Fertility and sibship size in a psychiatric patient population. A comparison with national census data

Pre-morbid fertility in psychosis: findings from the AESOP first episode study

Individuals with psychotic illnesses are known to have a reduced fertility. It is unclear whether this is due to biological or social factors. Most fertility studies have been conducted in chronic schizophrenia, where confounders like medication and hospitalisation make this difficult to elicit. A less severe reduction of fertility has been observed in some ethnic minorities, but results are inconsistent. We sought to investigate pre-morbid fertility in an ethnically diverse sample of individuals with first-onset psychosis. Data were derived from 515 people with a first psychotic episode (FEP) and 383 controls. We made case-control comparisons of differences in the proportion of those with children (fertility rates) and mean number of children (MNC). Analyses were then stratified by diagnosis, gender and ethnicity, and adjusted for potential confounders. We found that FEP showed a reduced fertility rate (age-adjusted OR of having children 0.47 [95% CI=0.39, 0.56]), irrespective of diagnosis, and there was little evidence of confounding by gender, ethnicity, religious background, education level, or history of past relationships (fully adjusted OR=0.55, 95% CI=0.37, 0.80). Women had a somewhat greater reduction in fertility rates than men (Men: age-adjusted OR 0.61 [95% CI 0.42, 0.89]; Women: age-adjusted OR 0.46 [95% CI 0.31, 0.69]) and we could not find any evidence of ethnic differences in the degree of fertility reduction. FEP who had previously experienced a stable relationship had an MNC that was comparable to that of the general population and had a later onset of illness. This is the largest case-control study to date to investigate fertility in first-onset psychosis. Our data suggests that fertility is affected, even prior to the onset of a psychotic illness, and there are likely to be biological and environmental factors involved, but the former seem to have a stronger influence.

Sex differences in the genetic risk for schizophrenia: history of the evidence for sex-specific and sex-dependent effects

Although there is a long history to examinations of sex differences in the familial (and specifically, genetic) transmission of schizophrenia, there have been few investigators who have systematically and rigorously studied this issue. This is true even in light of population and clinical studies identifying significant sex differences in incidence, expression, neuroanatomic and functional brain abnormalities, and course of schizophrenia. This review highlights the history of work in this arena from studies of family transmission patterns, linkage and twin studies to the current molecular genetic strategies of large genome-wide association studies. Taken as a whole, the evidence supports the presence of genetic risks of which some are sex-specific (i.e., presence in one sex and not the other) or sex-dependent (i.e., quantitative differences in risk between the sexes). Thus, a concerted effort to systematically investigate these questions is warranted and, as we argue here, necessary in order to fully understand the etiology of schizophrenia.

Reduced Fertility and Fecundity among Patients with Bipolar I Disorder and Schizophrenia in Egypt

OBJECTIVE

To evaluate reproduction among patients with bipolar I disorder (BP1) or schizophrenia (SZ) in Egypt.

METHODS

BP1 patients (n=113) were compared with community based, demographically balanced controls (n=124) and SZ patients (n=79, DSM-IV). All participants were evaluated using structured interviews and corroborative data were obtained from relatives. Standard indices of procreation were included in multivariate analyses that incorporated key demographic variables.

RESULTS

Control individuals were significantly more likely to have children than BP1 or SZ patients (controls 46.8%, BP1 15.9%, SZ 17.7%), but the BP1-SZ differences were non-significant. The average number of children for BP1 patients (0.37±0.9) and SZ patients (0.38±0.9) was significantly lower than for controls (1.04±1.48) (BP1 vs controls, p<0.001; SZ vs controls, p<0.001). The frequency of marriages among BP1 patients was nominally higher than the SZ group, but was significantly lower than controls (BP1: 31.9% SZ: 27.8% control: 57.3%). Even among married individuals, BP1 (but not SZ) patients were childless more often than controls (p=0.001). The marital fertility, i.e., the average number of children among patients with conjugal relationships for controls (1.8±1.57) was significantly higher than BP1 patients (1.14±1.31, p=0.02), but not significantly different from SZ patients (1.36±1.32, p=0.2).

CONCLUSION

Selected reproductive measures are significantly and substantially reduced among Egyptian BP1 patients. The reproductive indices are similar among BP1 and SZ patients, suggesting a role for general illness related variables. Regardless of the cause/s, the impairment constitutes important, under-investigated disability.

