What is DNA?

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.

DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.

An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.

DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone.
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Chromosome 4

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 4, one copy inherited from each parent, form one of the pairs. Chromosome 4 spans more than 191 million DNA building blocks (base pairs) and represents more than 6 percent of the total DNA in cells.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 4 likely contains between 1,300 and 1,600 genes. These genes perform a variety of different roles in the body.

Genes on chromosome 4 are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in chromosome 4 related to health conditions?
Many genetic conditions are related to changes in particular genes on chromosome 4. This list of disorders associated with genes on chromosome 4 provides links to additional information.

Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in chromosome 4.

Cancers
Changes in chromosome 4 have been identified in several types of human cancer. These genetic changes are somatic, which means they are acquired during a person's lifetime and are present only in certain cells. For example, rearrangements (translocations) of genetic material between chromosome 4 and several other chromosomes have been associated with leukemias, which are cancers of blood-forming cells.

A specific translocation involving chromosome 4 and chromosome 14 is commonly found in multiple myeloma, which is a cancer that starts in cells of the bone marrow. The translocation, which is written as t(4;14)(p16;q32), abnormally fuses the WHSC1 gene on chromosome 4 with part of another gene on chromosome 14. The fusion of these genes overactivates WHSC1, which appears to promote the uncontrolled growth and division of cancer cells.

Facioscapulohumeral muscular dystrophy
Facioscapulohumeral muscular dystrophy results from a deletion of genetic material from a region of DNA known as D4Z4. This region is located near the end of the long (q) arm of chromosome 4 at a position described as 4q35. The D4Z4 region normally consists of 11 to more than 100 repeated DNA segments, each of which is about 3,300 DNA base pairs (3.3 kb) long. However, in people with facioscapulohumeral muscular dystrophy the D4Z4 region on one copy of chromosome 4 is abnormally short, containing between 1 and 10 repeats.

It is uncertain how a shortened D4Z4 region causes the progressive muscle weakness and wasting characteristic of facioscapulohumeral muscular dystrophy. Researchers have proposed several possible mechanisms, but none have yet been proven. It appears that the D4Z4 region influences the activity of other genes located nearby on the long arm of chromosome 4. An abnormally short D4Z4 region may somehow disrupt the normal regulation of these genes. However, it is unclear which genes are influenced by D4Z4 and what role, if any, those genes play in muscle cells. Researchers suspect that genetic factors other than the shortened D4Z4 region may also be involved in facioscapulohumeral muscular dystrophy.

Wolf-Hirschhorn syndrome
Wolf-Hirschhorn syndrome is caused by a deletion of genetic material near the end of the short (p) arm of chromosome 4 at a position described as 4p16.3. The signs and symptoms of this condition are related to the loss of multiple genes from this part of the chromosome. The size of the deletion varies among affected individuals; studies suggest that larger deletions tend to result in more severe intellectual disability and physical abnormalities than smaller deletions.

The region of chromosome 4 that is deleted most often in people with Wolf-Hirschhorn syndrome is known as Wolf-Hirschhorn syndrome critical region 2 (WHSCR-2). This region contains several genes, some of which are known to play important roles in early development. A loss of these genes leads to developmental delay, a distinctive facial appearance, and other characteristic features of the condition. Scientists are working to identify additional genes at the end of the short arm of chromosome 4 that contribute to the characteristic features of Wolf-Hirschhorn syndrome.

Other chromosomal conditions
Some deletions of genetic material from the short (p) arm of chromosome 4 do not involve the critical region WHSCR-2. These deletions cause signs and symptoms that are distinct from those of Wolf-Hirschhorn syndrome, including mild intellectual disability and, in some cases, rapid (accelerated) growth. People with this type of deletion usually do not have seizures.

