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N G Martin

Publications and source records attributed to N G Martin.

At least 19 recordsLinked to original sources
PubMed1992

Increasing incidence of cutaneous melanoma in Queensland, Australia.

BACKGROUND: Queensland, Australia, had the world's highest incidence rates of invasive cutaneous melanoma in the 1970s. PURPOSE: The purpose of this study was to monitor trends in melanoma incidence in Queensland. METHODS: We studied two time periods in which ascertainment was comparable. RESULTS: In the 7.5 years up to 1987, the incidence of invasive melanoma in Queensland increased by more than one half in women (to 42.89 per 100,000) and more than doubled in men (to 55.81 per 100,000), with the most dramatic increase seen in men over age 50 years. This higher increase in men is a reversal of the previously higher rates in women. In Queensland, cumulative risks of total cutaneous melanoma (in persons aged 0-74 years), including preinvasive melanoma, have increased to one in 14 in men and to one in 17 in women. There were large increases in age-standardized incidence rates of thin lesions (less than 0.75 mm) in both sexes but not of in situ lesions, and there were also increases in thicker lesions, especially on the backs of males. CONCLUSIONS: Although increased awareness and earlier diagnosis appear to have accompanied increased incidence, increased exposure to solar UV radiation during the past 50 years appears to be the most likely explanation for the rise in incidence rates. IMPLICATIONS: A better understanding is needed of the causes of melanoma and of the complex relationships between constitutional factors, ambient UV radiation, and sun-exposure behavior.

Adolescent↗
PubMed1992

Protease inhibitor (Pi) locus, fertility and twinning.

In a sample of 160 Dutch twin pairs and their parents, we found that mothers of dizygotic twins had frequencies of the S and Z alleles at the protease inhibitor (Pi) locus that were 3 times higher than a control sample. Mothers of identical twins also had a higher frequency of S than controls. The S allele may thus both increase ovulation rate and enhance the success of multiple pregnancies. There was also an increased frequency of the S allele in fathers of dizygotic twins; however, this may be a secondary effect of assortative mating for family size (indicating by the number of siblings of the parents), for which a correlation of 0.2 was observed. Parents of dizygotic twins came from larger families than parents of monozygotic twins, but no effect of Pi type on family size was seen.

Alleles↗
PubMed1992

Religion and education as mediators of attitudes: a multivariate analysis.

The transmission of social attitudes has been investigated as a possible model of cultural inheritance in a sample of 3810 twin pairs from the Australian National Health and Medical Research Twin Registry. Six social attitude factors were identified and univariate genetic models fitted to scores on each factor. A joint multivariate genetic analysis of the six attitude factors, church attendance, and education indicated that the attitudes were correlated--the same genes and shared environments influenced more than one attitude factor. A current controversy regarding social attitudes is whether the significant loadings on this shared environmental component represent true cultural influences or are actually the genetic consequences of phenotypic assortative mating for church attendance and educational attainment (Martin et al., 1986). In our data, church attendance is almost entirely due to the impact of the shared environment. The large shared environmental component on church attendance also accounts for a substantial part of the family resemblance in social attitudes, suggesting that not all of the apparent cultural effects found in earlier studies can be ascribed to the genetic effects of assortative mating. However, church attendance and education do not completely account for the cultural component. Therefore, effects in addition to church attendance, education, and assortative mating for church attendance and education must be involved in the cultural component of the inheritance of attitudes.

Adolescent↗
PubMed1992

Pathways to hysterectomy: insights from longitudinal twin research.

OBJECTIVE: We hypothesized that genetic influences act on "liability" to hysterectomy, that secular influences might differentially affect relative importance of genetic and environmental influences, and that the sources of genetic influences could be identified from reported risk factors. STUDY DESIGN: Hysterectomy data from an Australia-wide volunteer sample of female adult monozygotic and dizygotic twins are reported. In 1980 through 1982 a mailed questionnaire was completed by 1232 monozygotic female twin pairs and 751 dizygotic female twin pairs (3966 women) from the Australian Twin Register (wave 1). The same twins were surveyed by questionnaire 8 years later (wave 2). RESULTS: A total of 366 had undergone hysterectomy by wave 1 and a further 198 at wave 2. The twin-pair correlations for liability to hysterectomy at wave 1 (0.61 +/- 0.06 for monozygotic and 0.20 +/- 0.11 for dizygotic) and wave 2 (0.65 +/- 0.05 for monozygotic and 0.32 +/- 0.09 for monozygotic) indicated a substantial genetic contribution. Reported risk factors accounted for only 15% of total variance. CONCLUSION: Genetic influences on liability to hysterectomy were substantial and stable across birth cohorts, but the important sources of genetic influence on liability to hysterectomy are yet to be identified.

