Genetic Risk Factors for Periodontitis Bryan Michalowicz, D.D.S - PowerPoint PPT Presentation

Genetic Risk Factors for Periodontitis Bryan Michalowicz, D.D.S Division of Periodontology

Pathogenic Susceptible Bacteria Host Modifying Environmental Factors Periodontitis is a COMMOM, COMPLEX, MULTIFACTORIAL disease.

Periodontitis Diagnoses • Aggressive Periodontitis (Grade II or III, Stage C under new scheme) – Localized – Generalized • Chronic (Adult) Periodontitis

Localized Aggressive Periodontitis • Incisors and 6-year molars • Saucer-like defects

Disorder Protein or Tissue Defect CD18 ( b -2 integrin chain of the LFA Leukocyte Adhesion Deficiency Type I molecule) Leukocyte Adhesion Deficiency CD15 (neutrophil ligand for E and P Type II selectins); inborn error in fucose metabolism Chronic and Cyclic Neutropenias Various Chediak-Higashi Syndrome Abnormal transport of vesicles to and from neutrophil lysosomes caused by mutations in the lysosomal trafficking regulator gene Ehler-Danlos Syndrome [types IV Type III collagen for EDS type IV, & VIII] unknown for EDS type VIII Papillon-Lefevre Syndrome Cathepsin C (dipeptidyl aminopeptidase I) Hypophosphatasia Tissue non-specific alkaline phosphatase

Cyclic Neutropenia

Leukocyte adhesion deficiency

Papillon-Lefèvre Syndrome

Papillon-Lefèvre Syndrome • several point mutations in the cathepsin C gene are associated with the phenotype • mutations may be missense, nonsense, insertions or deletions • almost total loss of enzyme activity in PLS patients (i.e., homozygotes or compound heterozygotes) • reduced enzyme activity in obligate carriers

Cathepsin C • lysosomal protease present in neutrophils and macrophages • dipeptidyl aminopeptidase I (removes dipeptides from amino terminus of protein) • chromosomal location: 11q14.1-q14.3

Approaches to Evaluate Genetic Risk in Humans • Segregation Analyses • Twin and Family Studies • Association (Case-Control) Studies – Candidate gene approach – Genome-wide associations (GWAS)

Segregation Analyses of Aggressive Periodontitis • AR, AD, and X-linked modes of inheritance have all been proposed • Largest collection of families to date favors AD inheritance • Frequency of disease allele greater in blacks than whites • Highlights genetic heterogeneity

TWIN STUDY DESIGN • Differences between MZ (identical) twins of a pair are due to differences in environment. • Differences between DZ twins of a pair are due to differences in environment plus unshared genes. • Differences (in correlations) between MZ and DZ twins is due to the effects of one-half the genetic variance (the difference in gene sharing between mz and dz twins) • Twice this difference [2(rMZ-rDZ)] is heritability

Classic twin study assumptions • Twins are representative of non-twins • The environments are similar for MZ and DZ twins (especially relevant for behavioral studies) • Genes and environment don’t interact (for estimating heritability as described)

Reared Together and Apart Twin Correlations for Clinical Measures 0.9 0.8 0.7 0.6 MZT 0.5 MZA 0.4 DZT 0.3 0.2 0.1 0 AL PD Gingivitis Michalowicz et al., 1991

Twin Correlations for Presence of Periodontal Pathogens 0.5 MZ DZ 0.4 0.3 0.2 0.1 0 P.i. P.g. A.a. E.c. F.n. Michalowicz et al, J Periodontol. 1999;70(3):263-73.

Conclusions • Approximately 50% of the population variance for attachment loss and probing depth is attributed to genetic variance • Genetic factors do not significantly influence levels of plaque or calculus, or the presence of specific bacteria in subgingival plaque • The family environment does not significantly influence measures of disease in adults

All twin studies combined Excluding those where disease was self-reported Other family studies Nibali et al. J Dent Res. 2019 Jun;98(6):632-641

Twin study of dental caries • 20,839 complete twin pairs with known zygosity and caries data Results of variance decomposition for caries indices and caries trajectories. Each bar represents a caries trait, and the stacked components represent the relative contributions of components A (additive genetic factors), C (shared environmental factors), and E (nonshared environmental factors) to variation in that trait. DMFSa and DFSa refer to proximal surfaces. • From cross sectional data, heritability ranged from 49 to 63%. J Dent Res. 2020 Mar;99(3):264-270 .

