Indian Journal of Research in Pharmacy and Biotechnology ISSN: (Print) ISSN: (Online)

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1 Influence of Genetic factor on Dental Caries Darshana Bennadi 1 *, Veeara Reddy 2, Nandita Kshetrimayum 3 1. Senior Lecturer, Dept. of Public Health Dentistry, Sree Siddhartha Dental College and Hospital, Tumkur, India 2. Senior dental health officer, General hospital, Molkalamuru, Chitradurga District, Karnataka. 3. Assistant Professor, Dept. Of Public Health Dentistry, Regional Institute of Medical sciences, Dental College, Lamphelpat, Imphal, West Manipur, India *Corresponding author:e.mail:darmadhu@yahoo.com; Phone: ABSTRACT Caries remains the most prevalent non-contagious infectious disease in humans. Dental caries is a multi factorial infectious disease, with many contributory environmental factors, there is also strong evidence for a genetic component in the etiology of this disease. Genetics is defined as that branch of biology which deals with laws or principles of heredity and variation. Oral health is an integral component of general health and both share a dynamic relation. Studies of twins, families, and animal models have all indicated that caries has a genetic component. Evidence of a genetic contribution to caries is based on four questions examining inheritance that altered the dental hard tissues; the immune response; sugar metabolism & consumption; salivary flow, salivary constituents; & salivary defense systems. Improved knowledge of genetic and application of newer genetic techniques, helps to understand genetic risk factor relationships between dental caries and individual s phenotypic expression and above all, to prevent genetic diseases. Key words: Caries vaccine, Dental Caries, Genetics, Genes 1. INTRODUCTION As it is said, men evolved from men, imbibing some characters from their ancestors and fitting them to the present environment. The former is called inheritance and latter is called evolution. Genetics is defined as that branch of biology which deals with laws or principles of heredity and variation as observed in plants, animals, and in man. Its function is to discover and explain the mechanism of the origin and transmission of the hereditary substances from one generation to the next, as well as process of interaction of these hereditary substances with the external and internal environment of the individual during its development. (Colin, 1956). Scientific progress in genetics has practical implications for human well-being. Improved knowledge of genetic cause of an increasing number of human diseases helps the mankind to redefine diagnosis, to find new therapeutic approaches, and above all, to prevent genetic diseases. Oral health is an integral component of general health and both share a dynamic relation. Most of the oral diseases are complex in nature, resulting from infectious microbial agents coupled with hereditary and environmental factors (Wright, 2002). With application of newer genetic techniques, an increased understanding of genetic risk factor relationships between dental caries and individual s phenotypic expression is coming into light. Integration of information from human genome and other related technologies like microbial genomics will provide contribution to both etiology and susceptibility to this disease and will also help in developing new strategies for its diagnosis, management and risk assessment (Wright, 2002). The notion that dental caries in animals is an infectious transmissible disease was first demonstrated by Keyes (1960) (Caufield, 1993). It was several years later that the leading candidate responsible for caries was found to be similar to the streptococci isolated from a British child in 1924 by Clarke, which he named streptococcus mutans. Today, a heterogeneous group of gram-positive, caries associated streptococci are called Mutans Streptococci (MS): there are seven species, with Streptococci mutans and Streptococci sobrinus being the most prevalent caries-associated organisms in humans (Caufield, 1997). The remainder is found in animals or, if present in humans, are not highly cariogenic. The relationship of S sobrinus to caries in humans is not as well understood as that between MS and caries, and only recent studies identify the species separately (Axelsson, 2000). Lactobacilli which do not participate in the original colonization of the teeth and is more associated with carbohydrate consumption and the progression of disease process (Anderson, 2002). Also associated with the etiology of dental caries, but considered to be less cariogenic than S. mutans, S. sobrinus, and Lactobacillus, are Actinomyces odontologica, Actinomyces naeslundii (Axelsson, 2000). Caries Tetralogy (Newbrun 1982) includes a fourth factor, time to a still existing concept of Keyes, IJRPB 2(3) May-June 2014 Page 1196

2 depicting the significance of changes taking place over a period (Tandon, 2001). Risk factor is an environmental, behavioral or biologic factor confirmed by temporal sequence, usually longitudinal studies, which, if present, directly increases the probability of a disease occurring. If absent or removed, it reduces the probability. Risk factors are part of the casual chain or they expose the host to the casual chain. Once disease occurs, removal of the risk factors may not result in cure. The Keyes diagram is a specific application of a general model of disease termed the non-exclusive contributory disease model. This model has three elements: Environment, Genetic, and Infectious agent. This disease model states that any specific element may contribute to, but does not necessarily cause, the specific outcome of a cavity (Anderson, 2002) Cariogenicity of Mutans Streptococci - (Virulence): The most commonly isolated species of mutans streptococci are Streptococcus mutans (serotype c, e, and f) and Streptococcus sobrinus (sertypes d, g; Loeshe, 1986). Streptococcus mutans is found to be the leading cause of dental caries (tooth decay) worldwide and is considered to be the most cariogenic of all of the oral streptococci. It can be subdivided into atleast 8 serotypes (a-h) on the basis of carbohydrate antigens associated with the cell wall. In addition to carbohydrates, lipotechoic