GENETICS,STUDY DESIGNS

GENETICS,STUDY DESIGNSPRESENTED BYDr Harshavardhan Patwal

CONTENTSINTRODUCTIONTERMINOLOGYCENTRAL DOGMASTRUCTURE OF GENESTUCTURE OF DNASTUDY DESIGNS STUDIES PERTAINING TO:CHRONIC PERIODONTITISAGGRESSIVE PERIODONTITISIMPLANTSEPIGENETICSFUTURE PROSPECTS

INTRODUCTIONGenetics is defined as the science of heredity .

The word GENETICS was coined by William Bateson in 1907

In 1903 , Walter Sutton and Theodor Boveri independently proposed that chromosomes carry the hereditary factors. Chromosomal theory of inheritance-Chromosomes contain the DNA which is the genetic material

Gregor John Mendel is the father of genetics

INTRODUCTIONMendels laws of heredity;

Law of segregation -the character of an organism are determined by pairs of factors of which only one can be present in each gamete.

Law of independent segregation-when two or more pairs of characters are brought together in a crossover ,they segregate independently of each other.

Periodontitis is a multifactorial disease. While microbial and other environmental factors are believed to initiate and modulate periodontal disease progression, there now exists strong supporting evidence that genes play a role in the predisposition to and progression of periodontal diseases.

TERMINOLOGYAllele one of several possible alternative forms of a given gene differing in DNA sequence assumed to arise by mutation and often affecting the function of a single product. Humans carry two sets of chromosomes, one from each parent. Single nucleotide polymorphisms may render two sets of equivalent genes different.

Alternative splicing the generation of multiple protein isoforms from a single gene via the splicing together of nonconsecutive exons during RNA processing of some but not all of RNA transcripts. Believed to the mechanism involved with the high number of proteins produced from a smaller number of genes in humans.

Autosome chromosomes other than sex chromosomes.

Autosomal dominant the dominant effect of one gene located on an autosome regardless of the presence of the other, normal copy.

Autosomal recessive A gene on an autosome that is required in two copies to be active in an individual. An individual who carries two such copies of the same abnormal gene will be subjected to effects from that gene.

Complementary DNA (cDNA) the DNA sequence produced by the enzyme called reverse transcriptase from messenger RNA. Very frequently used in cloning experiments.

Chromosome a nuclear structure carrying genetic information arranged in a linear sequence. Humans have 23 pairs (including a pair of sex chromosomes XX or XY).

Chromatin : Condensation of the DNA with histones and other chromosomal proteins.Chromatin is further organized into chromosomes.

Cloning the generation of sufficient copies of a target DNA sequence that allows it to be sequenced or studied further.

Dizygotic twin fraternal twins as a result of fertilization of two separate eggs. They are no more similar genetically than are siblings.

Exon the expressed portion of DNA or RNA that will ultimately be translated into protein. Multiple exons are spliced together to remove introns during RNA processing.

Frameshift mutation A type of mutation as a result of an insertion or deletion of one or more nucleotides into a gene causing the coding regions to be read in the wrong frame.

Gene a hereditary unit that occupies a specific position (locus) within a genome or chromosome that has one or more specific effects upon the phenotype of the organism.

Gene expression the process involving use of the information in a gene via transcription and translation leading to production of a protein affecting the phenotype of the organism determined by that gene.

Genetic code in RNA and DNA, the consecutive nucleotide triplets (codon) that specify the sequence of amino acids for protein synthesis (translation).

Genome a term used to refer to all the genes carried by an individual or cell.

Genotype the genetic makeup of an organism or cell distinct from its expressed features or phenotype.

Homozygous the presence of identical alleles of one or more specific genes (e.g. A/A).

Heterozygous the presence of differing alleles of one or more specific genes (e.g. A/B).

Intron the intervening (non-coding) portion of DNA or RNA that is removed during RNA processing.

Isoforms a protein with equivalent function and similar or identical sequence but derived from a different and usually tissue-specific gene.

Linkage the tendency for certain genes to be inherited together due to their presence on the same chromosome.

