The 10 Most Common Inherited Diseases

Hereditary diseases are transmitted from parents to children depending on their dominance pattern and the location of the mutations.

Written and verified by el biólogo Samuel Antonio Sánchez Amador.

Last update: 09 July, 2023

Genetics is the secret of life. The chromosomes locked in our somatic cells explain every process that takes place in the body, as through transcription and translation, DNA is converted into proteins, and these are used to form tangible tissues and processes. Unfortunately, there are common inherited diseases that disrupt these mechanisms.

There are more than 6,000 diseases that can be explained by genetics; some of them appear spontaneously or due to a poor distribution of chromosomes in the formation of gametes. Almost all of them meet the same pattern: They’re inherited from parents to children.

The basics of hereditary diseases

Before starting, it’s important to establish a series of criteria. Each human being has in the nucleus of its cells 2 sets of homologous chromosomes and, for this reason, we’re called diploids (2n). This trait is derived from sexual reproduction, as half of our genetic information comes from the maternal ovum (n) and the other half from the paternal sperm (n), which are haploid cells.

When both incomplete gametes come together, a zygote is formed with 23 pairs of chromosomes, or 46 total. In the set of chromosomes that characterize us, we have about 20,000 to 25,000 genes, as indicated by the United States National Library of Medicine. Each of these genes has 2 or more forms, which are known as alleles.

An allele can be dominant (A) or recessive (a). The dominant allele doesn’t require the allele of its homologous partner to be the same in order to express itself phenotypically, so a person can be (AA) or (Aa) for a specific trait and manifest it in both cases. In contrast, a recessive allele requires its partner to be equal to it (aa) in order for it to be evidenced in the phenotype.

Types of inherited diseases

This little introduction was necessary because, in the following lines, we’re going to talk about genetics, homozygous, and heterozygous constantly. Monogenic inherited diseases (which are only encoded by one gene) can be divided into the following categories:

• Autosomal recessive: For a person to manifest it, the 2 alleles that encode it are required to be the same (rr), as it’s a recessive trait (r). The probability that a child inherits this condition from their parents is 25%.
• Autosomal dominant: Only one copy of the conflicting allele is needed for the disease to occur (RR or Rr). Unfortunately, in this case, the probability that a child will be born with the disease is 50%.
• Sex-linked: If the mutation is located on the X or Y chromosome, the pathological balance leans toward the biological male (XY) or female (XX) sex.

The 10 most common inherited diseases

Now we’re ready to explore the 10 most common inherited diseases and their characteristics. We’ll do a brief and simple review, so don’t miss it.

1. Cystic fibrosis

Cystic fibrosis is a disease that causes thick mucus to build up in the lungs, digestive tract, and other areas of the body. Symptoms include a characteristic salty taste to the skin, persistent cough, frequent lung infections, wheezing, shortness of breath, poor growth, and difficulty with bowel movements.

This condition is caused by mutations in the CFTR gene, as indicated by the Rare Diseases portal. In addition, it’s autosomal recessive, which means that it’s linked to a non-sexual chromosome and that the patient must carry two defective copies of the gene. The probability that a child is born ill if both parents are carriers is 25%.

2. Fragile X syndrome

Fragile X syndrome is the most common form of presentation of non-neurotypic patterns in heritable form. This is considered one of the most common hereditary diseases.

The genetics of Fragile X syndrome are complex to decipher. It’s an X-linked dominant condition, but it doesn’t follow normal inheritance patterns. Simply put, it’s encoded by an increase in the number of CGG trinucleotide repeats in the FMR-1 gene. When a pathological threshold is exceeded, the syndrome manifests itself.

Thus, this mutation isn’t immediately expressed in the offspring, but the probability increases between generations. When the number of unit repeats in the defective gene exceeds a threshold (230), fragile X syndrome appears. This disease that causes intellectual disability affects 1 in 4,000 men and 1 in 6,000 women.

3. Hemophilia

Hemophilia is a rare disorder in which the blood doesn’t clot properly. People with this inherited disease lack or have a low amount of clotting factor.

In hemophilia A, the deficit occurs in coagulation factor VIII; in B, it’s IX; and in C, it’s in the XI. Patients are characterized by excessive and sometimes fatal bleeding.

This condition is X-linked and recessive in nature. For a woman to express it, she must present the 2 defective sex chromosomes (XX) for the aforementioned coding factor and gene, while in men, only one failed gene is required (remember that the male sex chromosome is XY). For this reason, almost all hemophiliacs are male.

