Genetic Disorders, Definition, Types, Examples, Key Details

Genetic Disorders are medical conditions that occur due to irregularities in a person’s DNA that impact the development, functioning and overall health. The disorders require careful study as it plays a decisive role in both clinical practice and medical research. The correct knowledge of genetic disorders is important not only for diagnosis but also for appropriate treatment and long-term management. This makes genetics an important branch of modern medicine. In this article, we are going to cover the importance of genetics disorders, its causes, examples.

Genetic Disorders

Genetic Disorder is a disease or health problem that happens due to abnormalities at the genetic level. While some irregularities occur due to mutations within single genes, structural alterations in chromosomes or variations in chromosome number. The disorders are inherited directly from one or both parents, or may emerge  as spontaneous mutations without prior family history. Examples of genetic disorders include cystic fibrosis, sickle-cell anemia and down syndrome. All these diseases are present with a specific group of symptoms, complications and challenges in management. The diagnosis of these disorders require genetic testing and counselling play an important role in guiding both treatment approaches and family  planning decisions. The breakthroughs in gene therapy and personalized medicine have been promising for developing future treatments, offering patients better outcomes and improved quality of life.

Genetics Disorders Types

Genetic Disorders are classified into two main categories: 

1. Mendelian Disorders
2. Chromosomal Disorders

Mendelian Disorders

Mendelian disorders are conditions that happen from mutations in a single gene. These may be classified into several forms: autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked recessive, and mitochondrial disorders.
To check such conditions, pedigree analysis is conducted. The mode of inheritance depends on whether the defective gene lies on an autosome or a sex chromosome, and whether it is recessive or dominant in nature.
In the case of autosomal recessive disorders, the condition manifests only when both copies of the defective gene are present. Parents of such patients usually carry one defective allele and one normal allele. Both males and females stand an equal probability of being affected since autosomes are not sex-linked.

Mendelian Disorders Examples

• Cystic Fibrosis (autosomal recessive)
• Hemophilia (sex-linked recessive)
• Albinism (autosomal recessive)
• Sickle Cell Anemia (autosomal recessive)

Hemophilia

Hemophilia is a sex-linked recessive disorder. It is caused by the deficiency of one protein in the blood-clotting cascade. Due to this an affected individuals suffer prolonged bleeding even from minor injuries. Historically, this disorder is found in the family tree of Queen Victoria, who was a carrier of the hemophilia gene and passed it on to many descendants.

Sickle Cell Anemia

Sickle cell anemia is an autosomal recessive disorder transmitted when both parents are carriers. The disease is controlled by a pair of alleles, HbA and HbS. Under conditions of low oxygen tension, the defective hemoglobin forms polymers, which distort red blood cells into sickle shapes. This structural abnormality results in blockage of blood vessels, anemia, and numerous complications.

Chromosomal Disorders

Unlike Mendelian disorders, chromosomal disorders happen when there are abnormalities in chromosome numbers or structural arrangements. Such defects are often caused by improper segregation of chromatids during cell division.
These abnormalities occur as:

• Aneuploidy (loss or gain of a chromosome)
• Trisomy (presence of an additional chromosome)
• Monosomy (absence of one chromosome from a pair)
• These  conditions frequently lead to severe developmental and physiological consequences.

Chromosomal Disorders Examples

The following diseases are caused due to Chromosomal Disorders:

• Down’s Syndrome: Caused by the presence of an extra copy of chromosome 21 (trisomy 21). Individuals typically have short stature, a round head, furrowed tongue, partially open mouth, and broad palms with a single crease. Their physical and cognitive development is significantly delayed. The condition was first described by Langdon Down in 1866.
• Turner’s Syndrome: Results from the absence of one X chromosome in females (45, XO). Such women are sterile, have rudimentary ovaries, and show underdeveloped secondary sexual traits along with other distinctive features.
• Klinefelter’s Syndrome: Occurs in males with an extra X chromosome (47, XXY). Such individuals are sterile and may present with feminized physical characteristics.
• Additionally, polyploidy can occur when cytokinesis fails after telophase in cell division, leading to organisms with increased chromosome sets. This phenomenon is more common in plants.

Mitochondrial Inheritance

Genetic disorders occur from mutations in mitochondrial DNA, which is inherited from the mother. Examples include:

• Leber’s Hereditary Optic Atrophy (LHON)
• Myoclonic Epilepsy with Ragged Red Fibres
• Mitochondrial Encephalopathy
• Lactic Acidosis

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