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PubMed2005

Multiple sclerosis and birth order: a longitudinal cohort study.

BACKGROUND: Genetic epidemiological studies suggest both genetic and environmental factors have a role in multiple sclerosis (MS). Environmental effects are strongly suggested from geographical gradients, migration data, and discordance rates in twins. In epidemiological studies, risk of MS in offspring of small families and in those with an early birth-order position has been reported and interpreted in the context of the hygiene hypothesis, which is that infections at an early age, introduced by older siblings, are protective. We aimed to study the effect of birth order on MS risk. METHODS: A longitudinal, population-based sample of individuals with MS and their healthy siblings were identified from the Canadian Collaborative Project on Genetic Susceptibility to MS. Data were grouped according to single (simplex) or multiple (multiplex) siblings with MS in a sibship. Separate analyses were done for each sibship size. FINDINGS: We studied 10 995 individuals with MS and 26 336 healthy siblings, and found no relation between MS risk and birth-order position. In simplex sibships of at least seven siblings, slightly more siblings who were born late in the birth order had MS; the same was found for the first-born sibling with MS in a multiplex sibship. Siblings with MS were slightly younger (p<0.0001) than those without MS, contrary to the expected age at onset bias. INTERPRETATION: These findings do not support the hygiene hypothesis and could be due to a cohort effect resulting from increasing MS incidence. Birth order has no effect on MS risk in most families, and there is no support for the hypothesis that having older siblings protects against MS.

Birth Order↗
PubMed1992

[A study on effects of parents age, birth order and mental retardation of unknown etiology].

On this report 461 matched cases of mental retardation of unknown aetiology were analysed on the relationship between the diseases and the parents age, birth orders with conditional Logistic regression. These cases were accurately diagnosed and selected from the Epidemiologic Survey of genetic diseases of Sichuan, China. The results found that mental retardation of unknown aetiology is related to the age of parents and birth order. The paternal age is the main factor while the maternal age in not a significant effect and birth order also in not a significant effect after readjusting the other factors. Compared to paternal age group of under 25. There are significant increase of relative risks of age group 30-34 and 45 above, about 1.8 and 2.7 fold increase in univariate analysis and 1.9 and 3.3 fold increase in controlling the maternal age and birth order, a chi-square test for trend of distribution of paternal age also indicates a significant dose response relationship between increasing risk with age. The significance of result and methods of analysis were discussed.

Adult↗
PubMed1991

Birth order effects and time allocation.

"In this paper, a model is developed in which the explanation for birth-order effects does not rely on absence of capital markets, but follows from optimal allocation of parental time and goods among children over the childrearing years. The model yields two key results, which are then tested using 1967-1968 household survey data from urban Colombia.... It is shown that first and last-born children of mothers who do not work have an advantage over middle-borns.... At the same time, as predicted, there are no differences by birth order among children of working mothers. The persistence of birth-order effects even in high-income families indicates that such effects are at least in part due to the time constraint modelled; this is a strong result given the possibility of better substitutes for mother's time than allowed for in the model, and the likelihood that high-income families are able to purchase better substitutes."

Americas↗
PubMed1981

Birth order and risk of multiple sclerosis: are they associated and how?

By analyzing birth order distribution in 107 patients with multiple sclerosis. Conditionally to the number of siblings in the 107 families, patients' mean birth order is significantly greater than expected. The number of patients whose bith order is equal to one is significantly smaller than the corresponding expected value. The present finding is in contrast to recent results observed by Isager et al. (1980) and this potential association deserves to be further investigated.

Birth Order↗
PubMed1980

Risk of multiple sclerosis inversely associated with birth order position.

The aim of this study was to ascertain whether there is an association between risk of multiple sclerosis (MS) and birth order position. Our reference population was 198,000 persons born in the period 1930-50 and recorded in the register of school health records from the school health service of the Copenhagen council. We compared 46 persons from the register who had developed MS with matched controls from the register, three for each case. An inverse association between risk of MS and birth order position was found. Early birth orders tend to delay exposure to an infectous agent from early childhood to a later age. Therefore, our finding supports the hypothesis that MS is causally related to an infection that is inapparent when it occurs in early childhood, while infection later in life may result in severe disease

Birth Order↗
PubMed1979

Choice of ascertainment model II. Discrimination between multi-proband models by means of birth order data.

