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D L Duffy

Publications and source records attributed to D L Duffy.

72 records · Page 4Linked to original sources
PubMed1994

Inferring the direction of causation in cross-sectional twin data: theoretical and empirical considerations.

A recent multivariate extension of the classical twin study in theory allows the inference of the direction of causation between correlated traits solely using cross-sectional data. In this paper we briefly review this model and assess its usefulness by applying it to a number of pairs of biological and psychological variables between which the nature of the causative relationship is already known. We conclude that the method has a number of biases and limitations. If a causative relationship at the phenotypic level exists between two traits, the correct direction of causation is usually identifiable, providing the reliability and validity of the measures are known. Failure to correctly specify a measurement model can lead to incorrect tests of hypotheses. Difficulties can also occur when discriminating between a direct causative relationship and a correlation due to common genetic or environmental determinants, but these occur in predictable situations. If these considerations are taken into account in interpretation of results, the true nature of the association between traits can often be correctly identified, or at least included in a subgroup of best fitting models.

Bias↗
PubMed1994

Biometrical genetic analysis of the cotwin control design.

The twin-cotwin matched case-control design can be interpreted in terms of bivariate genetic factor models. I derive expressions for the expected intrapair difference for a trait correlated with the variable on which discordance was selected.

Analysis of Variance↗
PubMed1994

Type A personality in Australian twins.

We examined the genetic and environmental determinants of Type A behavior in 200 pairs of same-sex twins as measured by the structured interview (SI) of Rosenman and Friedman and by the Bortner questionnaire (BARS). As noted previously, these measures are poorly correlated (r = .30). Quite different heritabilities were found for the two measures (63% for SI, 23% for BARS), and the correlation between the two was found to be largely genetic. Although the sample size meant that differences in correlation between MZ and DZ twins on the BARS were not significant in univariate analyses, they were suggestive of twin competition effects, as other twin studies have found. We conclude that further genetic analyses should concentrate on component behaviors rather than the overall Type A construct.

Adolescent↗
PubMed1993

Risk factors for atherosclerosis in twins.

We performed multivariate genetic analyses of cardiovascular risk factors from two sets of data on US and Australian female twins. Similar models for body mass index (BMI), serum low density (LDL) and high density (HDL) lipoproteins, including age as a covariate, were fitted successfully to both groups. These suggested that BMI, or genes responsible for a significant proportion of the variance of BMI, explained correlations between lipid subfractions, as well as those between blood pressure and lipid subfractions, especially HDL.

Adolescent↗
PubMed1993

Psoriasis in Australian twins.

BACKGROUND: Occurrence of psoriasis has been found to be strongly genetically controlled in Northern European and U.S. twin and family studies. OBJECTIVE: Our purpose was to assess cumulative incidence and heritability of psoriasis in the Australian population. METHODS: Australian twins reporting psoriasis on a screening questionnaire received from 3808 pairs were mailed a detailed instrument designed to validate the diagnosis, supplemented by telephone interview and examination of medical records. RESULTS: Only 94 of 160 subjects who screened positive were confirmed to have psoriasis. The cumulative incidence of confirmed psoriasis was 2% in 30- to 60-year-old subjects. The monozygotic twin casewise concordance for confirmed psoriasis was 35% (12 of 34 pairs), and the dizygotic twin concordance 12% (5 of 43 pairs), giving an estimated heritability of 80%, was similar to that found in a genetic reanalysis of three previous twin studies. A case-control analysis of psoriasis-discordant twin pairs found no evidence for influences of alcohol or coffee intake, overweight, birth weight, or personality in the origin of psoriasis. CONCLUSION: Occurrence of psoriasis in the Australian population is highly heritable, but identical twins are often discordant; the factor responsible for the onset of disease in one twin and not the other is unclear.

Adult↗
PubMed1993

Lower respiratory tract symptoms in Queensland schoolchildren: risk factors for wheeze, cough and diminished ventilatory function.