acids associated with the membranes and cell walls of S mutans are highly antigenic and cause wide serological cross-reactions throughout the streptococci. Lipotechoic acids may play a role in the adherence of oral streptococci to the tooth surface (Marsh, 1984). There are some characteristics of mutans streptococci that contribute to their cariogenicity, such as their ability to: Transport sugar; it has both high and low affinity transport systems which can operate over a wide range of conditions to ensure substrate uptake, even under extreme conditions, e.g. low ph. Produce acid; an efficient glycolytic pathway rapidly produces low terminal ph values in plaque. Tolerate acids (aciduricity); Cells are able to survive, metabolize and grow at low ph values. Produce extracellular polysaccharides (EPS); contributes to the plaque matrix, consolidates attachment of cells, and may localize acidic fermentation products. Produce intracellular polysaccharides (IPS); allows acid production to continue in the absence of dietary sugars. In Pre genomics era, the important role of sucrose in the cariogenic properties of S. mutans was recognized. These organisms were demonstrated to metabolize sucrose, as well as other sugars, rapidly to lactic acid and to convert a portion of the dietary disaccharide to glucan and fructan polymers. One of the earliest genetic approaches to characterization of the virulence of an oral pathogen was the demonstration, by Tanzer and colleagues, those spontaneous or chemically induced mutants of S. mutans defective in glucan synthesis or intracellular polysaccharide storage were attenuated in virulence when examined in a rat dental caries model. These findings, together with a comparison of the physiological properties of different oral streptococci, as well as clinical studies showing a positive correlation between the presence of S. mutans in specific plaque sites with the probability of caries development, confirmed the important role of these organisms in human dental caries. Furthermore, Hillman (1978) isolated a chemically induced mutant of S. mutans which was defective in lactic dehydrogenase activity and was also attenuated in dental caries induction in the rat model. This provided a genetic basis for confirmation of the important role of lactic acid production in caries formation (Tsu, 2003). 1.2.Extracellular polysaccharide: Glucosyltransferases (GTFs) and fructosyltransferases (FTFs), and the extracellular-polysaccharides produced by S. mutans, facilitate bacterial adherence and biofilm formation, and enhance the virulence of Streptococcus mutans because they catalyze the extracellular synthesis of glucans that are necessary for bacterial accumulation in dental biofilms (Browngardt, 2004) Glucosyltransferases (GTFs): S. mutans and S. sobrinus each synthesize several glucosyltransferases. The deduced sequences of these enzymes vary from 1400 to nearly 1600 amino acid residues and contain considerable sequence homology, despite differences in the water-solubility and linkages among the glucans synthesized. Genes responsible for glucan synthesis in S. mutans are gtf B, which synthesizes an 1,3-linked insoluble glucan, gtf C, which synthesizes glucan with both -1,3 and -1,6 linkages, and gtfd, which synthesizes a soluble {alpha}-1,6-linked glucan. Similarly, the products of gtfi and gtfs genes of S. IJRPB 2(3) May-June 2014 Page 1197

3 sobrinus synthesize insoluble and soluble glucan products, respectively (Smith, 2002) Fructosyltransferases (FTFs): Streptococcus mutans produces a fructosyltransferase (FTF) enzyme, ftf gene, which synthesizes fructan polymers from sucrose. Fructans contribute to the virulence of the biofilm by acting as binding sites for S. mutans adhesion and as extracellular nutrition reservoir for the oral bacteria (Rozen, 2004) Dextranases: Dextranases are kdal protein enzymes which break down polymers of glucose in α-1-6 linkage (dextrans). These dextranases are probably used by oral streptococci to modify the glucan product of GTF, clipping away the α- 1-6 linked oligomers and thereby increasing the proportion of α-1-3 linkages. Additionally, it is remotely possible that this may permit extracellular glucans to serve as energy stores. Dextranases may function in sucrose-independent adherence (via a SpaA-related epitope). Mutants lacking both dextranase and SpaA are found to be avirulent Glucan-binding proteins (GBPs): The synthesis of extracellular glucan is an integral component of the sucrose-dependent colonization of tooth surfaces by species of the mutans streptococci. Glucan-binding proteins are also found among the commensal oral streptococci. Extracellular polysaccharides are synthesized by one or more GTF enzymes in S. salivarius, S. gordonii, S. sanguis, S. oralis, and S.cristatus.S. mutans secretes at least three distinct proteins with glucan-binding activity: GbpA, GbpB, and GbpC (Banas JA, 2003) Intracellular polysaccharides (IPS): Many populations of oral streptococci are able to store and degrade intracellular polysaccharides. Strains of S. mutans serotype d characteristically have low IPS levels and, although this serotype is not as widely distributed as serotype c, a correlation was recently found between the presence of serotype d strains and the development of progressive carious lesions in man Adhesins: Bacterial attachment usually involves an interaction between a bacterial surface protein called an adhesin and the host cell receptor. This tropism (ability to gain access to a niche within the body), in association with the ability of the bacterium to breach mucosal barriers and invade the host, distinguishes pathogenic from commensal organisms. Colonization begins with the attachment of the bacterium to receptors expressed by cells forming the lining of the mucosa (Slavkin, 1999) Defense systems: S.mutans has developed defense systems to establish and sometimes dominate the microbial ecosystem. 1. This species is acidophilic, flourishing at a very low ph levels. Below a ph value of 4.5, not only is the competitiveness of cariogenic bacteria enhanced, but also the growth and metabolism of non-caries associated species are inhibited. Within three months of this pattern s being established, virulent bacteria can account for 75% of oral flora. 