Prion diseases are a special type of severe neurodegenerative ailments of humans and animals. They are characterized by progressive damage to the brain, in most cases they end in a quick fatal outcome.
What are prions?
These are special protein structures. They can be both normal and part of the 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 the so-called nucleic acids - DNA and RNA. Thanks to them, it becomes possible to multiply. Viruses, fungi, birds, animals “contain” nucleic acids. Previously, it was assumed that their absence in tissues means the impossibility of full reproduction. Prion squirrels completely reversed these ideas.
These molecules consist only of protein, but they differ in their 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 requires more time than the multiplication of bacteria or viruses, so it may take several years from the moment a molecule enters the body to develop a disease.
Prion Properties
Prions and prion diseases are highly resistant. Most disinfection methods are ineffective in dealing with them. Prions do not die when boiled, can withstand cold up to -40 degrees Celsius. They do not show sensitivity to UV radiation and radiation, 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 occurrence of a disease.
Prion diseases: a history of discovery
In 1982, Stanley Pruziner first described prion diseases, for which he was later awarded the Nobel Prize.
Long before their discovery, scientists in their works examined a number of pathologies of humans and animals, the cause of which they could not establish for a long time. In the XVIII century in the UK was registered "pruritus" of sheep. The animals suffered from severe itching, impaired movement and seizures, which indicated damage to the central nervous system. In 1957, Carlton Gaitushek described an affliction with the Fore tribe, whose inhabitants lived in the highlands of Papua New Guinea. Pathology was associated with cannibalism and was 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 primarily affected cattle. After a short period of time, “mad cow disease” became epidemic-wide, and prions became the cause of its occurrence. In the 90s, experts proved the transmission of this ailment to humans along with milk and cattle meat.
Currently, a detailed study of diseases with undiagnosed causes has contributed to the fact that scientists have made a number of proposals regarding the prion nature of development. These include Creutzfeldt-Jacob pathology, Alzheimer's disease. Symptoms and signs of these ailments have much in common. Despite large-scale successes in the study of these disorders, much remains beyond the comprehensible.
How does infection happen?
In modern medicine, three methods of infection are distinguished.
- Transmissible. Prions are transmitted from one species of mammal to another. Previously, the existence of so-called interspecific barriers was discussed. This means that transmission from the cow to the person is impossible. Today, scientists refute this point of view. Protein molecules can be transmitted from an infected animal or person. The causes of prion diseases are caused by the consumption of meat / milk of an infected animal, the use of its biological tissues (corneal transplant, blood products, etc.). Different biomaterials have an unequal degree of pathogenicity. The most infectious are the brain tissues, the next step is blood and its preparations.
- Hereditary. The disease develops against the background of a gene mutation that forms in the region of the 20th chromosome. It is this site that is responsible for the presence of a normal prion protein. Its functioning is still poorly understood. In the case of gene mutations, instead of a healthy prion, a pathological one is synthesized, which inevitably leads to the development of ailments.
- Sporadic (spontaneous appearance of an abnormal protein).
Thus, prion diseases can be both hereditary and infectious. Regardless of how the abnormal protein enters the body, it can cause infection in other people.
What causes prions in the body?
Pathological proteins are characterized by the ability to cause spongiform encephalopathies, that is, damage to the central nervous system. From a morphological point of view, this means the formation of cavities in 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 the accumulation of prions, the formation of amyloid plaques is observed. All these processes occur in the absence of obvious signs of inflammation.
What diseases are prion diseases?
Today, scientists can accurately name several ailments caused by abnormal protein structures:
- Creutzfeldt-Jakob disease;
- Kuru disease
- Alpers disease (progressive spongy encephalopathy);
- familial fatal insomnia;
- Gerstmann-Straussler-Scheinker disease.
Next, we consider each pathology in more detail.
Creutzfeldt-Jakob disease
Creutzfeldt-Jakob disease is distinguished by its diversity, so experts divided it into several forms:
- sporadic;
- family;
- iatrogenic;
- new atypical form.
