Male twins at birth and 18 years later

Nilsen, Stein Tore; Bergsjø, Per; Nome, Siri

doi:10.1111/j.1471-0528.1984.tb05894.x

Cited by 17 publications

(8 citation statements)

References 7 publications

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“…Consistent ®ndings are reported from a questionnaire survey of 474 Belgian twin pairs born in 1950 which reported lower marital and fertility rates among male (especially monozygotic) twins (Steeno & Vlietinck, 1989) although not apparently related to prematurity. Similar suggestions that male twins may be less well developed physically are reported from surveys of Norwegian military conscripts in which male twins were more than twice as likely to be un®t, mainly due to long-term sequelae of prematurity (Nilsen et al, 1984). The only twin study of testicular function reported to date identi®ed that familial factors account for a large proportion of the variability in blood levels of gonadotrophins (LH, FSH), sex steroids (total and free testosterone, oestradiol) and their metabolites (dihydrotestosterone, 3aandrostanediol glucuronide) and that genetic factors accounted for 25±76% of the variability of gonadotrophins and sex steroids (Meikle et al, 1987).…”

Section: Discussionsupporting

confidence: 75%

“…One caveat is that twins may not be representative of singletons. Perinatal effects of twin gestation including prematurity and gestational complications are more frequent among twins and may explain the lowered physical ®tness, fertility and longevity of twins compared with singleton siblings (Wyshak & White, 1969;Wyshak, 1978;Nilsen et al, 1984;Steeno & Vlietinck, 1989). As the perinatal period is critical for testicular development, such biological consequences of twinhood mean that factors identi®ed from twin studies should be veri®ed by sibling or other studies where possible.…”

Section: Discussionmentioning

confidence: 99%

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Estimating familial and genetic contributions to variability in human testicular function: a pilot twin study

Handelsman

1997

Int J of Andrology

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The biological basis for the remarkably wide variation in sperm output between and within men remains unclear. Although some contributing factors have been identified, the familial and genetic contributions to variation in human sperm output have been little studied, although such sources of variation are known to be significant in experimental animals. In order to identify such familial and genetic factors in a classical twin study design, we recruited monozygotic and dizygotic twins aiming to study the degree of resemblance between genetically identical and non-identical twins in sperm output, testis size and testicular endocrine function. From an approach to 160 twin pairs on the Australian Twin Register database, eventually 17 pairs of male twins (11 monozygotic and six dizygotic) participated in this study. Sperm concentration and output, right testis size and SHBG all exhibited a strong familial effect but a genetic component could not be confirmed. Total and free testosterone exhibited a genetic component. Although identifying for the first time a clear familial component to normal human spermatogenesis, this study had insufficient power to determine whether there was a genetic component, nor could its design distinguish between genetic or shared (early) environmental determinants for these familial effects. Implications for future twin studies of human testicular function including stronger recruitment strategies, multi-centre studies and surrogate variables for human spermatogenesis are suggested.

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Section: Discussionsupporting

confidence: 75%

Section: Discussionmentioning

confidence: 99%

Estimating familial and genetic contributions to variability in human testicular function: a pilot twin study

Handelsman

1997

Int J of Andrology

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“…twins and non-twins (Rutter & Redshaw, 1991). In general population adult samples, twins probably have a slight reduction in intelligence (Record et al 1970), although this has not been found in all studies (Nilsen et al 1984).…”

mentioning

confidence: 77%

The treated incidence of psychotic and affective illness in twins compared with population expectation: a study in the Swedish Twin and Psychiatric Registries

et al. 1996

Psychol. Med.

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SynopsisTwin studies of psychiatric illness assume that the genetic and environmental risk factors for psychiatric illness are similar in twins and non-twins and in monozygotic (MZ) and dizygotic (DZ) twins. To test this assumption, we examine whether the treated incidence of psychiatric illness in twins deviates from population expectations or differs between MZ and DZ twins. Using first admissions to the Swedish Psychiatric Registry for the years 1979–83 for all twins born 1886–1958 from the Swedish Twin Registries, we calculated Standardized Morbidity Ratios (SMRs) using national incidence rates together with individually computed person-years at risk in the twin cohort. The diagnoses examined, for which there was more than 393000 person-years of risk, were schizophrenia, other non-affective psychoses (ONAP), bipolar affective illness (BPAI), unipolar affective illness (UPAI) and neurotic depression (ND). The SMRs (and 95% CIs) for all twins were: schizophrenia 0·86 (0·69–1·06), ONAP 1·05 (0·88–1·24), BPAI 1·09 (0·90–1·32), UPAI 1·05 (0·85–1·29) and ND 0·99 (0·88–1·10). This pattern of results did not differ substantially when examined separately by gender or birth cohort. Relative risks for first admissions for MZ v. same-sex DZ twins or same v. opposite-sex DZ twins did not differ significantly from unity for any of the disorders examined. In Sweden, the treated incidence of psychotic and affective disorders in twins does not differ from that found in the general population and does not differ across zygosity groups. These results support the validity of the twin method for the study of psychotic and affective disorders.

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“…Most studies that have found differences between singletons and twins have examined young twins. A host of studies comparing older twins with singletons have failed to find differences in physical characteristics and cognitive abilities, 6 suggesting that any differences between twins and singletons are ‘washed out’ by five years of age. In addition, most studies have not matched twins with singletons in terms of genetic background nor early environmental experiences.…”

Section: Are Twins the Same As Singletons?mentioning

confidence: 99%

The validity of twin studies

Evans

Martin

2000

GeneScreen

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The classical twin study is the most popular method for assessing the relative contribution of genes and environment to traits in human populations. Critics argue that several assumptions of the twin method are unjustified, and therefore results from twin studies are misleading. Specifically, it has been suggested that twins differ in important aspects from singletons, that monozygotic (MZ) and dizygotic (DZ) twins are not matched in their degree of environmental similarity, and that MZ twins are neither matched genetically nor in their prenatal environments. These criticisms are addressed and it is suggested that they do not provide serious impediments to the validity of the twin study.

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Male twins at birth and 18 years later

Cited by 17 publications

References 7 publications

Estimating familial and genetic contributions to variability in human testicular function: a pilot twin study

Estimating familial and genetic contributions to variability in human testicular function: a pilot twin study

The treated incidence of psychotic and affective illness in twins compared with population expectation: a study in the Swedish Twin and Psychiatric Registries

The validity of twin studies

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