Genetic Disorders

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Introduction

Genes are the basic functional unit of heredity. Genes are composed of DNA that holds the genetic information to instruct the cells to translate different proteins and other hereditary components. DNA or many times RNA is the genetic material in almost all living organisms. RNA is more unstable than DNA which is why DNA is the genetic component in all organisms except some. Sometimes, under some faulty conditions, the genes undergo mutation causing to falter the genetic code. Faulty genes produce faulty proteins that do not work properly. This leads to malfunctioning and genetic disorders.


Some of these genetic disorders are present by birth and some are quired due to mutations in genes. Hence, genetic disorders are categorized into two categories:

  • Mendelian disorders which are acquired due to mutation in the genes.

  • Chromosomal disorders which are from the mutation in the chromosome.

We will explore more about genetic disorders in this chapter.


Types of Genetic Disorders

Mendelian Disorder

Mendelian disorders are either autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked recessive, or mitochondrial and occur due to mutations in a single gene. These disorders can be detected by pedigree analysis. The genetic locus at which the mutation takes place may be a sex chromosome or an autosome and it may be in a recessive or a dominant mode. An autosomal recessive disease is articulated when the mutant gene is present in the homozygous state. In such cases, both the parents are heterozygous, carrying one copy of the mutant gene and one copy of a normal functional gene. In autosomal traits, females and males are equally expected to be affected. Other types of Mendelian disorders are Autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked chromosomal, and mitochondrial.


Examples of Mendelian Disorders are:

  • Autosomal Recessive Disorder - Cystic Fibrosis.

  • Sex - Linked Disorder- Hemophilia.

  • Autosomal Recessive Disorder - Albinism and Sickle Cell Anemia.


Chromosomal Disorders

Genetic disorders arising due to mutation in the chromosome are chromosomal disorders. Alteration in the number and functioning of the chromosomes leads to chromosomal disorders. A chromosomal disorder affects many genes at a time and can be fatal. It may occur due to the loss or gain of a whole chromosome.


Examples of Chromosomal Disorders are as Follows:

  • Down’s Syndrome which occurs due to the addition of a chromosome on chromosome 21.

  • Turner’s syndrome is marked by the absence of an X chromosome.

  • Kleinfelter’s syndrome is marked by the addition of an X chromosome, and so on.


Multifactorial Genetic Inheritance

Multifactorial inheritance also refers to polygenic inheritance. When many factors occur at the same time leading to genetic anomalies, it is known as multifactorial genetic inheritance. In such cases, environmental factors take place along with gene mutation.


Examples of Multifactorial Diseases are as Follows:

  • Heart Disease

  • High Blood Pressure

  • Alzheimer’s Disease

  • Obesity

  • Diabetes

  • Cancer

  • Arthritis


Mitochondrial Inheritance

These kinds of genetic disorders arise as a result of mutations in the non-nuclear mitochondrial DNA. Generally, in such cases, each mitochondrion has 5 to 10 pieces of DNA. These anomalies are inherited from the mother. Examples of such diseases are:

  • Leber’s Hereditary Optic Atrophy (LHON).

  • Myoclonic epilepsy with ragged red fibers.

  • Mitochondrial encephalopathy.

  • Lactic acidosis.


List of Some Genetic Disorders

  • Cystic Fibrosis

  • Thalassemia

  • Huntington’s Disease

  • Hemochromatosis

  • Turner’s Syndrome

  • Klinefelter's Syndrome

  • Leber’s Hereditary Optic Atrophy

  • Cancer

  • High Blood Pressure

  • Obesity

  • Albinism

  • Apert Syndrome

  • Down’s Syndrome


Genetic Counselling

Genetic counseling is the process of communication to help individuals or families understand and adapt to the medical implications of genetic disorders. It is the way of detecting if the child before birth will have a genetic disease or can develop any genetic disorder. Counselors in this field can help individuals and their families cope with the effects of a genetic disorder and treat them in some ways.


A few genetic disorders are treated by gene therapy. Research is still underway to know more about genetic diseases and how to treat them. Medical science professionals are trying their best to deal better with such anomalies.

FAQ (Frequently Asked Questions)

1. When Should one go for Genetic Counseling?

Ans. Genetic counseling is necessary if:

  • Either of the parents has a family history of genetic disease or a previous child with a genetic disease such as heart defects, mental retardation, defect in the neural tube, short height, psychiatric disorders, cancer, etc.

  • Either of the parents or both have an autosomal dominant disease.

  • If the mother carrying the child is 35 or above years old.

  • The mother suffers from conditions like depression, alcoholism, diabetes, thyroid, schizophrenia, etc.

2. What are Genetic Disorders?

Ans. Sometimes, under some faulty conditions, the genes undergo mutation causing to falter the genetic code. Faulty genes produce faulty proteins that do not work properly. This leads to malfunctioning and genetic disorders. Some of these genetic disorders are present by birth and some are quired due to mutations in genes.

3. What are the Types of Genetic Disorders?

Ans. Genetic disorders are categorized into two categories:

  • Mendelian disorders which are acquired due to mutation in the genes.

  • Chromosomal disorders which are from the mutation in the chromosome.

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