Genetic Disorders & its Types

Genetic disorders are diseases or conditions caused by an abnormality in the DNA of a person and can cause several challenges to patients in developmental or health domains. Genetic disorders must be understood for diagnosis, management, and effective treatment, hence genetic research holds significant importance in the medical field. This article aims at an in-depth study of the types of genetic disorders along with their causes, examples, and recent advances in diagnosis and treatment.

What are Genetic Disorders? 

• A genetic condition is a disease or malady brought forth because of genetic abnormalities in the affected person. Such anomalies may be gene mutations in a single gene or structural changes in chromosomes or an abnormality in a gross chromosome number. 
• These inherited conditions could either be passed down from one or both parents or just spontaneously arise due to a mutation. 
• Some common genetic disorders include cystic fibrosis, sickle cell anaemia, and Down syndrome, each with a characteristic set of symptoms and health issues. 
• The diagnosis typically involves genetic testing and counselling, which would be useful when making decisions about the management of the condition and family planning. 
• The advent of gene therapy and personalised medicine provides hope for potential treatments for better management of many of these disorders, thus improving the quality of life of patients.

Read our detailed article on Genes and Genetics.

Types of Genetic Orders

Genetic disorders are classified based on the nature of genetic abnormalities. The main types include:

• Genetic disorders may be grouped into two categories –
  • Mendelian disorders and 
  • Chromosomal disorders.

Mendelian Disorder

• They are classified into Mendelian disorders, which are autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked recessive, or mitochondrial, and are caused by mutation within a single gene. 
• Pedigrees are analyzed to detect these disorders. The site on which the mutation occurs may be a sex chromosome or an autosome with a recessive or dominant mode. 
• An autosomal recessive form of a disease is expressed only when the mutant gene is homozygous. 
• Both parents are heterozygous in that they carry one copy of the mutant gene and one copy of the normal gene. 
• In autosomal traits, the females and males have an equal probability of being affected. 
• Other types of Mendelian disorders are Autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked chromosomal, and mitochondrial.

Examples of Mendelian Disorders

Autosomal Recessive Disorder, Cystic Fibrosis, Sex-Linked Disorder, Hemophilia, Autosomal Recessive Disorder, Albinism and Sickle Cell Anemia.

Haemophilia

• This is a sex-linked recessive disease. In it, a single protein in the cascade of proteins involved in blood clotting is affected. 
• Due to this, in an affected individual, a simple cut will result in nonstop bleeding.
• The family pedigree of Queen Victoria shows several haemophilic descendants, as she was a carrier of the disease.

Sickle-Cell Anaemia

• This autosome-linked recessive trait can be transmitted from parents to offspring when both partners are carriers for the gene (or heterozygous). A single pair of alleles, HbA and HbS, control the disease.
• The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension, causing the RBC to change from a biconcave disc to an elongated sickle-like structure.

Chromosomal Disorders

• Chromosomal disorders, conversely, are caused by the absence, excess, or abnormal arrangement of one or more sex chromosomes. 
• Failure of chromatid segregation during the cell division cycle results in the gain or loss of a chromosome(s), called Aneuploidy. 
• Sometimes, though rarely, an additional copy of a chromosome may be included in an individual, or an individual may lack one pair of chromosomes. 
• These situations are known as trisomy or monosomy of a chromosome, respectively. 
• Such a situation leads to grave consequences for the individual. Down’s, Turner’s, and Klinefelter’s syndrome are typical examples of chromosomal disorders.

Examples of Chromosomal Disorders

Down’s syndrome

• The cause of this genetic disorder is the presence of an additional copy of chromosome number 21 (trisomy of 21).
• This disorder was first described by Langdon Down (1866). The affected individual is short-statured with a small round head, furrowed tongue and partially open mouth. 
• The palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded.

Turner’s syndrome 

• Such a disorder is caused due to the absence of one of the X chromosomes, i.e., 45 with X0. 
• Such females are sterile because their ovaries are rudimentary, among other features, including a lack of secondary sexual characteristics.

Klinefelter’s Syndrome

• This genetic disorder is also caused by an additional copy of the X-chromosome, resulting in a karyotype of 47, XXY. Such individuals are sterile.

Cytokinesis failure

• Failure of cytokinesis after the telophase stage of cell division results in an increase in the number of chromosomes in an organism, a phenomenon known as polyploidy. This condition is often seen in plants.

Mitochondrial Inheritance

Mutations in the non-nuclear mitochondrial DNA cause this type of genetic disorder. 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

Conclusion

• To conclude, genetic disorders comprise an extensive array of conditions affecting families and individuals to varying degrees. There is hope in the future that advances will make it possible to diagnose, manage, and even prevent such disorders in some cases, with ongoing research on the relevant genetic mechanisms and therapies.
• Therefore, as the field of genetics evolves, it is imperative for genetic testing and counselling to form part of healthcare, ensuring better outcomes for patients, as well as steering their family planning decisions. Addressing genetic disorders is not only beneficial for the affected individuals but also key to the progress of medical science and public health.

FAQs: Genetic Disorders

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