2. Behave differently depending on where in mouth it is found. 3. They like many gram-positive bacteria, produces its own antibiotics, called mutacins, which inhibit the growth of other gram-positive microorganisms and other streptococci (Dodds, 1995) Biofilms: Mutans streptococci are infectious organisms that form an intra-oral biofilm commonly referred to as dental plaque through there ability to adhere to tooth structure by laying down specific glucans thereby creating a highly sticky bacterial environment. One of the important virulence properties of these organisms is their ability to form biofilms (Anderson, 2002). Dental plaque formation on tooth surfaces involves three distinct steps: (i) formation of the conditioning film or acquired pellicle on the tooth enamel, (ii) subsequent cell-to-surface attachment of the primary colonizers, i.e. Adherence. Adherence to the solid surfaces by S mutans is necessary both before and after colonization. S mutans is able to attach to the surface by: ( Dodds, 1995). 1. Sucrose-independent adsorption, in which the bacteria attach to acquired pellicle through specific extracellular proteins (adhesions) of these organisms. 2. Sucrose-dependent mechanisms, in which bacteria require the presence of sucrose to produce extracellular polysaccharides, or by glucans, which allow attachment and accumulation. 3. Cell-to-cell interactions of late colonizers with one another as well as with the primary colonizers Gene expression in biofilms: Biofilm formation is initiated by interactions between planktonic bacteria and a surface in response to appropriate environmental signals. In addition, to responses to physical and chemical signals, bacteria regulate diverse physiological processes in a cell IJRPB 2(3) May-June 2014 Page 1198

4 density-dependent manner, commonly called quorum sensing. Molecules called quorum-sensing signals help trigger the regulation of gene expression in biofilms. Bacteria constantly secrete low levels of these signals and sense them through the corresponding receptors. The receptors do not trigger any behavioral changes until there are enough bacteria to allow the signal concentrations to exceed a critical threshold. Once this occurs, bacteria respond by adopting communal behavior, such as forming biofilms. LuxS-mediated quorum sensing has recently been shown to regulate important physiologic functions and virulence in a variety of bacteria. Reporter gene fusions in a study done by Wen et al (2004) showed that inactivation of LuxS resulted in a down-regulation of fructanase, a demonstrated virulence determinant, by more than 50%. The LuxSdeficient strain (TW26) showed increased sensitivity to acid killing but could still undergo acid adaptation (Wen, 2004) Genetics (Anderson, 2002): There is increasing evidence that there are genetic risk factor relationships between dental caries and an individual s phenotypic expression. This clearly manifest in the transmission of the S mutans infection between mothers and their children. If a mother harbors a significant infection, then there is prima fasciae evidence that the particular strain of S mutans resident in the mother is able to successfully compete with the mother s immune response. In saliva, the primary immunologic response is secretory immunoglobulin A, which exhibits its influence by selectively binding to the surface of S mutans at areas used by the organism to attach to a solid surface. Children manifest the mother s immune system for the first months of life. This immunity is transferred both by the placenta and via colostrums found in lactation products. Since the child s temporarily acquired immune system is not particularly effective against the strain of S mutans resident in the mother, acquisition is more likely to occur from the mother than the others. Inherited disorders that affect tooth development or salivary flow and immune system competency increase the incidence of caries. Three concepts have been put forward for studying the natural history of dental caries with emphasis on Mutans streptococci (MS) as the prototype for cariogenic biota (Caufield, 1997): 1. The temporal aspects of colonization, which is termed as window of infectivity. 2. The fidelity of transmission, which addresses source of MS to infant Mothers: Many other researchers suggest that children acquire MS from their mothers after teeth emerge. 21 This assumption seems reasonable, since mothers usually enjoy frequent and intimate contact with their infants in the first two years of life, when MS are initially transferred (Caufield, 1993). The evidence comes from several studies showing that isolate of MS harbored by mothers and their children exhibit similar or identical bacteriocin profiles and identical plasmid or chromosomal patterns (Ajdic, 2002) Spouses: Transmission among the human population is assumed to be by direct contact and through saliva, which carries a flora representative of that of mouth. Genotypic similarities of bacteria between spouses have shown the possibility of transmission among adults. Nie et al (2002) using DNA fingerprinting investigated the transmission between 11 married couples in Chinese families. It was concluded that there may be transmission between adults in Chinese families, but may be difficult for Mutans streptococci to colonize another mouth permanently Breast-feeding: Perinatal influences including nurturing practices and duration and intensity of exposure to individuals harboring MS might affect time and fidelity of transmission of MS into infants. Investigators have proposed that intensity of contact between mothers and their infants influences immunological levels in saliva. Breast milk contains both immunoglobulins and other immunoregulatory factors that may influence the selection and stability of indigenous bacteria (Li, 2000). The notion of clonality, which says that MS differs in their virulence or ability to cause caries, with some strains more virulent than others Factors which determine a child s susceptibility to dental caries are (Slavkin, 1999): The child s own genetics Genetics of the child s parents Genetics of infectious microorganisms Transmission of infectious microbes and age of infant or child Mucosal immunity Diet and nutrition Biofilms and microbial ecology Relative susceptibility of incisor and molar teeth Prevention measures IJRPB 2(3) May-June 2014 Page 1199