BACKGROUND: The occurrence of respiratory symptoms and abnormal lung function in children is known to be influenced by genetic and many environmental factors. The association between specific respiratory symptoms in children of school age and their parents has been examined. METHODS: Respiratory symptoms and ventilatory function were recorded for 4549 schoolchildren in Queensland, Australia. RESULTS: The cumulative prevalence of wheezing was 23.1% of 8 year olds and 20.8% of 12 year olds, and the prevalence of wheezing within the previous 12 months was 13.9% and 10.5% respectively. A parental history of asthma or wheeze and hayfever was associated with wheeze in the child, but did not affect either the age of onset or frequency of episodes. A history of frequent cough in children who had never wheezed was associated with a parental history of frequent bronchitis, but less strongly with parental wheeze. These familial aggregations were not mediated by common exposure to cigarette smoke. Both a history of parental wheeze and maternal cigarette use were associated with a decrease in FEF25-75 in the child and these effects were additive. CONCLUSIONS: The association of specific symptoms (wheeze and cough without wheeze) in parent and offspring is interpreted as evidence for different mechanisms of familial transmission, which may be genetic.

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

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

Informativeness of twin-nuclear family and nuclear family designs for segregation analysis.

This brief note examines the precision of segregation parameter estimates from both twin-nuclear family and conventional nuclear family designs. The program MENDEL was used to derive expected frequencies of different family patterns of affectation (with fixed sibship size) under various single gene models, and then to estimate the standard errors (and information) associated with gene frequency and penetrance values at given sample sizes. As might be expected, a 2- to 5-fold increase in relative efficiency was found for the same family size if families included an MZ twin pair among their offspring. The methods used allow convenient calculation of expected informativeness of a given study design.

Epidemiologic Methods↗
PubMed1991

Respiratory symptoms in Queensland schoolchildren: an association between month of birth and respiratory illness.

We have examined the relationship between month of birth and episodes of wheezing, productive cough, eczema and hayfever, and also standardized maximum mid-expiratory flow (FEF25-75) in a representative sample of 4549 Australian primary schoolchildren (mean age 10.1 years). Children experiencing frequent wheezing (one or more episodes per month) were more likely to be born in spring and summer (odds ratio = 1.6, 95% confidence interval = 1.1-2.4), but this was not seen for less severe disease. No effect of season or birth month was seen for the other illnesses examined or for lung function.

Australia↗
PubMed1990

Genetics of asthma and hay fever in Australian twins.

The occurrence of self-reported asthma/wheezing and hay fever among 3,808 pairs of twins from the Australian National Health and Medical Research Council Twin Registry was examined for evidence of genetic transmission by path analytic methods. The cumulative prevalence of asthma or wheezing was 13.2% and of hay fever, 32%. There were significant correlations in liability to reported disease among twins, and these were higher in monozygotic twins (MZ) (r = 0.65) than in dizygotic twins (DZ) (r = 0.25), and in male MZ twins (r = 0.75) compared with female MZ twins (r = 0.60). Analysis under the assumptions of the classic twin model suggested that there were genetic factors common to asthma and hay fever, with a correlation in genetic liability to the traits of 0.52 for men and 0.65 for women. These genes acted substantially in a nonadditive fashion in men but not in women. As the genetic correlation was significantly less than unity, this implied additional genetic factors influencing either or both diseases individually. The estimated heritability of these diseases was 60 to 70% in this population. Environmental causes of both diseases also were correlated (r = 0.53 for men and 0.33 for women). Cigarette smoking was only weakly associated with wheezing.

Adult↗
PubMed1980

Communication skills of house officers. A study in a medical clinic.

The communication skills of house officers in medical clinic were studied. Ten communication skills were identified as being central to the doctor-patient relationship. Twenty interns and residents were observed in 60 clinic visits. Skills well-demonstrated by the house officers related to listening, history taking, assessing patient compliance, examining the patient, and prescribing therapy. Underdeveloped skills were those that involved obtaining the patient's understanding of his illness, social history, and emotional response and the doctor's explanation of the illness. To enhance performance of these skills, changes are recommended in four areas of ambulatory teaching: liaison psychiatry, faculty development, medical precepting, and the relationship between faculty and house officers.

Communication↗