Large recurrent microdeletions associated with schizophrenia

Reduced fecundity, associated with severe mental disorders, places negative selection pressure on risk alleles and may explain, in part, why common variants have not been found that confer risk of disorders such as autism, schizophrenia and mental retardation. Thus, rare variants may account for a larger fraction of the overall genetic risk than previously assumed. In contrast to rare single nucleotide mutations, rare copy number variations (CNVs) can be detected using genome-wide single nucleotide polymorphism arrays. This has led to the identification of CNVs associated with mental retardation and autism. In a genome-wide search for CNVs associating with schizophrenia, we used a population-based sample to identify de novo CNVs by analysing 9,878 transmissions from parents to offspring. The 66 de novo CNVs identified were tested for association in a sample of 1,433 schizophrenia cases and 33,250 controls. Three deletions at 1q21.1, 15q11.2 and 15q13.3 showing nominal association with schizophrenia in the first sample (phase I) were followed up in a second sample of 3,285 cases and 7,951 controls (phase II). All three deletions significantly associate with schizophrenia and related psychoses in the combined sample. The identification of these rare, recurrent risk variants, having occurred independently in multiple founders and being subject to negative selection, is important in itself. CNV analysis may also point the way to the identification of additional and more prevalent risk variants in genes and pathways involved in schizophrenia.

Fertility of first-degree relatives of patients with schizophrenia: a three generation perspective

We explored the fertility in three generations; fertility of parents, siblings and offspring to patients with schizophrenia, to test the hypothesis that the decreased reproductive rate in the patients is compensated by an increased rate in their first-degree relatives. A population-based national database was created by linking the Swedish Multi-Generation and Hospital Discharge Registers. To maximize follow-up time for schizophrenia and reproductive history, three birth cohorts were selected: parental generation, born 1918-1927 (n=274464); affected generation, born 1932-1941 (n=108502) and offspring to affected generation, born 1951-1960 (n=103105). Ratios of estimated mean number of offspring were measured (fertility ratios), comparing the study subjects to the general population. The fertility among males with schizophrenia was decreased by over 70% (fertility ratio(patients/population)=0.29, 95% CI 0.25-0.35), whereas female patients had less than half as many offspring as the general female population (fertility ratio(patients/population)=0.48, 95% CI 0.42-0.55). When accounting for selection bias of larger families, no statistically significant difference was found among parents of patients with and without a diagnosis of schizophrenia. Further, the fertility among siblings of schizophrenic patients did not differ from the general population. A reduction in fertility was found among offspring to patients with schizophrenia, male offspring had 12% fewer offspring (fertility ratio(offspring/population)=0.88, 95%CI 0.77-1.01), while female offspring had 6% fewer offspring (fertility ratio(offspring/population)=0.94, 95% CI 0.84-1.05). In conclusion, we found reduced fertility in patients with schizophrenia and among their offspring that was not compensated by higher parental or sibling fertility.

Fertility and pregnancy in women with psychotic disorders

The majority of women with psychotic disorders have children but their pregnancies are at an increased risk of obstetric and psychiatric complications. This paper reviews research into the fertility of women with psychosis and complications occurring during their pregnancies and in the postpartum period. Mesh terms were used to search electronic databases (Medline, Embase, Psychlit and the Cochrane database of systematic reviews). Recent studies have confirmed earlier findings of a low fertility in women with schizophrenia, though fertility is less affected by mood disorders. Psychotic relapse during pregnancy is rare but women with a history of mood disorders (affective psychoses) are at high risk of postpartum relapse. There is a high risk of obstetric complications, mixed evidence of stillbirths and neonatal deaths and there is some weaker evidence of an association with sudden infant death syndrome. A significant proportion of mothers with psychotic disorders have parenting difficulties and lose custody of their infant. Close liaison between all health professionals during pregnancy and postpartum is essential for optimal management of these high risk pregnancies.

Paternal age and risk of schizophrenia in adult offspring

OBJECTIVE

The study examined the relation between paternal age at the time of birth and risk of schizophrenia in the adult offspring.

METHOD

Data from the birth cohort of the Prenatal Determinants of Schizophrenia study were used in this study. Virtually all members of this birth cohort had prospective information about paternal age at the time of the offspring's birth. Subjects with schizophrenia and other schizophrenia spectrum disorders (N=71) among members of this birth cohort were previously ascertained. In separate analyses, paternal age was modeled as a continuous variable and as a categorical variable, and its relation with the risk of adult schizophrenia and other schizophrenia spectrum disorders and with the risk of schizophrenia separately were examined.