Trisomy 4 occurs when cells have three copies of chromosome 4 instead of the usual two copies. Full trisomy 4, which occurs when all of the body's cells contain an extra copy of chromosome 4, is not compatible with life. A similar but somewhat less severe condition called mosaic trisomy 4 occurs when only some of the body's cells have an extra copy of chromosome 4. The signs and symptoms of mosaic trisomy 4 vary widely and can include heart defects, abnormalities of the fingers and toes, and other birth defects. Mosaic trisomy 4 is very rare; only a few cases have been reported.
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How are changes in the LETM1 gene related to health conditions?

Wolf-Hirschhorn syndrome – associated with the LETM1 gene
The LETM1 gene is located in a region of chromosome 4 that is deleted in people with the typical features of Wolf-Hirschhorn syndrome. As a result of this deletion, affected individuals are missing one copy of the LETM1 gene in each cell. Studies suggest that a loss of this gene alters the structure of mitochondria; however, it is unclear how this abnormality is related to the signs and symptoms of Wolf-Hirschhorn syndrome. Specifically, a loss of the LETM1 gene has been associated with seizures or other abnormal electrical activity in the brain.
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What is the normal function of the LETM1 gene?

What is the normal function of the LETM1 gene?
The LETM1 gene provides instructions for making a protein whose function is not well understood. This protein is active in mitochondria, which are structures within cells that convert the energy from food into a form that cells can use. The LETM1 protein may be involved in the transport of charged calcium atoms (calcium ions) across membranes within mitochondria. Researchers suspect that the protein also plays a role in determining the shape and volume of mitochondria.
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What is the official name of the LETM1 gene?

What is the official name of the LETM1 gene?
The official name of this gene is “leucine zipper-EF-hand containing transmembrane protein 1.”

LETM1 is the gene's official symbol.

The LETM1 gene is also known by.
LETM1_HUMAN
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How do people inherit Huntington disease?

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. An affected person usually inherits the altered gene from one affected parent. In rare cases, an individual with Huntington disease does not have a parent with the disorder.

As the altered HTT gene is passed from one generation to the next, the size of the CAG trinucleotide repeat often increases in size. A larger number of repeats is usually associated with an earlier onset of signs and symptoms. This phenomenon is called anticipation. People with the adult-onset form of Huntington disease typically have 40 to 50 CAG repeats in the HTT gene, while people with the early-onset form of the disorder tend to have more than 60 CAG repeats.

Individuals who have 27 to 35 CAG repeats in the HTT gene do not develop Huntington disease, but they are at risk of having children who will develop the disorder. As the gene is passed from parent to child, the size of the CAG trinucleotide repeat may lengthen into the range associated with Huntington disease (36 repeats or more).
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Autosomal dominant genes

Chromosome
Genes
Genetics Autosomal dominant is one of several ways that a trait or disorder can be passed down through families.

If a disease is autosomal dominant, it means you only need to get the abnormal gene from one parent in order for you to inherit the disease. One of the parents may often have the disease.

Information
Inheriting a disease, condition, or trait depends on the type of chromosome affected (autosomal or sex chromosome). It also depends on whether the trait is dominant or recessive.

A single, abnormal gene on one of the first 22 nonsex chromosomes from either parent can cause an autosomal disorder.

Dominant inheritance means an abnormal gene from one parent is capable of causing disease, even though the matching gene from the other parent is normal. The abnormal gene "dominates" the pair of genes. If just one parent has a dominant gene defect, each child has a 50% chance of inheriting the disorder.

For example, if four children are born to a couple and one parent has an abnormal gene for a dominant disease, statistically two children will inherit the abnormal gene and two children will not. Children who do not inherit the abnormal gene will not develop or pass on the disease.

If someone has an abnormal gene that is inherited in an autosomal dominant manner, then the parents should also be tested for the abnormal gene.

Examples of autosomal dominant disorders include Huntington's disease and neurofibromatosis.

