Genetics in dentistry 4
Caries
 Multifactorial disease with endogenous and exogenous factors
 predisposing factors:
 inheritance- relation to caries or caries resistance
 diet rich in carbohydrates
 fluorine content in drinking water-resistant dental caries have higher fluorine
content in hard tissues
 personal hygiene-enhanced plaque formation by a lack of hygiene
 tooth- shaped teeth with fissures – more caries
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Caries (caries dentium)
• dekalcification of hard dental tissues
• bacteria-Lactobacillus acidophilus and Streptococcus that break down sugars, food debris, forming organic
acids causing decalcification-proteolytic enzymes break down organic ingredients
• plaque-thin coating of bacteria, mucus and desquamated epithelial cells
• other effects-type food composition of saliva, pH
• Decalcification of enamel-whitish chalk stain, softening, a cavity filled with food residue and bacteriaspreading
further decay process affects dentin, spreads thrue the dentin tubules until marrow - occurs
pulpitis
• Mutations in the genes that cause structural failure of enamel formation (AMLEX, Enam, KAL4 and
MMP20) lead to the formation of the enamel more susceptible to tooth decay.
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Periodontal disease
Multifactorial disorder
Environmental factors
Conception of periodontal disease
Page & Kornman
Microbial
infection
Immune
reaction
Metabolism
of ECM –
Alveolar
bone and
connective
tissues
Clinical signs
of disease and
its progression
Genetic risk factors
Ab
PMNs
LPS+
Ag Ck
PG
MMP
Syndromic Forms of Periodontitis
• Severe periodontitis presents as part of the clinical manisfestations of
several monogenetic syndromes.
• Significance of these conditions is that they clearly demonstrate that
a genetic mutation at a single locus can impart susceptibility to
periodontitis.
Papillon LeFevre Syndrome
• Clinically characterized by:
• Palmoplantar hyperkeratosis
• Severe early onset periodontitis that results in
premature loss of the primary and secondary dentition
(distinguishes PLS from other plamoplantar
keratoderma)
• Prevalence 1/ 4million
• No gender or racial predilection
CTSC gene encodes for Cathepsin C protease
• CTSC gene lies on chromosone 11q14-q21; seven exons encoding for lysosomal protease
cathepsin C.
• It is expressed at high levels in a variety of immune cells including polymorphonuclear
leucocytes, macrophages, and in epithelial regions commonly affected by PLS, including
the palms, soles, knees, and oral keratinized gingiva (RT-PCR) (Hart et al., 1999).
• Cathepsin C is a protease enzyme that processes and activates a number of granule
serine proteases critical to immune and inflammatory responses of myeloid and
lymphoid white blood cells
Mutations in CTSC gene
• Mutations in Cathepsin C (CTSC) gene are implicated for PLS
• For example:
• One exon 1 nonsense mutation (856CT): introduces a premature stop codon
at amino acid 286.
• Three exon 2 mutations:
• single nucleotide deletion (2692delA) of codon 349: introduces a frameshift and premature
termination codon,
• 2 bp deletion (2673-2674delCT): introduces a stop codon at amino acid 343, and
• GA substitution in codon 429 (2931GA): introduces a premature termination codon.
• Truncated or altered conformation of the protein may not be transported to the organelle and
may not be able to activate protein kinases
• In other words, Cathepsin C activity in these patients is nearly absent
Polymorphism Studies on Periodontitis
• Host response is predominantly influenced by genetic make-up.
• Several features of host’s innate immune response may contribute to
susceptibility to AgP and include epithelial, connective tissue,
fibroblast, and PMN defects.
• Aspects of the host inflammatory response namely cytokines are
crucial variants influencing host respone in periodontitis.
Immunological Polymorphisms
• MHC or HLA genes determine our response to particular antigens.
• Japanese study of AgP pts found a significant association for pts with
atypical BamH1 restriction site in the HLA.DQB gene (Takashiba et al.
