Genetic disorders are caused by the mutations or abnormalities that occur in a chromosome or genome. These abnormalities may appear phenotypically at any time of a human life. It is being estimated that there are around 4,000 genetic disorders which affect the human life. But this number keeps changing as we know more about our gene and genome. Types of mutations like single nucleotide mutation, chromosomal aberration, mitochondrial genome and also environmental factors play a role in inducing these genetic disorders in humans.
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. For example Cystic fibrosis is an example for single gene disorder. Cystic fibrosis condition is caused by a mutation in chromosome 7 gene known as cystic fibrosis transmembrane conductance regulator (CFTR). The mutation in the gene CFTR produces the abnormal non-functional protein, which affect the movement of sodium chloride in the body cell. This leads to the formation of abnormal thick mucus in the lungs. This in turn makes it difficult for patients to breathe and digest. This is also an example for recessive genetic disorder. Recessive genetic disorders are the one when both the alleles of a gene are defective then only the condition occur phynotypically. That is both the parents should pass the defective gene to their offspring then only this condition appears in once life.
2. Multifactorial Genetic Disorders: Multifactorial genetic disorders are caused by combination of many factors like gene mutation, small variations in the chromosome structure and also environmental factors. Cancer, heart conditions or disease are best examples for this type of genetic disorder.
A single mutation in the gene will not induce skin cancer. Rather multiple DNA mutations caused by environmental factors like X-ray or UV rays may increase the chances of developing skin cancer. This type of genetic disorders is very difficult to diagnose, treat. 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.
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. For example Cystic fibrosis is an example for single gene disorder. Cystic fibrosis condition is caused by a mutation in chromosome 7 gene known as cystic fibrosis transmembrane conductance regulator (CFTR). The mutation in the gene CFTR produces the abnormal non-functional protein, which affect the movement of sodium chloride in the body cell. This leads to the formation of abnormal thick mucus in the lungs. This in turn makes it difficult for patients to breathe and digest. This is also an example for recessive genetic disorder. Recessive genetic disorders are the one when both the alleles of a gene are defective then only the condition occur phynotypically. That is both the parents should pass the defective gene to their offspring then only this condition appears in once life.
2. Multifactorial Genetic Disorders: Multifactorial genetic disorders are caused by combination of many factors like gene mutation, small variations in the chromosome structure and also environmental factors. Cancer, heart conditions or disease are best examples for this type of genetic disorder.
A single mutation in the gene will not induce skin cancer. Rather multiple DNA mutations caused by environmental factors like X-ray or UV rays may increase the chances of developing skin cancer. This type of genetic disorders is very difficult to diagnose, treat. 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.
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