Problems in the assessment of relative risk of chronic disease among biological relatives of affected individuals

Sporadic Hemiplegic Migraine is an Aetiologically Heterogeneous Disorder

In order to better understand sporadic hemiplegic migraine (SHM) and particularly its relation to familial hemiplegic migraine (FHM), migraine without aura (MO) and typical migraine with aura (typical MA), we investigated the occurrence of MO and typical MA among probands with SHM and their first-degree relatives. The pattern of familial aggregation of MO and typical MA was assessed by population relative risk calculations. A total of 105 SHM probands and 483 first-degree relatives were identified in the Danish population. Compared with the general population, SHM probands had no increased risk of MO, but a highly increased risk of typical MA. First-degree relatives of all SHM probands had an increased risk of both MO and typical MA, whereas first-degree relatives of probands with exclusively SHM had no increased risk of MO but an increased risk of typical MA. Our data suggest that SHM is a genetically heterogeneous disorder.

Familial risk of venous thromboembolism: a nationwide cohort study

BACKGROUND

Venous thromboembolism has genetic determinants, but population-based data on familial risks are limited.

OBJECTIVES

To examine the familial risk of venous thromboembolism.

METHODS

We undertook a nationwide study of a cohort of patients with deep venous thrombosis or pulmonary embolism born after 1952. We used the Danish National Registry of Patients covering all Danish hospitals, for the years 1977 through 2009, to identify index cases of venous thromboembolism, and assessed the incidence among their siblings. We compared standardized incidence ratios (SIRs) of the observed and expected number of venous thromboembolism cases among siblings, using population-specific, gender-specific and age-specific incidence rates.

RESULTS

We identified 30,179 siblings of 19,599 cases of venous thromboembolism. The incidence among siblings was 2.2 cases per 1000 person-years, representing a relative risk of 3.08 (95% confidence interval [CI] 2.80-3.39) as compared with the general population. The risk was higher for both men (SIR 3.36, 95% CI 2.96-3.82) and women (SIR 2.81, 95% CI 2.45-3.23). The risk was similar among siblings of index cases with venous thrombosis and those of index cases with pulmonary embolism.

CONCLUSION

Venous thromboembolism has a strong familial component.

Chronic rhinosinusitis gives a ninefold increased risk of chronic headache. The Akershus study of chronic headache

We studied the association of chronic headache and chronic rhinosinusitis in 30 000 persons aged 30–44 years from the general population. They received a mailed questionnaire. Those with possible chronic headache were interviewed by neurological residents. The criteria of the American Academy of Otolaryngology—Head and Neck Surgery were applied to diagnose headache attributed to chronic rhinosinusitis (HACRS), otherwise the International Classification of Headache Disorders was used. The questionnaire response rate was 71%, and the participation rate of the interview was 74%. Compared with the general population, persons with chronic rhinosinusitis have an at least ninefold increased risk of having chronic headache. A 3-year follow-up showed that HACRS symptoms were significantly improved after treatment with nasal surgery, nasal corticosteroids, discontinuation of overused headache medications and discontinuation of nasal decongestants or unspecified reasons. Chronic rhinosinusitis is significantly associated with chronic headache, and HACRS is likely to be a distinct type of headache.

Interrelation of Chronic Tension-Type Headache With and Without Medication Overuse and Migraine in the General Population: The Akershus Study of Chronic Headache

We studied the interrelation of chronic tension-type headache with and without medication overuse (CTTH) and migraine in a random sample of 30 000 persons aged 30–44 years. They received a mailed questionnaire. Those with a possible chronic headache were interviewed by neurological residents. The International Classification of Headache Disorders was used. A total of 386 persons had CTTH. Compared with the general population, men had a 2.8-fold and women a 2.4-fold significantly increased risk of migraine without aura (MO). The risk of migraine with aura (MA) was not increased. The mean age at onset of CTTH was significantly higher in those with than in those without co-occurrence of MO. Bilateral MO attacks were significantly more frequent in those with age at onset of CTTH prior to age at onset of MO compared with those with age at onset in reverse order. CTTH and MO are interrelated, possibly in a complex matter. In contrast, CTTH and MA are not interrelated.