Linkage disequilibrium the occurrence of some genes together more often than would be expected by random distribution.

Locus (plural loci) the physical location a gene occupies within a chromosome or portion of genomic DNA.

Monozygotic twin identical twins having identical sets of nuclear genes as a result of separation of blastomeres.

Mutation alteration of the genomic sequence compared to a reference state. Not all mutations have harmful events (silent mutation).

Phenotype the observable characteristics displayed by an organism as influenced by environmental factors and independent of the genotype of the organism.

Polymorphism a region on the genome that varies between individual members of a population present in a significant number of individuals.

Single nucleotide polymorph (SNP) a polymorphism caused by the change in a single nucleotide believed to be the most common genetic variation between individual humans.

Splicing the removal of introns from transcribed RNAs. The removal of exons results in the formation of splice variants or alternatively spliced protein isoforms allowing different proteins to be produced from the same initial RNA or gene.

X-linked disease a disease of genetic origin as a result of a mutation on the X-chromosome.

Wild type the non-mutated, naturally-occurring form of a gene.

Diseases with etiologies that include both genetic and environmental factors are refferred to as multifactorial.

Genetic marker refers to any gene or nucleotide sequence that can be mapped to a specific location or region on a chromosome.

Trait and disease might be caused by a single gene (monogenic), several genes (oligogenic), or many genes (polygenic).

In monogenic disorders, genes are referred to as causative because almost everyone with the mutation develops the condition.

Environmental factors generally play a minor role in determining the phenotype. In contrast, genes involved in complex multifactorial disease are called susceptibility genes.

Penetrance refers to the probability that a particular phenotype will result from a genotype.

HUMAN GENOMIC PROJECTEarly in 2001, man heralded one of the greatest scientific achievements-a draft of the human genome.

The human genome contains 30,000-40,000 genes.(Baltimore,2001)

In periodontics genetics of both humans and pathogens and the interaction between them is studied.

Presently the complete sequence of P.gingivalis has been sequenced.

CHROMOSOMEWaldeyer in 1888 coined the term chromosome Chromosome consists of:70%-protein20%-DNA10%-RNA

GENE1st proposed by MENDEL in 1865 he called it as factor .The word gene was coined by JOHANNSON in 1909

Promoter Sequence of nucleotide left (upstream) of the coding region starting with nucleotide position -1(not as triplets)

Coding region Reading frame starting at nucleotide Position +1 containing triplets or codon. Exons (true coding region ) - nucleotide bases contained in noncontiguous segments called the EXONS(expressed sequences).

INTRONS(non coding region) - Exons are separated by other sequences not present in mature mRNA called INTRONS (intervening sequences).

DNA

Discovered in 1953 by Watson and Crick by X ray diffraction pictures

CENTRAL DOGMA

CENTRAL DOGMA

Transcription requiresDNA templateRNA polymerases I, II, III.Transcription factors

GENE TRANSCRIPTION(Lewin,1994)

21

Factor chart

TRANSCRIPTION FACTORS:

CLASSIFIED Based on action (Papavassiliou,1995)

Basal factors To initiate transcription on the correct site.E.g.., TATA box-binding proteins (TBP), Polymerase II Transcription factors (TFIIA,TF IIB,TFIIE,TFIIF).

Upstream factors recognize specific DNA elements located upstream of the transcription start site.

Inducible factors - important regulators of gene transcription, eg hormones, growth factors act through this

Based on structure(Johnson & McKnight,1989)Zinc finger proteins e.g.steroid receptorszinc ion bound to 2 cysteines and 2 histidines

2.Leucine zipper proteinsproducts of c-fos and c-jun protooncogenes

Homeodomain proteins

Helix-loop-helix(HLH) family proteins important in the regulation of metabolism, cell differentiation and development. E.g. MyoD, c-myc protooncogene

TRANSCRIPTION

mRNA

mRNA ProcessingCapping (Sacchs,1993)Polyadenation(Wahl & Keller,1996)Splicing(McKeown,1992)

RIBISOMES

STEPS IN TRANSLATION

INITIATIONELONGATIONTERMINATIONRELEASE OF PEPTIDES

The ribosome reads 3 nucleotides at a time (CODON).The ribosome looks for the start codon where it begins building the aminoacid chain.There are 64 possible codons. One amino acid may be specified by one or more codons.Three codons do not specify any amino acid, they are stop codons.

tRNAs have an ANTICODON on one end and an AMINOACID on the other.The anticodon dictates which aminoacid it carries to the ribosome.The aminoacids are transferred to the ribosome by t-RNA molecules.

