STATEMENT OF THE PROBLEM

The currently available methods to detect susceptibility to periodontal diseases are

mostly based on subjective approaches, such as a patient’s family history, systemic

conditions or environmental exposures.

Recent advances in molecular genetics allowed the scientific community to search for

mechanisms to detect susceptibility on the genetic level. The new genetics could

expand our knowledge regarding the human molecular pathology. The main goal of

that approach is to develop successfiil methods for the diagnosis and prevention of

some common genetic diseases.

The new genetics have developed new methods that allow the finding o f the mutations

in human genes and their flanking regions. To date examples o f single base changes,

deletions of one or more bases or of entire genes, initiation or termination mutations

and mutations in the regulatory areas in the flanking regions of structural genes have

been found across the whole genome. These mutations which result in changes o f gene

expression, may explain, the variable clinical phenotype in many genetic diseases. So,

the development o f methods that could accurately predict the phenotypes associated

with different mutations may have huge prognostic value in the management o f many

diseases.

Restriction fragment length polymorphisms (RFLPs) were introduced by Kan and

Dozy (1978) and by Botstein et al. (1980). These polymorphisms were the first DNA

As discussed, they are based on a single base pair change that creates or removes a

cleavage site for a specific restriction enzyme. These variations are inherited.

Several studies have attempted to find associations between specific genetic markers

and infectious and autoimmune diseases. Also, as periodontal disease is an infectious

disease some investigators have tried to find a link between the same specific genetic

markers and periodontal disease onset and severity.

The association studies attempt to correlate the frequencies of specific polymorphisms

with disease expression. According to Pericak-Vance (1998) “ ...there are two types of

association studies. Case-control studies compare allele fi*equencies in a set of

unrelated affected individuals to a set of matched controls. The control populations

should be matched with respect to ethnicity as well as other factors such as age.

Family-based studies control for the possibility o f genetic differences between the case

and control populations by comparing the frequencies of alleles transmitted to the

affected child to the alleles not transmitted. The only samples necessary are those from

the affected individual and his or her parents (the TDT triad)..

Evidence for a genetic influence on periodontitis comes from multiple sources

including segregation analyses in families, linkage studies, twin studies of adult

periodontitis, and the association of periodontitis with certain Mendelian inherited

diseases (Hart 1994, Michalowicz 1993 and 1994, Moses et al. 1994). Additional evidence emerged from identification of genetic polymorphisms that correlate with

immune response phenotypes found in patients with periodontal disease (Komman et

The genetic polymorphisms examined have, for the most part, been in cytokine genes

and affect the regulation of transcription o f the cytokines, inducing alterations on the

production o f the respective cytokines. It is believed that as periodontal disease is

infectious it is possible higher levels of IL-1, IL-6, TNFa in the periodontium are

harmful to the host, leading to the severe destruction o f host tissues seen in

periodontitis (AGP or CP). These factors are important mediators o f the inflammatory

process. IL-lm acts as a suppressor of IL-1 activity, therefore mutations in IL-IRN

gene that influence the levels and the activity of IL -lm may result in even more severe

destmction o f periodontal tissues. Polymorphism in the IL-10 cluster that result in

reduced function or concentration of this antinflammatory cytokine, probably is a risk

factor of developing periodontitis. Also, as genetic polymorphisms in the VitD

receptor (VDR) have been associated with bone mineral disorders, like osteoporosis,

these could be risk factors of periodontal diseases, as bone loss is one o f the symptoms

o f these diseases. Furthermore, TLR4 is part of the innate immunity that is the first

line of defence against invading microorganisms and different polymorphisms of that

Toll receptor could explain the different susceptibility to sepsis among different

species and the species-specific responses to LPS stmcture. So, VDR and TLR4

polymorphisms are other genetic variations that could be susceptibility factors of

periodontitis. Thus, all the above polymorphisms could be good targets for association

studies.

In fact, the literature presents a number of positive associations between

despite several attempts to identify genetic markers for susceptibility to periodontal

disease, no definitive conclusion exists.

Hypothesis

Functional polymorphisms found in the genes involved in the immunoregulated

process are associated with increased risk to develop periodontal disease and may

influence the age of onset, the severity and the rate of progression o f periodontal

disease (Aggressive and chronic).

Aim of the study

To investigate both the possible association between the IL-1 A (-889), IL-IB (-511)

and IL-IB (+3954), IL-lRN (intron 2), IL-6 (-174), IL-10 (-627 and -1082) TNFa (-

308), VDR (+1056) and TLR4 (Asp299Gly and Thr399Ile) polymorphisms and

periodontitis (Aggressive and Chronic) and the possible differences in genotype and

CHAPTER 4