Probability models have been developed for family data, where each family has been selected or ascertained through a group of m probands, where m is a known parameter, not a random variable. The birth orders of the probands among the affected children are reported for each family. It is demonstrated that this information is sufficient for choice of ascertainment model. The conditional probability that an ascertained family with s children has r affected ones, depends, in addition to the segregation parameter, on the birth order of the youngest proband only. By means of the joint distribution of the birth orders of the other probands, it can be demonstrated if the ascertainment takes place through affected children near to or distant from each other in relative birth orders. Statistical methods have been developed for cases with two and cases with m probands.

Birth Order↗
PubMedDate not supplied

The association between birth order and adult stature.

First-borns are smaller than later-borns at birth. We investigated adult stature of families with three or more adult children, aged between 20 and 70 (mean 32) years. There was no significant correlation between size of the family and final adult stature of the siblings. We found a mean height reduction of first-borns compared to the mean of all sibs of -1.2 cm (P less than 0.02 using conventional analysis of variance, P less than 0.05 using nonparametric prediction configural frequency analysis). Males tend to increase in height with increasing birth order, whereas females do not beyond the second-born. These observations could not be explained by decreasing age of later-born sibs, nor by periods of malnutrition immediately after the war (1945-1948). Thus, we conclude that birth order is a factor that contributes significantly to the variance of adult height within sibships.

Adult↗
PubMed2007

Supplementary analyses regarding Langevin, Langevin, and Curnoe's (2007) findings on fraternal birth order in homosexual men.

A recent article by Langevin, Langevin, and Curnoe (2007) reported mixed results regarding the fraternal birth order effect, that is, the repeatedly observed finding that older brothers correlate with homosexuality in later-born males. Using a fraternal birth order index computed as older brothers minus younger brothers, Langevin et al. found that the "homoerotic" probands were born later among their brothers than were the "heteroerotic" probands in their full sample (N = 1194) and in their subsample over age 19 (N = 1122), but not in their subsample over age 31 (N = 698) or in their subsample with mothers over age 46 at the proband's birth (N = 727). The present writer concluded that the results obtained with the larger samples are more reliable, based on analyses demonstrating that (1) the larger samples are unlikely to be seriously affected by incomplete sibships, and (2) the smaller samples have poor statistical power. A separate analysis, based on an approximate reconstruction of Langevin et al.'s raw data, indicated that their heteroerotic probands reported a ratio of 104 older brothers per 100 older sisters, which is close to the normative population value of 106, whereas their homoerotic probands reported a ratio of 137, indicating a statistically significant excess of older brothers. These results suggest that Langevin et al.'s data showed significant evidence of a fraternal birth order effect and that their data were consistent with previous studies of this phenomenon.

Age Factors↗
PubMed2005

Birth order and sexual orientation in men: evidence for two independent interactions.

Birth order is correlated with male sexual orientation, but the reason(s) for this relationship is unclear. In the present study, data from a Canadian sample of homosexual and heterosexual men (N=604) were used to present evidence of two independent birth order interactions--one with height and the other with parental age--predicting sexual orientation in men. If these findings prove reliable, it raises the possibility that different aetiological factors underlie the birth order/sexual orientation relationship in men.

Adolescent↗
PubMed2003

Birth order, family environments, academic and affective outcomes.

Relations were examined among birth order, family social status, family learning environments, and a set of affective and academic outcomes. Data were collected as part of an Australian longitudinal study (4,171 females and 3,718 males). Analysis suggested that birth order continued to have small but significant associations with adolescents' self-concept and educational aspirations and with young adults' educational attainment, after taking into account differences in family social status and family learning environments.

Adult↗
PubMed1989

Birth order of patients with DSM-III-R somatization disorder.

A sample of 143 patients, 76 meeting strict DSM-III-R criteria for somatization disorder and 67 somatizers, was studied using Slater's index to measure birth order position. The results showed that birth order position was not associated with the diagnosis of somatization disorder and that sibship position in both groups occurred by chance. Thus, although environmental factors may influence the development of somatization disorder, the expression of environmental influence through birth order is unlikely.

Adult↗
PubMed1993

Maternal age and birth order of young IDDM patients. A study from southern India.

