**2.4. Use of biomarkers in Marfan's syndrome**

According to the definition of the National Intitutes of Health, a biomarker is "a characteristic that can be quantified and evaluated in an objective way as an indicator of normal biological processes, pathogenic processes or pharmacological answers to a therapeutic intervention" [6]. The employment of biomarkers facilitates the identification of patients at risk, and they are usually molecules that can be identified by a blood analysis.

Nowadays we don´t have many specific bibliography about circulatory biomarkers for the thoracic aortic aneurysm. The not circulatory biomarker that is in use with more frequency is the diameter of the aneurysm.

Below we will detail the biomarkers that could have importance in the clinical management of the thoracic aortic aneurysms, as in Marfan syndrome:

#### *D-dimer*

438 Aneurysm

200 subjects.

used for the genetic study.

a de novo mutation.

pathologies.

clinical follow-up.

d. The familial consegregation must be demonstrated if possible, and the absence of the mutation in at least 40 chromosomes of the same etnia, that is to say, at least in

e. The pathogenicity is high probably in the identified mutations by genetic linkage.

The sensibility to find a mutation in a patient with MFS is high, varying between 76 and 93% in recent studies. It depends on several factors, as the age, the familial history or the method

Marfan syndrome is known as an autosomal dominant connective tissue disorder. Hereby, the risk that a son of an affected father has the disease is 50%. Approximately, 75% of the patients with MFS has one of his parents affected, and only in 25% the affected one presents

The penetration of the mutations in FBN1 is in general high, being considered to be near to 100%. It has been communicated exceptional cases of incomplete penetration. It is necessary

Those patients with severe and progressive forms of the disease (called "The neonatal Marfan Syndrome") usually have mutations in the central part of the gene, between exons 24 and 32 of FBN1. Affected individuals are generally diagnosed at birth or shortly thereafter. Congestive heart failure associated with mitral and tricuspid regurgitation is the main cause of death, whereas aortic diseection is uncommon; survival beyond 24 months is rare. As a general rule, the mutations that produce insertions or deletions with change or displacement of the frame of reading or *splice site mutations*, are usually associated to severer forms of the disease. The patients with mutations that alter the terminal-C-propeptide procesate have been related to predominantly skeletal affectations of the disease. It is evident that it is necessary to compile information about the clinical consequences and the phenotype associated with different mutations, since mutations with the same mechanism can have very different clinical consequences, as it is demonstrated in other genetic

The diagnosis of the MFS can be realized without needing a genetic study. Nevertheless, it

1. It is of great relevancy in patients who do not fulfill clinical criteria, especially in patients with ectopia lentis and patients with cardiovascular suggestive features

2. It is very useful in relatives of affected patients, especially children, to know if they have inherited the mutation of their parents and so they will need periodic controls. 3. It must be realized in patients in whom the genetic diagnosis can influence their way of life, as in high competitive sports, for the initiation of the treatment or programming of

4. It can be useful for prenatal diagnosis, analyzing DNA extracted from foetal cells obtained of the chorionic villus between 10 and 12 weeks´ gestation. It might be done whenever a causal mutation had been identified in the relative, with pathogenicity

combined with skeletal findings or in sporadic cases in young subjects.

to consider that many of the manifestations appear with the age.

has a great importance in the following suppositions:

It has been demonstrated that the concentrations of D-dimer allow to detect the Stanford type A acute aortic dissection. The concentration of the D-dimer obtained during the hospital admission is correlated by the survival of these patients. Thus, elevations in the concentration of D-dimer in patients who come to Emergency Room for thoracic pain it should be realized a tomography computerized to reject acute aortic dissection as well as acute pulmonary embolism.

#### *Cellular biomarkers*

There have been identified two types of cells that are associated with the evolution of an aneurysm, the CD 28 T-lymphocytes and the natural citolytic lymphocytes or natural

killer. It has been demonstrated in studies the presence of population of natural killer lymphocytes in greater number in patients with abdominal aortic aneurysm compared with healthy subjects. The CD 28 T-lymphocytes appear in diverse inflammatory disorders, and express in a more frequent form with the age. It has been observed in patients with aneurysms greater quantity of this cellular type in peripheral blood compared to healthy controls. In addition, on a contradictory way, highest rates are found in patients with smaller aneurysms in comparison with patients with big aneurysms, appearing the hypothesis about the intervention of Cd 28 T-lymphocytes in the genesis of the aneurysms.

#### *Biomarkers in plasma and serum*

Several circulating biomarkers have been identified with the aneurysms, in relation to their appearance, diameter or expansion. These can be classify in inflammation biomarkers, indicators of tissue turnover, and others as homocysteine, serum amyloid A, osteopontin, osteoprotegerin and the concentrations of plasmin / antiplasmin complex.

Inflammation biomarkers have been the more widely studied. At present, the formation of the aortic aneurysm is understood as an inflammatory process. Many studies relate diverse inflammatory cytokines (interleukin-1, interleukin-6, tumor necrosis factor-α, interferon γ and cold-reactive proteins) to the formation, expansion or rupture of the aneurysm. Its disadvantage is the lack of specificity, being able to rise their concentrations in other inflammatory processes, reason why their clinical utility as aortic aneurysm biomarker is limited.

Special mention is deserved to the matrix metallooproteinases (MMPs). Their main function is the degradation of the extracelular matrix. The MMPs are active in many pathological processes, either in trivial ones as periodontitis or others more serious as heart failure. In experimental models with animals, there has been demonstrated that MMP's inhibition, by genetic deletion directed or by pharmacological intervention, determines a minor progression of the abdominal aortic aneurysms. In patients with abdominal aortic aneurysm, the circulating concentrations of MMP-9 presented a direct correlation with the concentrations of MMP-9 in the aortic wall. It has been observed an increase in the concentration of MMP-1 and MMP-9 in the thoracic aortic walls with aneurysms or dissections in comparison with healthy controls. It has also been observed an increase of the quotient MMP-9/TIMP-1 (tissue inhibitor of metalloproteinases-1), favoring the proteolysis of the aortic wall. Other studies have documented a correlation of MMP's activity, especially MMP-9, with the genesis and evolution of the thoracic aortic aneurysms.

#### *Molecular biomarkers*

It has been studied the RNA of circulating leukocytes and there have been identified characteristics of expression that relate to the appearance of thoracic aneurysms, with an accuracy up to 78%. In the same line, there has been identified a hyperexpression of certain genes in patients with thoracic and abdominal aortic aneurysms. Among these genes, we must emphasize those who codify the intracellular adhesion molecule-1, v-yes-1 oncogene, mitogen activated protein kinase and the MMP-9.

In short, it does not exist a perfect biomaker for a pathological process. In case of the thoracic aortic aneurysms, the best described biomarker and with wide diffusion in the clinical practice is the diameter of the same one. Big advances have been achieved in circulating biomarkers, though further study is required to be able to generalize it to the daily clinical practice.
