Male-male Pairs Research Articles

Genomewide Significant Linkage to Recurrent, Early-Onset Major Depressive Disorder on Chromosome 15q

A genome scan was performed on the first phase sample of the Genetics of Recurrent Early-Onset Depression (GenRED) project. The sample consisted of 297 informative families containing 415 independent affected sibling pairs (ASPs), or, counting all possible pairs, 685 informative affected relative pairs (555 ASPs and 130 other pair types). Affected cases had recurrent major depressive disorder (MDD) with onset before age 31 years for probands or age 41 years for other affected relatives; the mean age at onset was 18.5 years, and the mean number of depressive episodes was 7.3. The Center for Inherited Disease Research genotyped 389 microsatellite markers (mean spacing of 9.3 cM). The primary linkage analysis considered allele sharing in all possible affected relative pairs with the use of the Z(lr) statistic computed by the ALLEGRO program. A secondary logistic regression analysis considered the effect of the sex of the pair as a covariate. Genomewide significant linkage was observed on chromosome 15q25.3-26.2 (Zlr=4.14, equivalent LOD = 3.73, empirical genomewide P=.023). The linkage was not sex specific. No other suggestive or significant results were observed in the primary analysis. The secondary analysis produced three regions of suggestive linkage, but these results should be interpreted cautiously because they depended primarily on the small subsample of 42 male-male pairs. Chromosome 15q25.3-26.2 deserves further study as a candidate region for susceptibility to MDD.

A twin study of erectile dysfunction.

The extent of genetic influence on erectile dysfunction (ED) is unknown. This study determines the contribution of heredity to ED in a sample of middle-aged men. A classical twin study was conducted in the Vietnam Era Twin Registry, a national sample of male-male pairs (mean birth year, 1949) who served on active duty during the Vietnam era (1965-1975). A 1999 male health survey was completed by 890 monozygotic (MZ) and 619 dizygotic (DZ) pairs. The prevalence and heritability of 2 self-report indicators of ED, difficulty in having an erection and in maintaining an erection, are estimated. The prevalence of difficulty in having an erection is 23.3% and in maintaining an erection is 26.7%. Twin correlations for dysfunction in having an erection are 0.35 (95% confidence interval [CI], 0.28-0.41) in MZ and 0.17 (95% CI, 0.09-0.27) in DZ pairs. For dysfunction in maintaining an erection, the twin correlations in MZ and DZ pairs are 0.39 (95% CI, 0.32-0.45) and 0.18 (95% CI, 0.09-0.27), respectively. The estimated heritability of liability for dysfunction in having an erection is 35% and in maintaining an erection is 42%. The heritable influence on ED remained significant after adjustment for ED risk factors. The present study demonstrates an ED-specific genetic component that is independent of genetic influences from numerous ED risk factors. The results suggest that future molecular genetic studies to identify ED-related polymorphisms are warranted.

THE CORRELATION BETWEEN INTIMACY AND OBJECTIVE SIMILARITY IN INTERPERSONAL RELATIONSHIPS

The purpose of this study was to investigate the correlation between interpersonal intimacy and objective similarity of behavioral tendency. Sixty pairs were measured for the intimacy by Rubin's (1970) Love and Liking scale and objective similarity of behavioral tendency by Tuzuki's (1964) TestDELB(Bform). ANOVA of similarity score indicated a significant main effect of gender make up. The similarity score (measured similarities between the 2 persons) of male-male pairs were higher than male-female pairs. A significant positive correlation between similarity score and liking and the perceived similarity factor was observed for the female of male-female pairs.

Do reproductive strategy and breeding season influence the presence of mate recognition in the intertidal snail Littorina?

Summary To test the assumption that littorinid snails do not discriminate between mates prior to copulation, I studied mate recognition behaviour in two species of Littorina on Swedish rocky shores: L. littorea (which has pelagic development and a distinct reproductive season) and L. saxatilis (non-pelagic development; reproduces throughout the year). Copulating pairs were sampled in five populations of each species to determine the occurrence of maladaptive (male-male or male-juvenile) matings. To complement the field sampling I did laboratory experiments on mucous-trail following, to reveal possible discriminating behaviour among potential mates when following mucous trails. In L. littorea about 5% of copulating pairs were between males, while in L. saxatilis, 33–38% were male-male or male-juvenile pairs. In contrast to L. littorea, this study showed that males of L. saxatilis did not discriminate between sexes from mucous trails, but followed any mucous trail (irrespective of sex of marker snail) for longer than females did. Thus, mate recognition behaviour by trail following can explain the difference in the proportion of maladaptive mating pairs between the two species studied. Among the 19 recognized species of the snail Littorina, nine show pelagic larval development, while 10 have direct, non-pelagic development. From the literature a clear relationship between reproductive strategy and the presence or absence of breeding season in Littorina snails was found. Species with pelagic development always have a distinct reproductive season, while species with non-pelagic development either reproduce throughout the year, or show variation between regions in seasonal or non-seasonal reproduction. The hypothesis that reproductive strategy and breeding season may influence the presence of mate recognition in Littorina snails is discussed.

