Biomedical subjects

N G Martin

Publications and source records attributed to N G Martin.

At least 145 records · Page 8Linked to original sources

PubMed1997

Nicotine withdrawal in women.

Associations between self-report symptom profiles for nicotine withdrawal, personality (TPQ, EPQ-R), life-time history of psychopathology and smoking history were examined in data obtained from 553 female adult Australian twins (246 regular smokers), aged 32-48 years, who had participated in a telephone interview survey that included life-time assessments of smoking history, nicotine dependence and symptoms of withdrawal. Two hundred and two respondents were from high-risk pairs where either the respondent or the respondent's co-twin had reported a life-time history of alcohol dependence; 351 were from control pairs. Latent class analysis was used to identify subtypes ('classes') of smokers reporting similar withdrawal symptom profiles. Three major classes were identified which appeared to represent a continuum from mild to severe nicotine withdrawal. Smokers from the severe withdrawal class were best characterized by hands shaking and by the prominence of depressive features. There were marked increases in life-time alcohol dependence rates as a function of severity class. In contrast, significantly elevated rates of major depression, conduct disorder and anxiety disorder were observed only among smokers from the most severe withdrawal class. Neuroticism was the only personality factor strongly associated with the development of withdrawal symptoms.

Adult↗

PubMed1997

Smoking and intoxication after alcohol challenge in women and men: genetic influences.

In an earlier analysis, men and women who were current or former smokers were found to report feeling less intoxicated on average than nonsmokers after ingestion of a challenge dose of alcohol. Here, we examine whether differences in subjective response to alcohol and a tendency to smoke cigarettes are transmitted together in families; and, if so, whether this association might be entirely explained by the same heritable factors that influence alcohol intake (as we might expect if both smoking and subjective intoxication are influenced by some general susceptibility for substance use). Alcohol challenge data on 388 Australian male and female twins (194 complete pairs) were reanalyzed using multivariate genetic analysis to evaluate the association between cigarette smoking and self-report intoxication after a standard dose of alcohol. In women, we could not reject the hypothesis of complete genetic overlap between effects on intoxication rating and history of smoking, and a significant residual genetic correlation between smoking and postalcohol intoxication persisted even when genetic influences on alcohol consumption were controlled for. In men, the familial association seemed to be largely environmentally mediated and associated with differences in drinking history. These findings prompt the question of whether, in some individuals, cigarette smoking may contribute to the development of tolerance to the effects of alcohol.

Adolescent↗

PubMed1996

Reliability of computer image analysis of pigmented skin lesions of Australian adolescents.

BACKGROUND: The diagnosis of melanomas at an early stage is associated with improved survival, so the recognition of changes in pigmented skin lesions over time is important. We have developed a computer imaging system with the aim of assisting clinicians in differentiating early melanomas from benign pigmented skin lesions. The objective of this study was to investigate the system's reliability over time in measuring diagnostic characteristics of pigmented skin lesions, including their color, size, shape, and distinctness of boundary. METHODS: We captured video images of 5 lesions, all larger than 2 mm in greatest dimension, on each of 66 Australian adolescents on 2 occasions approximately 1 month apart. Features extracted by computer image analysis included area, perimeter, and regularity of outline of the lesions, the mean and standard deviation of reflectance at red, green, and blue wavelengths, and the mean and standard deviation of the gradients of red, green, and blue reflectance at the lesion boundary. RESULTS: All measurements showed moderate to high reliability (intraclass correlation coefficients 0.66-0.94), except for the standard deviations of the color gradients, whose reliability improved to moderate levels (0.68-0.71) when the mean of 5 lesions was considered. For most outcomes, reasonable within subject reliability was achieved when five lesions per subject were measured. CONCLUSIONS: These results, in combination with previous work demonstrating the reasonable ability of this computer imaging system to discriminate between malignant melanomas and other pigmented lesions, indicates that the system has the potential to become a useful tool for clinicians in following people with pigmented lesions over time to detect early malignant changes.

Adolescent↗

PubMed1996

Genetic contribution to DZ twinning.

