Genetic disorders are generally caused by abnormalities in normal genome. They are generally present from birth, but most of the genetic disorders are rare affect one person in every thousand or million. They are divided mainly into two categories, hereditary (inherited from parents) and caused by mutations after birth. There are several types of genetic disorders:-
1. Single gene disorder – Single gene disorder is a result of a mutation in the single gene. At present, there are above 4000 diseases that are caused by single gene disorder. Single gene disorders are inheritable; they can be transferred from one generation to other. They can be Autosomal, recessive, X linked and Autosomal. For example, achondroplasia is a dominant disorder, in children’s it can cause problems in skeletal muscles. Sickle cell anemia is a recessive disorder. Malaria in early childhood can be considered as a dominant disorder.
2. Autosomal dominant – Autosomal dominant is a condition in which only one gene is enough to cause a genetic disorder and if children are having a genetic disease than there is only one parent affected. The chance the child inherited the mutated gene will be 50%, but sometimes the situation is a bit different even a parent having the mutated gene but there will be no disease in children. Examples- Huntington’s disease, neurofibromatosis type 1 and neurofibromatosis type 2, Marfan syndrome, Tuberous sclerosis. Birth defects are also called congenital anomalies.
3. Autosomal recessive – Autosomal recessive is a case there must be genes from both the parent that are affected. An affected individual may have both the parents normal but they are a carrier for the disease. And in this case, there will be 25% chance of having an affected first baby. Examples of this disorders are:- Albinism, medium-chain acyl CoA dehydrogenase deficiency, cystic fibrosis, sickle cell disease, Tay Sachs diseases, spinal muscular atrophy, Roberts syndrome.
4. X- Linked recessive – X-linked recessive conditions are also caused by mutations in genes on the X-chromosomes. Males are more affected than females. The sons are not affected by recessive condition and daughter carries one copy of the mutated gene. When the women who are a carrier of the X-linked recessive disorder has a chance of having 50% chance of having sons and 50% in daughters. Examples: – Hemophilia A, Duchene muscular dystrophy, Lesch-Nyhan syndrome, male type baldness, color blindness.
5. X- Linked dominant – X-linked dominant disorders are caused by mutations in genes on X-chromosome. Males and female both are affected, males more severally affected than females. There are some disorders that are fatal for a male like- Rett syndrome, incontinent pigment type 2, Aicardi syndrome.
6. Y-linked – Y-linked disorders also called holandric disorders are caused by a mutation on Y chromosome. These are generally transmitted from heterogametic sex to offspring of the same sex; Y-linked disorders are transmitted from male parents to sons and women never affected in this case because of the absence of Y chromosome. The main example of this disorder is infertility.
7. Mitochondrial – mitochondrial genetic disorder is also known as maternal inheritance applies in mitochondrial DNA as only egg cells contribute mitochondria to the developing embryo and only mothers can pass it to their children.