Prion diseases: causes, symptoms, diagnosis, treatment

Prion diseases are a special kind of severe neurodegenerative ailments of humans and animals. They are characterized by a progressive lesion of the brain, in most cases result in an immediate fatal outcome.

What are prions?

These are special protein structures. They can be both normal and enter the composition of tissues of healthy people and animals, and pathological, causing various kinds of diseases. A few decades ago it was believed that a living structure must necessarily contain so-called nucleic acids - DNA and RNA. Thanks to them, it becomes possible to multiply. Viruses, fungi, birds, animals "contain" nucleic acids. Earlier it was assumed that their absence in tissues means the impossibility of full reproduction. Prion proteins completely turned these ideas.

These molecules consist only of protein, but at the same time they differ in the ability to multiply. Penetrating into the body, they provoke the transformation of the normal prions contained in it into pathological ones, thereby increasing their number. This process takes more time than the multiplication of bacteria or viruses, so a few years can pass from the moment the molecule enters the body to the development of the disease.

Properties of prions

Prions and prion diseases are characterized by high stability. Most disinfection methods are ineffective in controlling them. Prions do not die by boiling, they can withstand the cold to -40 degrees Celsius. They do not show sensitivity to UV radiation and radiation, they retain their properties when processed with formalin.

The special structure of protein molecules leads to the fact that the human body can not fight them. He is not able to produce antibodies against prions, does not attack them with lymphocytes, as if he does not notice. This means that the penetration of such molecules into the human body entails the emergence of a disease.

Prion diseases: the history of discovery

In 1982, Stanley Prusiner first described prion diseases, for which he was later awarded the Nobel Prize.

Long before their discovery, scientists in their works have studied a number of pathologies of humans and animals, the cause of which for a long time could not be established. In the XVIII century in the UK was registered "scrapes" of sheep. Animals suffered from severe itching, movement disorders and seizures that indicated CNS damage. In 1957, Carlton Gaydushek described the ailment of the Fore tribe, whose inhabitants lived in the highlands of Papua New Guinea. Pathology was associated with cannibalism and transmitted from one person to another.

Since 1986, in England, and then in many other countries, scientists have recorded several outbreaks of the disease, later called "mad cow disease". It mainly affected cattle. "Mad cow disease" after a short period of time acquired the scale of the epidemic, and the cause of its emergence were prions. In the 90s, specialists proved the transmission of this disease to a person along with milk and cattle meat.

At present, a detailed study of diseases with undetected causes has contributed to the fact that scientists have made a number of proposals regarding the prion nature of development. These include the Creutzfeldt-Jakob pathology, Alzheimer's disease. Symptoms and signs of these ailments have much in common. Despite the large-scale successes in the study of these disorders, much remains beyond the comprehensible.

How does the infection occur?

In modern medicine, there are three ways of infection.

1. Transmissible. Prions are transmitted from one species of mammal to another. Earlier it was said about the existence of so-called interspecific barriers. This means that the transfer from the cow to the person is impossible. Today, scientists refute this view. Protein molecules can be transmitted from an infected animal or human. The causes of prion diseases are caused by the consumption of meat / milk in an infected animal, the use of its biological tissues (corneal transplantation, blood preparations, etc.). Different biomaterials have a different degree of pathogenicity. The most contagious are the tissues of the brain, the next step is occupied by blood and its preparations.
2. Hereditary. The disease develops against the background of a gene mutation that forms in the region of the 20th chromosome. This area is responsible for the presence of normal prion protein. Its functioning is still poorly understood. In the case of gene mutations, instead of a healthy prion, a pathological mutation is synthesized, which inevitably leads to the development of ailments.
3. Sporadic (spontaneous appearance of abnormal protein).

Thus, prion diseases can be both hereditary and infectious. Regardless of how an abnormal protein enters the body, it can cause other people to get infected.

What causes prions in the body?

Pathological proteins are characterized by the ability to cause spongiform encephalopathy, that is, CNS damage. From a morphological point of view, this means the formation of cavities in the brain cells, the death of neurons, the growth of connective tissue in their place and the final atrophy of the brain. Against the background of a cluster of prions, formation of amyloid plaques is observed. All these processes occur in the absence of obvious signs of inflammation.

What diseases are prionic?

To date, scientists can accurately identify several ailments, the cause of which are abnormal protein structures:

• Creutzfeldt-Jakob disease;
• Kuru disease;
• Alpers disease (progressive spongiform encephalopathy);
• Familial fatal insomnia;
• The Gerstmann-Streussler-Sheinker disease.

Next, consider each pathology in more detail.