4. Huntington’s disease

This disease is one of the most common inherited diseases, but it’s still very rare. As the Mayo Clinic indicates, it’s characterized by a constant and progressive degeneration of nerve cells in the brain. It causes movement and thought disorders and psychiatric failure.

Symptoms of the disease appear at any time in the patient’s life, but especially after the age of 30. The mutation that codes for it is found in the HTT gene, located on chromosome number 4, which codes for the huntingtin protein. It’s autosomal dominant, so every person with the genetic defect is bound to present symptoms sooner or later.

5. Duchenne muscular dystrophy

This inherited disease is a type of muscular dystrophy that quickly worsens. It’s caused by a mutation in the gene that codes for the dystrophin protein, although curiously, it often occurs in patients with no clear family history of the disease.

Symptoms are rapid onset and can include fatigue, learning disabilities, chronic muscle weakness (beginning in the legs and pelvis), shortness of breath, breathing problems, and loss of ability to walk (by age 12). Its inheritance pattern is recessive and is linked to the X chromosome.

6. Sickle cell anemia

This alteration of the blood causes the red blood cells to become deformed and acquire a sickle appearance. Red blood cell deformation impairs circulation and triggers vascular obstructions, organic microinfarctions, and hemolysis.

Sickle cell anemia is one of the most common inherited autosomal recessive diseases. It can be explained by a genetic defect located on chromosome 11, specifically in the beta-globin gene, which encodes part of the hemoglobin conformation of red blood cells.

7. Thalassemia

According to the Centers for Disease Control and Prevention (CDC), thalassemia is a type of inherited disorder that occurs when the body doesn’t produce enough hemoglobin. In the absence of this essential part, red blood cells have poorer functioning and live less time.

Although it seems like a simple condition to explain, it should be noted that we’re talking about a group of diverse, broad-spectrum diseases. Thalassemia is called by various names depending on the number of genes affected, and it can range from asymptomatic to life-threatening anemia.

Be that as it may, thalassemia follows an autosomal recessive Mendelian inheritance pattern. Up to 5% of the world’s population carries at least one defective gene in terms of hemoglobin synthesis, which translates into about 4.4 affected newborns per 10,000 deliveries.

8. Tay-Sachs disease

Although this is a very rare disorder in general, it’s one of the most common and famous inherited diseases. Simply put, there’s an accumulation of a fatty substance in the brain. Sick children seem to develop normally during the first few months, but little by little, they lose their faculties.

It’s an autosomal recessive anomaly, that is, carriers don’t manifest the disease, and the affected patient must have two defective copies/alleles for the causative gene. Tay-Sachs disease causes blindness, hearing loss, paralysis, and an inability to learn. Most patients die before 2 years of age.

9. Angelman syndrome

Again, we’re talking about another of the most common hereditary diseases that affect the nervous system in one way or another. This disease is characterized by a delay in psychomotor development, epilepsy, intellectual disability, null linguistic ability, poor motor coordination, and serious difficulties in maintaining balance and walking.

This is a classic example of a hereditary condition dependent on epigenetics, that is, on the action of environments on the genome of the individual. The expression of the genes found in the chromosomal section related to the disease is very different depending on the nature (if it’s paternal or maternal).

10. Spinal muscular atrophy (SMA)

Spinal muscular atrophies (SMA) are a group of inherited genetic diseases that damage and kill motor neurons. These cells control the movement of the arms, legs, face, chest, throat, and tongue, so the symptoms of these types of conditions are mostly motor.

As neurons die, muscles begin to weaken and atrophy. Muscle injuries increase over time and affect all essential biological functions, from speech and swallowing to breathing. The condition is linked to the SMN1 gene, a telomeric copy involved in neuronal maintenance. It’s autosomal recessive.

A diverse group of diseases

Talking about the most common hereditary diseases is to a certain extent, ironic, as all the ones that we’ve mentioned have a very low prevalence compared to others that are acquired over time, such as cancer, type-2 diabetes, or heart disease. These conditions are undoubtedly rare and aren’t often thought about when making a diagnosis.

Many of these diseases are disabling from childhood. Therefore, the patient can’t have offspring and pass the conflicting genes on to their children. The problem lies in recessive conditions because when a parent is a carrier and has no symptoms, it can lead to sick offspring.