Host genes and dental caries.

With the attention now being given to molecular genetic analysis of cariogenic microorganisms, the role of host genes in influencing susceptibility to caries should not be forgotten. Increasing knowledge in this field will lead to identification of individuals at particular risk of dental decay and will help in planning rational strategies for management and prevention.

Coefficients of relationship by isonymy among oral cancer registrations in Scottish males.

The role of inherited susceptibility to oral cancers was studied by comparing groups of cancer patients and controls in terms of the coefficient of relationship by isonymy (Ri), both within and between Regions of mainland Scotland. Surname distributions for 3658 male cancer cases were derived from the Scottish Cancer Register for the years 1959-85. Control distributions were derived from a total of 32,468 male deaths in Scotland for 1976. For cancer of the floor of mouth, there was no evidence for increased isonymy in patients compared to controls and therefore no indication that familial factors contribute to cancer at this site. For cancer of the tongue there was a suggestion of increased isonymy within but not between Regions, perhaps reflecting environmental risk factors common to members of the same family. For cancers of the lip and salivary gland there was evidence of increased isonymy both within and to a lesser extent between Regions, suggesting a genetic contribution. There is corroborative evidence from other sources for a heritable component in salivary gland cancer but the reasons for the similar pattern of results in cancer of the lip are less clear.

Coefficients of relationship by isonymy among registrations for five common cancers in Scottish males.

STUDY OBJECTIVE: The aim was to assess the relative importance of genetic factors in carcinoma of the stomach, colon, rectum, prostate, and bladder in Scottish males. DESIGN: Cancer cases and controls were compared in terms of the coefficient of relationship by isonymy (Ri). SETTING: Surname distributions for cancer cases were derived from the Scottish Cancer Register for the years 1959-85. Control distributions were derived from all births, marriages and deaths in Scotland for 1976. SUBJECTS: Analysis was carried out on a total of 60,933 cancer registrations and 101,836 births, marriages, and deaths over the 12 local government regions of Scotland. MAIN RESULTS: Comparisons of Ri within and between regions indicated that inherited susceptibility was of greatest importance in carcinoma of the prostate and colon, of intermediate importance in carcinoma of the rectum and stomach, and of minimal importance in carcinoma of the bladder. Familial aggregation of cancers was most pronounced in Highland, Tayside, and Borders Regions. For Highland, this appeared to be the result of region-specific familial influences, while Tayside and the Borders shared genetic factors contributing to cancer aetiology with neighbouring regions in south east Scotland. CONCLUSIONS: Surname analysis is a simple but useful tool for studying population genetic structure and its relationship to disease incidence.

Coefficients of relationship by isonymy among Scottish males with early and late onset cancers.

Studies of certain cancers suggest that early onset cases tend to have a more pronounced hereditary component than late onset cases. We have analysed data from 60,924 Scottish males with cancer of the stomach, colon, rectum, prostate or bladder, using the coefficient of relationship by isonymy to compare patients whose age at registration was below the median with those whose age at registration was equal to or above the median. There was no evidence for greater isonymy in younger patients suggesting that, although known genetically determined cancers may have earlier onset than other cancers at the same site, early age at onset is not widely associated with a familial predisposition to malignancy.

Chronic atrophic oral candidiasis among patients with diabetes mellitus--role of secretor status.

Non-diabetic individuals who are non-secretors of blood group antigens are prone to superficial infections by Candida albicans. In this study, 216 patients with diabetes mellitus who were denture wearers were examined for the presence or absence of denture stomatitis. There was an overall trend for non-secretors to be prone to denture stomatitis compared with secretors. Stepwise linear discriminant analysis was used to dissect the contribution of secretor status and other variables to the development of the disease. Secretor status was found to be a contributory factor among patients with non-insulin dependent diabetes but not among those with insulin-dependent diabetes. The possible reasons for this are discussed.

Genetic approaches in the study of periodontal diseases.

Periodontal diseases are essentially infectious in origin, their outcome depending on interaction between the pathogenic challenge and host response. Host genotype has been implicated in certain of the more unusual forms, but together these account for only a small proportion of periodontal patients. Nevertheless, the genes for these rarer conditions, some of which have already been located and/or cloned, are of considerable importance, since they may ultimately provide clues leading to a better understanding of the whole spectrum of periodontal disease. For the majority of periodontal patients, although inherited susceptibility is suspected, evidence of a significant genetic component is scanty. The priority here is therefore to establish the existence of contributing genes. This may be possible by using approaches designed to minimise the confounding effect of environmental variation that has probably been a source of confusion in the past.

