Question

What aspects of the transmission of scrapie or other spongiform encephalopathies act like genetic diseases? What aspects act like transmittable diseases?

Short answer

Spongiform encephalopathies act like genetic diseases through inheritable mutations in the PRNP gene and like transmittable diseases through transmission of infectious prions.

Step-by-step solution

- Definition of Spongiform Encephalopathies

Understand that spongiform encephalopathies are a group of progressive, invariably fatal, conditions that affect the brain and nervous system of many animals, including humans.

- Understand Genetic Disease Characteristics

Genetic diseases are typically inherited through mutations in DNA, meaning they are passed down from parents to offspring. Consider how certain spongiform encephalopathies may be inherited.

- Identify Genetic Aspects of Spongiform Encephalopathies

Discuss how specific cases of spongiform encephalopathies, such as familial Creutzfeldt-Jakob disease, are inherited due to mutations in the PRNP gene, making them behave like genetic diseases.

- Understand Transmittable Disease Characteristics

Transmittable diseases are those that are spread through direct or indirect contact with an infected individual or their secretions. Consider how spongiform encephalopathies might be transmitted between individuals.

- Identify Transmittable Aspects of Spongiform Encephalopathies

Discuss how diseases like scrapie and variant Creutzfeldt-Jakob disease are caused by prions, which are infectious proteins that can be transmitted between animals and humans, respectively, thus behaving like transmittable diseases.

Key concepts

Genetic Diseases

Genetic diseases are disorders caused by abnormalities in an individual's DNA. These can be inherited from the parents due to mutations in the genes. Mutations can be either dominant or recessive. In spongiform encephalopathies, such as familial Creutzfeldt-Jakob disease (fCJD), the disease is inherited through mutations in the PRNP gene. This gene provides instructions for making prion proteins. When there is a mutation, the prion proteins can misfold, leading to brain diseases.

• Inherited through genes
• Result from DNA mutations
• Can be dominant or recessive

Familial CJD shows how spongiform encephalopathies can inherit genetic traits, making them act like genetic diseases.

Transmittable Diseases

Transmittable diseases spread from one individual to another through various methods such as direct contact or exposure to bodily fluids. Unlike genetic diseases, these are not passed down through DNA. Instead, they are acquired through interaction with an infected individual or environment. Spongiform encephalopathies like scrapie and variant Creutzfeldt-Jakob disease (vCJD) act like transmittable diseases because they can spread between individuals. Prions, the infectious agents in these diseases, cause other proteins to also misfold, spreading the disease.

• Spread through contact
• Not inherited via DNA
• Acquired through interaction

This explains why certain spongiform encephalopathies behave like transmittable diseases.

Prions

Prions are proteins that can fold in multiple ways, one of which is abnormal and disease-causing. Unlike bacteria and viruses, prions lack genetic material but can still replicate by inducing nearby normal proteins to also assume the abnormal prion form. This transformation causes brain damage, leading to diseases such as CJD, scrapie, and kuru. Prions resist traditional methods of disinfection because of their robustness.

• Infectious proteins
• No genetic material
• Cause other proteins to misfold

Understanding prions is crucial to grasp how spongiform encephalopathies can act like both genetic and transmittable diseases.

PRNP Gene

The PRNP gene provides crucial instructions for making the prion protein, known as PrP. This protein is located on the surface of cells, especially in the brain. When mutations occur in the PRNP gene, the PrP protein can misfold, leading to neurodegenerative conditions. More than 30 different mutations in this gene have been linked to inherited prion diseases like CJD and familial insomnia.

• Produces prion protein (PrP)
• Located on cell surfaces
• Mutations lead to diseases

Knowing the role PRNP gene plays helps explain the genetic aspect of spongiform encephalopathies.

Familial Creutzfeldt-Jakob Disease

Familial Creutzfeldt-Jakob disease (fCJD) is a type of spongiform encephalopathy that is inherited. It is caused by mutations in the PRNP gene, making it a genetic disorder. In fCJD, the misfolded prion proteins lead to the death of neurons, resulting in brain damage. Symptoms typically include memory loss, behavioral changes, and coordination problems. Since fCJD is passed down in families, it serves as a clear example of how some spongiform encephalopathies can act like genetic diseases.

• Inherited disease
• Caused by PRNP mutations
• Leads to neuron death

This case illustrates the genetic nature of certain spongiform encephalopathies.