Genetic Disease

A genetic disease or disorder is any disease that is caused by an abnormality in an individual's genome. The abnormality can range from minuscule to major -- 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.

1). Single gene inheritance -- Also called Mendelian or monogenic 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.
Some examples of single gene inheritance are cystic fibrosis, sickle cell anemia, Marfan syndrome, Huntington's disease, and hemochromatosis. Single-gene disorders are inherited in recognizable patterns: autosomal dominant, autosomal recessive, and X-linked.

2). Multifactorial inheritance -- Also called complex or polygenic inheritance. This type of inheritance is 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. Multifactorial inheritance also is associated with heritable traits such as fingerprint patterns, height, eye color, and skin color.

3). 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.