Learn about Hereditary Diseases

Genetic disorders are caused due to genetic mutation or due to alteration in the genome of the organism, which causes chromosomal abnormalities. Most genetic abnormalities are inherited from parents to offspring and form a part of genetically inherited diseases. Such conditions can occur due to change or mutation in a single gene or multiple genes or chromosomes. Hereditary diseases can be defined as diseases caused due to the transfer of mutated genes from parents to offspring.

Genetic Mutations and their impact on causing Genetic disorders

Genetic mutations are caused due to alterations in the DNA or RNA structure and uncorrected errors in the genes. The genes undergo mutation, which changes the instruction for protein production and leads to the formation of a genetic disorder. There are some disorders which are innate, i.e. present at birth. Some gene mutations are acquired due to exposure to environmental conditions. Innate genetic disorders are inherited by offspring from parents. Acquired disorders are caused due to mutations that occur randomly or due to exposure to chemicals or radiations like UV radiations, cigarette smoke, X-rays, etc. 

Types of Genetic Disorders 

1. Mendelian disorder 

• These disorders are also known as single-gene inheritance or monogenic disorders. They are caused due to mutations in a single gene. 
• Such disorders are categorised as autosomal dominant, autosomal recessive, sex-linked dominant and sex-linked recessive. 
• Autosomal dominant and recessive disorders are inherited genetic disorders. In autosomal dominant disorders, the disease is caused by one altered gene copy. In autosomal recessive disorder, the disease is caused by both altered gene copies. 
• Examples of autosomal dominant disorder are Huntington’s disorder, myotonic dystrophy, neurofibromatosis, etc. Examples of autosomal recessive disorder are cystic fibrosis and sickle cell anaemia.

2. Multifactorial genetic inheritance

• They are also known as polygenic inheritance. 
• They are caused due to several multiple gene mutations and environmental factors. 
• The major risk factor for such genetic disorders is a family history of these diseases. 
• Examples of such disorders are breast cancer, autoimmune diseases, diabetes, obesity, high blood pressure, Alzheimer’s disease, etc.

3. Chromosomal disorder

• These genetic disorders are caused due to alterations in the structure or number of the chromosome. It can be the result of whole chromosome loss or gain.
• Some disorders caused by chromosomal abnormalities are Down Syndrome (trisomy of chromosome 21), Kleinfelter’s syndrome (addition of X chromosome leading to XXY sex chromosome), etc. 

4. Mitochondrial inheritance 

• Mitochondrial genes are only inherited from the mother. Hence, any mutation in the mitochondrial DNA causes several genetic disorders. 
• Some diseases caused due to mitochondrial inheritance are mitochondrial, encephalopathy, lactic acidosis, etc. 

Hereditary diseases list

• Achondroplasia

This genetic disorder is an example of an autosomal dominant disease, which leads to stunted growth or dwarfism. It is caused by mutation in the FGFR3 gene, which is located in the fourth chromosome. 

• Down Syndrome

It is an autosomal dominant disease caused due to the presence of an extra copy of a chromosome in chromosome 21. It makes the face round, chin narrow, and eyes bulge. 

• Hereditary Spherocytosis

It is a congenital hemolytic disorder in which genetic mutation leads to a phenotypic change in the erythrocytes. It changes the shape of the erythrocytes and makes them spherical. It is an autosomal dominant disease. 

• Tay Sachs Disease 

It is an autosomal recessive disease. It impacts the nervous system and causes loss of motor skills. Common symptoms of the disease include dementia, delayed growth, irritability, etc. 

• Usher Syndrome 

It is an autosomal recessive disease caused by a faulty gene. It is further categorised into three types: type 1 patients are congenitally deaf, type 2 patients are born deaf and lose vision, and type 3 patients tend to lose the power of sight and hearing. 

• Haemophilia

It is a blood related genetic disorder that prevents the ability to thicken and clot blood. It is a sex-linked chromosome passed from the father to the daughter. 

• Muscular dystrophy

It is a type of genetically inherited muscle disorder that causes muscle wasting. It is a sex-linked condition that leads to the degeneration of cells and tissues in muscles. 

Conclusion 

Genetic disorders are caused due to mutation in the gene or chromosome, and they impair functions in the body. There are four major categories of genetic disorders: mendelian disorders, multifactorial genetic inheritance, chromosomal disorders and mitochondrial inheritance.