RESULTS

There was a marginally significant, monotonic association between advancing paternal age and risk of adult schizophrenia and schizophrenia spectrum disorders. The association held after the analysis controlled for the effects of maternal age and other potential confounders. Similar results were observed when only subjects with schizophrenia were included in the analysis.

CONCLUSIONS

Advanced paternal age at the time of birth of the offspring may be a risk factor for adult schizophrenia.

Genetic epidemiology and schizophrenia: a study of reproductive fitness

Genetic epidemiological studies have demonstrated markedly reduced rates in reproduction among schizophrenic patients. According to evolutionary theory, behavioral and psychological phenotypes are selected based on ecological "fit". Where differential survival or reproductive success exists, genotype frequencies are altered in subsequent generations. In the case of schizophrenia, lower rates of reproduction constitute a negative selection factor that should reduce genes in the population associated with the expression of the disease--ultimately leading to decreases in prevalence. However, studies reveal a stable prevalence of about 1% over time. Attempts to explain the apparent contradiction between negative selection and stable prevalence have taken several forms. One explanation suggests that reproductive rates in relatives of schizophrenic patients are increased--compensating for reproductive loss in affected family members. Family data from schizophrenic patients at the Maryland Psychiatric Research Center were compared with those of healthy volunteers and volunteers with schizophrenia spectrum personality (SSP) disorders. Controlling for important socio-cultural and demographic variables, a multiple regression model revealed a significant increase in the number of siblings associated with schizophrenia. No differences in reproductive fitness were found among normal and SSP volunteers. This observed pattern in reproductive fitness provides one mechanism by which prevalence rates can remain stable despite lower reproductive rates among individuals with schizophrenia. Evidence of increased reproductive fitness in relatives suggests the need to consider the complex interactions of proximate and ultimate (evolutionary) mechanisms in the expression of schizophrenia.

Mitochondrial genetic analyses suggest selection against maternal lineages in bipolar affective disorder

Previous reports of preferential transmission of bipolar affective disorder (BP) from the maternal versus the paternal lines in families suggested that this disorder may be caused by mitochondrial DNA mutations. We have sequenced the mitochondrial genome in 25 BP patients with family histories of psychiatric disorder that suggest matrilineal inheritance. No polymorphism identified more than once in this sequencing showed any significant association with BP in association studies using 94 cases and 94 controls. To determine whether our BP sample showed evidence of selection against the maternal lineage, we determined genetic distances between all possible pairwise comparisons within the BP and control groups, based on multilocus mitochondrial polymorphism haplotypes. These analyses revealed fewer closely related haplotypes in the BP group than in the matched control group, suggesting selection against maternal lineages in this disease. Such selection is compatible with recurrent mitochondrial mutations, which are associated with slightly decreased fitness. Although such mismatch distribution comparisons have been used previously for analyses of population histories, this is, as far as we are aware, the first report of this method being used to study disease.

Relative hand skill predicts academic ability: global deficits at the point of hemispheric indecision

Population variation in handedness (a correlate of cerebral dominance for language) is in part genetic and, it has been suggested, its persistence represents a balanced polymorphism with respect to cognitive ability. This hypothesis was tested in a sample of 12,770 individuals in a UK national cohort (the National Child Development Study) by assessing relative hand skill (in a square checking task) as a predictor of verbal, non-verbal, and mathematical ability and reading comprehension at the age of 11 years. Whereas some modest decrements were present in extreme right handers the most substantial deficits in ability were seen close to the point of equal hand skill ('hemispheric indecision'). For verbal ability females performed better than males, but the relationship to relative hand skill was closely similar for the two sexes; for reading comprehension males close to the point of equal hand skill showed greater impairments than females. Analysed by writing hand the relationship of ability to hand skill appeared symmetrical about the point of 'hemispheric indecision'. The variation associated with degrees of dominance may reflect the operation of continuing selection on the gene (postulated to be X-Y linked) by which language evolved and speciation occurred.

Reduced fertility in schizophrenia: here to stay?

Studies of reproduction among individuals with schizophrenia published in this century are reviewed. Past studies suggesting normalization of reproductive deficits are disputed in view of recent reports of a persistent impairment. The handicap appears to be more significant among men with schizophrenia. The implications of these findings for genetic research in schizophrenia are discussed.

