**4.2 Prothrombin (PTB, factor 2 or F2)**

The G20210A mutation of prothrombin causes a G to A transition at the nucleotide position 20,210. This mutation increases circulating prothrombin activity and levels [13]. PTB is a vitamin K-dependent coagulation factor, which in its active form is cleaved, forming in this way the thrombin. The thrombin catalyzes many other coagulation-related reactions and acts as a serine protease that converts fibrinogen to fibrin. PTB mutations are the second-most common inherited thrombophilia. In the United States, the heterozygous carrier frequency is about 1–2%, accounting for approximately 6–18% of VTE cases. Hyperthrombinemia has been associated with a mutation in the 3′ termination of the PTB gene, called c.∗97G > A, which results in increased production, due to the increased PTB mRNA expression and stabilization. An increased amount of circling prothrombin can lead to higher thrombin generation in the plasma, followed by coagulation activation and thrombosis. This mutation is also more common in the Caucasian population and is rare in other ethnic groups. Homozygosity, for this mutation, is found in about 1 in 10,000 individuals. Transheterozygosity for FVL and prothrombin c.<sup>∗</sup> 97G > A affects about 1 in 1000 individuals. Additional variations identified in the 3′-untranslated region of the prothrombin gene include changes at positions 20,207, 20,209, 20,218, and 20,221. High PTB levels also inhibit APC-mediated inactivation of activated FV and factor VIII. The prevalence of prothrombin G20210A mutation varies in different countries and ethnic groups, being highest in Caucasians, especially those in Southern Europe, and in the Mediterranean region [14].

### **4.3 Polymorphism in the MTHFR enzyme**

Hotoleanu, in his article Genetic Risk Factors in Venous Thromboembolism, described that MTHFR acts on homocysteine metabolism, reducing 5.10-Methylenetetrahydrofolate to 5-methylenetetrahydrofolate. The enzyme polymorphisms generally occur at two sites, at position C677T, which characterizes the substitution of alanine for valine at codon 222, and at position A1298C, which occurs due to the substitution of glutamine for alanine at codon 429, the second mutation being less aggressive than C677T, which is homozygous and in the presence of low levels of folate decreases enzyme activity leading to hyperhomocysteinemia, a risk factor for thrombophilia [15].

Simoni et al. corroborate this theory, when they describe that mutations in the MTHFR enzyme reduce its activity leading to hyperhomocysteinemia. Increase in homocysteine levels is a risk factor for thromboembolism [16].

Considering patients with COVID-19, especially those seriously ill, there are several potential risk factors for venous thromboembolism, including infection, immobilization, respiratory failure, mechanical ventilation, and use of a central venous catheter [17, 18]. Wang et al. reported in their Lancet article that patients at a high risk for venous thromboembolism had worse results with COVID-19 than patients at a low risk for venous thromboembolism, suggesting that these patients may require more attention in the event of rapid deterioration [6].


#### **Table 1.**

*Summary of the data set described by Malas et al. [19].*

A systematic review and meta-analysis done to analyze the thromboembolism risk on COVID-19 patients showed that its occurrence is high and associated with the worst clinical development. A total of 8271 patients from 425 eligible studies were included in the meta-analysis. In summary, the data set showed that COVID-19 patients had a higher risk of mortality, as described in **Table 1** [19].

Our suggestion of early detection and greater attention in COVID-19 patients with aggravating factors of thromboembolism may be addressed to the data found by Wang and colleagues [6]. Considering the correct prophylaxis, the majority of the venous thromboembolism occurrences could be prevented, mainly on patients with a higher risk for it. In spite of that, from the 140 patients investigated in the cohort, only 7% (10 patients) were maintained under anticoagulant therapy during their hospitalization. Among them, one received rivaroxaban and nine received heparin. It is a low proportion compared to the total number of patients with high risk to develop venous thromboembolism in their cohort. This finding possibly indicates that the prophylactic approach applied in the patients with COVID-19 was not adequate.

Other coagulation disorders observed in patients with COVID-19 also support the idea that a preliminary analysis of the genetic factors involved may better guide the therapeutic approach to be adopted. COVID-19-associated coagulopathy and disseminated intravascular coagulation (DIC) are being described as common findings in these patients. It is known that the pathophysiology of DIC associated with COVID-19 differs from that of septic DIC, and in this context both thrombotic and hemorrhagic pathologies must be observed. Thrombosis events in COVID-19 include macrothrombosis (MAT) and microthrombosis (MIT), and it is important to note that the diagnosis of MIT depends on coagulation and fibrinolysis markers. Consequently, molecular nuances can have a major impact on the worsening of the thrombohemorrhagic condition in different individuals [20, 21].

#### **5. Conclusion**

Screening and inclusion of COVID-19 patients with genetic abnormalities in thrombophilic conditions could guide the medical team to identify possible aggravating complication factors even if their patients are not in the group predetermined risk, described by the World Health Organization (WHO) [8].

#### *Biomarkers and Bioanalysis Overview*

The treatment of COVID-19 is based on antiviral therapy, treatment to contain the cytokine storm, and treatment of thrombosis. Rather than providing uniform treatment, a method best suited for severity and stage should be selected. Considering the molecular profile of each individual can be an important tool in this race against time that characterizes care for patients with COVID-19. In this scenario, COVID-19 could be another exponent for a pharmacogenomics approach to the treatment of human diseases and it proved to be a challenge for humanity in the 21st century. The complications, sequels, and deaths took on catastrophic proportions. Despite the speed with which a significant range of vaccines were presented, comprehensive coverage worldwide is likely to face dares.