5 Early detection of dental caries 1.4. Clonality (Caufield, 1997): Tightly linked to the concept of fidelity is the concept of clonality. Because bacteria divide by binary fission, each generation is clonally related to the next. Mutations can arise at any time and given enough generations, mutations that introduce diversity within a given species can accumulate. In the case of human indigenous biota, S mutans as a prototype little is known about the degree of clonality that exists among different strains from different individuals. Two important concepts relating to clonality which can affect management of dental caries are: It may turn out that some clones are more cariogenic (virulent) than other clones. The correlation between virulence and clonality has been shown with H influenzae. Subsets of MS are also clonal. So could it be that an infant acquires one or several strains of MS from its mother or other source, some of which may be virulent, others non virulent? Could this explain why we see varied caries experience, even within family units? High levels of MS may indicate the presence of existing caries but does not mean that high levels of MS do not predispose an individual to caries. Hence, mere presence of MS is a poor predictor of caries. If we can genetically identify different clones, then that might be predictive in terms of caries risk. Clonality is the notion that hosts and their obligate parasites co-evolve. That is, indigenous bacteria habitating humans undergo mutational changes in parallel, at different rates, with their human hosts. So it is, possible then, that an insight into human evolution can be gained from studying the evolution of these co-evolving parasites. Study among families from the Philippines showed a suggestive linkage between low caries experience and loci 5q13.3, 14q11.2, and Xq27.1. Moreover, high caries experience was linked to loci 13q31.1 and 14q24.3 (Alexandre, 2012) Saliva: Saliva is essential for a lifelong conservation of the dentition. Various functions of the saliva are implicated in the maintenance of oral health and the protection of teeth (Van Nieuw, 2004) Major Salivary Proteins: The salivary immunoglobulins belong primarily (>85%) to the IgA subclass and to a lesser extent to the IgG subclass. Together, they make up 5-15% of total salivary proteins. Salivary IgA is synthesized by B lymphocytes located in the vicinity of secretory epithelia and subsequently secreted into saliva. IgG in saliva is mainly derived from crevicular fluid leaked into the oral cavity. The entire population of salivary immunoglobulins binds the majority of microorganisms present in saliva, thus presenting a broad-spectrum defense system. In contrast to immunoglobulins in serum, IgA in saliva does not function as an opsonizing agent. Also components of the complement system, which in serum cause direct killing of bacteria are absent in saliva. Thus, the main functions of salivary immunoglobulins tentatively will be inhibition of bacterial adherence and colonization. E.g. by blocking surface structures involved in binding (Van Nieuw, 2004) Mucins, constitute another important class of salivary glycoproteins. In unstimulated whole saliva they are the major components, making up 20-30% of the total protein. Two types of genetically different salivary mucins can be distinguished: MGI, high molecular weight mucin (Mr MDa), encoded by MUC5B gene, now designated MUC5B, and the low molecular weight MG2 (Mr ~ 130 KDa), the translation product of the MUC7 gene, now designated MUC7. Characteristic of mucins is the abundance of carbohydrates side chains which are covalently attached to the polypeptide backbones, forcing the molecule into an extended conformation. On a weight basis, the carbohydrates compromise 60% of MUC7 and 80% of MUC5B which are responsible for the viscoelastic nature (Van Nieuw, 2004) Minor Salivary Proteins: Saliva also has important anti-bacterial constituents including lactoferrin, lysozyme and peroxidase. Inherited deficiency of lactoferrin in man and lysozyme in rabbits has been described and different forms of human salivary peroxidase are known. Studies of the relationship between caries experience and these substances have, however, produced conflicting results. [27] Several domain are present within the polypeptide chain of lactoferrin that exhibit antimicrobial properties. One of these is lactoferricin, an N-terminal peptide of 40 amino acid residues that is liberated upon combined pepsin and trypsin digestion. Another domain of lactoferrin has been implicated in the binding to salivary agglutinin, suggesting that both salivary proteins can act together Salivary Peptides: In saliva atleast three types of antimicrobial peptides can be distinguished: histatins, defensins and hcap18/ll37, a human cathelicidin. These antimicrobial peptides have a IJRPB 2(3) May-June 2014 Page 1200

6 broad antimicrobial activity not only against bacteria but also against yeasts Hereditary Diseases Affecting Salivary Function: Cystic fibrosis is the most common lethal recessive inherited disease in Caucasians. About 4-5% of Caucasians are heterozygous for cystic fibrosis transmembrane regulator gene. In essence, the deletion causes increased mucoid secretions in every exocrine gland, including the salivary glands (the sublingual gland in particular). Patients with cystic fibrosis need many in between meal snacks and sugarrich drinks to provide them with necessary energy. This, diet is thought to carry a high cariogenic potential (Aps, 2002). Chisholm et al stated that salivary levels of sodium, chloride, calcium, phosphorous, protein, glycoprotein, urea and uric acid are elevated in patients suffering from cystic fibrosis (Kinirons, 1983). Familial amyloidotic polyneuropathy (FAP) is a hereditary systemic disease and patients suffering from this disease frequently complain of mouth dryness and increased need for dental treatment. A study done by Johansson I (1992) 30 showed that FAP patients frequently have a decreased rate of saliva secretion. The concentrations of