Familial aggregation of Parkinson's disease: a meta-analysis

We sought to determine the relative risk (RR) of Parkinson's disease (PD) for having a first-degree relative with PD versus having no first-degree relative with PD. Studies of familial aggregation of PD were identified by searching Medline and other sources. From each study, RRs were extracted or calculated based on the published data. Studies were categorized according to methodological characteristics, as well as by first-degree relationship type and age at PD onset restrictions. Meta-analyses and meta-regressions were based on random effect models. Twenty-nine studies of familial aggregation of PD were identified with results for first-degree relatives. The best estimate of the RR of PD for having a first-degree relative with PD was 2.9 (95% CI: 2.2, 3.8; P = 2.2 E-14), based on the studies with the most rigorous methods. The RR for sibling pairs was 4.4 (95% CI: 3.1, 6.1; P < 1.0 E-30), while for child-parent pairs it was 2.7 (95% CI: 2.0, 3.7; P = 3.6 E-10). The RR for early onset PD was 4.7 (95% CI: 3.2, 6.8; P = 6.7 E-16), while for late onset PD it was 2.7 (95% CI: 1.9, 3.9; P = 1.8 E-8). Inclusion of methodologically less rigorous investigations tended to increase the RR estimates. Summary RRs were clearly elevated above one for all study methods, all first-degree relationship types, and all age at onset categories. Familial aggregation of PD is strong and unlikely to be due to chance or to deficiencies in study methodology.

European principles of management of common headache disorders in primary care

The objective of this study was to investigate the importance of genetics in tension-type headache. A MEDLINE search from 1966 to December 2006 was performed for "tension-type headache and prevalence" and "tension-type headache and genetics". The prevalence of tension-type headache varies from 11 to 93%, with a slight female preponderance. Co-occurrence of migraine increases the frequency of tension-type headache. A family study of chronic tension-type headache suggests that genetic factors are important. A twin study analysing tension-type headache in migraineurs found that genetic factors play a minor role in episodic tension-type headache. Another twin study analysing twin pairs without co-occurrence of migraine showed a significantly higher concordance rate among monozygotic than same-gender dizygotic twin pairs with no or frequent episodic tension-type headache, while the difference was minor in twin pairs with infrequent episodic tension-type headache. Frequent episodic and chronic tension-type headache is caused by a combination of genetic and environmental factors, while infrequent episodic tension-type headache is caused primarily by environmental factors.

Genetics in primary headaches

This tutorial describes different methods and results of genetic studies of primary headaches. A positive family history is imprecise, because it does not specify the number of affected, family size or relation to the proband. Nor does it include an interview of the possibly affected family members. Calculation of the familial aggregation after confirmation of the diagnosis by a physician is more precise. Compared to the general population, first-degree relatives of probands with migraine without aura, migraine with aura, chronic tension-type headache and cluster headache has a significantly increased risk of the proband's disorder. These data are confirmed in twin studies. The primary headaches are caused by a combination of genetic and environmental factors. A major breakthrough was identification of 3 different genes all causing the rare autosomal dominant inherited familial hemiplegic migraine. The genes encode ion channels. So far no genes have been identified to cause the more common types of primary headaches.

Subtyping schizophrenia: implications for genetic research

Phenotypic variability and likely extensive genetic heterogeneity have been confounding the search for the causes of schizophrenia since the inception of the diagnostic category. The inconsistent results of genetic linkage and association studies using the diagnostic category as the sole schizophrenia phenotype suggest that the current broad concept of schizophrenia does not demarcate a homogeneous disease entity. Approaches involving subtyping and stratification by covariates to reduce heterogeneity have been successful in the genetic study of other complex disorders, but rarely applied in schizophrenia research. This article reviews past and present attempts at delineating schizophrenia subtypes based on clinical features, statistically derived measures, putative genetic indicators, and intermediate phenotypes, highlighting the potential utility of multidomain neurocognitive endophenotypes.

Familial aggregation of fainting in a case–control study of neurally mediated hypotension patients who present with unexplained chronic fatigue

AIMS

We hypothesized that family history of fainting is a risk factor for adult-onset neurally mediated hypotension (NMH) in patients who present with chronic fatigue rather than fainting.

METHODS AND RESULTS

A nested case-control study of Gulf War veterans gathered fainting histories directly from 197 first-degree relatives of 16 fatigued NMH cases, 26 fatigued controls, and 17 healthy controls. NMH status was determined by tilt testing. Female relatives of fatigued controls reported more fainting than female relatives of cases (P<0.01); there were no significant differences in the frequency of fainting in male relatives by case or control status, or in either gender by age at first faint or by familial relationship to the proband. The odds of NMH patients giving any family history of fainting were 0.56 (95% CI 0.15, 2.07). Recurrence risks calculated using lifetime prevalences of fainting in male military personnel of similar age to our participants were low (1.5-1.7) and did not differ by case or control status.

CONCLUSION

Family history of fainting is not a risk factor for adult-onset NMH in fatigued veterans. Our findings may differ from other studies of familial aggregation in NMH because of study methods or because NMH-fatiguers may differ from NMH-fainters.

Dissecting complex disease: the quest for the Philosopher's Stone?