Coefficients of relationship by isonymy among the parents of Scottish twins: a test of familial aggregation.

The ability of the coefficient of relationship by isonymy Ri to detect familial aggregation of conditions suspected of being under a degree of genetic control was tested on groups of fathers and mothers of like-sex twins, fathers and mothers of unlike-sex twins, and fathers and mothers of singleton controls born from 1977 to 1981 in Scotland. No statistically significant difference of within-group or between-group Ri was found, either for all surnames or for rare surnames only. However, the overall pattern of results for rare surnames showed a measure of agreement with what is already known of the genetics of twinning. The relatively high within-group Ri for mothers of unlike-sex twins is consistent with a maternal genetic influence on dizygous twinning, whereas the relatively high between-group Ri for fathers with mothers of unlike-sex twins suggests that paternal as well as maternal genes may be involved. Values of Ri for the parents of like-sex twins raise the possibility of a paternal but not a maternal genetic contribution to monozygous twinning.

Dentistry and the new genetics.

As environmental causes of disease become better controlled, so genetic factors assume relatively greater importance. Opportunities to investigate the genetic contribution to disease have increased dramatically through the remarkable technological developments of recent years. These developments have implications for both education and practice in dentistry, just as in any other branch of the biomedical sciences.

Coefficients of relationship by isonymy within and between the regions of Scotland.

The distribution of surnames for births, marriages and deaths in 1976 among residents of the 12 Local Government Regions of Scotland was analyzed in terms of the coefficient of relationship by isonymy, Ri. Differences between sexes and events for Ri within Regions were consistent with greater inter-Region mobility among males compared with females and among young adults compared with the elderly. There were near zero correlations of geographical distance with Ri between Regions based on all surnames or common surnames. With Ri based on rare surnames, there was a small though statistically nonsignificant negative correlation. The best-fitting two dimensional relationship derived from Ri values based on rare surnames showed a fair correspondence with the map of Scotland, indicating a degree of genetic isolation between the Regions.

Host genotype, pathogenic challenge and periodontal bone loss in the mouse.

Periodontal bone loss was induced in mice of different genotypes by oral inoculation with Actinomyces viscosus. Relatively high bone loss occurred in the mutant X-linked immune deficiency, implicating the humoral immune system. Maximum bone loss was always associated with inoculations of 1.6 x 10(7) colony forming units (c.f.u.), while inoculations of 1.6 x 10(6) or 1.6 x 10(9) c.f.u. resulted in bone loss little different from that in uninoculated controls. This 1000-fold range in inoculum size was not reflected in the number of A. viscosus organisms recovered from the molar teeth at the end of the experimental period, suggesting that differences in bone loss stemmed from the host response to the initial inoculum.

Cleft lip with or without cleft palate: identification of sporadic cases with a high level of genetic predisposition.

Previous studies have suggested that asymmetry for certain bilaterally represented features may be an indicator of genetic predisposition to cleft lip with or without cleft palate and may therefore be of value in the individual assessment of recurrence risk, particularly for sporadic cases. An asymmetry score has been devised that may be of use in identifying those with a high level of genetic predisposition. Stepwise logistic regression selected nine variables that together correctly classified 85% of familial cleft patients and unrelated non-cleft controls. Applying the same regression equation to sporadic cases, 26% fell into the range occupied by the majority of familial patients, suggesting that these had a high level of genetic predisposition.

Sweat pore count, hair density and tooth size: heritability and genetic correlation.

In 109 subjects from 50 families without major inherited disorders, sweat pore count showed the anticipated reduction with age but also unexpected systematic differences between sides and between fingers. After adjustment for age and sex, significant genetic variation was found for sweat pore count, hair density and tooth size. The three traits were not phenotypically correlated but there was a significant negative genetic correlation between hair density and sweat pore count. The findings suggest that the same genes influence these two traits in opposite directions and that genetic and environmental influences may act on them through different physiological mechanisms.

Difficulties in obtaining a sample of young adult cleft lip and palate subjects and their relatives.

Families of individuals aged 15-24 yr born with cleft lip, with or without cleft palate, and suitable control families were required for a study of inherited predisposition to the malformation. Cleft patients were identified through hospital discharge listings, but the overall yield of participating patients was only 8% of the cases listed. An attempt to recruit control subjects by the same method, using patients who had been hospitalized for dissection tonsillectomy, yielded only 4% of those identified as suitable in the discharge listings. The results highlight the value of specialized, regularly updated disease registers in the recruitment of subjects for research purposes.