Creutzfeldt-Jakob disease

The Creutzfeldt-Jakob disease differs in its variety, so the specialists divided it into several forms:

• Sporadic;
• Family;
• Iatrogenic;
• New atypical form.

The sporadic variant of the disease was previously considered the most common. His first symptoms appear at the age of 55 years. However, in the last few years, statistics have changed. After the appearance of the information about the epidemic of "mad cow disease", cases of atypical form due to infection with cattle began to be recorded more often. This species is characterized earlier appearance. In most cases, young people suffer. Symptoms of the disease are divided into two conditional groups: neurological and mental. Initially, the infected have headache, sleep disturbance, decreased appetite. Gradually, these symptoms are added to memory impairment, loss of vision. Mental disorders manifest themselves in the form of hallucinations and delusions. The disease is characterized by rapid development, in the latter stage is characterized by complete immobility of the body. The person loses control over the function of the pelvic organs. With this diagnosis, people live no more than two years.

The appearance of the family form is due to mutations at the gene level in the zone of the 20th chromosome. The disease is characterized by an autosomal dominant character. The first signs appear about 5 years earlier than in the sporadic variant.

Iatrogenic form develops due to infection of a person during surgical intervention. Statistical information on this variant of the disease is absent, since it is difficult to prove the pathogenesis of prion diseases. The duration of the incubation period varies from 7 months to about 12 years. It is determined by a combination of several factors: the way of penetration of abnormal proteins into the body, their quantity, the initial genotype of a person. The fastest disease develops with the direct penetration of prions into the brain tissue as a result of surgical intervention. More time is required for infection with corneas or dura mater transplantation. Patients gradually develop cerebellar ataxia, speech and muscle tone disorders, dementia.

"Mad rabies" began to acquire relevance after the epidemic in the cattle in the 90's. Prion disease, the symptoms of which occur between the ages of 30 and about 40, are fatal to humans. As with the iatrogenic variant, neurological signs predominate over the psychic.

Family fatal insomnia

This disease is an autosomal dominant character, which is transmitted exclusively by inheritance. Fatal insomnia is rare. She has been known in science since 1986. Its first symptoms appear at the age of 25 years to about 71 years.

The epidemiology of prion diseases of this type is poorly understood. Insomnia is the main symptom of familial fatal insomnia. The body gradually loses the ability to regulate fully the phases of wakefulness and sleep. Also, patients have impaired motor activity and muscle weakness. There are cases of autonomic disorders, which are manifested by increased blood pressure, excessive sweating. Of mental disorders, it can be noted panic attacks, visual hallucinations and short-term episodes of confusion. Due to the constant insomnia, the body is exhausted, the patient dies.

Kouru disease

Infectious forms of prions have been studied in detail due to this disease, more precisely, the tribe of ogres. Until 1956, among the inhabitants of Papua New Guinea, the traditions of so-called ritual cannibalism-the eating of the brain of a deceased person-were common. It is believed that one of the members of this tribe had an infection, which subsequently spread to other people after the ritual. Since the abolition of this tradition, cases of morbidity have become fixed several times less often, today this ailment practically does not occur.

The duration of the incubation period is from 5 to about 30 years. This is why Kuru's disease is classified as a "slow viral infection". The disease manifests itself in cerebellar disorders with uncontrolled laughter, swallowing dysfunction and muscle weakness. In the terminal stage, dementia develops. People with this diagnosis live no more than 30 months.

Alper's disease

The disease mainly develops in young children (up to 18 years). The disease is transmitted by autosomal recessive type, in case of coincidence of two pathogenic genes of the father and mother. Among the main symptoms can be a violation of vision and epileptic seizures. In medical reference books there are descriptions of acute conditions of the disease, proceeding according to the type of stroke. Alper's disease is also characterized by liver damage, which quickly develops into chronic hepatitis and ends with cirrhosis. Patients die due to intoxication of the body within 12 months from the time of diagnosis of the first symptoms.

The Gerstmann-Streussler-Sheinker Syndrome

This variant of the disease is attributed to the hereditary type. It is very rare (one case for about 10 million people). The appearance of the first signs is usually noted in patients after 40 years. The development of the syndrome begins with cerebellar disorders. Initially there is dizziness. As the development of the disease progresses, coordination disorders, gradually independent movement becomes impossible. Along with the listed symptoms there are violations of muscle tone, there is a decrease in vision and hearing, problems with swallowing and sound reproduction. In the terminal stage, doctors fix the manifestations of dementia. The life expectancy of patients with this diagnosis is up to 10 years.