Is the search for the causes of complex disease akin to the alchemist's vain quest for the Philosopher's Stone? Complex chronic diseases have tremendous public health impact in the industrialized world. Much effort has been expended on research into their causes, with the aim of predicting who will be affected or preventing effects before they arise, but progress has been halting at best. In this paper, we discuss possible reasons including the use of models and methods that fit point-source and Mendelian diseases but may not be as appropriate for complex diseases, reliance on causal criteria that may not be as relevant as they are for communicable diseases, and the biology of complex disease itself. Finally, we ask whether most complex diseases are even good candidates for the kind of prediction and prevention that we have come to expect based on experience with infectious and Mendelian disease.

Epidemiology and genetics of cluster headache

Cluster headache, the most severe primary headache, is characterised by unilateral pain, ipsilateral autonomic features, and, in many cases, restlessness. Recent epidemiological studies indicate that the prevalence of cluster headache is about one person per 500. Genetic epidemiological surveys indicate that first-degree relatives are five to 18 times-and second-degree relatives, one to three times-more likely to have cluster headache than the general population. Inheritance is likely to be autosomal dominant with low penetrance in some families, although there may also be autosomal recessive or multifactorial inheritance in others. To date, no molecular genetic clues have been identified for cluster headache. Identification of genes for cluster headache is likely to be difficult because most families reported have few affected members and genetic heterogeneity is likely. Future focus should be on ion channel genes and clock genes. This review summarises the epidemiology and genetics of cluster headache.

Increased risk of migraine with typical aura in probands with familial hemiplegic migraine and their relatives

We investigated the occurrence of migraine without aura (MO) and migraine with typical aura (MA) amongst probands with familial hemiplegic migraine (FHM) and their first degree relatives in order to evaluate the relations between these syndromes. A total of 44 FHM probands and 240 first degree relatives were identified in the Danish population. The pattern of familial aggregation was assessed by population relative risk (PRR) calculations. Amongst FHM probands the PRR of MO was 1.5 (95% CI: 0.8-2.2), whereas the PRR of MA was 7.1 (95% CI: 5.0-9.2). Thus, compared with the general population, FHM probands had no increased risk of MO but a significantly increased risk of MA. A similar pattern was seen amongst their first degree relatives, who had no increased risk of MO, whereas the risk of MA was significantly increased; 7.6 times in FHM-affected first degree relatives and 2.4-times in non-FHM-affected first degree relatives. These results are contrary to a sharing of genetic mechanisms between FHM and MO. Furthermore, they suggest that the genetic abnormality causing FHM may also cause attacks with the symptomatology of MA.

Epidemiology of vitiligo and associated autoimmune diseases in Caucasian probands and their families

Generalized vitiligo is an autoimmune disorder characterized by acquired white patches of skin and overlying hair, the result of loss of melanocytes from involved areas. The most common disorder of pigmentation, vitiligo occurs with a frequency of 0.1-2.0% in various populations. Family clustering of cases is not uncommon, in a non-Mendelian pattern suggestive of multifactorial, polygenic inheritance. We surveyed 2624 vitiligo probands from North America and the UK regarding clinical characteristics, familial involvement, and association with other autoimmune disorders, the largest such survey ever performed. More than 83% of probands were Caucasians, and the frequency of vitiligo appeared approximately equal in males and females. The frequency of vitiligo in probands' siblings was 6.1%, about 18 times the population frequency, suggesting a major genetic component in disease pathogenesis. Nevertheless, the concordance of vitiligo in monozygotic twins was only 23%, indicating that a non-genetic component also plays an important role. Probands with earlier disease onset tended to have more relatives affected with vitiligo, suggesting a greater genetic component in early onset families. The frequencies of six autoimmune disorders were significantly elevated in vitiligo probands and their first-degree relatives: vitiligo itself, autoimmune thyroid disease (particularly hypothyroidism), pernicious anaemia, Addison's disease, systemic lupus erythematosus, and probably inflammatory bowel disease. These associations indicate that vitiligo shares common genetic aetiologic links with these other autoimmune disorders. These results suggest that genomic analysis of families with generalized vitiligo and this specific constellation of associated autoimmune disorders will be important to identify the mechanisms of genetic susceptibility to autoimmunity.

Familial occurrence of migraine with aura in a population-based study

OBJECTIVE

To better define a possible genetic basis for migraine with aura (MWA).

METHODS

We investigated the familial occurrence of migraine with aura in a sample of (MWA) subjects recruited from an epidemiologic study of migraine with aura involving the general population. The sample with migraine with aura (n = 26) was selected out of a total of 1392 subjects (842 women and 550 men) representative of the general population aged 18 to 65 years in the southern Italian town of San Severo. A family history of migraine with aura was determined via direct interviews with all living first-degree relatives of the 26 subjects who could be reached by investigators, 119 people: 71 women and 48 men. The diagnosis of migraine with aura was made according to the 1988 International Headache Society (IHS) criteria.