The genetic contribution to dizygotic (DZ) twinning was investigated using 6,596 twin pairs from the Australian Twin Registry who provided information on other twins in their families. Responses were classified by the zygosity (DZ; monozygotic [MZ]) of the proband twins and by the relationship and zygosity of related twins. MZ probands and MZ twins reported by DZ probands were used as controls and assumed to be independent of any genetic influence. Significantly higher proportions of DZ twins were found in the families of DZ probands compared to the families of MZ probands for the following relationships: sibs of probands, proband mothers, offspring of sisters of proband mothers, and offspring of female probands (P < 0.001 in each case). The latter 2 relationships were used to estimate risk ratios of 1.7 for sisters of mothers of DZ twins, and 2.5 for offspring of female DZ twins. No greater tendency to DZ twinning in close relatives was found in mothers who bore DZ twins at a younger age than at an older age.

Australia↗

PubMed1996

Seasonal changes in mood and behavior. The role of genetic factors.

BACKGROUND: Seasonal rhythms in mood and behavior (seasonality) have been reported to occur in the general population. Seasonal affective disorder, a clinically diagnosed syndrome, is believed to represent the morbid extreme of a spectrum of seasonality. Two types of seasonality have been clinically described: one characterized by a winter pattern and a second by a summer pattern of depressive mood disturbance. METHODS: By using methods of univariate and multivariate genetic analysis, we examined the relative contribution of genetic and environmental factors to the risk of seasonality symptoms that were assessed by a mailed questionnaire of 4639 adult twins from a volunteer-based registry in Australia. RESULTS: Seasonality was associated with a winter rather than a summer pattern of mood and behavioral change. In each behavioral domain (ie, mood, energy, social activity, sleep, appetite, and weight), a significant genetic influence on the reporting of seasonal changes was found. Consistent with the hypothesis of a seasonal syndrome, genetic effects were found to exert a global influence across all behavioral changes, accounting for at least 29% of the variance in seasonality in men and women. CONCLUSIONS: There is a tendency for seasonal changes in mood and behavior to run in families, especially seasonality of the winter type, and this is largely due to a biological predisposition. These findings support continuing efforts to understand the role of seasonality in the development of mood disorders.

Adult↗

PubMed1996

Structure of disordered eating in a twin community sample.

OBJECTIVE: To describe the types of eating problems experienced by women in an Australian twin population. METHOD: Questions assessing preoccupation with weight or shape, use of various methods of weight control, difficulties with weight control, disordered eating, or binging, were administered to a group of 3,869 female twins. Exploratory and confirmatory factor analyses were used to summarize and describe problematic eating behaviors. RESULTS: For those women experiencing problems with eating, five groups could be identified. These were overweight women who were dissatisfied with their weight and shape, underweight women struggling with anorexic behaviors, women who were having problems with binging, women who were using more extreme methods of weight control such as vomiting, laxatives, and starvation, and overweight women who were using slimming and fluid tablets for weight control. Confirmatory factor analysis suggested that this factor model is an acceptable fit to the data and that the factor structure generalizes well across two groups viz, the first-born and second-born twins. DISCUSSION: It was concluded that future studies aiming to develop a general description of eating problems in the community should specifically assess the purging behaviors used by women.

Adult↗

PubMed1996

Genetics of educational attainment in Australian twins: sex differences and secular changes.

The relative effects of genetic and environmental factors in producing individual differences in educational achievement are compared across women and men and over birth cohorts. In a large sample of Australian twin pairs, the heritability of self-reported educational attainment did not vary among women and men born before and after 1950. In a "psychometric" model of twin resemblance, based on separate self-reports in 1981 and 1989, genetic factors explained 57% of the stable variance in educational achievement, while environmental factors shared by twins accounted for 24% of the variance. Corrections for phenotypic assortative mating for educational level, however, suggested that estimated common-environmental effects could be entirely explained by the correlation between additive genetic values for mates. Taking this into account, heritability "true" educational attainment in Australia may be as high as 82% with the remaining variation being due to individual environments or experiences. Unlike previous studies in Scandinavian countries, results in Australia suggest that factors influencing educational success are comparable between women and men and for individuals born at different points during this century.

Adult↗

PubMed1996

Social contact, social attitudes, and twin similarity.