salivary protein, amylase, lysozyme, salivary peroxidase, secretory IgA, hexosamines, sialic acid, fucose, phosphatase, potassium and the degree of protein glycosylation was higher in FAP patients than in control patients (Johansson, 1992) Secretory Immunity: Specific immune defense against the bacteria that are commonly held responsible for the initiation of caries, the mutans streptococci, mainly comprising streptococci mutans and streptococci sobrinus is thought to depend upon salivary antibodies. The major salivary immunoglobulin (Ig) is secretory IgA(S-IgA) which occurs at widely ranging concentrations in resting whole saliva (approx g/ml in adults). S-IgA is the product of the common mucosal immune system which consists of B and T lymphocytes and their progeny (Russell, 1999). Human IgA occurs in two subclasses, IgA1 and IgA2 and both occur in saliva, usually with a predominance of IgA1 (approximately 60%). IgA1 is unique in having an elongated, proline-rich, and o- glycosylated hinge region that is susceptible to cleavage by bacterial IgA1 proteases. Humans have high levels of circulating monomeric IgA in contrast to other mammals where it is monomeric in nature. Table 1 shows Possible mechanisms of antibody mediated intervention against mutans streptococci (Russell, 1999) Maternal influences on neonatal immunity: Although the neonate s immune system is functionally developed and ready to respond to antigenic challenge, at birth it is still effectively virgin; only about 1% of its circulating IgG is endogenous, and the fetus receives maternal IgG by receptor-dependent placental transfer. After birth, this supply ceases and by about 6 months of age, infants own production of IgG is still not fully developed but reaches adult levels in ensuing 1-2 years. Following birth, the breast-fed infant receives maternal Igs mostly in form of S-IgA which is abundant in colostrum (12mg/ml) but declines in mature milk. Smaller quantities of IgM and IgG also occur in milk. Maternally derived Igs not only provide passive protection in accordance with the specificities of antibodies transferred to the infant, but may also influence the development of the infant s own immune responses. Although the precise ways in which this occurs have not been fully explored, two main mechanisms can be postulated: (Russell, 1999). Colostral (mainly S-IgA) antibodies influence the microbiota that colonizes the infant, and thereby determine which antigens are available to stimulate the infant s immune system. Placentally transferred (IgG) antibodies may regulate the immune response to absorbed antigens by complexing with them and modulating their processing within antigen-presenting cells, or by modulating idiotypic networks. Though environmental interactions are important in determining colonization of oral cavity, maternal influences exert a major effect through the passive transfer of antibodies that modulate the immune response (placental transfer of IgG) or that influence microbial colonization (S-IgA from milk) as well as through genetic factors and exposure to maternal microbiota. Better understanding of these effects should allow strategies to be developed for improving the maternal influence on the infant s endogenous immunity. Likewise, altering the oral microbiota of the mother prior to birth may result in delay or prevention of infection of the infant s oral cavity with cariogenic bacteria (Russell, 1999). Although at birth the gastrointestinal tract and oral cavity are sterile, the neonate is immediately exposed to commensal as well as potentially pathogenic microbes. Salivary IgA antibodies are virtually absent at birth but begin to develop during the first few weeks of life, reaching adult levels within IJRPB 2(3) May-June 2014 Page 1201

7 about 6 months. During this time, protection against oral pathogens is provided by S-IgA antibodies from breastmilk, the innate salivary defense factors such as lactoferrin, lysozyme, peroxidases and antimicrobial peptides and possibly the placentally transferred maternal IgG antibodies(russell, 1999) Genetic markers: Major Histocompatibility Complex (Joerde, 1995): Includes a series of atleast 80 genes that lie in a 4-Mb region on the short arm of chromosome 6. The MHC is commonly classified into three groups: Class I, Class II and Class III Class I: Form a complex with foreign peptides that is recognized by receptors on the surface of cytotoxic T- lymphocytes: These molecules are encoded by the highly polymorphic HLA A, B and C loci on chromosome 6. In addition to presenting foreign peptides on the surfaces of infected cells, they can also bring about transplant rejection when foreign MHC molecules stimulate cytotoxic T-cells. Class II: They are found only on the surfaces of the immune systems APCs (phagocytes and B lymphocytes): In addition to, including the genes encoding major class II systems (such as HLA DP, DQ and DR), the class II region includes genes that encode peptide transporter proteins (TAP1 And TAP2). Class II MHC is heterodimers. Both class I and class II MHC molecules guide T-cell receptors (cytotoxic and helper) to specific cells. This is called MHC restriction. Class III: They include genes which encode for complement proteins: The immunoglobulins, T-cell receptor and MHC genes are members of gene family; MHC molecules vary between individuals. A significant number of diseases are associated with specific MHC alleles. Some of these associations are the result of linkage disequilibrium, but most are likely to result from casual associations involving autoimmunity. Eg: Type I Diabetes DR3 and DR4 Squamous cell carcinoma DQW3 MHC (HLA) MHC (HLA) 1.7.2: Other Genetic Markers: Blood Group and Caries (Walker, 1985): The bearing of blood groups on proneness to dental caries is a subject of controversy. Aitcheson and Carmichael (1962) reported a high percentage of blood group O and low percentage of blood group A in caries-resistant subjects. O Roark and Leyshon (1963) noted that the MN blood group was associated significantly with increased caries, however the correlation was not apparent in younger and older segments. Witkop (1963) in Chilean children found no association between ABO and MN blood groups and caries scores. In USA Green et