Affinities between contemporary and skeletal Jewish and non-Jewish groups based on tooth morphology.

Samples from five Jewish and six non-Jewish populations were compared in terms of the frequencies of 19 dental morphological variables. All but one of the samples came from Europe, North Africa, or the Middle East. Nine were from contemporary populations, and two were skeletal. Of the skeletal groups, one was Jewish, excavated on Mount Zion, Jerusalem, and dated at around 3,000 years old; and the other non-Jewish, excavated on the east coast of Australia, and dated at between 1,000 and 200 years old. Assessment of affinity between the different groups was based on smallest space analysis and cluster analysis. The results demonstrated relative proximity of the Jewish groups (with one exception), despite the fact that they came from a wide geographical area. In particular, the sample from Mount Zion showed greater affinity with three of the four living Jewish populations than with most non-Jewish groups. The skeletal Australian sample formed a cluster of its own, distinct from all the other groups. For six of the groups, the relationships based on tooth morphology showed good correspondence with known relationships based on single locus polymorphisms. The similarity of the Jewish groups to each other in terms of both tooth morphology and single locus polymorphisms was of special interest, since differences in other morphological and anthropometric characteristics, thought to be the result of selection, are known to exist between the Jewish populations.

Heritability estimation from concordant twin pairs alone.

Heritability estimation is possible from concordant twin pairs alone, based on the proportion of like-sexed pairs among all concordant affected pairs. The method is limited to conditions found in both sexes in the prevalence range 0.1% to 10%, and a relatively large population size is required to give an adequate sample of twin pairs. However, the method has the considerable advantage that zygosity determination is not required and that any bias due to incomplete diagnosis/ascertainment is likely to be small. The method is particularly suited to diseases where registration is obligatory and computerised so that the register can be scanned for pairs of individuals with the same date of birth, place of birth and birth surname.

Developmental stability in the mouse vertebral column.

The effects of six mutant genes (Sd, T, vt, Sp, un, Ph) on the axial skeleton of the mouse were studied both alone and in combination with 24 hours starvation on Day 8 of gestation. Normal controls showed a craniocaudal gradient of size variation and relatively low variability towards the boundaries of the cervical, thoracic and lumbar vertebral classes. Gene-induced craniocaudal gradients of abnormality were observed in response to Sd and T, and to Ph, which have direct and indirect effects respectively on the primitive streak and/or notochord. By contrast, vt, which influences the paraxial mesoderm, and Sp and un, which act later, during somite formation and sclerotome differentiation respectively, did not produce craniocaudal gradients of abnormality. For all genes there were indications of relative resistance to their effects towards the vertebral class boundaries. Starvation did not materially influence these patterns of abnormality. The division of the axial skeleton of the mouse into its morphologically distinct classes of vertebrae thus appears to originate at the earliest stage of axial development, even before somite formation, with the positions of the future vertebral class boundaries established both axially and paraxially as regions of relative stability that persist into later stages of development. The primary craniocaudal gradient associated with the advancing primitive streak, from which the vertebral class boundary positions may be derived, appears to be restricted to the axial structures themselves and to be lost after the somites appear.

Dental extractions in Paget's disease of bone.

The results of a postal questionnaire completed by 360 patients with Paget's disease of bone, on behalf of themselves and their unaffected spouses, suggest that dental practitioners have some awareness of the potential problems associated with extractions for patients with Paget's disease, but that nevertheless patients still suffer from greater difficulty at extraction and more post-extraction complications than normal.

A family study of Paget's disease of bone.

Familial aggregation of Paget's disease of bone occurs occasionally and an exclusively genetic aetiology has been proposed in the past. On the other hand, epidemiological surveys point to an important environmental contribution, and evidence is accumulating to suggest that the disease may be caused by a slow virus infection. Analysis of 407 family history questionnaires completed by patients with Paget's disease confirmed the familial nature of the disease. Overall, the findings were consistent with the hypothesis that Paget's disease is caused by infection with a common and widespread virus superimposed on genetic variation for susceptibility and perhaps severity of the disease.

Experimental oral infection of mice with a pathogenic and a non-pathogenic strain of the yeast Candida albicans.

Oral infection by Candida albicans is thought to be related more to host susceptibility than to virulence of the organism. Using a mouse model of oral candidosis, differences in colonization and infection between two strains of C. albicans were demonstrated.