syndrome have an extra copy of the X chromosome, which can cause a variety of physical and psychological changes.
5. X monosomy (Turner syndrome): Girls with this syndrome are missing one of the two X chromosomes, which can lead to physical and psychological disorders.

Aneuploidy can result from errors in the processes of meiosis (sexual cell division) or mitosis (atypical cell division). It can lead to serious medical consequences and often requires medical monitoring and intervention.

Aneuploidy and mutation are two different genetic phenomena, although they can be related in some cases. Here are their main differences:

1. Aneuploidy:

   • Definition: Aneuploidy is a genetic alteration involving a change in the number of chromosomes in a cell or organism, that is, the presence of extra or missing chromosomes.
   • Cause: Aneuploidy is not usually the result of point mutations (substitutions, insertions, or deletions in nucleotides), but rather is due to errors in meiosis or mitosis during cell division.

2. Mutation:

   • Definition: A mutation is a change in the nucleotide sequence of DNA that can include substitutions, insertions, deletions, and other changes in genetic information.
   • Cause: Mutations can occur due to a variety of factors, including random errors during DNA copying, chemical or physical mutagens, exposure to radiation, and other factors.

Distinctions:

• Aneuploidy involves a change in the number of chromosomes, while mutation involves a change in a specific sequence of nucleotides in the genome.
• Aneuploidy usually involves changes involving a large number of genes, as it affects an entire chromosome or even multiple chromosomes. The mutation may affect one or more genes.
• Aneuploidy can cause several medical problems at once because it changes the way many genes work. Mutations can be either neutral or harmful, depending on their location and the consequences for gene function.

Although different, some types of aneuploidy can be caused by mutations in genes responsible for processes related to cell division or chromosomes, which can exacerbate the medical consequences of aneuploidy.

Genomic aneuploidy

It is a type of aneuploidy in which abnormalities in chromosome number involve the entire genome, that is, all the chromosomes of an organism, as opposed to random changes in one or a few chromosomes.

Examples of genomic aneuploidies include:

1. Polyploidy: This is a condition in which cells or organisms have additional sets of chromosomes. For example, triploidy (3n) means having three sets of chromosomes instead of two, and tetraploidy (4n) means having four sets.
2. Autoploidy: In this case, all chromosomes of complementary sets of the same species (e.g., two sets of chromosomes of the same species).
3. Alloploidy: In this case, the extra sets of chromosomes belong to different species or subspecies.

Genomic aneuploidies can result from errors in meiosis (sexual cell division) or from abnormalities in cell deletion. They can have serious consequences for the development and life of the organism, and are often associated with various medical conditions and syndromes.

One of the best known examples of genomic aneuploidy is Down syndrome (trisomy 21), in which a person has an extra copy of the 21st chromosome and a total of 47 chromosomes instead of the standard 46. This syndrome results in characteristic physical and mental features.

Aneuploidy syndrome

It is a group of genetic syndromes associated with a change in the number of chromosomes in cells or organisms. Aneuploidy can result in the presence of extra chromosomes (trisomy) or missing chromosomes (monosomy) in cells. Some of the best known aneuploidy syndromes include:

1. Down syndrome (trisomy 21): This syndrome is caused by having an extra copy of the 21st chromosome. Symptoms include mental retardation, physical features (such as a creased face), increased risk of heart disease, and other medical problems.
2. Edwards syndrome (trisomy 18): This syndrome is caused by the presence of an extra copy of the 18th chromosome. It is accompanied by severe physical and mental impairment and medical problems that can severely limit life expectancy.
3. Patau syndrome (trisomy 13): This syndrome is caused by the presence of an extra copy of the 13th chromosome. It is also characterized by severe physical and mental disabilities and a shortened life span.
4. Klinefelter syndrome (XXY): This syndrome is associated with the presence of an extra X chromosome in males (usually XXY). Symptoms may include delayed sexual development and other physical and mental features.
5. Turner syndrome (X0): This syndrome is associated with the absence of one of the X chromosomes in females (X0). Symptoms may include short stature, abnormal genital development, and other medical problems.

These aneuploidy syndromes can cause a variety of medical and mental disorders and are usually associated with changes in chromosome number that result from errors in the cell division process during embryonic development.