RESULTS

Of the 26 subjects with migraine with aura, 7 (6 women and 1 man) had a positive family history, with a total of 7 first-degree relatives affected by the disease (1 mother, 2 fathers, 1 brother, 1 sister, and 2 children). Based on the lifetime prevalence rate of migraine with aura (1.6%) in the San Severo general population, the relative risk of migraine with aura in the first-degree relatives of the subjects was 3.68 (4.16 for women and 2.77 for men).

CONCLUSION

Our subjects' relative risk rate for familial occurrence of migraine with aura was similar to that reported by one investigator, but markedly lower than that reported by another group.

Risk of tremor and impairment from tremor in relatives of patients with essential tremor: a community-based family study

Essential tremor (ET) is a common condition that is present in as many as 23% of elderly individuals. Our objective was to determine the risk of ET and to study the impairment resulting from ET among relatives of ET cases compared to relatives of controls. ET cases and matched controls from the Washington Heights-Inwood community, New York, and their first- and second-degree relatives underwent a standardized tremor examination. The risk of having ET in relatives of cases vs relatives of controls was compared using Cox proportional hazards models. Five hundred ninety-one subjects were examined (59 ET cases, 72 controls, 234 case relatives, and 226 control relatives). ET was present in 25 (22.5%) of the 111 first-degree relatives of cases compared to 6 (5.6%) of 107 first-degree relatives of controls [relative risk (RR) = 4.67, 95% confidence interval (CI) = 1.90-11.49, p = 0.0008]. RRs were higher in relatives of cases with onset < or =50 years than in those with later onset (RR = 10.38 vs 4.82). Sixteen (64%) of twenty-five affected first-degree case relatives exhibited moderate tremor while performing tasks such as writing, drinking, or pouring. Relatives of ET patients are five times more likely to develop the disease than are members of the population and ten times more likely if the proband's tremor began at an early age. The majority of the affected relatives can expect to experience impairment resulting from tremor.

Increased familial risk of cluster headache

The authors studied the occurrence of cluster headache in the families of 220 Italian patients with cluster headache. A positive family history was found in 20% (44/220) of the families. Compared with the general population, first-degree relatives had a 39-fold significantly increased risk of cluster headache. Second-degree relatives had an eightfold significantly increased risk. The increased familial risk strongly supports the hypothesis that cluster headache has a genetic component in some families.

Is the genetic liability in multifactorial disorders higher in concordant than discordant monozygotic twin pairs? A population-based family twin study of migraine without aura

Migraine without aura (MO) is a multifactorial disorder. Expression of a disorder with multifactorial inheritance depends on the genetic liability and on environmental factors. A high liability is reflected by a high frequency of affected relatives. We have previously shown that monozygotic (MZ) twin pairs have a significant higher concordance of MO than dizygotic twin pairs. The incomplete concordance among MZ twin pairs may be due to a lower genetic liability among discordant than concordant MZ twin pairs. The present study analysed the genetic liability in MZ twin pairs concordant and discordant for MO by the population-relative risk of MO among parents and siblings. The twin pairs were from the population-based Danish Twin Register. First-degree relatives of 29 concordant and 34 discordant MZ twin pairs were blindly telephone interviewed by a physician. The participation rate of the eligible first-degree relatives was 96%. The population-relative risk of MO among parents and siblings was 2.73 (2.39-3.06) in concordant and 2.37 (2.03-2.71) in discordant MZ twin pairs. The relative risk of MO was significantly higher in female first-degree relatives of concordant than of discordant MZ male and female twin pairs. An opposite effect was observed in male first-degree relatives, although this was not significant for male first-degree relatives of female MZ twin pairs. The present study found no statistically significant difference in genetic liability to MO among concordant and discordant MZ twin pairs. However, a difference in genetic liability among MZ and DZ twin pairs is anticipated to be small. Thus, it may be possible to show the effect in a larger study population or by investigating a more frequent trait than MO.

Evaluation of potential sources of bias in a genetic epidemiologic study of breast cancer

Systematic errors, or bias, can arise at several stages of a study, including selection of subjects, measurement of exposure and disease, and data analysis. Little attention appears to have been paid to potential sources of bias in genetic epidemiologic studies, despite the fact that the study of units (families) and members (relatives) within those units produces unique opportunities for bias to be introduced. The ability to evaluate whether selection bias has occurred is rare. In 1944, a case-control family study of breast cancer was initiated at the Dight Institute for Human Genetics at the University of Minnesota. A follow-up study of these 544 families is currently being conducted on sisters, daughters, nieces, and granddaughters of the probands, and a control group of women who are spouses of male first- and second-degree relatives. Updated data are collected on females who are 18 years or older through telephone interviews and questionnaires. The availability of detailed family history information on these families at baseline provided an opportunity to evaluate several potential sources of bias. Analyses were performed to determine if families lost to follow-up differed from those who were successfully located or excluded (ineligible), and whether participation rates within a family differed by relationship to proband, age, and family history of cancer. The latter participation rates for individuals were examined with respect to a telephone interview, a mailed questionnaire, and screening mammography. There were no statistically significant differences in the cancer histories of families that were excluded, those that were lost to follow-up, and those that participated. Within families, degree of relationship to the breast cancer proband was significantly associated with age-adjusted participation rates on mailed questionnaires (P < 0.005) and mammography (P < 0.005), but not telephone interviews (P = 0.29). After adjustment for age, marry-ins with a family history of breast cancer were not significantly more likely than marry-ins without a family history to undergo mammography (P = 0.11) or return mailed questionnaires (P = 0.74). Although non-participation is a potentially serious source of bias to a genetic epidemiologic study and the effect of variable participation rates should be explored when investigating the genetic component of a disease, it does not appear to be a problem for this particular study.