The nature of the relationship between social contact and attitude similarly between twins was investigated using longitudinal data from a sample of Australian twins. Earlier research has suggested that social attitudes are not explained solely by shared environment; rather there are both genetic and environmental components that explain variance in social attitudes. Using three types of analyses we investigated the magnitude of the relationship and the direction of causation between attitude similarity and social contact. Longitudinal analysis of within-pair variance by level of contact suggests that attitude similarity leads to contact among the females and that similarity is both genetically and environmentally based. Analyses using a crosslag regression model suggest that similarity causes contact among MZ females. Biometrical analyses indicate differences in direction of causation for males and females. Among females, both genetic and shared environmental parameter estimates could be equated across contact groups, suggesting little relationship between contact and similarity. Among males, findings of smaller estimated heritability in the high-contact group suggest that similarity causes contact. However, an increased estimate of the contribution of shared environmental variance in the high-contact males could additionally suggest that contact leads to similarity.

Adolescent↗

PubMed1996

The Queensland Familial Melanoma Project: study design and characteristics of participants.

Family history of melanoma is associated with an increased risk for the disease. Neither the relative contributions of genetic and shared environmental factors to familial risk nor how genetic susceptibility is mediated are known. The Queensland Familial Melanoma Project was undertaken to investigate (a) the role of genetic susceptibility as indicated by skin type, pigmentation and the prevalence of naevi and (b) exposure to solar ultraviolet radiation, and their interaction in the aetiology of familial melanoma. After obtaining doctor's consent, a brief family history questionnaire was mailed to all Queensland residents with a first primary cutaneous melanoma diagnosed between 1982 and 1990. Detailed information on melanoma history and standard melanoma risk factors was sought from all responding twins and familial cases, from a sample of non-familial cases and from cases' relatives. Medical confirmation was sought for all relatives reported to have had melanoma. The final sample comprises 15,907 persons in the 1,912 families of 2,118 melanoma cases, including 509 families in which there are two or more individuals with confirmed melanoma. Melanoma history and risk factors were obtained for 9,746 relatives, including 94 twins of cases. This is the largest family and twin study of cutaneous melanoma yet conducted in an unselected, geographically-defined population. We describe the design of the study and the characteristics of the total study population.

Adult↗

PubMed1996

Accuracy of case-reported family history of melanoma in Queensland, Australia.

A positive family history is used in clinical practice as an indication of increased melanoma risk, yet there are no data on the accuracy of reported family histories of melanoma. The validity of case-reported family history of melanoma was assessed in the course of a family and twin study of melanoma in Queensland, Australia, conducted among the families of 2,118 melanoma cases diagnosed in Queensland between 1982 and 1990. A total of 913 melanoma cases made 1,267 reports of melanoma among their first-degree relatives. A total of 1,040 of these reports were checked, first through relatives themselves and then, if the relative also said they had had melanoma, through the relative's medical records. Medical confirmation of melanoma as the diagnosis was obtained for 623 reports (59.9%; 95% confidence interval 56.9-62.9): a false-positive reporting rate by cases of 40.1%. The level of false-positive reporting was lower for cases under 70 years of age, for women, for cases whose own diagnosis of melanoma was more than 5 years earlier, and for cases with three or more relatives with melanoma. Media campaigns in Queensland aimed at increasing skin cancer awareness, and confusion between melanoma and other more common actinic neoplasma (basal and squamous cell carcinomas), may partly explain the high false-positive reporting rate observed here. For this reason, It is difficult to generalize these findings to northern hemisphere populations where skin cancer is not such an important public health issue.

Adolescent↗

PubMed1996

Alcohol reactions in subjects of European descent: effects on alcohol use and on physical and psychomotor responses to alcohol.

Self-reports of reactions to small amounts of alcohol, obtained between 1990 and 1992, were compared with reports of alcohol use, obtained in 1990-1992 and also in 1979-1981, in twin subjects of European descent. Data on subjective, physiological, psychomotor, and metabolic responses to a test dose of alcohol, taken in 1979-1981, were also available. Alcohol reactions were more common in women than in men, and were associated with less alcohol use, both at the time that information about reactions was obtained and as recorded on average 12 years previously, in both sexes. Physiological and psychomotor responses to alcohol were similar across the reaction groups, except that deterioration in standing steadiness was greater in those who subsequently reported adverse reactions to alcohol. Contrary to expectation, skin temperature changes after alcohol were less in the subjects who reported always reacting to alcohol than in the other groups. Subjective reports of intoxication were greatest in subjects who subsequently reported alcohol reactions. The pattern of twin pair concordance for reactions suggests low heritability, so alcohol reactions in subjects of European descent are not caused by a single gene of high penetrance of the type found in the Asian alcohol flush reaction.