Evidence for linkage to psychosis and cerebral asymmetry (relative hand skill) on the X chromosome

The hypothesis that psychosis arises as a part of the genetic diversity associated with the evolution of language generates the prediction that illness will be linked to a gene determining cerebral asymmetry, which, from the evidence of sex chromosome aneuploidies, is present in homologous form on the X and Y chromosomes. We investigated evidence of linkage to markers on the X chromosome in 1) 178 families multiply affected with schizophrenia or schizoaffective disorder with a series of 16 markers spanning the centromere (study 1), and 2) 180 pairs of left-handed brothers with 14 markers spanning the whole chromosome (study 2). In study 1, excess allele-sharing was observed in brother-brother pairs (but not brother-sister or a small sample of sister-sister pairs) over a region of approximately 20 cM, with a maximum LOD score of 1.5 at DXS991. In study 2, an association between allele-sharing and degree of left-handedness was observed extending over approximately 60 cM, with a maximum lod score of 2.8 at DXS990 (approximately 20 cM from DXS991). Within the overlap of allele-sharing is located a block in Xq21 that transposed to the Y chromosome in recent hominid evolution and is now represented as two segments on Yp. In one of two XX males with psychosis we found that the breakpoint on the Y is located within the distal region of homology to the block in Xq21. These findings are consistent with the hypothesis that an X-Y homologous determinant of cerebral asymmetry carries the variation that contributes to the predisposition to psychotic illness.

Is schizophrenia the price that Homo sapiens pays for language?

The dichotomy between schizophrenia and manic-depressive illness is, as E. Kraepelin suspected, flawed; no unequivocal separation can be achieved. There are no categories of psychosis, but only continua of variation. However, the definition of nuclear symptoms by K. Schneider reveals the fundamental characteristics of the core syndrome--it is independent of the environment and constant in incidence across populations that have been separated for thousands of years. The associated genetic variation must be as old as Homo sapiens and represent a component of diversity that crosses the population as a whole. The fecundity disadvantage that accompanies the syndrome requires a balance in a substantial and universal advantage; this advantage, it is proposed, is the speciation characteristic of language; language and psychosis have a common evolutionary origin. Language, it is suggested, originated in a critical change on the sex chromosomes (the 'speciation event'--the genetic change that defined the species) occurring in East Africa between 100 and 250 thousand years ago that allowed the two hemispheres to develop with a degree of independence. Language can be understood as bi-hemispheric with one component function--a linear output sequence--confined to the dominant hemisphere--and a second--parallel distributed sampling occurring mainly in the non-dominant hemisphere. This mechanism provides an account of the generativity of language. The significance of nuclear symptoms is that these reflect a breakdown of bi-hemispheric coordination of language, perhaps specifically of the process of 'indexicalisation' (the distinction between 'I' and 'you') of self- versus other-generated references. Nuclear symptoms can be described as 'language at the end of its tether'; the phenomena and population characteristics of the nuclear syndrome of schizophrenia thus yield clues to the origin of the species.

Fertility and schizophrenia: evidence for increased fertility in the relatives of schizophrenic patients

Fertility has been observed to be reduced in patients with schizophrenia, although the disorder was seen to occur at a steady rate in the general population. The hypothesis of increased fertility in the healthy relatives of the patients, which maintained the genetic contribution to the disorder has been proposed but has not received much support. The present study reports the fertility rate in 100 schizophrenic patients and their relatives (grandparents, parents, uncles, aunts and siblings). The fertility of the different family members was compared, taking into account the completion of age of maximum reproductivity, i.e. up to 50 years of age. The trends in fertility rates over three generations of patients' families were compared with those in the general population of India over a corresponding period from 1950 to 2000 AD. The patients were observed to be hypofertile, but their parents showed a higher fertility than all other relatives, as well as the general population. The siblings of the patients also tended to have higher fertility rates than the general population. This increased fertility in parents and sibs, who are the probable carriers of the abnormal gene, could compensate for the reduction in genetic contribution to morbid risk for schizophrenia due to reduced reproductivity of the patients themselves.

Fertility in schizophrenia: results from a contemporary US cohort

To investigate procreation in schizophrenia, as well as gender-related differences, female patients with schizophrenia (n = 79, DSM-III-R criteria) were compared with screened female controls (n = 124) and subsequently with male patients (n = 86). Two outcomes were investigated: (i) the proportion of subjects with one or more children (an index of fertility) and (ii) the number of children per subject among those with one or more children (an index of fecundity). Multivariate analysis was used to control for confounding variables. No significant differences in fertility between female patients and controls were detected, but reduced fecundity was noted among female patients past the reproductive period. Male patients showed a significant reduction in both fertility and fecundity compared to female patients. These results suggest that there is a relatively small impairment of fecundity among female patients compared with controls, but that there are more significant gender-related differences in both fertility and fecundity. The latter have important implications for the genetics of schizophrenia.