1994).
• Hodge & Kinane (1999) found no assoc. in caucasian AgP pts and this
restriction site.
IL-1 Gene Polymorphisms
• In 1997 Kornman et al found an association between polymorphisms
in genes enconding for IL-1a(-889) and IL-1B(+3953) and an increased
severity of periodontitis.
• The specific genotype of the polymorphic IL-1 cluster (called PSTperiodontitis
susceptibility trait) was associated with severity of PD in
only non-smokers, and distinguished individuals with severe
periodontitis from those with mild disease.
Genetic control of IL-1: Genes and Locus of SNPs associated with controlling IL-
1 biological activity
Genes Polymorphism
Locus
Current Locus
assessed with test
Controlled product
IL-1A Allele 2 -889 Allele 2 IL-1A +4845 IL-1 alpha
IL-1B Allele 2 +3953 Allele 2 IL-1B +3954 IL-1 beta
IL-1RN Protein receptor antagonist
(impedes IL-1 alpha and beta)
Genetic Susceptibility Test for periodontitis: tests for the
presence of at least one copy of allele 2 at the IL-1A +4845 loci
and at least one copy of allele 2 at the IL-1B +3954 locus.
*IL-1A +4845 is being used because it is easier to identify than IL-1A -889 and it is essentially concordant
with it.
** IL-1B +3953 has been now renumbered as IL-1B +3954 because the current convention indicates that the
numbering of the transcription should begin at +1 instead of zero.
Interleukin 1
• A proinflammatory multifunctional cytokine.
• Enables ingress of inflammatory cells into sites of infection
• Promotes bone resoroption
• Stimulates eicosanoid (PGE2) release by monocytes and fibroblasts
• Stimulates release of MMP’s that degrades proteins of the ECM.
• Forms IL-1α and IL-1B
IL-1 as modulator for Periodontitis
• Kornman et al. (1997)
• Genotype-positive non-smokers  18.9 times more likely to have severe periodontitis (when
compared with genotype-negative non smokers)
• No significant association between periodontal status and genotype detected when smokers
were included in the statistical analysis.
• 86% of the severe periodontitis patients were accounted for by either smoking or IL-1
genotype
• Presence of allele 2 at IL-1A -889 or IL-1B +3953 did not significantly increase the risk of
periodontitis among smokers and non-smokers.
+IL-1 genotype and IL-1 protein
• The specific periodontitis-associated IL-1 genotype consists of a variant in the IL-B gene that is
associated with high levels of IL-1 production.(Poiciot et al 1992)
• Patients positive for composite IL-1A (+4845) and IL-1B (+3954) periodontitis-associated genotype
has higher level of IL-1B in GCF, but not in gingival tissue before and after treatment (Kornmann et
al 1999)
• Carriage of allele 2 in the (-889) locus resulted in an almost four fold increase of IL-1 protein levels
in chronic periodontitis patients (Shirodaria et al., 2000)
• Attachment loss
Kornman et al. (1997)
• Reported 18.9 times greater risk (OR=18.9) of finding severe periodonitis among nonsmokers
genotype-positive.
McDevitt et al. (2000)
• Among non-smokers or former smokers, genotype positive individuals had 3.75 greater
odds of having moderate to advanced periodontitis than genotype-negative.
• Genotype and tooth loss
McGuire and Nunn (1999)
• Genotype-positive individuals had a 2.7 greater chance than genotype-negative patients
of losing a tooth.
• Combined effect of being genotype-positive and heavy smoker increased the odds of
tooth loss to 7.7 compared with genotype-negative non-smokers.
• PST can be helpful in treatment planning.
Prevalence of genotype positive individuals in different
ethnic groups
• Frequency of many genetic alleles varies between ethnic groups, therefore, it is necessary to establish allele frequencies in populations
before genetic test can be evaluated and used.