Adult↗

PubMed1996

The control of ovulation in mothers of dizygotic twins.

Dizygotic twinning is familial, suggesting that there may be an inherited abnormality of the control of ovulation that predisposes to double ovulation and, therefore, dizygotic twins. The present study examines 17 mothers of dizygotic twins (MODZT) and 8 control mothers of singletons by daily blood sampling throughout an entire menstrual cycle. Blood samples were assayed for LH, FSH, estradiol, progesterone, and inhibin. The process of follicular development was followed by transvaginal ultrasound. The pituitary LH response to iv GnRH was also assessed. Three of the 16 MODZT double ovulated during the study compared to none of the 8 control mothers (P < 0.05). The number of small follicles (<6 mm) declined significantly in control women at midcycle, but not in MODZT. There was no significant difference in serum FSH, LH, estradiol, or inhibin levels between the 2 groups at any stage of the menstrual cycle. During the follicular phase, serum progesterone levels were significantly higher in MODZT. The response to GnRH stimulation was not different between MODZT and controls. In conclusion, this study demonstrates an increased tendency to double ovulate in MODZT that may be due to a reduced rate of atresia in advanced follicles. Furthermore, the elevated progesterone levels in MODZT during the follicular phase suggest altered intrafollicular steroidogenesis that is independent of gonadotropins.

Adult↗

PubMed1996

Reliability and reporting biases for perceived parental history of alcohol-related problems: agreement between twins and differences between discordant pairs.

OBJECTIVE: Previous research suggests that family history of alcoholism assessments may be biased by characteristics of the informant. In this report, the reliability and potential biases in offspring reports of paternal and maternal alcohol-related problems were examined in a large community sample of adult twins. METHOD: Subjects were volunteer participants in the Australian NH&MRC twin registry. Agreement between twin pairs on reports of paternal and maternal alcohol problems was assessed in 2,657 twin pairs (1,444 female-female pairs, 626 male-male pairs, and 587 female-male pairs). In addition, to detect systematic reporting biases, like-sex twin pairs whose paternal alcohol problems reports disagreed (n = 164) were contrasted on measures of personality, state anxiety and depression, parental rearing, alcoholism, and alcohol use. RESULTS: Twin agreement for parental alcohol-related problems was good, with overall kappas of .66 for paternal and .58 for maternal alcohol problems. When discordant twin pairs were compared, we found that women who reported that their father had alcohol problems were significantly lower on EPQ-R Social Conformity than their twin sister who denied paternal alcohol problems: and there was a trend for men who reported that their father had alcohol problems to be higher in negative perceived parenting from father than their twin brother who denied paternal alcohol problems. Twins discordant for reporting paternal alcohol problems did not, however, differ on the major dimensions of personality, state anxiety and depression, alcoholism, or current alcohol use. CONCLUSIONS: The results of this study bolster our confidence in using the family history method to examine characteristics of offspring of alcoholics versus offspring of nonalcoholics on self-reported measures of personality and psychopathology, but suggest that some caution should be exercised when using this method to examine differences in offspring-reported perceptions of parental rearing practices.

Adult↗

PubMed1996

Assessing the prevalence of eating disorders in an Australian twin population.

OBJECTIVE: This paper examines the prevalence of disordered eating in a female Australian twin population aged between 28 and 90 years in 1993. METHOD: In two waves of data collection, the eating behaviour of 3869 female twins was first assessed in 1988-1989 by self-report questionnaire and then in 1992-1993 with a telephone interview, using the Semi-Structured Assessment for the Genetics of Alcoholism interview. RESULTS: It was found that about 0.4% of the women have a lifetime prevalence of anorexia nervosa and 1.8% of the group have suffered from bulimia nervosa. The incidence of bulimia nervosa but not anorexia nervosa was markedly higher for those women under 45 (2.3% bulimia nervosa) than for those women 45 years or older. Furthermore, one in three women have at some stage in their life used some extreme method of weight control. CONCLUSIONS: The levels of bulimia nervosa and anorexia nervosa found are commensurate with those found in smaller studies in Australia and other parts of the world. The finding of widespread use of extreme weight control methods is of concern as this behaviour is a well-recognised precursor to more serious eating disorders.

