Human Genetic Disorders: Definition, Types, Development, Examples, Facts

Human genetic disorders are medical conditions arising due to an abnormality in the DNA of an individual. These may or may not be inherited from parents and may be caused due to mutation as well. Genetic disorders also form an important part of human health and the topic is covered within the class 12 chapter Principles of Inheritance and Variation in Biology. This article includes a genetic disorder definition, types of genetic diseases, hereditary and inherited disorders, and examples of common genetic conditions.

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This Story also Contains

1. Genetic Disorders
2. Types of Genetic Disorders
3. Causes of Chromosomal Disorders
4. Genetic Counselling
5. List of Genetic Disorders

Genetic Disorders

Genetic disorders are the result of abnormalities in a person's DNA. The resultant disorder may be passed down the line or may appear as a mutation. In most cases, these disorders may manifest with abnormalities at the single gene, several genes, or even chromosome levels and have, quite variably, different effects on diverse body functions and development.

The study of genetic disorders is important in helping people understand the cause of various diseases and developing better diagnosis, treatment, and prevention strategies. It may also uncover several pieces of information about human development and the functioning of genes, hence leading to medical research and public health.

Genetic inheritance is the passing on of genes and traits from parents to offspring. This takes place in different patterns, autosomal dominant, autosomal recessive, X-linked, and mitochondrial inheritance. Each one of these patterns refers to a degree and mode by which a genetic disorder is passed on to successive generations of a family.

Types of Genetic Disorders

The types of genetic disorders are described below:

Single Gene Disorders

Single gene disorders are caused by mutations of a single gene and follow any pattern of inheritance during their transmission, either autosomal dominant, autosomal recessive, or even X-linked inheritance.

Examples:

• Cystic Fibrosis: Respiratory and gastrointestinal problems caused by a mutation in the CFTR gene.

• Sickle Cell Anemia: Abnormal haemoglobin production gives rise to deformed red blood cells. This abnormality results from a mutation in the HBB gene.

• Hemophilia: A disorder of blood clotting, caused by mutations in either the F8 or F9 genes disrupting the production of clotting factors.

Inheritance Patterns

• Autosomal Dominant: Only one copy of the gene needs to be mutated for a disorder to be expressed. For example, Huntington's disease.

• Autosomal Recessive: Two copies of the gene must be mutated for a disorder to express. For example, cystic fibrosis.

• X-linked: A gene with a mutation is located on the X chromosome. Thus, for example, haemophilia will have more serious effects in males.

Chromosomal Disorders

These are caused because of an abnormality in the number or the structure of the chromosomes, leading to developmental and physical problems.

Examples:

• Down Syndrome: An extra copy of chromosome 21 causes Trisomy 21, resulting in intellectual disability and physical abnormalities.

• Turner Syndrome: A condition wherein females have only one sex chromosome X that has problems in development and reproductive functions.

• Klinefelter Syndrome: A disorder found in males who bear an extra X chromosome. The presence of the extra X chromosome makes them XXY, which is associated with reduced levels of testosterone and, as a result, infertility.

Also Read:

• MCQ Practice on Human Genetic Disorder
• Principles of Inheritance and Variation
• Genetics
• Molecular Basis of Inheritance

Causes of Chromosomal Disorders

Chromosomal abnormalities result from an error in cell division, involving either nondisjunction or translocation events. These abnormalities could further lead to physical and developmental abnormalities whose type depends on the specific chromosomes involved.

Multifactorial Disorders

These are caused by combined genetic and environmental factors and do not demonstrate any obvious Mendelian pattern. Moreover, they involve multiple genes.

Examples:

• Heart Disease: Determined by the interaction between genetic predisposition and behavioural factors such as nutrition and exercise.

• Diabetes: Caused by gene environment interaction between genetic susceptibility and environmental factors such as obesity and lack of exercise.

• Cleft Palate: This can be caused by genes and environmental exposures during pregnancy.

Multifactorial disorders point to gene-environment interplay. Indeed, the nature of these interactions is of crucial concern for the sake of success in prevention and cure.

Mitochondrial Disorders

These are caused by mutations in mtDNA, the DNA of the energy-producing structures in cells. These are singular disorders in that mitochondrial DNA is passed strictly maternally.

Examples:

• Leber's Hereditary Optic Neuropathy: Results in optic atrophy and loss of vision.

• MELAS Syndrome: Mitochondrial encephalomyopathy, lactic acidosis, and stroke like episodes, it is a multi-system involvement.

In general, mitochondrial disorders are maternally inherited disorders whereby affected individuals get the mutated mitochondrial DNA from their mother. As a result, these disorders usually affect organs or tissues with a high energy demand. Because brain and muscular tissue are predominantly concerned in the majority of cases.

Genetic Counselling

Genetic counselling is a process that provides individuals and families with information and advice about genetic disorders. Genetic counsellors advise a patient on the risks of inherited conditions and the implications of genetic testing, besides giving a patient options for the management and prevention of genetic disorders. This is very kind assistance, more so for those with a history of genetic disorders in their family, those intending to start a family, or a person who has been diagnosed with a genetic condition.

Genetic counselling is very important to enable people to make informed decisions about their health and the well-being of their families. Reasons include detailed family history, evaluation of genetic risks, discussion of possible genetic tests, a review of test results or any other findings, time for emotional support, and finally, availing proper resources and support groups to such families. It will ensure that the patients and families are truly informed and empowered to cope and live with genetic health problems.

List of Genetic Disorders

Following is the list of some genetic disorders:

• Cystic Fibrosis

• Sickle Cell Anemia

• Hemophilia

• Down Syndrome

• Turner Syndrome

• Klinefelter Syndrome

• Huntington's Disease

• Tay-Sachs Disease

• Phenylketonuria, PKU

• Duchenne Muscular Dystrophy

• Marfan Syndrome

• Fragile X Syndrome

• Leber's Hereditary Optic Neuropathy

• MELAS Syndrome

• Cleft Palate

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