al (1966) and Achimastos et al (1974), who investigated a very large series of Greek men aged year found no correlation between ABO and MN blood groups and caries scores PROP (6-N Propylthiouracil) Tasting (Lin, 2003): Sensitivity to taste is an inherited trait in children. Children can be supertasters, medium tasters, or nontasters as determined by subject s threshold. PROP paper is useful tool in determining genetic sensitivity to bitter and sweet tastes, as well as the burning sensation. Genetically, PROP tasting is produced by a dominant allele, T. Subjects with 1 dominant and 1 recessive allele (tt or Tt) or 2 dominant alleles (TT) are tasters. Those with two recessive alleles (tt) are nontasters) PTC (Phenylthiocarbamide) Tasting (Sofae, 1993): The ability to taste PTC is controlled by a single autosomal gene. Tasters have shown greater resistance to caries of the deciduous dentition than nontasters Red Cell Acid Phosphatase (Sofae, 1993: In Papua New Guinea, caries susceptibility has been reported to be influenced by allelic variation in the gene controlling the enzyme red cell phosphatase, the allele P (a) being associated with relative caries resistance Inherited Disorders: Reduced susceptibility: Hereditary fructose intolerance: A direct casual relationship exists between sugar ingestion and dental caries. Hereditary fructose intolerance, first, described in 1956 by Chambers and Pratt and confirm to autosomal recessive inheritance. Intolerance to fructose results from drastically reduced activity (2-5% of normal) of fructose-1-phosphate aldolase in liver, lower renal cortex, and small bowel. The defect probably involves a mutation of the structural gene of the enzyme. After intake of fructose, persons with hereditary fructose intolerance become nauseated, vomit, sweat excessively, and malaise, tremor, coma, and convulsions may develop. So, these patients require observation of life long self imposed, sucroserestricted diet, in which foods containing sucrose are consumed infrequently (Newbrun, 1980) Primary immunodeficiences: Relatively low caries experience is found in patients with primary IJRPB 2(3) May-June 2014 Page 1202

8 immunodeficiencies, probably as a result of prolonged antibiotic therapy (Sofaer, 1993) Chronic renal failure: Chronic renal failure, which occurs in a number of inherited disorders, appears to inhibit caries, probably through high salivary ph (Sofaer, 1993) Congenital chloride diarrhoea: Low caries experience has been found in patients with this autosomal recessive disorder. High salivary ph may be implicated since metabolic alkalosis is a feature of this disease(sofaer, 1993) Growth hormone deficiency: Study by Nikiforuk et al (1971) a sample consisting of ten children (mean age 8-9 years) who had growth retardation because of growth hormone deficiency were examined for caries status. Five of the children with primary growth hormone deficiency (group A) were caries-free. The most probable hypothesis to explain caries-resistance of deciduous dentition is the increased maturation time of enamel tissue before eruption in such children Turner syndrome: A symptom complex also called XO syndrome or Bonnevie-Ullrich syndrome. It is the most frequent chromosomal aberrations and characterized by the presence of only one normal functioning X chromosome. In women with 45, X chromosome complement, general somatic growth and development are affected. In the dentition, abnormalities of tooth form and size, enamel thickness, occlusion, and tooth eruption patterns have been reported (Lopez, 2002) Down syndrome: Trisomy 21, is a genetic disorder resulting in mental retardation, short stature, and phenotypic abnormalities, including oral, cardiovascular, hematopoietic, musculoskeletal, nervous, and behavioral anomalies. Subjects with Down syndrome are prone to develop infectious, malignant, and autoimmune diseases (Chaushu, 2002) Epidermolysis Bullosa: A group of hereditary and acquired disorders characterized by mechanical fragility and blistering of skin. EB frequently are reported to suffer from rampant carious destruction; which has been attributed to defective enamel, prolonged food retention in the oral cavity and changes in salivary consistency and quantity (Wright, 1994) Connective tissue disorders: Gross caries occurs in one form of Cutis Laxa, Rapp-Hodgkin ectodermal dysplasia and focal dermal hypoplasia (Sofaer, 1993) Rubinstein-Tyabi syndrome: The marked caries found in one-third of these patients is due to poor dental care resulting from a small mouth opening, malalignment of teeth and mental retardation (Sofaer, 1993) Klinefelter syndrome: Palin-Palokas et al (1990) [41] studied men with the Klinefelter syndrome (47, XXY males) and their brothers as regarding their caries experiences as part of a comprehensive study on oral facial growth and health in individuals with sex chromosome anomalies. The results showed that caries experience was greater among the 47, XXY men than among their normal brothers, and a greater proportion of the 47, XXY men's cumulative caries experience consisted of extractions Chromosome 18p deletion syndrome: It is caused by the deletion of a portion of genetic material on the short (p) arm of chromosome 18. Many of 100 prior case reports in the medical literature describing the dental health of subjects with this syndrome reported multiple caries associated with the syndrome (Sofaer, 1993) Vulnerability of Tooth Surfaces (Axelsson, 2000): The shape and size of the whole tooth may affect the degree of crowding and influence susceptibility to caries. Dental caries is initiated on the enamel surface, physical characteristics, such as a defective or rough enamel surface, and the chemistry of the enamel might also be determinants of tooth resistance Physical Characteristics of the Tooth Size: Tooth size may lead to extremely prolonged eruption time and subsequent rotation and tipping of teeth, which will increase plaque accumulation, hinder access for mechanical plaque control, and postpone occlusal contact and the beneficial frictional effect derived from chewing fiber-rich food Tooth morphology and cusp and fissures pattern: In a tooth brushing population, caries susceptibility in the permanent dentition may be ranked in the following order: 1. Fissures of the molars. 2. Mesial and distal surfaces of the first molars. 3. Mesial surfaces of the second molars and distal surfaces of the second premolars. 4. Distal and mesial surfaces of the maxillary first premolars. 5. Distal surfaces of the canines and mesial surfaces of the mandibular first premolars. 6. Approximal surfaces of the maxillary incisors. IJRPB 2(3) May-June 2014 Page 1203