The ribosome reads the next codon and another tRNA with anticodon binds.

POST-TRANSLATIONAL MODIFICATIONProtein folding and glycosylation

Folding of nascent polypeptides into 3-dimensional structures is assisted by accessory proteins and disulphide linkages, molecular chaperones(BIP,HSP,FO).

Modifications such as hydroxylation of proline and hydroxyl residues in collagen can occur only on unfolded polypeptides.

SORTING OF PROTEINSThe movement of protein from the site of protein synthesis to a different destination is known as targeting or sorting.(Heijne,1990)

TRANSLOCATIONThe movement of polypeptide across membranes of organelles and RER .This is followed by secretion of protein and then undergoing removal of extra sequences(Processing)

FACTORS THAT AFFECT PROTEIN PRODUCTION

DNA methylation mechanism by which gene expression is regulated.(Eden,1994)Methylated genes are inactive and the promoter activity is inhibited.Most environmental and physiological mediators affect gene transcription by modifying the synthesis of transcription factors.(Maniatis et al,1987)Synthesis of new transcription factors when neededCovalent modification of aminoacids and phosphorylation of certain residues modifies the binding of this particular transcription factor to the DNA response sequences.Many hormones, cytokines act by phosphorylation of the transcription factor APISteroid hormones, Vit D, sex hormones bind to their respective cytoplasmic DNA binding receptors.

GENETIC VARIANCES

Genes can exist in different forms or states (alleles)Allelic variants of a gene differ in their nucleotide sequences.

ALLELEA variant of the DNA sequence at a given locus is called anallele.Thegenotypefor each gene comprises the pair of alleles present at that locus

Allele that leads to an observable phenotype dominant allele

Allele does not lead to an observable phenotype- recessiveallele.

MUTATIONMutation can cause variation in alleles.A mutation is defined as a heritable alteration or change in the genetic material.

Basis of classificationTypesOriginSpontaneous TautomerismDepurinationDeaminationSlipped Strand PairingInducedChemicalRadiationViral infectionsCell typeGerm line reproductive cell(Hereditary disease)Somatic- somatic cell(Cancer,Congenital malformations)StabilityFixedSubstitution-base pair changeTransition - Pyrimidine to pyrimidine (T or C) / purine to purine (A or G). Transversion- Pyrimidine to purine / purine to pyrimidineInsertion: extra nucleotideDeletion- missing nucleotide.DynamicTrinucleotide repeat mutation

Basis of classificationTypesEffect on translationSynonymous mutationSilentNon Synonymous mutationMissenseNonsenseFrameshiftSubstitution/Addition of nucleotidePoint MutationSilentMissenseNonsenseFrameshift MutationInsertionDeletionEffect on functionLoss of function- NullNeomorphic-Gain in functionAntimorphic mutationHypomorphic- reduced function.Hypermorphic- increased functionEctopic expressionLethal mutationReversion

PolymorphismAllele is a variant form of a geneThe coexistence of multiple alleles at a locus is called Genetic polymorphism when they occur at more than one percent in a population.

Types of PolymorphismSNP: Single Nucleotide polymorphisms-The change in a single nucleotide found at a single location is called SNP.

VNTR: Variable number of Tandem Repeats.-Repeated base patterns consisting of several hundreds of base pairs

STR: Simple Tandem repeats.-2,3 or 4 nucleotide repeats on a variable number of locations.