Adolescent↗
PubMed1992

Platelet cytosolic free calcium concentration, total plasma calcium concentration and blood pressure in human twins: a genetic analysis.

1. We used path analysis and maximum-likelihood model fitting to evaluate the relative contributions of genetic and environmental factors to the relationships observed between level of blood pressure and both total plasma calcium concentration and platelet cytosolic free calcium concentration in 109 twin pairs. 2. Total plasma calcium concentration was positively associated with systolic (r = 0.26, P less than 0.001) but not diastolic blood pressure, a relationship which remained significant after adjustment for albumin, age and body mass index. A relationship between platelet cytosolic free calcium concentration and both systolic and diastolic blood pressure (r = 0.17 and r = 0.13, respectively, P less than or equal to 0.05) was no longer significant after adjustment for age and body mass index. 3. Additive genetic influences, unique environmental effects and age contributed to 60%, 30% and 10% of the variance in systolic blood pressure, respectively. Additive genetic effects explained 78% of the variance in plasma total calcium concentration and at least 48% of the variance in platelet cytosolic free calcium concentration in females and 37% in males. 4. Bivariate factor models provided evidence of genetic, but not environmental, co-variation of total plasma calcium concentration and systolic blood pressure, suggesting that a common genetic factor (or factors) contributes to their univariate relationship. In contrast, there was evidence of environmental, but not genetic, covariation of platelet cytosolic free calcium concentration and systolic blood pressure, suggesting that some of the individual experiences specific to each twin may be causing these two traits to vary together. 5. The possible confounding effects of adiposity and environmental factors should be considered in future studies investigating the role of intracellular calcium levels in the pathogenesis of hypertension.

Adolescent↗
PubMed1992

Genetic control of the renal clearance of urate: a study of twins.

Although a genetic predisposition to gout has been recognised for centuries, its mechanism has never been defined. This study was designed to determine whether this factor might be the renal clearance of urate, which is an important determinant of the concentration of urate in serum. In this study the renal clearance of urate was examined in 37 pairs of normouricaemic twins to determine whether this resemblance was genetically mediated. Monozygotic twins had more similar values of urate clearance and fractional excretion of urate than dizygotic twins. The heritability of the renal clearance of urate was estimated as about 60% (95% confidence limits 40 to 100%), whereas the heritability of the fractional excretion of urate was 87% (confidence limits 45 to 100%). This study supports the hypothesis that genetic factors exert an important control on the renal clearance of urate, which determines some of the familiarity of hyperuricaemia and gout.

Adolescent↗
PubMed1992

Fitting genetic models to Carabelli trait data in South Australian twins.

This study aimed to clarify genetic and environmental contributions to Carabelli trait variation on permanent first molar teeth in a large sample of South Australian twins. Estimates of polychoric correlations were obtained between pairs of monozygous (MZ) and dizygous (DZ) twins for Carabelli data and various gene-environment models fitted by a weighted least-squares approach. The favored model included additive genetic effects together with both a general environmental component and an environmental effect specific to each side. An estimate of heritability around 90% indicated a very strong genetic contribution to observed variation. The pattern of correlations for MZ and DZ data suggested that further studies involving other types of relatives would be worthwhile for detection of possible non-additive genetic effects of dominance or epistasis.

Adolescent↗
PubMed1992

Genetic differences in psychomotor performance decrement after alcohol: a multivariate analysis.

We reanalyzed data on the decline in performance on a battery of psychomotor tests, after a standard dose of ethanol (0.75 g/kg body weight), of 206 same-sex twin pairs. Principal components analysis identified two orthogonal factors. The first factor was strongly associated with increased body sway, self-rated intoxication and unwillingness to drive, and reported low average weekly alcohol consumption, but showed a very weak association with blood alcohol concentration. The second factor had high loadings on tests assessing psychomotor coordination, was strongly associated with blood alcohol concentration, but was unrelated to willingness to drive or self-rated intoxication. Multivariate genetic analysis indicated independent genetic and environmental determination of differences in sensitivity to the effects of alcohol on these two factors.

Adolescent↗
PubMed1992

Cleft lip with or without cleft palate: associations with transforming growth factor alpha and retinoic acid receptor loci.