Association Studies using candidate gene markers • Case-control study design • Exploit phenomenon that alleles at nearby loci co-segregate (are in “linkage disequilibrium”) • Focus on common genetic variations, e.g., single nucleotide polymorphisms (SNPs) with frequencies > 5%

Candidate Genes for Periodontal Disease • Cytokines, including interleukin-1 • Vitamin D receptor • N-formyl peptide receptor • Class II HLA antigens (DR, DQ, DP) • Cathepsins • Toll-like receptors • MMPs

Genotype distributions and frequencies of the minor alleles by periodontal diagnosis and race Genotype Caucasians p Blacks p Polymorphism Patients Controls Patients Controls IL6 −174 GG 124 (39.0%) 42 (29.2%) 81 (90.0%) 38 (84.4%) 0.35 0.12 CG 142 (44.7%) 74 (51.4%) 9 (10.0%) 7 (15.6%) CC 52 (16.4%) 28 (19.4%) 0 (0%) 0 (0%) IL6 −1363 GG 263 (85.7%) 112 (77.8%) 0.02 88 (98.5%) 43 (95.6%) 0.23 TG 48 (14.0%) 28 (19.4%) 1 (1.1%) 2 (4.4%) TT 1 (0.3%) 4 (2.8%) 0 (0%) 0 (0%) For −174, GG vs. CC + CG: p = 0.044 (OR = 1.6, 95% CI = 1.0–2.4) For −1363, GG vs. TT + GT: p = 0.017 (OR = 1.8, 95% CI = 1.1–2.8) Cytokine, Vol 45 (1), 2009, p50-54

Genome-wide associations studies (GWAS) • Uses a case-control study design • No pre-selection of “candidate gene” regions • More informative with larger patient sample sizes and more polymorphism genetic markers • Typically use SNPs (single nucleotide polymorphisms) • Include SNPs that are both assayed in patient samples and imputed • Test for SNPs whose alleles are distributed differently in cases and controls • Must control for false positive findings

Type 2 Diabetes GWAS (>380K SNPs) (www.broad.mit.edu/diabetes/scandinavs/type2.html)

Schaefer AS, et al. A genome-wide association study identifies GLT6D1 as a susceptibility locus for [aggressive] periodontitis. Hum Mol Genet. 2010;19(3):553 Cases Controls GWAS 1 141 500 GWAS2 142 479 Validation 155 341 sample Fine 461 1383 mapping

SNP rs1537415 GWAS1 GWAS2 Validation 1.8 x 10 –4 3.1 x 10 –4 5.7 x 10 –3 P -value OR (95% CI) 1.67 (1.27–2.18) 1.65 (1.26–2.17) 1.47 (1.12–1.93) Controls 11 (%) 187 (38.3) 185 (38.6) 128 (37.5) 12 (%) 236 (48.4) 233 (48.6) 156 (45.7) 22 (%) 65 (13.3) 61 (12.7) 57 (16.7) Cases 11 (%) 36 (26.3) 33 (24.6) 38 (25.0) 12 (%) 65 (47.4) 70 (52.2) 79 (52.0) 22 (%) 36 (26.3) 31 (23.1) 35 (23.0) Schaefer, A. S. et al. Hum. Mol. Genet. 2010 19:553-562

GLT6D1 • Glucosyltransferase • Impairment of a potential GATA-3 transcription factor binding site at rs1537415 • Minor (disease-associated) allele associated with decreased GATA-3 binding

Genome - wide association study of chronic periodontitis in a general German population (SHIP) • No genome-wide significant SNP associations • The proportion of the sex age, and smoking status adjusted variance explained by additive effects of all common SNPs (Heritability) was 23% and 14% for mean PAL (top) and CDC/AAP disease definition (bottom), respectively. J Clin Periodontol 2013, Vol 40 (11): 977-985

Genome - wide association study of chronic periodontitis in a general US population (D-ARIC) 761 had severe disease, 1920 moderate disease and 1823 healthy Genome-wide association results for severe (A) and moderate (B) chronic periodontitis. 2,135,236 SNPs tested, none reached genome-wide statistical significance For severe disease, the minor allele [C] of NIN showed a 3.5% enrichment among severe CP patients; OR = 1.89 (P = 3.5 × 10−7). Heritability for severe disease explained by all SNPs increased from 18 to 52% with the inclusion of a genome-wide interaction term with smoking . Divaris K et al. Hum. Mol. Genet. 2013;22:2312-2324

Nat Commun. 2019 Jun 24;10(1):2773.

Genome-wide analysis of dental caries and periodontitis combining clinical and self-reported data Trait name DMFS DFSS Nteeth Periodontitis Presence or Trait Decayed, missing and filled tooth surfaces # of natural teeth absence of periodontitis CDC/AAP definitions (4 studies) Two or more tooth surfaces with PD ≥ 5 mm, or at least Derived from clinical Phenotypic four tooth surfaces Derived from clinical dental records dental records or assessment with PD ≥4 mm (1 self-reports study) PD ≥5.5 mm in 2 or more sextants (1 study). Self report (1 study) # of studies in 9 9 7 primary analysis # of participants in 17,353 cases, 26,792 27,949 primary analysis 28,210 controls PD = probing depth

Caries/Dentures Periodontitis/ Loose teeth

Summary • For dental caries/dentures, identified 47 significant associations, 45 of which were new • For periodontitis/loose teeth, only one SNP reached genome-wide significance (an intronic variant within SIGLEC5 (OR for periodontitis = 1.05) • This same marker was identified in a previous study of aggressive periodontitis