MODIFYING DISEASE GENES FOR WHICH GENE POLYMORPHISM IS RISK FACTOR FOR PERIODONTITISACE genesCARD15CCR5CD14ER2ET1FBR geneFc receptor geneN-formyl peptide receptor geneIFNGR1Interleukin-1 alpha and beta gene IL-receptor antagonistIl2.4,6,10

LTAMMP-1,3,9MPONAT2PAI1RAGETGFBTIMP2TLR2,4Vitamin D receptorHLA genesN-acetyltransferaseTNF- and TNF- gene

Polymorphism Vs Mutation

MUTATIONSPOLYMORPHISMSHere a single gene locus causing mutation has a major physiological impact & considered to be deterministic to disease.Here the gentic alteration that contributes to complex disease has smaller effect.Seen less commonly in the populationAtleast or more than 1% of population.Mutation have causually linked with Mendelian disease.Here mutation is not causually linked to disease but alleles are seen more frequently in disease individuals.One-to-one correlation of a mutation & disease can be established.No one-to-one correlation.

3 Major Categories of Genetic Disorders

1. Major chromosomal disorders 2. Mendelian disorders 3. Non-Mendelian disorders

Major chromosomal disordersNumerical AbnormalityAneuploidyPolyploidyMonosomyTrisomyMosaicism-2 or more population of cellsStructural AbnormalityTranslocationIsochromosomesInversionsDeletionInsertionRing Chromosome

"Simple" Mendelian diseasesDiseases that follow predictable and generally simple patterns of transmission have been called "Mendelian" conditions. Genes involved are called as causative genes.The name reflects the fact that these diseases occur in simple patterns in families, and in most cases a single gene locus is the major determinant of the clinical disease phenotype. These diseases follow a classic Mendelian mode of inheritance: Autosomal dominant-Huntington disease Autosomal recessive-Cystic Fibrosis x-linked dominant- Aicardi Syndrome x-linked recessive - Hemophilia A

SYNDROMES ASSOCIATED WITH PERIODONTITIS(Simple Mendelian Diseases)

ConditionBiochemical/tissue defectInheritancePeriodontal DiseasePapillon Lefevre SyndromeCathepsin CAutosomal recessiveAPHalm Munk SyndromeCathepsin CAutosomal recessive APEhlers Dalnos Syndrome Type IVCollagenAutosomal DominantAPEhlers Dalnos Syndrome 8Collagen Autosomal dominantAPCyclic NeutropeniaNeutrophil ElastaseAutosomal DominantAP, CPChronic Familial NeutropeniaDefect unknownAutosomal dominantAP, CPChediak Higashi SyndromeLysosomal trafficking regulator geneAutosomal recessiveAPCongenital disorder of glycosylation Type 11CGlucose diphosphate fucose transporter 1Autosomal recessiveAPLeukocyte adhesion deficiency Type 1Leukocyte chain adhesion molecule CD18Autosomal recessiveAP, CP

Multifactoprial Diseases or Complex" diseases

Genetically complex diseases are much more prevalent (>1% of population) and is caused by susceptibility genes

This type is the result of the interaction of multiple different gene loci. Additionally, environmental factors are important in the disease process. Example:Periodontitis,

STUDY DESIGNSFamilial AggregationSegregation Analysis Twin Studies Linkage Analysis Association Studies

Familial AggregationFamilial aggregation of a trait or disease can suggest genetic etiology.However, families also share many aspects of a common environment, including diet and nutrition, exposures to pollutants, and behaviors such as smoking (active and passive). Certain infectious agents may cluster in families. Thus, familial aggregation may result from shared genes, shared environmental exposures and similar socioeconomic influences.To determine the evidence for genetic factors in familial aggregation of a trait, more formal genetic studies are required.

Familial Aggregation

AUTHOR,YEARSUBJECTSFINDINGSChung 1977In a Hawaii racially mixed populations. A total of 939 subjected from 241 nuclear families was included in the analysis. Sex, age, years of education and smoking were significantly associated. No significant contribution of genotype to susceptibility for periodontitis .It was concluded that common family environment was a determining factor of variability in pdl health. Beaty et al.1993 Studied familial aggregation of plaque index, gingival index and attachment loss. The sample included 178 volunturs from 75 families (mostli African-Americans)and was mainly block females < 40 years. Genotype influences plaque index, but not GI and attachment loss. Mother offspring correlation was stronger than father for both GI and attachment loss.