See also:

Autosomal recessive
Genetic counseling and prenatal diagnosis
Heredity and disease
Sex-linked dominant
Sex-linked recessive
Alternative Names
Inheritance – autosomal dominant; Genetics – autosomal dominant
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What are the different ways in which a genetic condition can be inherited?

Some genetic conditions are caused by mutations in a single gene. These conditions are usually inherited in one of several straightforward patterns, depending on the gene involved:

Patterns of inheritance Inheritance pattern Description Examples
Autosomal dominant One mutated copy of the gene in each cell is sufficient for a person to be affected by an autosomal dominant disorder. Each affected person usually has one affected parent. Autosomal dominant disorders tend to occur in every generation of an affected family. Huntington disease, neurofibromatosis type 1
Autosomal recessive Two mutated copies of the gene are present in each cell when a person has an autosomal recessive disorder. An affected person usually has unaffected parents who each carry a single copy of the mutated gene (and are referred to as carriers). Autosomal recessive disorders are typically not seen in every generation of an affected family. cystic fibrosis, sickle cell anemia
X-linked dominant X-linked dominant disorders are caused by mutations in genes on the X chromosome. Females are more frequently affected than males, and the chance of passing on an X-linked dominant disorder differs between men and women . Families with an X-linked dominant disorder often have both affected males and affected females in each generation. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons (no male-to-male transmission). fragile X syndrome
X-linked recessive X-linked recessive disorders are also caused by mutations in genes on the X chromosome. Males are more frequently affected than females, and the chance of passing on the disorder differs between men and women. Families with an X-linked recessive disorder often have affected males, but rarely affected females, in each generation. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons (no male-to-male transmission). hemophilia, Fabry disease
Codominant In codominant inheritance, two different versions (alleles) of a gene can be expressed, and each version makes a slightly different protein. Both alleles influence the genetic trait or determine the characteristics of the genetic condition. ABO blood group, alpha-1 antitrypsin deficiency
Mitochondrial This type of inheritance, also known as maternal inheritance, applies to genes in mitochondrial DNA. Mitochondria, which are structures in each cell that convert molecules into energy, each contain a small amount of DNA. Because only egg cells contribute mitochondria to the developing embryo, only females can pass on mitochondrial conditions to their children. Mitochondrial disorders can appear in every generation of a family and can affect both males and females, but fathers do not pass mitochondrial traits to their children. Leber hereditary optic neuropathy (LHON)

Many other disorders are caused by a combination of the effects of multiple genes or by interactions between genes and the environment. Such disorders are more difficult to analyze because their genetic causes are often unclear, and they do not follow the patterns of inheritance described above. Examples of conditions caused by multiple genes or gene/environment interactions include heart disease, diabetes, schizophrenia, and certain types of cancer. Disorders caused by changes in the number or structure of chromosomes do not follow the straightforward patterns of inheritance listed above. 

The Centre for Genetics Education

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Anthrax Vaccination

Anthrax Vaccination
Pronounced (An-thraks)
There is a vaccine to prevent anthrax, but it is not yet available for the general public. Anyone who may be exposed to anthrax, including certain members of the U.S. armed forces, laboratory workers, and workers who may enter or re-enter contaminated areas, may get the vaccine. Also, in the event of an attack using anthrax as a weapon, people exposed would get the vaccine.
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Institutional Review Boards

All research involving human participants that is conducted or supported by CDC must comply with the HHS Policy for Protection of Human Research Subjects (45 CFR part 46). This includes research conducted by CDC employees or supported by CDC through funding or provision of other tangible support, whether conducted inside or outside the United States. Unless exempt, all such research must be approved by an institutional review board (IRB) prior to the start of the research. HRPO facilitates the work of the IRB and provides assistance and training for CDC staff engaged in research involving human participants. Clinical investigations that involve the use of drugs, biologics, or devices—whether unlicensed or used outside standard medical practice—are subject to IRB review and approval under 21 CFR parts 50 and 56.

source from CDC

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