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Biomedical subjects

G Townsend

Publications and source records attributed to G Townsend.

At least 37 records · Page 2Linked to original sources
PubMed1995

Agenesis of permanent maxillary lateral incisors in South Australian twins.

The frequency of agenesis of maxillary lateral incisors (I2) in a sample of South Australian twins was determined, and associations with gender, zygosity, birthweight and dental crown size were investigated. Ten of the 446 twins examined (2.24 per cent) displayed agenesis of one or both I2, a similar frequency to that reported for Australian singletons. Seven of the ten affected individuals were monozygous female twins, including two pairs, while the three affected dizygous twins were each from different male twin pairs. Five pairs of monozygous twins were identified who displayed varying expressions of normal, small, peg-shaped or missing I2. These twin pairs displayed disparate birthweights suggesting they may have been mono-chorionic. These findings are consistent with a multifactorial threshold model linking size and number of I2 with developmental influences modifying phenotypic expression in those monozygous twins whose genetic predisposition places them near to the threshold for agenesis.

Adolescent↗
PubMed1991

Inactivation of thromboxane synthase with hydroperoxy-fatty acids.

Bovine lung thromboxane synthase was immobilized on phenyl-Sepharose beads by adsorption. The immobilized enzyme was catalytically active and synthesized both TXA2 and HHT. The structure-activity relationship of several hydroperoxy fatty acids and their ability to inactivate thromboxane synthase was investigated. Millimolar quantities of hydrogen peroxide and tert-butylperoxide were required to inactivate the enzyme: whereas micromolar quantities of C18 and C20 hydroperoxy fatty acids inactivated the enzyme. Pretreatment of the enzyme with long chain hydroperoxy-fatty acids resulted in a decreased synthesis of both TXB2 and HHT.

Animals↗
PubMed1991

Upper central incisor and canine tooth crown size in 47,XXY males.

Enamel and dentin thicknesses were measured in permanent tooth crowns of 47,XXY (Klinefelter syndrome) males. In 47,XXY males, enamel thickness in maxillary central incisors was significantly greater than that in control males or females, and dentin thickness in incisors and canines was significantly greater than that in control females, but smaller than that in normal males. These findings confirm the concept that human dental growth is affected by sex chromosomes. Amelogenesis is promoted by both X and Y chromosome genes, and sexual dimorphism in average tooth size is evidently determined by a promoting effect of the Y chromosome on dentin growth, probably through cell proliferation. This effect can also explain sex predilection for males in the numbers of supernumerary and ordinary teeth.

Amelogenesis↗
PubMed1990

Expression of the entoconulid (sixth cusp) on mandibular molar teeth of an Australian aboriginal population.

The expression and genetic basis of the entoconulid (sixth cusp) on mandibular molars were examined in a geographically isolated group of aboriginals from Yuendumu in the Northern Territory of Australia. Four grades of trait expression, ranging from trace to small, medium, and large cusps, were defined on dental casts of 399 subjects. Frequencies of occurrence were among the highest reported in human populations. Approximately 80% of dm2s showed the trait, whereas frequencies in the permanent dentition ranged from around 50% on M2 to 70% on M1 and 80% on M3. The degree of expression increased distally along the molar series, with only 3% of dm2s showing large cusps compared with 25% of M3s. Fluctuating asymmetry was highest for M2 and lowest for dm2. No strong evidence for sexual dimorphism in occurrence or degree of expression was found. Based on a quasi-continuous threshold model, a genetic contribution to entoconulid variability was observed that was strongest for M1. Significant associations were noted between entoconulid expression on mandibular molars and metaconule expression on maxillary molars, indicating that similar developmental mechanisms may influence these traits. The entoconulid and the metaconule both provide additional bulk on the distal occlusal surface of molar teeth, an area subjected to early wear during mastication in aboriginals.

Female↗
PubMed1990

Measurement of PGH synthase activity using a pan-specific monoclonal antibody.

A pan-specific monoclonal antibody that recognizes a variety of prostaglandin moieties and does not recognize arachidonic acid or the hydroxy-eicosatetraenoic acids was used to assess the general ability of a tissue to produce prostaglandins. Although this assay does not give a quantitative measure of PGH synthase activity, it does provide a sensitive and convenient means of screening a large number of samples for prostaglandin production.

Animals↗
PubMed1990

Twins and twinning, dentists and dentistry.

Comparisons of physical features within identical (monozygous) and non-identical (dizygous) twin pairs have provided valuable insights into the relative contributions of genetic and environmental influences to observed variability. The special nature of the twinning process itself also provides an opportunity to learn more about early human development, including how body symmetry is determined. The mechanisms of twinning, mortality and morbidity in twins, determination of body symmetry including the phenomenon of mirror-imaging, postnatal growth and development of twins, and zygosity determination are discussed. Twin studies with direct relevance to clinical dentistry are reviewed and illustrated by examples from an ongoing investigation of dentofacial morphology in South Australian twins.

Adolescent↗
PubMed1989

Gallstone growth, size, and risk of gallbladder cancer: an interracial study.

To investigate gallstone size, growth, and the relation between stone size and gallbladder cancer we have used cholecystectomy reports from 1676 female subjects (169 Whites, 531 Blacks, and 976 Native American Indians). Although the prevalence of gallstones differs markedly in these groups it appears that the estimated growth rate of gallstones in younger subjects, 2.0 mm per year (95% confidence interval: 1.7-2.3 mm) is homogeneous for all three groups. In both Indian and non-Indian populations the proportion of small stones diminished and the proportion of large stones increased over time. We found a strong relationship between gallstone size and gallbladder cancer. Large stones (greater than or equal to 3 cm) were found in 40% of patients with gallbladder cancer but in only 12% of all subjects of similar age. The relative risk for gallbladder cancer in subjects with stones greater than or equal to 3 cm was 9.2 compared with subjects with stones less than 1 cm. (95% confidence interval: 2.3-37). We estimate that one-third of all gallbladder cancers in subjects with calculi will be associated with large (greater than or equal to 3 cm) stones. We believe that stone size might be used to determine the risk of gallbladder cancer in patients with gallstones.

Adult↗
PubMed1988

Tooth crown size in human females with 45,X/46,XX chromosomes.

Permanent tooth sizes in 15 Finnish females with a 45,X/46,XX chromosome constitution were measured and compared with those of normal females, first-degree female relatives and 45,X females. Mesiodistal crown diameters of the 45,X/46,XX mosaic females were smaller than those of normal females but similar to those of females with pure 45,X chromosome constitution. Labiolingual crown diameters of the 45,X/46,XX mosaics were near normal, being consistently larger than those of 45,X females. The mesiodistal crown sizes are consistent with a decrease in enamel thickness in 45,X/46,XX mosaic females. The difference in labiolingual dimension between teeth of 45,X/46,XX mosaic females and 45,X females may relate to a gradual normalization of growth when normal 46,XX cells are mixed with defective 45,X cells.

Chromosome Aberrations↗