Segregation analysis

Pattern of transmission of disease through generation is studied in different families. It is compared with those expected under various models of inheritance to select the best fitting model.The pattern in which disease is transmitted across generations depends on whether disease alleles: Lie on autosome/sex chromosomes Dominant or recessive Fully or partially penetrant.

Adv: Can assess whether the disease gene is autosomal or sex linked, recessive or dominant.

Limitation:It has low power to resolve heterogeneity (Multiple causes)Cannot distinguish between genetic & environmental influences.Does not provide information about specific genes

AuthorStudyResultsBeaty TH et al 1987Proband with Juvenile periodontitis- 28 families.Different models of inheritance studiedAutosomal recessive mode of inheritance for JPHart TC, Marazita ML et al 1992Re-interpretation of X-linked mode of inheritance among Juvenile periodontitisFemale ascertainment bias and lack of father to son transmission interpreted in a different way.Marazita ML et al 1994EOP- 104 probands- 100 families, blacks and non blacks familiesAutosomal dominant mode of inheritance among blacks and non blacks with 70% penetranceMarazita ML et al 1996Segregation analysis of IgG2 levels in EOP among african americans and caucasiansAutosomal co-dominant mode of inheritance Hodge PJ et al 2000Caucasian family from Europe with EOPAutosomal dominant or X-linked mode of inheritanceDe Carvalho FM et al 2009Aggressive periodontitis- Brazilian populationSemi general mode of transmission: few loci with small effects contribute to periodontitis.

Twin StudiesInfluence of genetic and environmental factors on complex diseases can be estimated.Sir Francis Galton in 1875 was the first scientist to use this concept.Monozygotic twins: 100% similar genetic make up.Dizygotic twins: 50% similar genetic make upHeritability estimate can be made.Concordance degree of similarity between twins in one or more characteristics.Discordance- degree of dissimilarity between twins in one or more characteristics.

Two Types:

Classic twin study -monozygotic and dizygotic twins are Reared together and compared.

Monozygotic twins reared apart:MZA-Effects of shared genes without the confounding effects of a common family environment

AuthorStudyResultsCorey LA et al 19934908 twin pairs: questionnaire based study- history of periodontal disease. 116 MZ twin pairs and 233 DZ pairsConcordance rate of MZ twins: 0.23 to 0.38 and for DZ twins: 0.08 to 0.16Michalowicz et al 1999169 twin pairs: presence of P.ging, A.a, P.intermedia, E.corrodens, F.nucleatumP.ging-11%, A.a- 22%, P.intermedia- 19%, E.corrodens- 0.34%, F.nucleatum-40%. No difference in concordance rates between MZ and DZ pairs.Michalowicz BS et al 200064 MZ, 53 DZ twin pairs: influence of smoking and utilization of dental servicesChronic periodontitis- 50% heritability independent of smoking and dental services.

Linkage AnalysisUsed to map disease allele to specific regions on the chromosomes.

Linkage studies use sets of families with multiple affected individuals.

Complex statistical models are used to determine whether the marker allele and disease co segregate in the families under a given inheritance model.

Linkage can be detected if the marker and disease alleles are within 20-30 centimorgans of one another.

LOD(Logaritham of odds) score - Compare the likelyhood of two genes are indeed linked to the likely hood of observing this data purely by chance. Positive LOD score- presence of linkage Negative LOD score-less likely

Linkage studies usually start by identifying markers (SNPs) on a section of a chromosome and then narrowing the region down until the gene or gene variant of interest is identified. DISADVANTAGE-Complex diseases are due to combined effects of multiple genes of minor effect.