The sporadic variant of the disease was previously considered the most common. Its first symptoms appear after the age of 55 years. However, over the past few years, statistics have changed. After the emergence of information about the epidemic of "mad cow disease", cases of atypical form as a result of infection with cattle were increasingly recorded. This species is characterized by a 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 a headache, sleep disturbance, loss of appetite. Gradually, memory impairment and loss of vision are added to these symptoms. Mental disorders manifest in the form of hallucinations and delirium. The disease is characterized by rapid development, in the last stage it is characterized by complete immobility of the body. A 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 occur about 5 years earlier than with the sporadic variant.
The iatrogenic form develops as a result of infection of a person during surgery. There is no statistical information on this variant of the disease, since it is difficult to prove the pathogenesis of prion diseases. The incubation period varies from 7 months to about 12 years. It is determined by a combination of several factors: the method of penetration of abnormal proteins into the body, their quantity, and the original human genotype. The disease most quickly develops with the direct penetration of prions into the brain tissue as a result of surgical intervention. More time is required for infection against transplantation of the cornea or dura mater. Patients gradually develop cerebellar ataxia, impaired speech and muscle tone, dementia.
"Mad Cow" began to gain relevance after the epidemic in cattle in the 90s. Prion disease, symptoms of which occur between the ages of 30 and about 40, are fatal to humans. As with the iatrogenic variant, neurological signs prevail over mental ones.
Family Fatal Insomnia
This is an autosomal dominant disease that is transmitted exclusively by inheritance. Fatal insomnia is rare. She has been known in science since 1986. Its first symptoms appear between the ages of 25 and approximately 71 years.
The epidemiology of prion diseases of this type is poorly understood. The main symptom of familial fatal insomnia is insomnia. The body gradually loses the ability to fully regulate the phases of wakefulness and sleep. Also, patients develop impaired motor activity and muscle weakness. There are known cases of autonomic disorders, which are manifested by an increase in blood pressure, excessive sweating. Of the mental disorders, panic attacks, visual hallucinations, and short-term episodes of confusion can be noted. Due to constant insomnia, exhaustion occurs, the patient dies.
Kuru's disease
Infectious forms of prions have been studied in detail thanks to this disease, more precisely, the cannibal tribe. Until 1956, the traditions of the so-called ritual cannibalism were widespread among the inhabitants of Papua New Guinea - eating the brain of a dead person. It is believed that one of the members of this tribe developed an infection, which subsequently spread to other people after the ritual. Since the abolition of this tradition, cases of morbidity began to be recorded several times less often, today this ailment practically does not occur.
The incubation period is from 5 to about 30 years. That is why Kuru’s disease is classified as “slow viral infections”. The disease manifests itself in cerebellar disorders along with uncontrolled laughter, swallowing dysfunction, and muscle weakness. In the terminal stage, dementia develops. People with this diagnosis live no more than 30 months.
Alpers disease
The disease mainly develops in young children (under 18 years old). The disease is transmitted by an autosomal recessive type, in the case of the coincidence of two pathogenic genes of father and mother. Among the main symptoms, visual impairment and epileptic seizures can be distinguished . In medical directories, there are descriptions of acute conditions of the disease, proceeding as a stroke. Alpers disease is also characterized by liver damage, which quickly develops into chronic hepatitis and ends with cirrhosis. Patients die due to intoxication within 12 months of the diagnosis of the first symptoms.
Gerstmann-Streussler-Scheinker Syndrome
This variant of the disease is considered a hereditary type. It is very rare (one case per approximately 10,000,000 population). The appearance of the first signs is usually noted in patients after 40 years. The development of the syndrome begins with cerebellar disorders. Dizziness initially appears. As the disease develops, coordinating violations progress, gradually independent movement becomes impossible. Along with the listed symptoms, there are disorders of muscle tone, there is a decrease in vision and hearing, problems with swallowing and sound reproduction. In the terminal stage, doctors record manifestations of dementia. 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 signs of which are of a common nature, develop along a path similar to prion 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 catch these ailments. This means that amyloid fibrils are formed due to spoiled protein molecules, but the "healthy" effect of the "patients" does not apply.
