The causes of Crohn’s disease

Schematic of NOD2/CARD15 gene.

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The Causes of Crohn’s disease are still unknown. However, statistical studies (that do not give causative explanations but only strong suggestions) indicate that Crohn’s disease may be caused by both genetic and environmental factors (in other words a genetic predisposition may enhance the effects of an environmental factor). Today, I don’t want to just list the causes but I want also try to explain the scientific method used to achieve this knowledge.

Genetic Cause:

1)    To determine whether a disease has genetic causes the first thing to do is to statistically study the frequency of a disease first in a population (as shown in the previous post) and subsequently compare with the frequency in a specific family whose members show the pathology. If the frequency of the disease within the family members is higher than the average frequency of the general population, a genetic cause of the disease is highly probable (because the genetic errors are transmitted from parents to the offsprings).

Þ   As reported  by Satsangi and colleagues (see the paper here), statistical studies from clinical data show that 5-10% of Crohn’s disease patients have a first-degree relatives with the same pathology with a concordance for disease type (see previous post) of about 70-80%.  Therefore, the risk of developing Crohn’s disease for a person with a first-degree relative with the disease is about 15 times higher than the average risk in the population. Particularly important studies involve twins: a much higher correlation of Crohn’s disease is calculated in monozygotic twins (37%; twins with identical genome) than in dizygotic twins (7%; twins with non-identical genome).

2)    The second step is to find the gene or the genes responsible for the pathology that have been transmitted from parents to their children. One of the most common strategies used by scientist is the Genome Wide Scan to identify susceptibility loci (or region) in the Chromosomes. This approach consists in sequencing small regions (marker sequences such as micro-satellites, SNPs, RFLPs, etc…) throughout genome of all the members of an affected family in order to identify chromosomal loci transmitted with high frequency to the sick members of the family and with less frequency to the healthly members. The analysis of those frequencies using dedicated algorithms is called genetic linkage (for more technical information check here) and allow to find susceptibility loci where it is possible to identify and subsequently study several genes.

Þ   Using this approach, no single locus has been found but many susceptibility loci have been described on chromosomes 1, 3, 5, 6, 12, 14, 16 and 19 (for references see Baumgart and Carding). This result implicates that Crohn’s disease is a polygenic disease making even more difficult the challenge to describe the causes. More detailed studies have linked specific genes to the diseases: Nod2/Card15 a pattern recognition receptor involved in immune response against microbes present in the intestinal tract and its mutations have been associated with Crohn’s disease in white population; Mhc (major hystocompatibility complex) receptor responsible for the presentation of intracellular proteins to lymphocytes.

3)    Once the responsible genes are identify by statistical analysis, the scientists start studying the function of the proteins (codify by the genes) within the cell and how its disruption may affect the cell and the immune-response as whole. The possible experiments to be performed are in such a big number (depending also from the function of the protein its-self) that it is not possible to list them all. However, some common approaches are often very informative. One example is the disruption of the homologue gene (gene with the same function in a different specie) in a mouse model called “knockout” that allows to subsequently study the phenotype of the animal and the molecular outcome.

Þ   Structural studies of NOD2 have shown that it consists of 3 domains: a CARD domain responsible for activation of a signaling protein NFkB, a NOD domain responsible for the oligomerisation of the protein and a Leucine-rich region responsible for bacterial recognition (typical example of the modular structure of the proteins).

Þ   The knockout mouse model for NOD2 do not fully fit the human Crohn’s disease (further suggesting the multi-factorial causes for this disease) but it gives important notions. The absence of a functional NOD2 alter normal signaling within the intestinal cells leading to abnormal activation of NFkB and production of pro-inflammatory cytokines (which may be one cause of the chronic inflammation). It will be interesting also understand if and how a deregulation of NOD2 in intestinal cells may influence the activity of so called T helper 1 lymphocytes.

 

Environmental causes:

The evidences for environmental factors rely entirely on statistical analysis and therefore have to be intended only as suggestion of causes (for references see Baumgart and Carding).

The LIFE STYLE may be one of the major factors:

  • Smoking drastically aggravates the course of Crohn’s disease accelerating the need for surgical intervention.
  • Bacterial or viral infection may trigger an excessive immune-reaction
  • Excessive sanitation may reduce the exposure of children and adults to microbial and other environmental antigen limiting the fully maturation of mucosal immune system that subsequently may over-react to safe bacteria or antigen.
  • Stress seems to increase the incidence of relapse in patient with quiescent disease.
  • Diet may play a role although weak data are presented so far.

 

Many other studies will be required for a fully understanding of the molecular mechanism involved and the cells interaction. Remained tuned on E-ducereX to be updated!

 

The reasons for Flu Vaccines

3D model of an influenza virus.

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WHY: Why are the World Health Organisation and many countries so worry about the Pandemic Flu?

The influenza viruses are able to rapidly infect a high number of people and to rapidly spread around the world, nowadays helped by the globalization. Pandemics of influenza are present since our ancestors, with different rate of death in the population. The most lethal recorded pandemic flu was after the First World War (’18-’19). The “Spanish” flu hit worldwide causing between 50 to 100 million deaths. Below you can see the kinetics of deaths (as the weekly number of deaths per 1000 persons): the “Spanish” flu hit in 3 waves (spring ‘18, winter ’18-‘19, spring ’19).

Figure taken from Jeffery K. Taubenberger and David M. Morens, Emerging Infectious Disease, 2006. The figure shows weekly combined influenza and pneumonia mortality in the United Kingdom, 1918–1919.

