A genetic disorder is a disease that is caused by a change, or mutation, in a person’s DNA. The genetic disorders can be divided into three groups:
Single Gene Disorders
In this group, any genetic disorder is caused by defect in one particular gene, with following modes of inheritance:
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Dominant Disorders
These are the single gene disorders that occur when a person inherits one mutated copy of the relevant gene from one of the parent and one healthy copy of the gene from the other parent. The abnormal gene dominates and is enough to cause the disease. This disease can also occur as a new condition in a child when neither parent has the abnormal gene. Examples include Huntington's Disease and Marfan Syndrome.
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Recessive Disorders
These are the single gene disorders that occur when a person inherits two mutated copies of the relevant gene, one from each parent. The person requires two copies of the mutated gene to get affected by the disease. Examples include βeta Thalassaemia, Cystic Fibrosis and Spinal Muscular Atrophy.
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X-linked Disorders
These are the single gene disorders that occur when a person inherits a mutated gene on the X chromosome. X-linked disorders are more common in males as they only have one X chromosome. Examples include Hemophilia, Duchenne Muscular Dystrophy and Fragile X Syndrome.
Chromosomal Disorders
In this group, the genetic disorder is caused by changes in the number or structure of the chromosomes. Examples include Down Syndrome, Edward Syndrome and Patau's Syndrome.
Multifactorial Disorders
This is the group of complex diseases caused by changes in multiple genes, often in a complex interaction with environmental and lifestyle factors such as diet, cigarette smoking and lack of exercise. Examples include Cancers, Schizophrenia, Diabetes Mellitus, Alzheimer's disease, Obesity and Heart diseases.