Causes of the aneuploidies

Aneuploidy, a change in the number of chromosomes, can occur due to various genetic and environmental factors. Here are some of the main causes of aneuploidy:

1. Errors in meiosis: Meiosis is a sexual cell division that produces gametes (eggs and sperm). Errors in the processes of meiosis can lead to improper separation of chromosomes, which can cause aneuploidy in gametes.
2. Errors in mitosis: Mitosis is a type of cell division that produces somatic cells (not sex cells). Errors in mitosis can cause a change in the number of chromosomes in an organism's cells.
3. EnvironmentalExposure: Some chemicals, radiation, and other environmental factors may increase the risk of aneuploidy.
4. Genetic Mutations: The presence of genetic mutations or inherited factors can contribute to aneuploidy.
5. Syndromes and inherited diseases: Some genetic syndromes such as Down syndrome, Edwards syndrome, and others are associated with specific types of aneuploidy.
6. Maternal age: Women after age 35 have an increased risk of aneuploidy in their newborns, especially for Down syndrome.
7. Infections and diseases: Some infections and diseases, such as viral hepatitis, can increase the risk of aneuploidy.
8. Medications: Some medical drugs, such as chemotherapy, can also increase the risk of aneuploidy.

Different types of aneuploidy can have different consequences and can cause different medical conditions. The risk of aneuploidy can be reduced through genetic counseling, regular medical tests, and a healthy lifestyle.

Pathogenesis

Here are some of the underlying mechanisms that can lead to aneuploidy:

1. Errors in meiosis: Meiosis is the process of sexual cell division that produces gametes (eggs and sperm). Errors in meiosis, such as improper separation of chromosomes during meiotic division I or II, can result in the formation of gametes with the wrong number of chromosomes.
2. Errors in mitosis: Mitosis is the process of cell division that produces somatic (non-sexual) cells. Errors in mitosis can result in a change in the number of chromosomes in the new cells. For example, an error in mitosis can cause a cell to gain an extra copy of a chromosome or lose one.
3. Nondisjunction: Nondisjunction is the incorrect separation of chromosomes during cell division. It can occur in either meiosis or mitosis. For example, if the chromosomes do not divide evenly between daughter cells, this can lead to aneuploidy.
4. Mechanical abnormalities: Mechanical abnormalities during cell division, such as chromosomal helicity abnormalities or structural abnormalities of chromosomes, can cause errors in chromosome separation and lead to aneuploidy.
5. EnvironmentalExposure: Some chemicals, radiation, and other environmental factors can increase the risk of aneuploidy by affecting cellular processes.
6. Mitotic abnormalities: Mitotic abnormalities may involve aberrations during somatic cell division, which can lead to changes in the number of chromosomes in body tissues.

The mechanisms of aneuploidy can be diverse, and their exact nature may depend on the specific circumstances and type of aneuploidy. These changes can occur either during fetal development or in the cells of the body at different periods of life.

Forms

There are several different types of aneuploidy depending on the number of chromosomes that may be extra or missing:

1. Trisomy: This is the presence of an extra copy of one chromosome. For example, trisomy 21 leads to Down syndrome, where a person has three copies of chromosome 21.
2. Monosomy: This is a condition in which one chromosome of a pair is missing. For example, monosomy X (Turner syndrome) occurs when a woman is missing one of the two X chromosomes.
3. Polyploidy: This is the presence of extra sets of chromosomes. For example, triploidy means having three sets of chromosomes instead of the standard two.
4. Diploidy with genetic changes: In some cases, there may be changes within the chromosomes or changes in the structure of the chromosomes, which is also considered aneuploidy.
5. Hypoploidy: This is the presence of fewer chromosomes than normal. Hypoploidy may involve less than two sets of chromosomes.
6. Isochromia: Itis a condition in which one of the chromosomesis divided into two equal parts with the same material composition.
7. Triploidy: It is the presence of an extra set of chromosomes, resulting in the presence of three copies of each chromosome in a cell.

Group D chromosome aneuploidy refers to the presence of an abnormal number of chromosomes in the cells of an organism, and this aneuploidy is associated with chromosomes belonging to group D (usually chromosomes 13, 14, 15, 21, and 22). For example, the presence of an extra copy of one of these chromosomes (triploidy) or the absence of one of them (monosomy) can be a form of aneuploidy.

Aneuploidies can lead to various genetic disorders and syndromes such as Down syndrome (trisomy 21, characterized by the presence of a third copy of chromosome 21) or Patau (trisomy 13) and others.

However, aneuploidy on the D chromosomes can have different consequences depending on the specific chromosomal disorder and the organs it affects. Consultation with a geneticist or genetic disorders specialist is necessary to make an accurate diagnosis and understand the possible consequences of aneuploidy, as well as to develop treatment and support strategies.