Respiratory distress in heavier versus lighter twins.

We performed a retrospective study of twin pairs under 36 weeks gestation admitted to a regional neonatal unit over a three year period to determine if the larger twin of a twin pair is at increased risk of respiratory distress in the immediate postnatal period compared to the smaller twin. Gestation, gender, birth weight, mode and reason for delivery, birth order, and Apgar at 5 minutes were correlated with the need for added oxygen at 4 hours, the need for ventilation, oxygen requirement at 28 days and mortality. One hundred and twenty-four twin pairs were analyzed with a median gestation of 31 weeks (range 23-35). There were 47 female-female pairs, 40 male-male pairs and 37 mixed pairs. Multiple logistic regression revealed no significant increased risk for ventilation in male, heavier or second twins. The need for oxygen at 4 hours was strongly associated with being male and being the second twin, but not with being the heavier twin. However, on analysis of twins of 28 weeks gestation or above a significant association was found between a persisting oxygen requirement at 4 hours and being male (OR 2.2; 95% CI 1.15-4.16), being the heavier twin (OR 1.9; 95% CI 1.03-3.46), and being the second twin (OR 2.7; 95% CI 1.48-4.99). No association was found between mortality and being male, and being the second or smaller twins. Heavier twins above 28 weeks gestation are at increased risk of short term mild respiratory problems following delivery compared to lighter twins at the same gestation. This is not as strong a factor as birth order or male gender, but it is important to be aware of this in antenatal counselling of the parents as the smaller twin is usually perceived to be at greater risk of morbidity.

Genetic and environmental contributions to alcohol abuse and dependence in a population-based sample of male twins.

Most twin and adoption studies of alcoholism have ascertained cases through treatment settings or archival data; these subjects may differ from affected subjects identified epidemiologically. The authors studied the importance of genetic influences on risk of alcohol-related disorders in a new population-based twin sample. Structured personal interviews were used to assess DSM-III-R-defined and DSM-IV-defined alcohol abuse and dependence among 3,516 twins from male-male pairs born in Virginia between 1940 and 1974. The magnitude of resemblance among twin pairs was similar across several definitions of alcoholism and was substantially higher among 861 identical pairs than among 653 fraternal pairs. On the basis of a liability threshold model, 48%-58% of the variation in liability was attributed to additive genetic factors, with the remainder attributed to environmental influences not shared by family members. When a treatment-based proband concordance model was used, evidence for shared environmental as well as genetic influences emerged. In this first population-based study of male twins from the United States, it was found that genetic factors played a major role in the development of alcoholism among males, with similar influence for alcohol abuse and alcohol dependence. Prior findings implicating the influence of common environment may be attributable to sampling strategy; in this population-based sample, environmental factors shared by family members appear to have had little influence on the development of alcoholism in males.

Effects of fetal sex and race on risk of very preterm birth in twins

OBJECTIVE: Our purpose was to determine whether the risk of twin preterm birth correlates with the number of male fetuses. STUDY DESIGN: Among 8109 white and 1884 black twin pregnancies in the Missouri Successive Pregnancy Birth/Death Data Set, 1978 through 1990, risk for preterm birth at various gestational ages was determined with 0, 1, or 2 male infants. RESULTS: Studied as individuals, white preterm twins <35 weeks’ gestation demonstrated a 9.2% excess of male fetuses ( P < .001). Adjusted for monozygosity, risk for preterm birth <35 weeks’ gestation was 15.7% in white female-female pairs, 17.9% in unlike-sex white fetuses, and 20.2% in white male-male pairs ( r = .999, P = .01). The effect was absent in black pregnancies and was unrelated to birth order, cesarean delivery, parity, twins’ weight differential, year, or season. CONCLUSIONS: In white twin gestations the observed linear relationship between the number of male fetuses and the likelihood of preterm birth <35 weeks’ gestation suggests a fetal mechanism for preterm birth <35 weeks’ gestation linked to fetal sex. Studies of mechanisms for preterm birth must stratify by fetal sex and race. (Am J Obstet Gynecol 1998;179:762-5.)