Example:

AuthorStudyResultsBoughman et al 1986Localized Aggressive periodontitisAgP segrgates with dentinogenesis imperfecta. Localized to long arm of chromosome 4 near the gene for dentinogenesis imperfecta.Li Y et al 2004Localized Aggressive periodontitisDisease gene localized to chromosome 1.Tabeta K et al 2009Linkage disequilibrium block analysis- SNPs and Microsatellites in chromosome 19A single microsatellite marker allele 17 of 1902 G 31 on chromosome 19- associated with severe chronic periodontitis

Association StudiesFrequency of marker alleles at a given locus is compared between subjects with disease(cases) and healthy controls sampled from same population .Population based approachesFamily based approaches

Association suggest that the presence of an allele confers risk for disease within a defined environment.

Limitation Association does not necessarily imply a biologic link between the disease and the tested allele.

FAMILY STUDIES

AUTHOR,YEARSUBJECTSFINDINGSChung 1977In a Hawaii racially mixed populations. A total of 939 subjected from 241 nuclear families was included in the analysis. Sex, age, years of education and smoking were significantly associated. No significant contribution of genotype to susceptibility for periodontitis .It was concluded that common family environment was a determining factor of variability in pdl health. Beaty et al.1993 Studied familial aggregation of plaque index, gingival index and attachment loss. The sample included 178 volunturs from 75 families (mostli African-Americans)and was mainly block females < 40 years. Genotype influences plaque index, but not GI and attachment loss. Mother offspring correlation was stronger than father for both GI and attachment loss.

TWIN STUDIESAUTHOR,YEARSUBJECTSFINDINGSCiancio et al.1969

Investigated levels of gingival recession and crevice depth and indices of gingivitis, supra gingival plaque and calculus in 26 twin pairs aged 12-17 years . found no evidence of genetic influence Michalowicz et al 1991To estimate the genetic variance for alveolar bone height. Panoramic radiographs were obtained from 120 pairs of adult twins (mean age = 40.4 years, S.D. = 10.4 years), for comparison of 62 pairs of MZT ,25 like-sexed DZT and 33 pairs MZA. The intraclass correlations MZT = 0.70, DZT = 0.52, and MZA = 0.55. Significant genetic variance in the population for proportional alveolar bone height.Corey LA et al 19934908 twin pairs: questionnaire based study- history of periodontal disease. (VIRGINIA)116 MZ twin pairs and 233 DZ pairsConcordance rate of MZ twins: 0.23 to 0.38 and for DZ twins: 0.08 to 0.16

TWIN STUDIESAUTHOR,YEARSUBJECTSFINDINGSMichalowicz et al 1991Examined the relative contribution of environmental and host genetic factors to clinical measures of periodontal disease through the study 110 pairs of adult twins (mean age 40.3 years), including 63 MZT and 33 DZT and 14 MZASignificant genetic component for gingivitis, PD ,CAL, plaque.. 38% to 82% of the population variance for these periodontal measures of disease may be attributed to genetic factorsMichalowicz et al 1999169 twin pairs: presence of P.ging, A.a, P.intermedia, E.corrodens, F.nucleatumP.ging-11%, A.a- 22%, P.intermedia- 19%, E.corrodens- 0.34%, F.nucleatum-40%. No difference in concordance rates between MZ and DZ pairs.Michalowicz BS et al 200064 MZ, 53 DZ twin pairs: influence of smoking and utilization of dental servicesChronic periodontitis- 50% heritability independent of smoking and dental services.

ASSOCIATION STUDIES AUTHOR,YEARSUBJECTSFINDINGSKornman et al.1997 Composite IL-1 genotype consisting of at least one copy of the more rare Allele at both an IL-1 & and IL IB loci was associated with severe periodontitis in northern European adults. Association-18.9

Gore et al.1998 Composite genotype in caucasiansMore rare IL-1 sites were in linkage disequilibrium,

