Genetic disorders occur as a result of abnormalities or variations in the information encoded by the genes and chromosomes. As per the available information on genetic disorders, these disorders can be broadly classified into four different categories, which are as follows:
1. Single-gene Disorders: Also known as Mendellian or monogenic disorders, these occur when the changes or mutations occur in only a single gene. Some well-known examples of single-gene disorders include cystic fibrosis, sickle cell anemia, Marfan syndrome, Huntington’s disease and hereditary hemochromatosis. Single gene disorders can be further classified into autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive and Y-linked disorders.
2. Multifactorial Genetic Disorders: Also known as polygenic, these disorders occur as a result of mutations in multiple genes. These disorders are really complex, difficult to analyze and hard to treat. Some examples of multifactorial disorders include autism, coronary heart diseases, cleft palate, mental retardation, cancer and diabetes.
3. Chromosomal Disorders: These diseases occur as a result of abnormalities in the chromosomal structure such as missing or presence of extra copies of chromosomes. The most well-known chromosomal disorder is the Down syndrome or Trisomy 21 where a person has three copies of chromosome 21. Other examples include Klinefelter syndrome, Cri-du-Chat syndrome, Turner Syndrome and Williams’ syndrome.
4. Mitochondrial Disorders: These disorders occur when there are mutations in the mitochondrial DNA or the non-chromosomal DNA of the cell. These disorders are maternal in origin as only egg cells contribute mitochondria in a developing embryo. One very good example of a mitochondrial disorder is the Leber’s Hereditary Optic neuropathy.