More recently, scientists conducted a number of studies on mice that refuted this assumption. After the introduction of pathogenic proteins into the brain of an absolutely healthy animal, characteristic amyloid plaques appeared in it. This means that pathogenic protein can still infect healthy structures. This discovery belongs to specialists from the University of Texas. In the near future, another work of scientists from London will come out, which proves that Alzheimer's disease, symptoms and signs of the disease can be fully transmitted from one person to another.
Recall that Parkinson's disease is characterized by the gradual death of neurons that produce the dopamine mediator. Because of this, a person is disturbed in the regulation of movements and muscle tone, which is manifested by tremor, general stiffness. Parkinsonism suffers from every 100th person who has crossed a sixty-year milestone. The disease begins its development with slow motion, which is especially noticeable when a person dresses or takes food. Subsequently, speech, swallowing reflexes are disturbed. Unfortunately, today medicine cannot recommend effective treatment for people with a diagnosis of Parkinson's disease. Symptoms and signs of this ailment can be alleviated 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, as a result of which patients develop senile dementia. The first symptoms of this ailment may appear as early as age 40. It is diagnosed in most cases in poorly educated people. A person with a high level of intelligence is more likely to cope with Alzheimer's manifestations due to the numerous connections between neurons.
The disease begins its development with impaired memory. The primary stage usually goes unnoticed by others. The initial symptoms are often tried to hide or attribute to stress and excessive workload. As the disease progresses, the clinical picture changes. The patient ceases to navigate in space, his previously acquired writing, reading skills fall out of his memory. First, the events closest in time are forgotten. When the pathology begins to progress, it is necessary to use every opportunity to maintain a person's ability to self-service, try to prevent the occurrence of depression. A stronger hearing aid or properly selected glasses can help solve this problem. There is no specific treatment for Alzheimer's syndrome. When its primary symptoms appear, it is important to undergo a full examination by a neurologist. Specialists for treatment usually recommend drugs that facilitate the course of the disease and inhibit its development.
Diagnosis of prion diseases
No specific diagnostic measures are currently presented. For example, similar EEG results, as with Creutzfeldt-Jakob disease, are with other brain pathologies. MRI is characterized by low diagnostic significance, since 80% of the examined reveal nonspecific signals. However, this study recognizes brain atrophy. Its severity is exacerbated as prion diseases of a person progress.
Differential diagnosis is carried out with all pathologies, one of the manifestations of which is dementia (Alzheimer's disease, vasculitis, neurosyphilis, herpetic encephalitis and others).
Treatment approaches
Unfortunately, at present, all prion diseases are incurable. Patients are prescribed symptomatic therapy using anticonvulsants, which only alleviates the suffering. The forecast is disappointing. All known diseases of prion nature are fatal to humans.
Currently, scientists from around the world are actively seeking a universal medicine. Studies using animals. It is assumed that in the fight against such ailments, stem cells, as well as the most common yeast, will subsequently be used. Experimental preparations are currently not highly effective, so their appointment is considered inappropriate.
Preventive actions
It is almost impossible to protect oneself from the development of sporadic and hereditary variants of prion diseases. Some pathologies can be excluded by passing a special genetic examination. However, this is very difficult in our country, since laboratories performing such diagnostics are located mainly abroad.
In case of hereditary diseases, it is recommended that you consult with a geneticist before pregnancy. This will help in the future to avoid problems with the health of the child.
In order to protect yourself from Creutzfeldt-Jakob disease, it is recommended to refuse to eat meat from regions where cases of cattle disease are recorded. First of all, we are talking about European countries. Also, drugs made from the blood of animals or humans should not be used in treatment. 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 similar symptoms. Initially, a person’s appetite and vision disappear, coordination in space is disturbed. At the final stage, dementia develops when the patient cannot take care of himself on his own. The result of any disease is always the same - death. Currently, doctors do not have effective means against pathologies of this nature.