Alzheimer's Syndrome and Parkinson's Disease

Alzheimer's syndrome and Parkinson's disease, the symptoms and symptoms of which are of a general nature, develop in a way similar to the prion path ailments. Molecules of beta-amyloid, tau protein and other structures also form deposits of pathogenic nature in the brain tissues. However, it is impossible to become infected with these ailments. This means that amyloid fibrils are formed due to spoiled protein molecules, but the "healthy" effect of "sick" does not apply.

More recently, scientists have conducted a number of studies in mice that have refuted this assumption. After the introduction of pathogenic proteins into the brain of an absolutely healthy animal, characteristic amyloid plaques appeared. This means that the pathogenic protein can still infect healthy structures. This discovery belongs to experts from the University of Texas. In the near future there will be another work of scientists from London, which proves that Alzheimer's disease, symptoms and signs of ailment can be fully transmitted from one person to another.

Recall that Parkinson's disease is characterized by the gradual death of neurons that produce a mediator dopamine. Because of this, a person is disturbed by the regulation of movements and muscle tone, which is manifested by tremors, general stiffness. Parkinsonism affects every hundredth person who has crossed the sixty-year mark. The disease begins its development with slow motion, which is especially noticeable when a person dresses or takes food. Subsequently, speech is broken, swallowing reflexes. Unfortunately, today medicine can not recommend effective treatment to people diagnosed with Parkinson's disease. Symptoms and signs of this ailment can be mitigated by symptomatic therapy. However, most of these drugs cause a number of side effects.

Alzheimer's syndrome is a disease characterized by the death of neurons, which results in senile dementia in patients. The first symptoms of this illness can appear at the age of 40 years. In most cases, it is diagnosed in poorly educated people. A person with a high level of intelligence is more likely to cope with the manifestations of Alzheimer's due to the numerous connections between neurons.

The disease begins to develop with memory impairments. The primary stage usually goes unnoticed to others. The initial symptoms are often trying to hide or write off on stress and excessive workload at work. As the disease progresses, the clinical picture changes. The patient ceases to orient in space, from his memory the skills of writing, reading acquired earlier fall out. First, events that are close in time are forgotten. When pathology begins to progress, it is necessary to use every opportunity to maintain a person's ability to self-service, to try to prevent the onset of depression. In solving this problem can help a stronger hearing aid or properly selected glasses. There is no specific treatment for Alzheimer's syndrome. When there are primary symptoms it is important to undergo a complete examination with a neurologist. Specialists for treatment usually recommend drugs that facilitate the course of the disease and restrain its development.

Diagnosis of prion diseases

Specific diagnostic measures are not currently available. For example, similar results of EEG, as in the case of Creutzfeldt-Jakob disease, occur in other pathologies of the brain. MRI is characterized by low diagnostic significance, since 80% of the examinees identify nonspecific signals. However, this study makes it possible to recognize the atrophy of the brain. Its severity is exacerbated as the human prion diseases progress.

Differential diagnosis is performed with all pathologies, one of the manifestations of which is dementia (Alzheimer's disease, vasculitis, neurosyphilis, herpetic encephalitis and others).

Approaches to treatment

Unfortunately, at present all prion diseases are incurable. Patients are prescribed symptomatic therapy using anticonvulsants, which only alleviates suffering. The forecast is disappointing. All known diseases of prion nature are deadly to humans.

Now scientists from all over the world are actively searching for a universal medicine. Studies are conducted using animals. It is assumed that stem cells, as well as the most common yeast, will subsequently be used to combat these ailments. Experimental preparations currently do not have a high efficiency, therefore their purpose is considered inexpedient.

Preventive actions

From the development of sporadic and hereditary variants of prion diseases, it is almost impossible to secure yourself. Some pathologies can be excluded by going through a special genetic examination. However, this in our country is very difficult, because the laboratories performing this kind of diagnostics are mainly abroad.

In the case of hereditary diseases before pregnancy, it is recommended to consult with a geneticist. This will help in the future to avoid problems with the health of the child.

In order to protect themselves from Creutzfeldt-Jakob disease, it is recommended that meat should not be eaten from regions where cases of cattle disease are documented. First of all, we are talking about European countries. Also, do not use in the treatment of drugs made from the blood of animals or humans. It is better to replace them with synthetic analogues.

Prion diseases are insufficiently studied forms of infectious and hereditary lesions that occur in the human body against the background of the penetration of abnormal proteins. In most cases, they affect the central nervous system. The clinical picture is characterized by a similar symptomatology. Initially, a person's appetite and vision are lost, coordination in space is disrupted. At the final stage, dementia develops, when the patient can not take care of herself. The result of any disease is always the same - death. Currently, doctors do not have effective means against pathologies of this nature.