Since then, biological research made a lot of improvements: in 1933 the influenza virus was isolated (Smith et al. Lancet 1933;2:66-68), strong antibiotics have been discovered to treat opportunistic infections, hygiene conditions and containment measures have been improved, antiviral drugs have been developed.

However, the WHO estimates that every year the influenza hits up to 1 billion people worldwide of which 3 to 5 million cases result in severe disease and between 300,000 and 500,000 deaths annually.

How: how do we design flu vaccines?

The Influenza virus is a RNA virus with 8 chromosomes. These features make Flu virus highly susceptible to spontaneous mutations and rearrangement between strains eluding the immunological response. This explains why an individual can be infected multiple times during his life. Lambert and Fauci, on New England Journal of Medicine, summarize life cycle of influenza virus, highlighting the step where immune response act to stop infection.

Vaccines can be used to control influenza infections. However, the high mutagenesis rate of influenza deny the possibility of eradicating flu virus with one vaccine. That means that seasonal flu vaccines, in contrast to other vaccines, are used as prophylactic treatment and not to prevent the pathology in general. “Universal” vaccines, which protect against a wide range of flu strains, are needed.  Wei and colleagues published in Science (Vol. 329 no. 5995 pp. 1060-1064) how a two step vaccination strategy can elicit production of antibody-reactive against multiple influenza virus strains. The tab below shows the flu-reactive antibody titer following vaccination strategies.

Who: who shall we vaccinate?

The pathology cause by influenza virus is usually quite mild. It is therefore usually useless to get vaccinated as the pathology itself elicits a more potent immune response and consequentially immune “memory”. The statistics indicate that the majority of death due to influenza, occur in the elderly population, hitting in particular persons with chronic pathologies that compromise their health. It is therefore important to use the seasonal flu vaccines as prophylactic treatment to protect those weak people. To reach optimal results, vaccination treatment on a wider scale should be used once a “universal” vaccine will be completely developed, in the attempt to eradicate also this disease from hearth as for smallpox.

Vaccination: the success over infectious diseases

None - This image is in the public domain and ...

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As I mentioned in “The idea behind Educere X” , studying science helps to demolished wrong prejudices that negatively impact on human life. Today I want to demolish the prejudice against Vaccination and to demonstrate instead that vaccines are one of the main cause for improvement of world health.

Historically, vaccination has been seen as an invasive treatment associated with subsequently pains and in some cases the transmission of the disease it was aimed to protect from. In addition, most of the vaccination campaigns were imposed by governments that can be easily corrupted by the giant pharmaceutical companies, which look for increasing their business. These elements may explain why vaccines are still considered suspiciously nowadays, although vaccination has reached such impressive results (like eliminating the small pox virus as a epidemic pathogen) and many incredible advances has been achieved in vaccine design and safety. The concern for vaccines is also expressed by many blog where they describe a conspiracy for reducing world population. So let’s apply the scientific method to answer the question:

Are the vaccines useful for human health and survival?

  • We can split the question above in 2 easier questions: Are the vaccines able to protect against pathogens?

Here I report a typical experiment performed in mouse model to determined that vaccination protect from disease caused by a pathogens:

The experiment is performed in parallel by treating a mouse with a vaccine consisting of attenuated pathogens emulsionated into adjuvant (that help to stimulate the immune response) and a mouse treated only with emulsionated adjuvant in a physiologic solution. If later (a month or so) the mice are infected by the living pathogens, the vaccinated one will remain completely healthy while the non-vaccinated one will develop the symptoms of the disease. This evidence is further sustained by the mechanistic correlation between protection and the systemic antibody level as shown by the plot on the right. It is easy to observe that while non-vaccinated mouse does not produce any antibody against the pathogen, the vaccinated one has a pick of antibody production some days after vaccination (usually around 7 days). The antibody level drops after pathogen clearing but didn’t go back to zero. The residual amount of antibody in mouse system (indicating the presence of long- living lymphocyte B memory cells that produce antibody) represents the “memory” of the immune system that is able to promptly protect against an infection of the same pathogen keeping healthy the vaccinated mouse. This process occurring during a vaccination can be repeated many times obtaining always the same result: protection of vaccinated mouse from the pathogens.

  • Is this true also for human being?

That’s is definitely the case. The biggest success of vaccination is the world eradication of the smallpox virus. After being firstly described by Edward Jenner in 1796 with an unethical experiment on a 8 years old boy (a kind of experiment as shown above), the smallpox vaccines protect millions of people in Europe. As described in the 1996 annual report, a project of the World Health Organization (WHO) aimed to use the vaccination to prevent the 10-15 million people per year getting sick with 2 million people per year dieing in the poor countries. After 10 year of vaccination the small pox was eradicated from hearth. Nobody is infected by small pox anymore, since 30 years (1980 is the official declaration of smallpox eradication http://globalhealthchronicles.org/smallpox). They also proof the economical convenience of the vaccination campaign: they spent 313 million $ that have been largely repaid by saving on international surveillance activity and medical treatments, without considering the invaluable saving in human life.

Strengthened by this success, the WHO is now aiming to eradicates many other diseases of the third word countries by vaccinations: typhoid diarrhea, diarrheal disease caused by rotavirus, Streptococcus pneumoniae, Haemophilus influenzae and others. The GAVI association (http://www.gavialliance.org/index.php) strongly contribute in fund rising.

However new infectious disease are becoming predominant as killing agent such as West Nile virus, Dengue Virus and some old infection agent are still predominant such as malaria and AIDS because of lack in efficient treatments.

The research community is challenged to find treatment for these diseases. To reach this aim, money shouldn’t be the priority of government and pharmaceutical companies that deliberately don’t invest in this kind of research because the poor countries cannot buy the vaccines.