ASSOCIATION STUDIESAUTHOR,YEARSUBJECTSFINDINGSKobayashi et al.1997Neutrophil IgG receptor with CP in Japanese populationAssociation was found with FCRIIIb-NA2Engebretson et al. 1999IL-1 composite genotype in US populationElevated levels of IL-1 Beta in GCF.Galbreuth et al. 1998 TNF genotypes were determined in 32 Caucasian patients with adult periodontitis and 32 orally-healthy matched controls, and correlated with TNF-alpha production by oral polymorphonuclear leukocytes (PMN)No association between CP and TNF- 1 genotype was correlated with elevated TNF- production by oral PMNs in patients with advanced disease. Polymorpheisms.Armitage et al 2000Association of CP with Composite genotype in Chinese PopulationNo association

AGGRESSIVE PERIODONTITIS

PEDIGREE ANALYSIS AUTHOR,YEARSUBJECTSFINDINGSBenjamin et al., 1967 Twelve families (52 individuals) XD mode. The female to male ratio was3:1

Butler 1969

A family The proband and his sister had JP. Hismother and maternal aunt and grandfather had become edentulous at an early ageXD modeFourel, 1972 A family (more than 20 individuals)AR mode

Jorgenson et al., 1975 A familyAR modeMelnick et al., 1976 Two familiesFamily 1: five of six siblings, three of them female, had JPFamily 2: four of eight siblings, all females, had JPXD mode with decreased penetrance.The female to male ratio was 2:1

AUTHOR,YEARSUBJECTSFINDINGSSussman et al., 1978Proband, 17, female .Mother and grandmother were affectedAD modeVandesteen et al., 1984A family (29 individuals in the pedigree trees) The proband and six siblings all had JP; both parents were edentulous since early adulthood; both maternal grandparents and at least two siblings of the motherhad been affected Paternal side: two of the fathers siblings were affected, but the paternal grandparents were not affectedXD modeSpektor et al., 1985 One large family (40 individuals in the pedigree trees) The proband had JP Father (healthy) mother (affected)Twelve siblings (six affected, sixunaffected) Both maternal grandparents of the probandhad become edentulous at an earlyage. Four of 10 siblings of the probands mother had EOP. The paternal grandparents did not have EOP and periodontitis was not unusually prevalent in the siblings of the probands fatherXD mode

Page et al., 1985 A family (six individuals) The parents had JP in their teens, andhad two affected chidren and two unaffected childrenXD mode

SEGREGATION ANALYSISAUTHORGENETIC ANALYSISSUBJECTSFINDINGSMelnick et al., 1976 Segregation analysis andpedigree analysisTwo families Family 1: five of six siblings,three of them female, had JPFamily 2: four of eight siblings,all females, had JPCaucasian & African -AmericanXD modeSaxen, 1980 Simple segregation analysis Thirty-one families (158 subjects: 60 parents, 64 siblings and 3 children) Neither parents nor the children were affected with JP. 11 64 siblings were affectedFinnish groupAR modeSaxen et al. 1984 Simple segregation analysis Thirty families (60 parents and 52 siblings).No parents were affected;9 52 siblings were affected(Finnish group)AR mode

Beaty et al., 1987Complex segregation analysisTwenty-eight families (372 individuals: 62 had JP, 95 were unaffected and 215 unknown)(US Sample)AR modeLong et al. 1987 Complex segregation analysis 33 families (199 individuals)Compared the likelihoods of 33 kindreds(Caucasian & African American & Asian)AR mode

SEGREGATION ANALYSIS

AUTHORGENETIC ANALYSISSUBJECTSFINDINGSBoughman et al., 1988 Complex segregation analysis28 families (372 individuals: 62 had JP,95 were unaffected and 215 unknown)(Triracial isolate)AR modeMarazita et al., 1994Complex segregation analysis One-hundred families (631 individuals in total)AfricanAmericansDominant mode withpenetrance of about70%

Hodge et al., 2000Segregation analysisand linkage studyA large family (40 individualsin the pedigree trees)North European CaucasiansDominant mode

TWIN STUDYNo twin study on aggressive periodontitis has been reported

LINKAGE ANALYSIS

AUTHORGENETIC ANALYSISSUBJECTSFINDINGSBoughman et al., 1988 Linkage studyA large, five-generation family from southern Maryland (more than 70 individuals)An AD mode of JP: its localization to chromosome 4 and linkage to dentinogenesis imperfecta and Gc

