Genetic Disorders

Table of Contents

• Genetic Disorders
• Types of Genetic Disorders
• Genetic Counselling
• List of Genetic Disorders

Genetic disorders are due to alterations or abnormalities in the genome of an organism. A genetic disorder may be caused by a mutation in a single gene or multiple genes. It can also be due to changes in the number or structure of chromosomes.

Genes are the basic unit of heredity. They hold the genetic information in the form of DNA which can be translated into useful proteins to carry out life processes. These genes undergo a mutation sometimes, which changes the instructions to formulate the protein, due to which the protein does not work properly. Such disorders are known as genetic disorders.

Some genetic disorders are innate, i.e., present by birth, while others are acquired due to mutations in a particular gene. The genetic disorders that are present by birth are inherited from parents, e.g. cystic fibrosis, haemophilia, sickle cell anaemia, etc. The genetic disorders that are acquired during the lifetime are not inherited from parents, these occur due to mutations that occur randomly or due to exposure to certain chemicals, environments or radiations such as cigarette smoke, UV radiations, etc. Cancer is one such disease.

The genetic disorders can be categorized into two types, namely Mendelian Disorders, i.e., a disorder in a single gene that follows Mendelian inheritance pattern, and Chromosomal Disorders, i.e., damage or alteration in the chromosomes structure or number, the chromosomes are either missing, duplicated or a part is translocated.

Let us explore genetic disorder notes to know about the different types of genetic disorders.

Mendelian Disorder

• These disorders occur due to mutations in a single gene and can be easily detected by pedigree analysis.

• These disorders can be autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked recessive, and mitochondrial.

The most common Mendelian disorders include:

• Cystic fibrosis (autosomal recessive)

• Haemophilia (sex-linked recessive)

• Albinism (autosomal recessive)

• Sickle cell anaemia (autosomal recessive)

Chromosomal Disorder

• These disorders are caused by any alteration in the number or structure of the chromosomes.

• Sometimes the whole chromosome is gained or lost.

• This type of disorder is usually fatal and affects many genes.

Some of the major chromosomal abnormalities are:

• Down’s syndrome- the addition of a chromosome 21 (trisomy)

• Turner’s syndrome-absence of an X chromosome (XO)

• Kleinfelter’s syndrome-addition of an X chromosome (XXY)

Multifactorial Genetic Inheritance

This is also known as polygenic inheritance. These are caused as a result of environmental factors and gene mutations. Some of the examples of this kind of disorder are:

• Heart disease

• High blood pressure

• Alzheimer’s disease

• Obesity

• Diabetes

• Cancer

• Arthritis

Mitochondrial Inheritance

This type of genetic disorder is caused by mutations in the non-nuclear mitochondrial DNA. The mitochondrial DNA is inherited from the mother. Some of the diseases caused due to mitochondrial inheritance are:

• Leber’s Hereditary Optic Atrophy (LHON)

• Myoclonic epilepsy with ragged red fibres

• Mitochondrial encephalopathy

• Lactic acidosis

Genetic counselling is one of the remarkable ways of detecting whether a child to be born will be having a genetic disease, or if the person is going to have a genetic disorder. Genetic counsellors can help a person with the diagnosis and treatment of a particular disorder.

Some genetic disorders have been treated by gene therapy. Few of the techniques are under trial and will soon be implemented in medical science to cure genetic disorders.

There are many reasons one should go for genetic counselling:

• Family history or a previous child with a genetic disease, heart defects, mental retardation, defect in the neural tube, short height, psychiatric disorders, cancer, etc.

• A parent with an autosomal dominant disease.

• If the pregnant lady is 35 years or older.

• Mother suffering from any disorder such as depression, alcoholism, diabetes, thyroid, schizophrenia, etc.

Following is the list of genetic disorders that occur in humans:

1. Cystic fibrosis
2. Thalassemia
3. Huntington’s disease
4. Hemochromatosis
5. Turner’s syndrome
6. Kleinfelter’s syndrome
7. Leber’s Hereditary Optic Atrophy
8. Cancer
9. High Blood Pressure
10. Obesity

For more information on Genetic Disorders and a list of genetic disorders, register at BYJU’S and refer to the genetic disorder notes for reference.

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