L-5-hydroxytryptophan can prevent nociceptive disorders in man

Prevention of primary pain is a new topic, endowed with social and economic interest. We observed that L-5-HTP can induce a significant decrease of the cropping out of migraine, the commonest primary pain. This finding seems interesting, since it represents the first data in the field and was obtained in a prospective, long-term, placebo controlled study. The result obtained suggests that CNS abnormalities underlying the mechanism of migraine can be changed by L-5-HTP, if the amino acid is administered to subjects who are predisposed to headache.

Familial occurrence of chronic tension-type headache

Chronic tension-type headache (CTTH) assessed by proband report was evaluated in a family study of CTTH. A clinical interview of first-degree relatives by a physician was used as index of validity. Familial occurrence of CTTH in first-degree relatives was also investigated. Patterns of familial aggregation of CTTH were assessed by calculating the population relative risk. A neurological resident carried out all the interviews of probands and their first-degree relatives. The operational diagnostic criteria of the International Headache Society were used. The 122 probands had 377 first-degree relatives. Sensitivity, specificity, predictive values, and chance-corrected agreement rate for the diagnosis CTTH were 68%, 86%, 53% (PVpos), 92% (PVneg), and 0.48, respectively. The low sensitivity of CTTH assessed by proband report indicates that a clinical interview by a physician is necessary in family studies of CTTH. Clinically interviewed parents, siblings, and children had a 2.1 to 3.9-fold significantly increased risk of CTTH compared with the general population. The gender of the probands did not influence the risk of CTTH among first-degree relatives. The significantly increased familial risk of CTTH and no increased risk of CTTH in spouses suggest that a genetic factor is involved in CTTH.

Familial predisposition of left ventricular hypertrophy

OBJECTIVES

The study evaluated the contribution of familial predisposition to the risk of left ventricular hypertrophy (LVH).

BACKGROUND

Left ventricular hypertrophy is a multifactorial condition that serves as an important predictor of cardiovascular mortality. At present it is unclear whether familial predisposition contributes to the manifestation of LVH. Thus, we determined whether siblings of subjects with LVH are at increased risk to present with an elevation of LV mass or an abnormal LV geometry.

METHODS

Echocardiographic and anthropometric measurements were performed in 2,293 individuals who participated in the echocardiographic substudies of population-based MONICA Augsburg surveys. In addition, a total of 319 siblings of survey participants with echocardiographic evidence of LVH were evaluated. The risk of these siblings to present with LVH or abnormal LV geometry was estimated by comparison with 636 subjects matched for gender and age that were selected from the entire echocardiography study base.

RESULTS

Blood pressure, body mass index, age, and gender (i.e., known determinants of LV mass) were comparable in LVH-siblings and the matched comparison group. However, septal and posterior wall thicknesses, relative wall thickness as well as LV mass index were significantly elevated in LVH-siblings (p < 0.001, each) whereas LV dimensions did not differ. Likewise, the prevalence of LVH was raised in LVH-siblings, as was the relative risk of LVH after adjustment for confounders (p < 0.05). More specifically, LVH-siblings displayed increased prevalences of concentric remodeling and concentric LVH (p < 0.05) but not of eccentric LVH.

CONCLUSIONS

Familial predisposition appears to contribute to increased LV wall thickness, to the development of LV hypertrophy and abnormal LV geometry.