Gender-Typed Toy Play in Dizygotic Twin Pairs: A Test of Hormone Transfer Theory

Hormone transfer theory predicts thatopposite-sex twins will be affected in utero by thehormones their twins produce. This study examines theprediction that opposite-sex dizygotic twins should showless stereotyped toy play than same-sex dizygotictwins should show less stereotyped toy play thansame-sex dizygotic twins as a result of exposure toopposite-sex hormones in utero. Participants in thisstudy included 32 male-female dizygotic twin pairs,27 female-female pairs, and 24 male-male pairs. Allranged in age from 7 to 12 years and were primarilyCaucasian and middle class. Differences in the amount of time children played with feminine,masculine, and neutral stereotyped toys during free playwere examined. Results did not support hormone transfertheory. Girls played with feminine toys more than boys and boys played with masculine toys morethan girls, but there were no significant differencesbetween children with opposite- vs. same-sextwins.

Effects of social interaction on the development of starling song and the perception of these effects by conspecifics.

To examine the effects of contact with a conspecific in the absence of species-typical song models, the authors raised starlings in male-male pairs in acoustic isolation. The songs of these birds differed significantly from those of either individual isolates or wild adults and resembled in some respects the songs of starlings tutored by live conspecifics. Operant conditioning techniques were used to demonstrate that these differences among songs were perceptually salient to conspecifics. The results indicated that (a) wild-caught adult starlings are capable of forming open-ended categories for isolate and wild song, (b) starlings perceive the songs of isolated pairs as more "isolatelike" than "wildlike," and (c) starlings can distinguish the songs of isolated pairs from those of individual isolates. Both experiments point to the importance of social factors in avian song development.

Further defining the risks confronting twins

OBJECTIVE: We report the absolute and relative risks for neonatal and infant death, low and very low birth weight, and delivery at <33 and <35 weeks' gestation in twin pregnancy stratified by maternal race and age, as well as gender pair combinations of the twins. STUDY DESIGN: Data on 324,141 twin infants were obtained from the 1985 to 1988 U.S. Linked Birth/Infant Death Data Sets. In this observational cohort study, we analyzed the outcomes of 138,779 twin pregnancies of white and black women that ended with the delivery of two live-born infants. RESULTS: Rates for the aforementioned outcomes are increased for black infants, for male-male pairs compared with male-female pairs (with female-female pairs being intermediate), and for young mothers. For male-male twins born to young ( ≤22 years old) black women, relative risks range from 2.1 for both pair members being low birth weight (<2500 gm) to 5.0 for both pair members dying in infancy, when male-female pairs born to older ( ≥28 years) white women served as the reference group. CONCLUSIONS: Although all twin pregnancies are at higher risk than singletons, risk is influenced by maternal race and age, as well as gender pair combination. These analyses provide useful information for counseling women pregnant with twins. Furthermore, they suggest that failure to consider variations in baseline risk may have seriously flawed studies evaluating prophylactic interventions in twin pregnancy. (Am J Obstet Gynecol 1996;175:1522-8.)

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

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. 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. 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. 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.

Influence of gender on susceptibility to multiple sclerosis and age of onset in concordant sibships.

Research has produced conflicting findings about whether there is an excess of like-sexed pairs among concordant multiple sclerosis (MS) sibships. Although a positive correlation in onset age among sibling pairs overall has been reported, no data have been published describing age at onset correlations for like-sexed versus unlike-sexed pairs. The purpose of this study was to provide additional information on both issues. Patients with an MS sibling were sought through the files of the University of Alberta MS clinic (Edmonton, Canada). The clinic neurologist either reviewed clinical/autopsy material or assessed relatives of index cases prior to accepting the relative as having MS. Pairs of siblings (excluding twins) were divided into (1) male-male pairs, (2) female-female pairs, and (3) female-male pairs. A total of 62 concordant sibling pairs were identified. There were 33 like-sexed pairs (6 male-male/27 female-female) and 29 unlike-sexed pairs. The observed number of like-sexed pairs was not significantly different from the expected frequency using 2 x 2 chi2 analysis, where expected values represent the binomial distribution predicted from the frequency of each sex as determined by total number of males and females. The age at onset intraclass correlation coefficient was -0.09 for sibling pairs overall, -0.22 for like-sexed pairs and +0.02 for unlike-sexed pairs. This study does not provide evidence for an association between disease susceptibility and gender in siblings concordant for MS; nor does it suggest that genetics plays a role in onset age.

