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Many human diseases have a genetic component to them.

  • A genetic disease is any disease that is caused by an abnormality in an individual's genome, the person's entire genetic makeup.
  • There are over 6,000 genetic disorders, many of which are fatal or severely debilitating.
    • Genetic disorders may be hereditary, meaning that they are passed down from the parents' genes. In other genetic disorders, defects may be caused by new mutations or changes to the DNA. In such cases, the defect will only be passed down if it occurs in the germline.
    • The abnormality can range from a discrete mutation in a single base in the DNA of a single gene to a gross chromosome abnormality involving the addition or subtraction of an entire chromosome or set of chromosomes.
    • A genetic disease is caused by a mutation in DNA and can be divided into 4 major groups:
      • Single-gene mutation -- occur when an alteration occurs in a gene causing one gene to stop working. An example of a single gene disorder is sickle-cell anaemia.
      • Multiple genes mutations -- occur as the result of mutations in multiple genes, frequently coupled with environmental causes. An example of a multifactorial disorder is diabetes.
        • Some birth defects may be due to several problems, or a combined effect of genes and the environment.
        • Examples include heart defects, cleft lip or cleft palate, and neural tube defects (defects in the spine or brain).
      • Chromosomal changes -- the entire areas of the chromosome can be missing or misplaced, duplicated or otherwise altered. Down Syndrome is a prominent example of a chromosomal abnormality.
        • About 1 out of 150 live newborns has a detectable chromosomal abnormality. Yet even this high incidence represents only a small fraction of chromosome mutations since the vast majority are lethal and result in prenatal death or stillbirth.
        • 50 percent of all first-trimester miscarriages and 20 percent of all second-trimester miscarriages are estimated to involve a chromosomally abnormal fetus.
      • Mitochondrial mutations -- the maternal genetic material in mitochondria can mutate; are rare disorders caused by mutations in non-chromosomal DNA located within the mitochondria. (The mitochondria are subcellular organelles.) These disorders can be found to affect any part of the body including the brain and the muscles.
  • Some genetic disorders are inherited from the parents, while other genetic diseases are caused by acquired changes or mutations in a preexisting gene or group of genes.
  • Mutations can occur either randomly or due to some environmental exposure.

Genetic Disease Testing:

  • Genetic testing is a medical test that identifies changes in chromosomes, genes or proteins to confirm or rule out a suspected genetic condition.
  • There are more than 2,000 genetic tests are currently in use.
    • Testing usually involves taking a blood or tissue sample or a sample of or cells from the womb (amniotic fluid) or cells in the placenta (Chorionic villi cells) and analyzing the DNA in these cells.
  • Genetic testing can be used to find out whether you're carrying a particular genetic mutation that causes a medical condition. They can have a number of purposes, such as:
    • diagnosing certain genetic conditions
    • predicting your likelihood of developing a certain condition
    • determining if any children you have are at risk of developing an inherited condition
  • Families at risk for genetic diseases may want to consult a certified genetic counselor. A careful family pedigree (chart of members of the family) and history may help determine risks for certain problems. Genetic counseling also helps parents understand the effects of a disorder and ways it may be prevented or treated.
    • It may be necessary to check each parent's DNA to learn about some genetic inheritance patterns. Prenatal testing is also available to check the fetus for problems. Testing may include ultrasound (using sound waves to look at internal structures), chorionic villus sampling (testing the tissues around the fetus), or amniocentesis (withdrawing a sample of the amniotic fluid).

The NHS recently started a major research project looking at all the DNA in 100,000 patients. It's the largest project of its type in the world. (from: https://www.nhs.uk/conditions/genetics/ NHS - Genetic inheritance])

Genes and human disease

  • The human body is made up of millions of cells each specializing in a particular function like the sensing light and smell or even the absorption of oxygen into the blood.
    • Chromosomes are sub-cellular structures that exist in the nucleus of each cell that makes up the human body. There are 23 pairs of chromosomes existing in the human cell. Quite simply chromosomes are responsible for transferring genetic information from one generation to another.
    • Humans have two types of chromosomes - sex chromosomes and autosomes.
    • There are two sex chromosomes, the X chromosome and the Y chromosome. They determine the sex of the individual.
      • A male child inherits a Y from his father and X chromosome from the mother whereas a female child inherits X chromosomes from both her parents.
      • About 1 in 400 male and 1 in 650 female live births demonstrate some form of sex chromosome abnormality, although the symptoms of these conditions are generally much less severe than are those associated with autosomal abnormalities.
  • Chromosomes are made up of tightly packed lengths of DeoxyriboNucleic Acid commonly referred to as DNA, which in turn contain information needed to control the production of proteins.
    • DNA controls which proteins will be produced in what quantity and when.
    • Genes are made up of deoxyribonucleic acid (DNA). DNA is a long molecule made up of a combination of four chemicals: adenine, thymine, cytosine and guanine, represented as letters A, T, C and G.
    • These "letters" are ordered in particular sequences within your genes. They contain the instructions to make a particular protein, in a particular cell, at a particular time.
    • Proteins are molecules that play an important role in determining the structure and function of the body’s cells tissues and organs. Proteins are made up of amino acids.
    • Genes are specific lengths of DNA that determine the order of amino acids used to make protein. Some proteins are needed in the functioning of all cells, others are not. In the second case, the gene coding for the needed protein is switched off allowing different structures to exist at the same time.
    • Genes are also known to play a role in the occurrence of infectious diseases like tuberculosis and AIDS as well as some non communicable diseases like cancer and diabetes.

Specific Genetic Disorders

From: NIH - Specific Genetic Disorders

Many human diseases have a genetic component. Some of these conditions are under investigation by researchers at or associated with the National Human Genome Research Institute (NHGRI).

  • Below is a list of selected genetic, orphan and rare diseases. This list is by no means comprehensive. If the condition you are looking for is not listed below, other resources are available at: Genetic and Rare Diseases Information Center (GARD)
  • Clinical research studies initiated and pursued by NHGRI researchers and scientists can be found at: Current NHGRI Clinical Studies
  • Clinical research studies initiated and pursued by National Instutes of Health (NIH) researchers and scientists can be found at: ClinicalTrials.gov
  • Undiagnosed Diseases

Genetic Disorders

Other sites listing disorders:

  1. HealthDirect - Genetic disorders (26 disorders listed)
  2. Wikipedia - List of genetic disorders (The list is of genetic disorders and if known, type of mutation and the chromosome involved. Although the parlance "disease-causing gene" is common, it is the occurrence of an abnormality in these genes that causes the disease.)
  3. NIH, Generic & Rare Disease Information - Browse A-Z (A list of rare diseases and related terms to find topics of interest to you. This list includes the main name for each condition, as well as alternate names. Inclusion on this list does not serve as official recognition by the NIH that a disease is rare. Some conditions that are not considered rare are on this list and are labeled accordingly.)
  4. Table of Genetic Disorders

If a condition is not listed above, other resources of information can be found at: NIH - Online Health Resources.

Last  Reviewed: May 18, 2018

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