Genetic epidemiology of migraine and cluster headache

Migraine. The present genetic epidemiological survey of migraine was based on semi-structured interviews by a physician. The operational diagnostic criteria of the International Headache Society were used. Three thousand males and 1,000 females aged 40 were drawn from the Danish National Central Person Registry. They received a questionnaire by post regarding migraine and the response rate was 87%. People with self-reported migraine and a random sample reporting no migraine were invited to a headache interview and physical and neurological examination. Those not reacting to the invitation were interviewed by telephone. The participation of the interview was 87%. Kappa was 0.77 validating self-reported migraine against a clinical interview by a physician. Non-responders did not differ from responders regarding migraine. The lifetime prevalence of MO and MA was 9.3% and 6.3% in males and 20.1% and 9.6% in females. People with MA were included as probands in the family study. An equivalent number of probands with MO and probands who had never had migraine were random samples of the people with MO) and those who had never had migraine, respectively. First-degree relatives and spouses were interviewed blindly by a physician. The 378 probands had 1,109 first-degree relatives and 229 spouses. Compared with the general population, the first-degree relatives of probands with MO had a 1.9-fold increased risk of MO and a 1.4-fold increased risk of MA, after standardization for sex and age. The first-degree relatives of probands with MA had a 3.8-fold increased risk of MA and no increased risk of MO. The first-degree relatives of probands who had never had migraine had no increased risk of either MO or MA. Spouses to pro-bands with MC) had a 1.5-fold increased risk of MO, while spouses to probands with MA had no increased risk of MA. The familial patterns indicate that MO and MA are distinct entities. The familial occurrence suggests that MO is caused by a combination of genetic and environmental factors, while MA is determined mainly or exclusively by genetic factors. The complex segregation analysis supports the importance of genetic factors and suggests multifactorial inheritance without generational difference in both MO and MA, but genetic heterogeneity cannot be excluded.

Analysis of 31 families with an apparently autosomal-dominant transmission of migraine with aura in the nuclear family

We analyzed 31 families selected for an apparently autosomal-dominant mode of inheritance of migraine with aura (MA) in the nuclear family. The nuclear families were expanded with first- and second-degree relatives. All interviews were made by physicians experienced in headache diagnoses. The criteria of the International Headache Society were used. The population relative risk among children in nuclear families was similar to the estimated population relative risk of MA assuming an autosomal-dominant mode of inheritance. The population relative risk tended to decrease among first-degree relatives outside nuclear families and further among second-degree relatives. Both first- and second-degree relatives outside the nuclear families had a statistically significant lower risk of MA than expected. Thus, autosomal-dominant inheritance with or without reduced penetrance was unlikely. Autosomal-recessive inheritance was unlikely because of the unequal sex distribution. Other modes of inheritance were considered as well. Mitochondrial and X-linked inheritance were excluded because of paternal transmission. The female preponderance was too low to explain sex-influenced inheritance. We conclude that MA most likely has a multifactorial inheritance even in high-risk families with MA.

Migrainous disorder and its relation to migraine without aura and migraine with aura. A genetic epidemiological study

Migrainous disorder was analysed in a large population-based study of 4000 forty-year-old males and females. All interviews were conducted by one physician and the diagnostic criteria of the International Headache Society were used. Of the 48 people with migrainous disorder, 40 had migrainous disorder without aura and 9 had migrainous disorder with aura. One person had co-occurrence of migrainous disorder with and without aura. The lifetime prevalence of migrainous disorder was 2.5% with a male:female ratio of 1:1.2. The first-degree relatives of probands with migrainous disorder were blindly interviewed. Compared with the general population, first-degree relatives of probands with migrainous disorder without aura had a slightly but less increased risk of migraine without aura than first-degree relatives of probands with migraine without aura. First-degree relatives of probands with migrainous disorder with aura had no increased risk of migraine with aura. We conclude that migrainous disorder without aura in some people is a type of migraine without aura and in other people not. Migrainous disorder with aura may be unrelated to migraine with aura.

Migraine without aura and migraine with aura are inherited disorders

The familial occurrence and mode of inheritance were analysed in families with migraine without aura (MO) and migraine with aura (MA). The probands were found among 4000 persons from the general population. All persons with MA were included as probands, and an equivalent number of probands with MO was selected as a random sample among those with MO. Spouses and first-degree relatives were blindly interviewed. All interviews were performed by one neurological research fellow. The distinct familial patterns indicate that MO and MA have a different aetiology. Compared with the general population, the first-degree relatives of probands with MO had a 1.9-fold increased risk of MO while spouses had a 1.5-fold increased risk of MO, indicating that both genetic and environmental factors are important in MO. The first-degree relatives of probands with MA had a four-fold increased risk of MA while spouses had no increased risk of MA, indicating that MA is determined largely by genetic factors. The complex segregation analysis indicated that both MO and MA have multifactorial inheritance without generational difference.

Increased familial risk and evidence of genetic factor in migraine

OBJECTIVE

To investigate familial occurrence of migraine with and without aura.

DESIGN

Familial occurrence of migraine with and without aura among first degree relatives and spouses of probands with migraine with or without aura and those who had never had migraine. All interviews of first degree relatives and spouses were done blindly by a neurological resident. The operational diagnostic criteria of the International Headache Society were used.

SETTING

General population from Copenhagen County.

SUBJECTS

The 378 probands had 1109 first degree relatives and 229 spouses.

MAIN OUTCOME MEASURES

Patterns of familial aggregation of migraine with and without aura as assessed by calculation of the population relative risk.