Reproductive fitness in familial schizophrenia

BACKGROUND

Reproductive fitness is an important factor in understanding inheritance in genetic disorders. The purpose of this study was to determine whether fitness is reduced in familial schizophrenia (FS) and if fitness in siblings differs from the norm.

METHOD

The number of offspring in 36 subjects with RDC schizophrenia or schizoaffective disorder (SZ) and their 101 siblings from large FS families was compared with age-adjusted census figures.

RESULTS

Fitness in the SZ group was significantly reduced: 23% of expected in males and 51% of expected in females. Fitness of unaffected siblings was within census expectations. However, female siblings with schizophrenia spectrum features had increased fitness over census norms. Reduced fitness was correlated with low marital rates, poor functioning and positive symptoms.

CONCLUSIONS

These results indicate that reduced fitness is an important genetic force in FS and is likely inherent to the illness. Sex differences are important and would need to be considered when examining maternal and paternal transmission of schizophrenia. The results support a proposed high mutation rate for schizophrenia, consistent with a dynamic mutation mechanism.

Reproductive behaviour in schizophrenia relative to other mental disorders: evidence for increased fertility in men despite decreased marital rate

Using case register data, the overall marital rate among 5158 patients with mental illness was found to be comparable to the general population. The proportion of those ever married was markedly reduced in the schizophrenic group relative to those with a manic or neurotic illness. Men with schizophrenia had a particularly low rate of marriage. The overall marital fertility of the 3 groups was comparable to each other and appeared to be higher than that in the general population. In the schizophrenic group only, married men, particularly those with a family history of mental disorder, produced more children than married women. Men might represent a more fertile group of schizophrenic patients with some biological advantage of increased fecundity, which may help to compensate for negative selection pressures.

Reproductive rates in schizophrenic outpatients

We investigated the marriage rates, the reproductive rates and the marital reproductivity of schizophrenic outpatients in Japan. A total of 553 patients with DSM-III-R-diagnosed schizophrenia at the Teikyo University Hospital, Tokyo, Japan were compared with age- and sex-matched outpatients at surgical clinics of the same hospital. Our findings indicate that the reproductivity of schizophrenics is reduced, even though the sample consists of outpatient population and modern operational diagnostic criteria have been used. The marriage rate and reproductive rate of the schizophrenics were reduced, especially in men. The number of married men was significantly less than that of married women and the reduced marital reproductivity was found in women but not men. These findings indicate that the reduced reproductivity of men in accounted for largely by a reduced rate of marriage, and that in women is accounted for partly by lower rate of reproductivity within marriage.

The genetic epidemiology of schizophrenia and the design of linkage studies

There are three aspects of schizophrenia that are challenges to the design of linkage studies. First, analysis of twin and family data have consistently failed to identify a single major gene effect. Second, ascertainment of multiplex families does not guarantee the sampling of families in whom a major gene is segregating even if such a gene exists. Third, environmental influences appear to play an essential role in the etiology of at least some schizophrenia. The implications of these features for linkage strategies in schizophrenia are discussed.

Sex differences in the familial transmission of schizophrenia

The hypothesis that schizophrenic men have a lower familial risk for schizophrenia than schizophrenic women was tested using the DSM-III-diagnosed samples of the Iowa 500 and non-500 family studies. Survival analyses were used to test for differences in the risk for schizophrenia and spectrum disorders, for sex of proband and sex of relative, controlled for fertility effects and ascertainment bias. Male and female relatives of schizophrenic men had a significantly lower risk for schizophrenia, schizophreniform, and schizoaffective disorders than relatives of schizophrenic women. However, the effect was not significant for the full spectrum nor when analysed by sex of relative. Sex differences in the risk for other psychiatric disorders among relatives of schizophrenic probands were not significant.

Schizophrenia as a recent disease

The hypothesis that schizophrenia is a recent disease can explain why descriptions of schizophrenia-like disorders were rare before 1800, why the prevalence of insanity in the Western world increased during the 19th but remained low in the non-Western world until the 20th century, and why schizophrenia has become milder in the West during recent decades. It also explains why schizophrenia has 'persisted' in spite of its associated low fertility. The evidence for the hypothesis is somewhat frail, but perhaps not more so than that for alternative hypotheses.