Adult↗

PubMed1995

Self-report psychiatric symptoms in twins and their nontwin relatives: are twins different?

While twin studies of psychiatric disorders have been conducted for over 65 years, surprisingly little is known about the comparability of psychiatric symptoms in adult twins and singletons. To address this question, we compared the means and variances of four-factor scores on the self-report Symptom Check List in twins and their relatives from the Virginia 30,000 twin-family study. The four factors were depression, panic-phobia, somatization, and insomnia. Twins had significantly higher scores on the panic-phobia factor than their relatives, by about one eighteenth of a standard deviation, and this was replicated in both subsamples. However, no consistent and significant mean differences between twins and their relatives were detected for the other three symptom factors. While some differences in variance were found between twins and their relatives, in no case were the differences replicated in both subsamples. With the possible exception of modestly elevated scores for panic-phobia, these results suggest that both the level and variability of common psychiatric symptoms reported by twins are similar to those found in the nontwin population.

Age Factors↗

PubMed1995

Osteoporosis in rheumatoid arthritis. A monozygotic co-twin control study.

OBJECTIVE: To quantify the magnitude and distribution of osteoporosis in rheumatoid arthritis (RA). METHODS: Bone mineral density (BMD) was measured by dual x-ray absorptiometry, in a monozygotic co-twin control study. RESULTS: BMD was reduced at most skeletal sites in the twin with RA compared with the co-twin (lumbar spine 4.6%, femoral neck 9.7%, total body 5.7%). Differences in lean soft tissue (5.6% for total body) correlated with differences in BMD between twins at multiple sites. CONCLUSION: Osteoporosis in RA is generalized and may be related to loss of mobility or muscle mass associated with the disease.

Arthritis, Rheumatoid↗

PubMed1995

Personality and the inheritance of smoking behavior: a genetic perspective.

In contrast to the extensive research effort to understand the genetic contribution to alcoholism risk, there has been little research directed at understanding genetic influences on smoking behavior. Data from large twin studies in Scandinavia and Australia are consistent with a major genetic influence on the probability that an individual will become a smoker ("initiation") and will persist in the smoking habit once smoking has started ("persistence"). We use data from the 1988/1989 follow-up survey of the Australian NH&MRC twin panel to determine to what degree personality measures (Tridimensional Personality Questionnaire, Eysenck Personality Questionnaire--Revised) and attitudinal and sociodemographic variables (social and political conservatism, education, religious involvement) might account for genetic or environmental influences on smoking. While we find significant phenotypic associations between these variables and smoking, these are too modest to account for much of the genetic variance. Possible mechanisms by which this genetic variance may arise are discussed.

Adolescent↗

PubMed1995

A twin-family study of self-report symptoms of panic-phobia and somatization.

Self-report symptoms of anxiety are widely used in mental health and social science research as an index of current psychiatric state. Previous twin studies have suggested that genetic factors account for a significant proportion of the variance in these symptoms. To replicate and extend these findings, we examined self-report symptoms of panic-phobia and somatization in the "Virginia 30,000" twin-family sample. Model fitting applied to 80 unique relationships in the twin-family pedigree produced the following major results: (i) genetic effects were significant for both symptom factors, accounting for between 25 and 49% of the total variance, with the exception of symptoms of panic-phobia in females, where they accounted for 15-16% of the variance; (ii) familial environmental effects were absent for symptoms of somatization, while for symptoms of panic-phobia they accounted for a very small proportion of variance in males (< or = 1.2%) and a modest proportion in females (6-17%); (iii) spousal correlations were present for both factors, ranging from +0.05 to +0.20; (iv) genetic factors which influenced symptoms were generally the same in males and females, although their effect was greater in males; (v) heritability estimates were lower in the population-based than in the volunteer sample; and (vi) when test-retest reliability was included in the model, results suggest that genetic factors account for at least half of the stable variance for all symptom factors, except panic-phobia in females. Our results support the validity of previous twin studies of self-report symptoms of anxiety and suggest that genetic factors significantly influence these symptoms but familial-environmental factors play little or no etiologic role.

Adult↗