Mendelian Disorder in Human

Mendelian disorders are a form of genetic disorder that is caused by the inheritance of single or multiple mutant genes from one or both parents. The function of the mutant gene determines how severe a Mendelian disorder is. The condition is typically severe if the gene controls a crucial function. Mendelian diseases include, for instance, Tay-Sachs disease, sickle cell anemia, and cystic fibrosis. These illnesses can be fatal and range in severity from mild to severe.

What are Mendelian Disorders?

Mendelian disorders are genetic disorder that is caused by a mutation in one or sometimes multiple genes. These mutations lead to several disorders like cystic fibrosis, sickle cell anemia, etc. These disorders can range from mild to life-threatening and follow the principles of mendelian disorders. To understand this let’s first understand the principles of mendelian disorders.

Principle of Mendelian Disorders

Johann Gregor Mendel outlined these principles in 1822. He has investigated how pea plants inherit traits genetically. He came to the conclusion that genes are passed in pairs and independently (one from each parent) to children as dominant or recessive traits. Nonetheless, mendelian problems would result from any mutations that occur in these genes. Both the autosomes and the sex chromosomes are susceptible to mutation. Thus, pedigree analysis can tell whether a mutation affects the sex chromosomes or the autosomes.

Types of Mendelian Disorders

The different types of Mendelian Disorders according to Mendel’s laws of inheritance are as follows:

Autosomal Recessive

Both sexes exhibit autosomal recessive characteristics equally. Nevertheless, these characteristics only manifest in the affected person when they have inherited one allele from each parent. The recessive allele frequently passes through several generations without producing the characteristic. Tay-Sachs disease is a well-known instance of a disorder brought on by autosomal recessive genes. Some qualities are able to cross generations.

Autosomal Dominant 

Both males and females can pass on autosomal dominant features to the next generation. They occur equally frequently in both sexes. This kind of trait does not pass from one generation to the next since each individual who carries it must have inherited the allele from at least one parent. For example- hypercholesterolemia is a condition where the blood cholesterol is greatly increased due to an effect on cholesterol transport.

X-linked Dominant

This mutation exists as a dominant allele on the X chromosome. One mutant gene on the X chromosome can generate a sex-linked dominant illness. An example of such an X-linked dominant trait is hyperphosphatemia, a bone-deforming disorder brought on by faulty phosphate transport.

X-linked Recessive

This mutation exists as a recessive allele on the X chromosome. Due to the fact that he contains just one X chromosome, a male who carries this mutation will be impacted. A female who carries a gene mutation in one X chromosome but has a normal gene on the other X chromosome usually has no symptoms. A condition that is inherited in this way is hemophilia A, or classical hemophilia. A protein necessary for the blood to clot is absent in people with this disease.

Example of Mendelian Disorder

Some of the most common mendelian disorders are as follows:

Hemophilia

It is a genetic disease, which prevents blood from clotting normally, even slight accidents can result in significant bleeding. Hemophilia is an autosomal recessive condition in which the body is unable to manufacture the clotting proteins.

Color blindness

A recessive sex-linked condition known as color blindness occurs when the eye cannot tell the difference between red and green. The gene for normal vision is dominant. X-chromosomes carry the normal gene and its recessive allele.

Sickle-cell anemia

It is an autosomal genetic condition that affects the hemoglobin molecules, the protein that carries oxygen in red blood cells. Red blood cells with sickle shapes are formed when mutant hemoglobin molecules bind to one another and form stiff, rod-like formations. These cells are rigid and have an uneven shape, which makes them difficult to pass through the smallest blood channels. In certain veins, RBCs frequently build up and form clots.

Phenylketonuria

Phenylketonuria (PKU) is an inherited recessive disorder during which the levels of an amino acid called phenylalanine are increased in the blood. This means that both alleles of the gene in each cell have mutations. Both the parents of an individual with this autosomal recessive condition carry one copy of the mutated gene each, but they act as carriers of the disease.

Cystic fibrosis

It is a genetic recessive disorder in which the lungs and the digestive system get blocked with abnormally thick and sticky mucus. Cystic fibrosis is caused by a single recessive gene that regulates the enzyme responsible for producing the glycoprotein. Both copies of the gene in each cell have mutations because this disorder is inherited in an autosomal recessive way.

Tay-Sachs disease

The brain deteriorates as a result of the genetic, Tay-Sachs illness. The Tay-Sachs allele encodes a defective version of the hexosaminidase A enzyme, which causes the disease. Gangliosides, a group of lipids found in the lysosomes of brain cells, are broken down by this enzyme. As a result, gangliosides accumulate in the lysosomes, which then expand and finally burst, releasing oxidative enzymes that cause cell death. This condition has no known treatment. Moreover, this illness has an autosomal recessive inheritance pattern.

How are Mendelian Disorders Diagnosed?

Mendelian illnesses can be diagnosed by a variety of approaches. One of the more popular ways to diagnose chromosomal abnormalities or gene mutations is through DNA testing. A Mendelian disorder risk assessment is another service offered by genetic counselors. It may be possible to determine people who may be at a higher risk of acquiring a Mendelian condition by looking at their family history. Moreover, certain Mendelian diseases like cystic fibrosis and sickle cell anemia can be identified by blood tests.

Conclusion

Mendelian disorders are a type of genetic disorder that is caused by the inheritance of a mutated gene from one or both parents. These disorders can range from mild to severe and may be life-threatening in some cases. common Mendelian disorders include cystic fibrosis, sickle cell anemia, phenylketonuria, Tay-Sachs disease, Huntington’s disease, and Down syndrome. Diagnosis of these disorders involves DNA testing, genetic counseling, family history, and blood tests. Treatment options for Mendelian disorders include medication, surgery, and lifestyle changes. The prognosis for Mendelian disorders is generally favorable, and with prompt treatment, most individuals can lead fulfilling lives.

FAQs on Mendelian Disorders

Question 1: What are Mendelian Disorders?

Answer:

Mendelian disorders are genetic disorders that occur due to mutation in genes.

Question 2: Give some examples of Mendelian Disorders.

Answer:

Sickle cell anemia, hemophilia, cystic fibrosis, etc.

Question 3: What is Thalassemia?

Answer:

Thalassemia is an X-linked recessive disease in which the body produces an abnormal amount of the protein, hemoglobin. It is caused by a single allele mutation in the HBA1 and HBA2 genes.

Question 4: Which disorders do not Skip Generations?

Answer:

Autosomal dominant traits.