Mutation and psychosis: a suggested explanation of seasonality of birth

The persistence of psychosis at a high and relatively constant prevalence in the various populations of the world is rendered difficult to explain by the absence of identified environmental precipitants and by reduced fertility of affected individuals. The problem is not confined to schizophrenia but applies also to affective disorder. The 'virogene' concept attempts to explain this paradox as follows. (1) Psychosis in general is, as suggested by Böök (1953) and Lewis (1958) for schizophrenia, associated with a high rate of mutation. (2) The new mutations occur at a specific site (a 'hot-spot') in the genome and consist of rearrangements (e.g. transpositions or new insertions occurring as a result of unequal recombination) in a sequence which has a degree of potential autonomy, i.e. an integrated pathogen or 'virogene'. (3) The mutations occur specifically in the courses of gametogenesis in the male. By its location in the scrotal sac and its extended time course, gametogenesis in the male is susceptible to insertional mutagenesis as a function of variations in environmental temperature. Such temperature-dependent mutations are reflected in the seasonality of birth seen in both schizophrenic and affective illnesses. The increased likelihood of such mutations occurring with time is held to account for the association of psychosis with increased paternal age. (4) Such new events are held responsible not only for 'sporadic' cases in individuals without a family history of psychosis, but also for increases in severity of illness between generations. Psychosis is viewed as a continuum extending from unipolar through bipolar affective disorder and schizoaffective illness to schizophrenia with increasing degrees of defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Is there an increase of reproductive rates in schizophrenics? I. Critical review of the literature

It is well-known that the fertility of schizophrenic patients, particularly males, is below the population average. The main measures of fertility (reproductivity) are marriage rate, marital fertility, and rate of reproduction. A review of the literature reveals the rate of reproduction of schizophrenic patients to be 30% to 80% of the general population, the reduction being mainly due to reduced probability of marriage. At least one investigation presented evidence for an increase in marriage rate and rate of reproduction in schizophrenic patients relative to the general population in recent time. If this increase were to be confirmed it would undoubtedly have practical as well as theoretical implications. The hypothesis of a compensatory higher fertility of healthy relatives of schizophrenics based on a physiological advantage is empirically unproven. Additionally, the concept of a balanced polymorphism in schizophrenia rests on a superficial analogy with Mendelian traits.

Nocturnalism: an ethological theory of schizophrenia

Schizophrenia is a human behavioral variant with a 1% phenotypic population frequency. As the major "mental illness" affecting human beings, it has defied all previous attempts to explain, predict or prevent its devastating clinical manifestations. In addition to unidentified nongenetic determinants, schizophrenia has genetic determinants in the absence of known specific neuropathological or biochemical correlates found in other entities conceptualized as genetic diseases. The fitness of schizophrenics is 0.7 of nonschizophrenics, and a 1% phenotypic population frequency is difficult to explain by mutation rate alone. An ethological theory of schizophrenia has been developed in which the genetic determinant is the nocturnal character of a postulated polymorphic trait termed when active. The nongenetic determinant is simply a sufficient intensity of specific frequencies of environmental light. According to the author's theory, a schizophrenic individual could be processing information while awake and exposed to light with a brain that is processing information as though he were asleep. The empirical data from which the theory is constructed are presented. THe theory is capable of explaining clinical schizophrenia within an ethological paradigm and makes several predictions, the most significant of which is that the absence of a sufficient intensity of specific frequencies of environmental light should ameliorate the major symptoms of clinical schizophrenia in individuals who possess its genetic determinant.

Differential fertility in bipolar affective illness

The fertility of 134 bipolar probands (60 males, 74 females) was compared with national census data and examined for sex and age-of-onset effects. Fertility was markedly reduced in certain age cohorts in both females and males. When illness onset was taken into account, significant reductions in fertility were observed in the two sexes both before and after onset. The overall reduction in females remained constant over time, but was greater after onset among males. The role of selective forces maintaining affective disorders in the population was discussed in light of genetic and sociodemographic hypotheses.

Factors affecting the distribution of age at onset in patients with affective disorders

We analyzed the age-at-onset distributions in a group of 285 patients diagnosed as having major affective disorder, recurrent, either unipolar or bipolar, in order to detect the possible existence of genetic and epidemiological factors affecting their age-at-onset distribution. In fact, since it is known that affective disorders are genetically heterogeneous with respect to the liability systems involved, methodological considerations support the hypothesis of the existence of different ages at onset also. We thus investigated several variables and the significant findings of our study were that bipolarity, at least one affected parent and a low position in the sibship are each associated with earlier age at onset of affective disease.