9 1.12. Tooth Alignment: Genetic variation contributes about 40% to interindividual differences of tooth alignment in man. (Sofaer, 1993) Eruption: Monozygous twins have been found to be more alike than Dizygotic twins with respect to the time required for a deciduous teeth to erupt, the number of teeth erupted in 11-year olds, the timing of deciduous teeth eruption and shedding, and the timing of permanent teeth eruption (Sofaer, 1993) Enamel structure: Enamel development is conventionally described in five histologically recognizable stages: secretion (matrix deposition and transition), cell organization, preabsorption, early maturation, and late maturation. In later work, only four stages are described, based on chemical composition. Developmental disturbances may occur at any stage. There is, however, no clear clinical evidence that aberrations in enamel structure affect resistance to dental caries, unless the defects are major and result in rough surfaces that enhance plaque retention (Axelsson, 2000). Trace elements may be essential for the development of normal enamel structure. It is conceivable that the extent to which trace elements can be used by the body to influence caries susceptibility is under the control of enzymes subject to genetic variation (Sofaer, 1993) Genetic susceptibility to dental caries: Human studies (Joerde, 1995): Two research strategies that are often used to estimate the relative influence of genes and environment in human s are: Twin studies Adoption studies These studies (twin or adoption) serve a useful purpose in providing a preliminary indication of the extent to which a multi-factorial disease may be caused by genetic factors. monozygotic twins had a more similar caries incidence than dizygotic twins and that different sex dizygotic twins had the greatest variance. It was concluded that heredity plays a subsidiary part in the incidence of caries. Family studies (Murray, 1986): The greatest problem in family studies relating to caries experience is to try to differentiate between possible inherited or genetic factors influencing caries and familial factors due to different members of a family sharing a similar environment with respect to diet and oral hygiene practices. Population Studies (Niswander, 1975): Studies of group of individuals with differing levels of inbreeding (eg children of marriages between cousins) and conversely, studies of out bred or hybrid populations (offspring of interracial marriages) offer opportunity for genetic studies. Inbreeding increases and hybridity decreases the incidence of recessive genetic disorders. Studies of inbred and hybrid groups have therefore been used to investigate the possible effects of recessive genes on caries susceptibility Racial differences (Sofaer, 1993): Racial differences of caries prevalence and severity appear to have a largely non-genetic basis, being attributable particularly to variation in the quantity of dietary sugar, ingested fluoride, and the use of fluoride toothpaste. Nevertheless, in the multiracial population of Hawaii, after correcting for ethnic differences in various sociological variables and oral hygiene practices, DMFT and the prevalence of caries free individuals were still found to vary between groups of different ethnic origin Dental caries an autoimmune disease? (Murray, 1986): In 1966, a revolutionary concept of dental caries aetiology, involving precise mathematical calculations, was put forward by Burch and Jackson, who stated that Specific random events appear to be implicated in the initiation of dental caries. We shall argue that these initiating events are possibly somatic mutations and they give rise to the growth of forbidden clones of cells producing autoantibodies. That is to say, spontaneous disturbed tolerance auto-immune factors may be involved in the pathogenesis of dental caries Genetics in prevention of dental caries: Caries vaccine: Naturally-induced immunity is not the same as artificially-induced hyperimmunization, as observed after vaccine administration. Hyperimmunization results in the elevation of antibody to therapeutic or preventive levels against a specific microorganism. Generally, the aim of a vaccine is to reduce the numbers of an offending pathogen or to interfere with its metabolic activity and pathogenic components. In order to use hyperimmunization, several important things must be considered: (1) What will be the microbial target (ie. what is the offending pathogen?) (2) Which component of the immune system should be targeted; and (3) Prior to designing a vaccine, is there any evidence that hyperimmunization will work IJRPB 2(3) May-June 2014 Page 1204

10 Several stages in the molecular pathogenesis of dental caries are susceptible to immune intervention (Smith, 2002). Micro-organisms can be cleared from the oral cavity by antibody-mediated aggregation while still in the salivary phase, prior to colonization. Antibody could also block the receptors necessary for colonization (e.g., adhesins) or accumulation (e.g., glucan-binding domains of GBPs and GTF), or inactivate GTF enzymes responsible for glucan formation. Modification of metabolically important functions may also be targeted. In addition, the antimicrobial activity of salivary IgA antibody may be enhanced or redirected by synergism with innate components of immunity, such as mucin or lactoferrin Several alternatives include: (1) Purification of the candidate antigens and use of a subunit vaccine or (2) Using recombinant DNA methods to place virulence factors from cariogenic organism into a noncariogenic, non-crossreactive bacterium Candidate Antigens Targets: Extracellular protein targets include glucosyltransferases (GTF), dextranases, adhesins (such as Spa A or SA I/II), and glucan-binding protein. Other nonprotein candidate antigens have also