• Caucasions:
• 29% of northern european caucasions were genotype positive (Kornman et al., 1997)
• African Americans:
• 14.5% of non-diseased individuals and 8% of patients with localized form of aggressive periodontitis were
genotype-positive. (Walker et al., 2000)
• Chinese:
• 2.3% of sample of 132 mod-severe periodontitis cases were genotype-positive (Armitage et al., 2000)
• Hispanics:
• 26% of hispanic individuals with peridontitis were genotype-positive (Lopez et al., 2005)
Take home message: Dissimilarity in the prevalence of genotypes in different ethnic
groups precludes extrapolating data from one group to another.
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 Porphyromonas gingivalis
 Bacteroides forsythus, newly Tanarella forsythensis
 Actinobacillus Actinomycemcomitans
 ……….
Microbial factors
• The bacteria themselves are not able to cause disease:
• A wide range of host susceptibility
• Differences in prevalence and extent between the teeth
BUT
Dental plaque biofilm infection
• Ecological point of view
• Ecological community evolved for survival as a whole
• Complex community of more than 400 bacterial species
• Dynamic equilibrium between bacteria and a
host defense
• Adopted survival strategies favoring growth in plaque
• “Selection” of “pathogenic” bacteria among microbial community
• Selection pressure coupled to environmental changes
• Disturbed equilibrium leading to pathology
• Opportunistic infectio
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Reaction of the organism to bacterial
infection
• Gate input - usually mucosal surfaces (violation of integrity)
• The fate of the host depends on:
- Immunity (largely genetically determined)
- Pathogenicity of bacteria (invasive ability, production of toxins, the ability to
resist the defense mechanisms of the host)
non-invasive - multiply the point of entry into the body
threatening in case of toxin production
(defense - only neutralizing Pt)
Invasive - penetrate into the organism (x extracellular intracellular)
(defense are Pt, complement, phagocytosis vs. macrophages)
- The size of the infectious dose
Identifying virulence factors
• Microbiological and biochemical studies
• In vitro isolation and characterization
• In vivo systems
• Genetic studies
• Study of genes involved in virulence
• Genetic transmission system
• Recombinant DNA technology
• Isogenic mutants
• Molecular form of Koch’s postulates (Falkow)
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Koch’s postulates
• A Molecular form of Koch’s postulates
• The phenotype should be associated with pathogenic species (strains)
• Specific inactivation of genes associated with virulence should lead to a
decrease in virulence
• Complementing inactivated genes with the wildtype genes should restore full
virulence
Falkow, 1988
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TLRs
• First described as a gene for type I transmembrane receptor
 important role in dorzoventral embryonic development of Drosophila
 absence of tolls has led to a serious brake-down of defense against fungi
and bacteria G+
Mammalian homologues - similar role??
TLRs receptors and ligands in
periodontal disease
Local problem?
Periodontitis• follows the loss of pulp vitality - the dead tooth
• Infection is usually odontogenic
• Trauma - one-time or repetitive microtrauma
• Acute periodontitis (apical)
• Hyperemia and serous exudation
• Suppuration, osteoclastic bone remodeling
• Strong pain at all stages, swelling in the later stages
• Relationship of polymorphisms in genes IL1B, IL1RN, FcγRIIIb, VDR and
TLR4 with an aggressive type of periodontitis.
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Periodontitis
Chronic periodontitis (periapical)
• Secondarily from acute periodontitis
Primarily chronic (more frequent)
• Forms:
Granulomatous
Granulomatous progressive - fistula (mucosal and cutaneous)
Diffusion - dismantled and alveolar bone
• granulation tissue
macrophages
Possibility of creating radicular cysts
• The type of chronic periodontitis is associated with polymorphisms in
genes for IL1B, IL1RN, IL6, IL10, VDR, CD14, TLR4 and MMP1.
• Meta-analysis of published data have associated variants
ofpolymorphisms IL1A-889, IL1B 3954, IL1B-511, TNFA-308 and IL6-
174 to aggressive and chronic periodontitis.
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