Hart et al., 1993Linkage studyFifteen AfricanAmerican andfour Caucasian families (228individuals)Exclusion of the 4q candidateregion for EOP

Li et al., 2004 Linkage studyFour AfricanAmerican families (28 subjects)L-AgP is linked to humanchromosome 1q25

ASSOCIATION ANALYSIS

AUTHORGENETIC ANALYSISSUBJECTSFINDINGSDiehl et al.,1999 Family-based associationstudyTwenty-eight AfricanAmerican and sevenCaucasianAmerican families(285 individuals with DNAavailable for 246)Allele 1 of both interleukin-1A-889 and interleukin-1B+3953 was transmitted morefrequently with the EOPphenotype

Ren et al.2009Family-based associationstudySeventy-three nuclear families(DNA available for 204subjects) from ChinaAllele A of S100A8 gene SNPrs3795391 (A G) showedsignificantly preferentialtransmission to the AgP-affectedindividuals in theadditive genetic model

GENETICS & IMPLANTSVery few studies have been reported addressing the influence of genetics on implant survival.

Wilson et al.1999 . Studied the effects of the IL-1 genotype,smoking status, and patients age on failed or failing implants was compared to successfully integrated implants .Statistical testing failed to indicate a relationship between implant failure, age, or IL-1 genotype status.

Rogers et al.2003. also failed to demonstrate a relationship between implant failure and the IL-1A (-899), IL-1B (+3953) composite genotype in Caucasian patients.[Systematic review by Huynh et al.2007on the role of the composite interleukin-1alpha and interleukin-1beta polymorphisms and their natural specific inhibitor, interleukin-1 receptor antagonists, with respect to the development of periodontitis and periodontal therapy , no conclusive evidence can be attributed to the genetic traits.

EPIGENETICSEpigeneticsis the study of changes produced ingene expressioncaused by mechanisms other than changes in the underlyingDNAsequence2 Major Mechanism are:DNA MethylationHistone Modification

The hypo or hyper methylation of sites upstream of promoter region of cytokine genes can regulate the gene expression thereby resulting in increased production of the cytokines.

Chung et al ,2003 has demonstrated for TNF alpha in Rheumatoid arthritis.

Oral infection may also lead to epigenetic alterations, locally within gingival tissue or more globally with widespread effects. Technology is available to determine genomic-wide epigenetic changes that can be applied to study tissues at the biofilm interface to compare diseased tissue to healthy control tissue.

Susceptibility profileCombination of gene polymorphisms constitute a profile.Help to classify patients as low, medium and high risk.Already in application in systemic disease such as Alzheimers disease .

FUTURE PROSPECTS

Screening for risk assessmentAggressive periodontitis: screening the siblings of probands for aggressive periodontitis.

ReferencesClinical Periodontology. Carranza, 10th edition.

Clinical Periodontology and Implant dentistry. Lindhe, 4th edition.

Biology of the Periodontal Connective Tissues.Naraynan AS, Bartold PM

Genes and gene polymorphisms associated with periodontal disease. Crit Rev Oral Biol Med. 2003: 14(6); 430-449.

The genetic basis of periodontitis. Kinane DF, Hart TC. Periodontology 2000, 2005; Vol 39: 91-117.

Genetic study of families affected with aggressive periodontitis.Huanxin et al. Periodontology 2000, 2011; Vol 56: 87-101.

The genetic relationship to periodontal disease.Nares.S. Periodontology 2000, 2003; Vol 32: 36-49.

Epigenetic Regulation of gene expression in the inflammatory response and relevance to common diseases.Wilson AG.J Periodontal 2008;79:1514-1519.

Gene polymorphisms in periodontal health and disease. Perio-2000. 2006: 40; 94-106.

Clinical utility of a genetic susceptibility test for severe chronic periodontitis A critical evaluation. JADA 2002: 133; 452-459.

Implications of Genetic Technology for the Management of Periodontal Diseases. JP 2005: 76; 850-857.