Monogenic disease

Monogenic disease
n., plural: monogenic diseases
[ˈmɑː.nəd͡ʒiːnɪk dɪˈziːz]
Definition: Genetic disorder caused by mutations in a single gene

Table of Contents

Monogenic Disease Definition

A monogenic disease is a diseased condition determined by the interaction of a single gene. This is in contrast to a polygenic condition wherein several genes (polygene) are involved. Monogenic diseases result from single-gene mutations that disrupt the normal functioning of the gene’s protein product. Because this entails a single gene, its inheritance pattern tends to adhere to Mendel’s laws of inheritance.

Such genetic diseases, as they are passed down from one generation to the next, can be determined in a predictable manner. Examples are glycogen storage diseases, sickle-cell anemia, Huntington’s disease, and so on.

Synonyms: Mendelian disorder; single-gene disorder; monogenic disorder
Compare: polygenic disease
See also: monogenic trait, monogenic inheritance

Monogenic Disease vs. Polygenic Disease

Polygenic disease is a disease resulting from the effects of the combined action or interaction of multiple genes in contrast to the monogenic disease that is associated with only one gene. Thus, polygenic diseases are often complex diseases. They do not follow a straightforward inheritance pattern, which most monogenic diseases do.

As monogenic diseases follow a pattern based on Mendelian inheritance, their underlying molecular mechanisms are more likely to be identified. Polygenic disorders may also be influenced by environmental factors apart from genetic variations, which further make them more complex, and therefore, the genetic basis may not be easily discerned.

Examples of Monogenic Diseases

Autosomal dominant monogenic disorders:

Familial hypercholesterolemia
Polycystic kidney disease
Neurofibromatosis type I

Autosomal recessive monogenic disorders:

Sickle cell anemia
Cystic fibrosis
Tay-Sachs disease
Phenylketonuria

Sex-linked Monogenic Disorders

In humans, sex-linked monogenic disorders involve the sex chromosomes, X and Y chromosomes.

X-linked monogenic disorders are genetic disorders caused by single-gene mutations in the X chromosome. Males tend to express the disorder when they inherit a faulty gene in the X chromosome since there is no second X chromosome to provide a functional version of the gene.
Examples are hemophilia and Duchenne muscular dystrophy.
Y-linked monogenic disorders are relatively rare genetic disorders associated with single-gene mutations in the Y chromosome. These are very rare diseases, being passed on from men to their sons.
Examples are Y-linked spermatogenic failure and Swyer syndrome.

Mitochondrial Diseases

In humans, monogenic diseases do not only involve the nuclear DNA but may also implicate the mitochondrial DNA (mtDNA). Monogenic disorders involving mtDNA could lead to human diseases inherited exclusively from the mother (since mtDNA is the non-nuclear DNA of the human genome that is passed on from the mother to the offspring).

Genetic Unveiling of Sickle-cell Anemia

Sickle-cell anemia is a monogenic inherited disease involving a mutated human gene (HBB gene) that produces hemoglobin proteins with an atypical structure when oxygen levels are low. This distorts the shape of the red blood cells (RBCs) and renders them less flexible. Sickle-shaped RBCs tend to get stuck in small blood vessels, consequently blocking blood flow.