The first association study of cleft lip with or without cleft palate (CL/P), with candidate genes, found an association with the transforming growth-factor alpha (TGFA) locus. This finding has since been replicated, in whole or in part, in three independent studies. Here we extend our original analysis of the TGFA TaqI RFLP to two other TGFA RFLPs and seven other RFLPs at five candidate genes in 117 nonsyndromic cases of CL/P and 113 controls. The other candidate genes were the retinoic acid receptor (RARA), the bcl-2 oncogene, and the homeobox genes 2F, 2G, and EN2. Significant associations with the TGFA TaqI and BamHI RFLPs were confirmed, although associations of clefting with previously reported haplotypes did not reach significance. Of particular interest, in view of the known teratogenic role of retinoic acid, was a significant association with the RARA PstI RFLP (P = .016; not corrected for multiple testing). The effect on risk of the A2 allele appears to be additive, and although the A2A2 homozygote only has an odds ratio of about 2 and recurrence risk to first-degree relatives (lambda 1) of 1.06, because it is so common it may account for as much as a third of the attributable risk of clefting. There is no evidence of interaction between the TGFA and RARA polymorphisms on risk, and jointly they appear to account for almost half the attributable risk of clefting.

Blotting, Southern↗
PubMed1991

Estimating genetic influences on the age-at-menarche: a survival analysis approach.

A survival analysis regression model is described for analyzing twin data on the age-at-menarche. The model includes latent genetic and environmental covariates and allows one to test hypotheses regarding the nature of familial aggregation for age-at-onset. Additionally, the model accommodates a variety of baseline survival distributions and therefore may be used to test different developmental hypotheses. Model-fitting results indicate that a survival model with a baseline gamma distribution gives an adequate fit to recalled age-at-menarche of 1,888 pairs of Australian female monozygotic and dizygotic twins. Further, results show that additive genetic and dominance genetic effects contribute to shared variation in age-at-menarche. If there are common environmental influences on the timing of menarche, they are completely obscured by nonadditivity in genetic factors, and information from other relationships would be required to detect their effect.

Adolescent↗
PubMed1991

Sexual orientation, sexual identity, and sex-dimorphic behaviors in male twins.

Sexual orientation, sexual identity, and sex-dimorphic behaviors were assessed concurrently and retrospectively, for childhood, in 95 pairs of male monozygotic (MZ) twins and 63 pairs of dizygotic (DZ) twins. There was a significantly higher rate of adult homosexuality among the MZ than among DZ twins. We employed a model-fitting approach using LISREL to test for genetic and environmental influences on variation for each trait singly and on the covariation among all six traits (three for childhood and three for adulthood). Univariate analyses confirmed the presence of familial factors for five of the six variables but were generally unable to distinguish shared environmental from genetic influences. Hierarchical tests of multivariate models supported the existence of an additive genetic factor contributing to the covariance among the variables. More restrictive multivariate models yielded a significant genetic influence on sexual orientation. Because of the different rates of orientation by zygosity and because of the restrictive nature of some of the multivariate models, our results are best considered tentative but do suggest that further biometrically oriented studies of sexual orientation and its correlates would be worthwhile.

Adult↗
PubMed1991

Elevation of follicular phase inhibin and luteinizing hormone levels in mothers of dizygotic twins suggests nonovarian control of human multiple ovulation.

OBJECTIVE: To determine whether multiple ovulation in mothers of spontaneous dizygotic (DZ) twins is because of higher hypothalamic stimulation or is in response to lower serum levels of ovarian inhibin. DESIGN: Serum hormone levels were measured at five times throughout the cycle in a sample of eight mothers of DZ twins and paired controls. On day 12, ovarian ultrasonography was performed. SETTING: Blood samples were collected in participants' homes except on day 12 when they were collected at the ultrasonography clinic. PATIENTS, PARTICIPANTS: Human volunteers who had at least one set of spontaneous DZ twins were paired with controls matched for age and parity. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Serum inhibin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and estradiol (E2) levels on approximate cycle days 1,2,8,12, and 21. RESULTS: Serum inhibin levels were elevated throughout the cycle (significantly on day 1) in mothers of DZ twins. Also elevated were early follicular FSH levels, LH levels throughout the follicular phase (significantly on days 1,2, and 8), and early to midfollicular E2 (significantly on day 8) in DZ mothers, indicative overall of greater follicular activity. CONCLUSION: It is concluded (1) that the primary cause of multiple ovulation in humans is not a decrease in inhibin secretion from the ovary; (2) the increased secretion of FSH and LH may be caused by elevated secretion of, or sensitivity to gonadotropin-releasing hormone; and (3) the elevated inhibin and E2 levels are a response to increased gonadotropin release.

Female↗