RESULTS

Compared with the general population the first degree relatives of probands with migraine without aura had 1.9 times the risk of migraine without aura and 1.4 times the risk of migraine with aura. The first degree relatives of probands with migraine with aura had nearly four times the risk of migraine with aura and no increased risk of migraine without aura. The first degree relatives of probands who had never had migraine had no increased risk of migraine either with or without aura. Spouses of probands with migraine without aura had 1.4 times the risk of migraine without aura whereas spouses of probands with migraine with aura had no increased risk of migraine with aura.

CONCLUSION

The different familial patterns indicate that migraine without aura and migraine with aura have a different aetiology. Migraine without aura seems to be caused by a combination of genetic and environmental factors whereas migraine with aura is probably determined largely or exclusively by genetic factors.

Selecting control groups for studies of familial aggregation of disease

In genetic-epidemiologic studies to determine the association between the disease status of family members, this association is measured by comparing rates of the disease in relatives of probands (index cases) with the disease, with the rates of the disease among individuals in a control group. Either of two types of control groups are generally used: (1) a control group consisting of a random sample from the population or the entire population if available or (2) a control group consisting of relatives of individuals without the disease under study. We examine the advantages and disadvantages of using these different types of control groups. We show two major results for family studies: (1) when there are no other factors associated with the disease status of an individual other than the disease status of a family member, both types of control groups will give a valid test of the null hypothesis of no familial aggregation. However, tests using a population control group will always be less efficient statistically, than those performed with a control group of relatives of probands without the disease under study, the degree of efficiency decreasing with increasing population prevalence of the disease. (2) When factors other than the disease status of a family member are also associated with the disease status of an individual, if this factor is a proband characteristic (which is not shared by relatives) population control groups cannot be adjusted to eliminate possible bias due to the potential confounding effect of this factor (unlike control groups consisting of relatives of probands without the disorder).

Familial occurrence of cluster headache

The familial occurrence of cluster headache was assessed in 421 patients with cluster headache, diagnosed according to the operational diagnostic criteria of the International Headache Society. The patients were recruited from a neurological clinic and two departments of neurology, covering east central Jutland and Copenhagen County respectively. They received a mailed questionnaire regarding the presence of cluster headache among their first and second degree relatives. All possibly affected relatives were interviewed by telephone. The response rate to the questionnaire was 88% (370/421). Seven patients belonged to three families. A positive family history of cluster headache was found in 7% (25/366) of the families. Compared with the general population, the first and second degree relatives of the 370 patients with cluster headache had a 14-fold and twofold increase in the risk of having cluster headache after standardisation for sex and age. This increase in familial risk strongly suggests that cluster headache has a genetic cause.

Familial occurrence of Hirschsprung's disease

We assessed the familial occurrence of Hirschsprung's disease from 224 probands born in Denmark after 1959. Probands who were still alive received a mailed questionnaire, and medical reports for the probands and their relatives with suspected Hirschsprung's disease were examined. The diagnosis of Hirschsprung's disease required a histologically verified biopsy or surgical colonic specimens, and exclusion of a secondary causes for Hirschsprung's disease. Familial occurrence was seen in 11 families. Ten first-degree, two third-degree and one fifth-degree relatives had Hirschsprung's disease. Both short segment agangliosis (the sigmoid colon or below) and long segment agangliosis (above the sigmoid colon) occurred in five of the 11 families, implying that the etiology of Hirschsprung's disease with short and long segment agangliosis is the same. Compared with the general population, the first-degree relatives of the 224 probands had a minimum of a 93-fold increased risk of Hirschsprung's disease. This strongly suggests that genetic factors play a role in Hirschsprung's disease.

Familial aggregation of cardiovascular diseases in African-American pedigrees

Familial aggregation of cardiovascular diseases and diabetes has been consistently demonstrated. However, virtually all of the evidence on the familial patterns of these diseases has come from white population samples. This study evaluates the level of familial excess risk among first degree relatives of 232 African-American pedigrees which included 1,420 individuals recruited from the Chicago, IL, area. Excess disease risk was observed among relatives (parents and offsprings) of affected probands compared to relatives of unaffected probands for coronary heart disease (odds ratio [OR] = 5.30; 95% confidence interval [CI] = 2.51-11.23); hypertension (OR = 1.98; CI = 1.41-2.80); stroke (OR = 3.24; CI = 1.08-9.70); and diabetes (OR = 2.95; CI = 1.55-5.62). The results of this study clearly show that coronary heart disease, hypertension, stroke, and diabetes aggregate in some African-American families and not others. Unaffected relatives of persons suffering from these diseases should be encouraged to have their blood pressure, lipid, and blood glucose levels measured at frequent intervals. These recommendations are particularly urgent in African-American communities because of the disproportionately high morbidity and mortality experienced from cardiovascular diseases and diabetes.

