Diseases

Genetic Disease Information

Chromosome abnormalities

Chromosomes, distinct structures made up of DNA and protein, are located in the nucleus of each cell. Because chromosomes are the carriers of the genetic material, abnormalities in chromosome number or structure can result in disease. Abnormalities in chromosomes typically occur due to a problem with cell division.For example, Down syndrome (sometimes referred to as "Down's syndrome") or trisomy 21 is a common disorder that occurs when a person has three copies of chromosome 21. There are many other chromosome abnormalities including:

• Turner syndrome (45,X0),
• Klinefelter syndrome (47, XXY), and
• Cri du chat syndrome, or the "cry of the cat" syndrome (46, XX or XY, 5p-).

Mitochondrial genetic inheritance

This type of genetic disorder is caused by mutations in the non-nuclear DNA of mitochondria. Mitochondria are small round or rod-like organelles that are involved in cellular respiration and found in the cytoplasm of plant and animal cells. Each mitochondrion may contain 5 to 10 circular pieces of DNA. Since egg cells, but not sperm cells, keep their mitochondria during fertilization, mitochondrial DNA is always inherited from the female parent.Examples of mitochondrial disease include:

• an eye disease called Leber's hereditary optic atrophy;
• a type of epilepsy called MERRF which stands for myoclonic epilepsy with Ragged Red Fibers; and
• a form of dementia called MELAS for mitochondrialencephalopathy, lactic acidosis and stroke-like episodes.

Multifactorial genetic inheritance

Multifactorial inheritance, which is also called complex or polygenic inheritance. Multifactorial inheritance disorders are caused by a combination of environmental factors and mutations in multiple genes. For example, different genes that influence breast cancer susceptibility have been found on chromosomes 6, 11, 13, 14, 15, 17, and 22. Some common chronic diseases are multifactorial disorders.Examples of multifactorial inheritance include:

• heart disease,
• high blood pressure,
• Alzheimer's disease,
• arthritis,
• diabetes,
• cancer, and
• obesity.

Single gene genetic inheritance

Single gene inheritance, also called Mendelian or monogenetic inheritance. This type of inheritance is caused by changes or mutations that occur in the DNA sequence of a single gene. There are more than 6,000 known single-gene disorders, which occur in about 1 out of every 200 births. These disorders are known as monogenetic disorders (disorders of a single gene).Some examples of monogenetic disorders include:

• cystic fibrosis,
• sickle cell anemia,
• Marfan syndrome,
• Huntington's disease, and
• hemochromatosis.