been proposed, including extracellular glucans and the serotype-defining antigen Various Strategies Include: Maternal immunization: Passive immunization can occur by oral immunization (secretory IgA is stimulated) of pregnant rats. The milk from immunized rat mothers confers protection to the weanlings. It is possible that any mammal can be protected in this fashion. Xenogeneic immunization: It has been shown that cows can be immunized against cariogenic bacteria and that antibodies against those bacteria appear in the cow's milk Genetic engineering in dental caries (Agarwal, 2003): It is a process which involves transfer of a piece of DNA from one organism to another by cutting one segment of DNA off from one organism, attaching it to the segment of bacterial DNA called a plasmid and then placing this new gene into another organism DNA. It is also termed as Genetic modification Recombinant DNA technology, Genetic Manipulation. Thus, bacteria and even higher animals may be genetically engineered to produce foreign proteins of interest by inserting a copy or multiple copies of the gene encoding for the protein into them. 1. Genetically modified Yoghurt 2. Genetically modified milk 3. Genetically modified mouthwash 4. Genetically modified apple 5. Transgenic plant antibody (Edible immunotherapy) Recombinant vaccines Replacement therapy Biomimetics on tissue engineering Table.1.Possible mechanisms of antibody mediated intervention against mutans streptococci Isotype Step in caries pathogenesis Mode of action Antibody specificity S-IgA Adherence to salivary pellicle Blocking of adhesion-receptor interaction. Reduction of hydrophobicity. Agglutination and clearance. AgI/II Surface antigens Surface antigens Binding to early colonizers Blocking of adhesion-receptor AgI/II interaction. Sucrose- dependent accumulation IgG Acid production and other metabolic activities Colonization of cervical tooth sites Invasion of dentinal tubules Inhibition of glucan production. Inhibition of substrate binding. Inhibition of polymer synthesis. Blocking of adhesion. Blocking of glucose uptake Synergism with: 1.Peroxidase(inhibition of acid production) 2.Lactoferrin(inhibition of iron acquisition) Opsonization and phagocytosis Inhibition of collagen binding GTF Catalytic region Glucan binding region GTF(glucan binding region) GBP Not known Not known Iron-uptake molecules? AgI/II; other surface antigens? AgI/II IJRPB 2(3) May-June 2014 Page 1205

11 CONCLUSION Clearly, the Science of Genetics and newer techniques associated with it has provided us with a tool for characterizing the complex etiology of this disease. Numerous human and animal studies have given an indication to inheritance of this disease. Dental caries is now known as a complex genetic disorder. With the understanding of secretory immunity s role, a way to combat this disease by means of caries vaccine is being tried. A lot of research has gone into understanding this disease but scientists are still working to solve the still unanswered questions related to this disease like: Whether inheritance plays a dominant or a recessive role in the etiology of this disease? Whether there are genetic factors underlying other organisms causing this disease? Could it be the reason that it is difficult to develop an effective, broad-coverage dental caries vaccine? Can the genetic susceptibility to this disease be identified? Can it be treated like any other genetic diseases by giving gene therapy, i.e. removing the faulty gene? Dental caries is due to acidogenic activity. Is it possible to genetically engineer these organisms to create an alkaline environment, unconducive to development of dental caries? Can it be the solution which scientist is trying to decipher? REFERENCES Agarwal S, Pandit IK, Srivastava N, Gugnani N, Genetic enginnering and dental acries, Indian J Dent Res, 14(4), 2003, Ajdic D, McShan WM, McLaughlin RE, Savic G, Chang J, Carson MB, Genome sequence of Streptococcus mutans UA159, a cariogenic dental pathogen, Proc Natl Acad Sci U S A, 99(22), 2002, Alexandre Rezende Vieira. Genetics and Caries Prospects. Braz Oral Res., (São Paulo) 2012;26 (Spec Iss 1):7-9 Anderson M. Risk Assessment and Epidemiology of Dental Caries: Review of Literature, Pediatr Dent, 24(5), 2002, Aps JKM, van Maele GOG, Martens LC. Caries experience and oral cleanliness in cystic fibrosis homozygotes and heterozygotes. Oral surg Oral Med Oral Pathol Oral radiol Endod, 93, 2002, Axelsson P. Etiologic Factors involved in Dental Caries. In: Axelsson P. Diagnosis and Risk prediction of dental caries. vol 2. Ist ed. London: Quintessence publishing co, Inc; 2000, 1-40 Axelsson P. Internal modifying factors involved in dental caries. In: Axelsson P Diagnosis and risk prediction of dental caries, vol 2. Ist ed. London: Quintessence publishing co, Inc; 2000, Banas JA, Vickerman MM, Glucan-binding proteins of the oral streptococci, Crit Rev Oral Biol Med, 14(2), 2003, Browngardt CM, Wen ZT, Burne RA, RegM is Required for Optimal Fructosyltransferase and Glucosyltransferase Gene Expression in Streptococcus Mutans, FEMS Microbiol Lett, 240(1), 2004, Caufield P.W. Dental Caries, A Transmissible And Infectious Disease Revisited: A Position Paper. Pediatr Dent, 19, 1997, Caufield PW, Cutter GR, Dasanayake AP, Initial Acquisition of Mutans Streptococci by Infants: Evidence for a Discrete Window of Infectivity, J Dent Res, 72(1), 1993, Chaushu S, Yefenof E, Becker A, Shapira J, Chaushu G, Severe impairment of secretory Ig production in parotid saliva of Down syndrome individuals, J Dent Res, 81(5), 2002, Colin EC, What Is Genetics? In: Colin EC. Elements of Genetics. 3rd ed. New York: McGraw Hill Book Company, Inc; 1956, 1-3. Dodds MWJ, Wefel JS, The Developing Carious lesion. In: Harris NO, Christen AG. 4th ed. Stamford (Connecticut): Appleton & Lange, 1995, [last accessed on 13/04/2011] pdf [last accessed on 27/09/2011] Joerde LB, Carey JC, White RL. Multifactorial inheritance and common diseases, In: Joerde LB, Carey JC, White RL. Medical genetics. Ist ed. Toronto: Mosby; 1995, Johansson I, Ryberg M, Steen L, Wigren L, Salivary hypofunction in patients with familial amyloidotic polyneuropathy, Oral Surg Oral Med Oral Pathol, 74, 1992, IJRPB 2(3) May-June 2014 Page 1206