Lack of gender differences in age at onset in familial schizophrenia

One of the most consistent findings in the epidemiology of schizophrenia is that males are younger at the onset of schizophrenia than females. However, the vast majority of studies focussing on gender differences have not considered the potential influence of genetic factors on age at onset. We investigated the impact of familial loading on gender differences in age at onset in families with at least two siblings with RDC/DSM-III-R schizophrenia or chronic schizoaffective disorder. A total of 106 sib pairs, including 38 male-male pairs, 29 female-female pairs and 39 mixed sex pairs of siblings as well as 260 male and 221 female isolated cases with no relative of first, second or third degree suffering from psychotic or major affective illness were investigated. We found no gender differences in age at onset in familial cases. An earlier age at onset in males compared to females was observed only in isolated cases. Our data strongly support the assumption that gender differences in age at onset of schizophrenia is not consistent across all subgroups of schizophrenics.

Schizophrenia and the androgen receptor gene: Report of a sibship showing co‐segregation with reifenstein syndrome but no evidence for linkage in 23 multiply affected families

Crow et al. [1993: Am J Med Genet (Neuropsychiatr Genet) 48:159-160] have reported excess sharing of alleles by male sibling pairs with schizophrenia, at a triplet repeat marker within the androgen receptor gene, indicating that mutations at or near this gene may be a risk factor for males. In this report, we describe a pair of male siblings concordant for both schizophrenia and Reifenstein syndrome, which is caused by a mutation in this gene. This provides support for the hypothesis that the androgen receptor may contribute to liability to develop schizophrenia. Because of this, we have examined a collection of 23 pedigrees multiply affected by schizophrenia for linkage to the androgen receptor. We have found no evidence for linkage by both the LOD score and affected sibling-pair methods, under a range of genetic models with a broad and narrow definition of phenotype, and when families with male-to-male transmission are excluded. However, because of the small number of informative male-male pairs in our sample, we cannot confirm or refute the excess allele sharing for males reported by Crow.

Male-male pairs in Greylag Geese (Anser anser)

For almost two decades a flock of 130 free-flying Greylag Geese (Anser anser) has been the focus of detailed ethological investigations at the Konrad Lorenz Institut in Grunau im Almtal, Austria. Gander pairs, i. e. male-male pairs, represent a prominent social unit in this flock and were the subject of a detailed behavioral investigation. Analysis of the composition and dynamics of the flock over a 15 year period indicated that the incidence of homosexual pairings closely paralleled the male bias of the sex ratio. The behavior of ganders in gander pairs was investigated and compared to that of gander and goose in heterosexual pairs. The behavior of the two males in a gander pair (1) was comparable in most aspects, (2) was similar to the behavior of the gander in heterosexual pairs, and (3) differed greatly from that of the heterosexually paired goose. Therefore, pseudo-female behavior in one partner cannot account for the formation of a pairbond between two males. As a unit, gander pairs were characterized by a higher frequency of offensive agonistic behavior compared to heterosexual pairs and spent significantly more time peripheral to, and away from the flock than did heterosexual pairs.

Gonadal hormones determine sex differences in timing of incubation by doves

Male and female ring doves express a sexually dimorphic pattern of incubation. The dimorphism is temporal rather than motoric. The male incubates for a block of time in the middle of the day and the female incubates the rest of the time. The present study explored the role of gonadal hormones in the control of the temporal dimorphism. Female-female pairs incubated their eggs, but it could not be predicted which of the partners would be sitting on the nest at any given time. Male-male pairs did not incubate and instead destroyed the nests that were provided and displayed aggressive behavior. Some intact males incubated when paired with gonadectomized males, although the castrates tended to ignore the nest. In contrast, when castrated birds were given heterotypical hormonal replacement therapy, they and their same-sex partners incubated the eggs that had been provided, with the gonadectomized birds sitting at a time appropriate to the hormonal state. The results indicate that gonadal hormones influence not only the expression of incubation behavior, but also its phase and duration.

Gestational duration and birth weight for twins related to fetal sex.

It has been postulated that male twin pregnancies, in contrast to male singleton pregnancies, differ in some distinctive biologic sense, leading to a shorter gestational duration and a lower individual birth weight than is the case in female twin pregnancies. To test this hypothesis in a relatively large dataset, information on gestational duration and birth weight for nearly all twins born in Sweden during a 4-year period (n = 3,472 twin pairs) was collected from the Medical Birth Registry, National Board of Health and Welfare. Included in the Medical Birth Registry are all pregnancies with a duration of at least 28 completed gestational weeks, or less if the newborns are alive at birth. Male-male pregnancies had a gestational duration similar to female-female pregnancies (median difference less than 2 days). The proportions of twins with a gestational age less than 36 weeks did not differ between male-male and female-female twin pregnancies (27.3 vs. 25.3%; chi 2 = 2.2, p greater than 0.05). Male-male pairs were heavier than female-female pairs (median difference 0.1 kg), and a significantly higher proportion of female-female twin pairs weighted less than 2,500 g (45.0 vs. 39.2%; chi 2 = 17.7, p less than 0.001). The results of this study in an unselected relatively large twin population seem to indicate that fetal sex does not influence gestational duration to any significant extent. Males are heavier than females indicating that the sex has a similar effect on birth weight in twin and in singleton pregnancy.