Group C chromosome aneuploidy means that a person or organism has an abnormal number of chromosomes belonging to group C chromosomes. Group C chromosomes usually means medium-sized chromosomes. The normal set of chromosomes for humans includes 46 chromosomes that are divided into 23 pairs. In aneuploidy, one of the chromosomes in this group may be either extra or missing, which can lead to various genetic and medical problems such as Down syndrome (trisomy 21) or other genetic abnormalities. Aneuploidies can occur due to errors in the process of cell division during mitosis (for somatic cells) or meiosis (for germ cells).

Group E chromosome aneuploidy refers to abnormalities in the number of chromosomes that belong to group E in the human karyotype. Group E includes chromosomes numbered 4 and 5. Such changes may include either extra copies of the E chromosomes (trisomy 4 or 5) or no copies (monosomy 4 or 5).

Examples of aneuploidy on group E chromosomes:

1. Trisomy 4: This is a condition in which a person has an extra copy of the 4th chromosome, that is, 47 chromosomes instead of the standard 46. This trisomy can have various medical consequences and can affect the development of the body.
2. Trisomy5: As with trisomy 4, trisomy 5 is associated with the presence of an extra copy of the 5th chromosome. This condition can cause medical problems and can have different manifestations.
3. Monosomy4: Monosomy 4 is a condition in which one of the 4th chromosomes is missing. It is a rare condition and can also have medical consequences.
4. Monosomy5: Monosomy 5 means that one of the 5th chromosome is missing. It is also a rare condition and can have a variety of medical consequences.

E chromosome aneuploidy, like other forms of aneuploidy, can cause a variety of medical conditions and syndromes, depending on the nature and exact location of the changes in the chromosomes. Diagnosis of such conditions is usually accomplished by cytogenetic techniques and genetic analysis.

Diagnostics of the aneuploidies

Diagnosis of aneuploidy, changes in the number of chromosomes, is done through various methods and tests. Here are some of the most common methods for diagnosing aneuploidy:

1. Amniocentesis: This is an invasive procedure in which a needle is used to take a sample of amniotic fluid from the amniotic membranes. This sample contains fetal cells that can be cytogenetically analyzed to determine the presence of aneuploidy.
2. Chorionic biopsy (CB): This is also an invasive procedure in which a sample of chorionic villi (placental tissue) is taken for cytogenetic analysis. A chorionic biopsy can be done earlier in pregnancy than amniocentesis.
3. Non-Invasive Prenatal Testing (NIPT): This method can detect the presence of aneuploidy as well as other fetal genetic abnormalities through a maternal blood test. NIPT is usually performed after the 10th week of pregnancy and has a low false positive rate.
4. Ultrasound: Ultrasound may be used to detect some signs of aneuploidy, such as increased thickness of the cervical villi or physical features of the fetus that may raise suspicion of an abnormality.
5. Genetic analysis: Cytogenetic analysis (the study of chromosomes) and molecular genetic analysis can be used to accurately determine the nature of aneuploidy and establish the type of chromosomal alterations.

The choice of how to diagnose aneuploidy can depend on many factors, including gestational age, medical conditions, risk of abnormalities, and parental wishes. The decision to diagnose and choose a method is usually made in conjunction with a gynecologist and a geneticist.

Differential diagnosis

Polyploidy and aneuploidy are two different types of changes in the number of chromosomes in cells or organisms. Here are their main differences:

1. Polyploidy:

   • Definition: Polyploidy means having additional sets of complete sets of chromosomes. For example, polyploid organisms may have two, three, or more complete sets of chromosomes.
   • Examples: Examples of polyploid organisms are some plants (e.g., wheat, bombardment) and some animal species (e.g., salmon).
   • Implications: Polyploidy can be stable and even positive for the survival of an organism, as extra copies of chromosomes can provide stability and diversity to a species.

2. Aneuploidy:

   • Definition: Aneuploidy means having the wrong number of chromosomes, including extra or missing chromosomes in the cells of an organism.
   • Examples: Examples of aneuploidy include Down syndrome (trisomy 21, when there is an extra 21st chromosome), Edwards syndrome (trisomy 18), and other genetic syndromes involving changes in the number of chromosomes.
   • Consequences: Aneuploidy is often associated with serious medical problems and can cause a variety of physical and mental abnormalities, as well as other conditions.

So, the main difference between polyploidy and aneuploidy is that polyploidy involves extra sets of complete sets of chromosomes, while aneuploidy involves a change in the number of chromosomes in cells or organisms, but without complete sets of extra chromosomes.