OBJECTIVE: To assess the effects of maternal age and birth order on the risk of IDDM in Asian Indians. RESEARCH DESIGN AND METHODS: Data from a diabetes registry in Madras, India, was used to find IDDM patients diagnosed before 20 yr of age. A questionnaire was used to elicit clinical details of subjects. RESULTS: Children with mothers < or = 24 yr of age had a higher percentage of IDDM. Children with lower birth orders had a higher prevalence of IDDM. CONCLUSIONS: The risk of IDDM in children is increased in children with lower birth orders, born of younger mothers.

Adolescent↗
PubMed1993

The influence of birth order and presentation on intrauterine growth of twins.

In order to evaluate the influence of birth order and fetal presentation on antenatal growth of twins we conducted a comparison of prospective measurements of five fetal biometric indices in 50 vertex-vertex and 47 vertex-breech twins. We compared (a) twin A to twin B in both groups; (b) the second and (c) the first twins of both groups. Both groups had similar maternal and neonatal characteristics. The growth curves of the twins were also very similar except for three significant (p < 0.05) deviations: (a) Twin A of the vertex-vertex group, had larger femur length (FL) at 18-19 weeks, abdominal circumference (AC) and estimated fetal weight (EFW) at 29 weeks, and EFW measurements at 36 weeks. (b) Second breech twins, compared to their second vertex cohorts, had significantly smaller biparietal diameter (BPD), head circumference (HC) and FL at 18-19 weeks, BPD and HC at 29 weeks, and EFW at 37 weeks. (c) First twins of the vertex-breech group, as compared to first twins of the vertex-vertex group, had significantly smaller BPD and AC at 18-19 weeks, FL and AC at 21-22 and 29 weeks, FL at 31 weeks, and EFW at 27-28 and 36 weeks' gestation. We concluded that significantly different sonographic fetal indices may be measured at about 20 and 30 weeks' gestation, but not later. An adaptive mechanism attributed to fetal presentation is suggested to explain similar birthweights in spite of these antepartum differences.

Adult↗
PubMed1995

Birth order, family environment, and young adults' occupational aspirations.

Relationships were examined among birth order, family environments, and occupational aspirations for 320 21-yr.-old Australians. The results indicated that relations between birth order and aspirations were mediated by associations between the young adults' perceptions of their parents' involvement in learning and the measures of aspiration.

Adolescent↗
PubMed1999

Influence of family size and birth order on menarcheal age of girls from Bilbao city (Biscay, Basque country).

From a sample of 895 girls from Bilbao 9.5 to 18.5 years of age, the possible influence of family size and birth order on menarcheal age was analyzed. The earliest mean ages of menarche occurred in girls from families of one or four or more children, or who occupied the first or last birth order in their families. Later mean ages of menarche occurred in girls belonging to sibships with two or three children or who occupied the second or third birth order in their families, the latest being girls belonging to sibships of three children or of third birth order. This may be due to the variations in the interval of time between births, leading to better care and less stress for the youngest individual of the family and, hence, may be indicative of psychological as well as biological factors affecting maturation. Am. J. Hum. Biol. 11:779-783, 1999. Copyright 1999 Wiley-Liss, Inc.

Journal Article↗
PubMed2000

Birth order and ratio of brothers to sisters in transsexuals.

BACKGROUND: As previous studies with homosexual males have revealed a later birth order, more older brothers and more brothers than sisters, this research was extended to a large series of transsexual males and females, some of whom are homosexual. METHODS: The male sample comprised 442 male-to-female transsexuals, subdivided by sexual partner preference: 106 homosexual, 135 heterosexual, 155 bisexual and 46 asexual. One hundred female-to-male transsexuals were also studied: 75 homosexual, 16 bisexual, seven heterosexual and five asexual. Birth order was computed by both Slater's Index and Berglin's Index. RESULTS: Homosexual male-to-female transsexuals have a later than expected birth order and more older brothers than other subgroups of male-to-female transsexuals. Each older brother increases the odds that a male transsexual is homosexual by 40 %. CONCLUSIONS: Hypotheses explaining the extension of prior findings to this large sample of transsexual males include a progressive maternal immunization to the male foetus either through the H-Y antigen or protein-bound testosterone or alterations in foetal androgen levels in successive pregnancies, all modifying male psychosexual development. Data on the sexual orientation of younger brothers of homosexual male transsexuals in this study are not consistent with the progressive immunization hypothesis.

Adult↗