Effect of Social-Housing Conditions on Aggression in an Intruder-Resident Paradigm in Cavia Porcellus

The resident-intruder method was used to study the agonistic behavior of male guinea pigs. Resident animals were housed in male-male or male-female pairs, while male intruders were isolated or housed with another male. Intruders were introduced singly into the home cage of the resident pairs over six 30-min. test sessions. Residents won significantly more encounters than did intruders. Sexual composition of resident pairs did not affect aggressive behavior. Residents which met isolated intruders exhibited significantly more aggression than those which met socially maintained intruders. Aggressive behavior decreased during sessions, but did not change appreciably across sessions. These results are discussed in conjunction with other recent findings which emphasize the importance of aggression-evoking properties of the intruders’ behavior.

The Development of Sociosexual Behaviour in Free-Living Baboons, Papio Anubis

The development of mounting behaviour and the communicatory functions of mounting were studied in a free-living troop of olive baboons in the Gombe Stream National Park, Tanzania, over a period of 16 months. 1. Early mounting attempts by baboon males were disoriented and incomplete. Components of mounting such as penile erection and pelvic thrusting at first occurred in isolation and in inappropriate contexts, but at 10-15 months of age, males became able, rather suddenly, regularly to orient themselves correctly to the female when mounting. 2. From about 10 months of age, thrusts became more rhythmical and increased in number per mount, and at about 12 months, intromission and the ejaculatory pause first occurred. At this age also, the frequency of male mounting reached a peak. Between 20 and 50 months of age, the characteristics of male-female mounting changed rather little, but after puberty, the proportion of mounts in which an ejaculatory pause occurred was twice as great as in younger age groups, and the number of thrusts required to reach ejaculation decreased. 3. Tumescent adult females were available for mounting by young males throughout the year, though young males could not gain access to females whilst they were maximally swollen and in consort with adult males. From about one year of age, males increasingly selected adult females as mounting partners. Male-male mounts, however, continued into adulthood. 4. The presence of cycling females in the troop with which young males could achieve intromission was thought to be particularly important for the development of the orientation and integration of male mounting patterns in baboons. This is supported by studies of captive peer-raised macaques, in which the course of development of male mounting behaviour tends to be delayed compared with that in naturalistic or wild groups of primates. 5. The nature and time scales of development of male mounting patterns in the genera Papio and Macaca appear to be very similar, though in olive baboons, unlike macaques, the ejaculatory pause occurred before puberty. In primates and in other mammals, important changes in mounting development seem to occur both during the early months of life and around puberty. 6. Mounts were observed in the contexts of 'dominance', play, appeasement/greeting, and enlisting as well as in a 'sexual context. Mounts between males were not always in the direction that agonistic status or play relationships would predict, and for any male-male pair, mounts could occur in either direction. The direction of mounting was dependent on the nature of the communication involved, and in one type of mounting (appeasement/greeting), it was generally the subordinate male that mounted. The general function of non-sexual mounting seemed to be to reduce the likelihood of aggression.

Sex differences in fighting and defense induced in rats by shock and d-amphetamine during morphine abstinence

Male and female rats were injected with morphine while a control group received water injections. Four days following the final morphine injection, the animals received d-amphetamine and then were tested for their reaction to a stuffed leather glove. Drugged animals, while not showing a higher incidence of attack, did show increased escape tendencies when compared to controls. Both drugged and control animals were then shocked in the presence of either a same or different sexed conspecific. Nine measures of aggressive behavior were recorded from the pairs. Factor analysis of the nine intercorrelated measures produced two orthogonal aggressive factors — one indicative of defensive-threat behavior and one relating to actual fighting. Male-male pairs under morphine abstinence plus d-amphetamine scored significantly higher than the other groups on the fighting factor while drugged male-female pairs scored significantly higher on the defensive-threat factor. Although the fighting exhibited in this study was essentially restricted to male pairs under the drugged condition, evidence is presented suggesting that the agonistic behavior observed is not the species typical intermale aggression.