The genetics of migraine without aura and migraine with aura

Studies of twins, spouses and familial aggregation strongly suggest that migraine without aura (MO) and migraine with aura (MA) are genetically determined. The mode of inheritance is most likely multifactorial in both MO and MA. However, autosomal dominant inheritance with reduced penetrance cannot be excluded in either MO or MA. At present the only evidence for genetic heterogeneity of MA is familial hemiplegic migraine with slowly progressive ataxia. This phenomenon can also be explained by linkage of different genes. All existing studies have been characterized by one or more of the following methodologic shortcomings: selection of probands from clinic populations, information obtained by questionnaire, family history obtained through probands, insufficient description of the attacks, lack of distinction between MO and MA. Useful strategies for future studies of migraine genetics are discussed.

Genes and environment in the inheritance of morbidity and mortality

During the past 30 years, the Danish Adoption Registry has been used in the analysis of the effect of genes and family environment on the development of mental disorders. During the last 15 years, the registry has also been used for similar analyses of somatic disorders, including obesity and premature death from somatic disorders. This article discusses the potential problems generally related to inference on morbidity from mortality data and particularly when using mortality data in adoption studies. We conclude that further insight into the question of nature, nurture or both requires extending the studies to include morbidity data as well as mortality data. We suggest that expanding the study by including biological and adoptive siblings and by using recently developed statistical methods will considerably strengthen the adoption study of morbidity and mortality.

Data collection strategies in genetic epidemiology: The Epilepsy Family Study of Columbia University

A large-scale study of genetic influences on seizure disorders is described here as a primer of tested methods for collection of family history data. 1957 adult probands with epilepsy were ascertained from voluntary organizations. Personal and family history data were obtained from probands in semistructured telephone interviews. To increase sensitivity, an independent family history was obtained from a second family informant in a similar interview. To increase specificity and diagnostic detail, family members reported to be affected were interviewed, and medical records of probands and affected relatives were collected. Participation rates for probands were 84-90%. Interviews were completed with second informants in 67% of families, and with 51% of eligible affected relatives. The main reasons for non-interview were lack of permission from probands and difficulties in locating relatives. Although 90% of probands gave verbal permission for medical record review, only 75% of these signed and returned consent forms for this purpose. Physicians returned 87% of the records requested. The resulting proportion of probands with medical records was 59%. These findings illustrate the complexity involved in assembling useful databases in genetic epidemiology.

An analytical method for assessing patterns of familial aggregation in case-control studies

This paper describes an analytical method that is used to assess patterns of disease aggregation within family based on family history information collected in case-control studies. In such a study, cases and controls are thought of as probands whose relatives are identified, and relatives' phenotypes and other covariates such as age, sex, and genealogical relationship with the probands are recorded. By modeling the dependence of relatives' phenotypes on case-control status and other covariates, this method yields adjusted odds ratios that quantify familial aggregation. The estimated standard errors are obtained for statistical inference since the method acknowledges the potential correlations between relatives' phenotypes by using the estimating equations technique. In population-based case-control studies, the estimates and statistical inferences are generalizable to the general population. To illustrate this method, we analyzed a case-control study of colorectal cancer involving 5,190 relatives of 792 cases and 4,478 relatives of 680 population-based controls conducted in Hawaii. Although detailed results will be presented elsewhere, the colorectal cancer was found to aggregate within family with an odds ratio of 2.74 (95% confidence interval (CI): 1.78-4.21). Among parents, the odds ratio for familial aggregation was 2.38 (95% CI: 1.25-4.54). The corresponding value for siblings was 3.09 (95% CI: 1.87-5.11). It was also found that the odds ratio increases from about 2.00 for relatives of the probands who were 50 years or older to 7.66 and 12.84 for relatives of the probands who were between 40 and 50 years and under 40 years, respectively, suggesting that the familial aggregation of colorectal cancer decreases as probands' age increases.

Applications of the concept of attributable fraction in medical genetics

Attributable fraction, the fraction of cases of a disease in a population attributed to a particular risk factor, is a useful measure in the design and interpretation of epidemiologic studies of disease etiology. We review here the applications of the concept of attributable fraction in medical genetics. Specifically, attributable fraction can be used 1) in studies of the association between genetic traits and specific diseases to quantitate the contribution of specific alleles to disease occurrence in a population; 2) in population studies of mutations and birth defects to estimate the impact of mutagens and teratogens; and 3) in genetic analyses of family data, to evaluate the contribution of putative single gene loci to disease etiology. In the latter context, the concept of attributable fraction can be contrasted with the more commonly used concept of heritability. Examples from the literature provide illustrations of the usefulness of attributable fraction in medical genetic studies.

Cancer risk in second degree relatives of children with soft tissue sarcoma

The risk of cancer in the second degree relatives of a population-based series of children with soft tissue sarcoma was studied in relation to (i) various characteristics in these relatives, (ii) certain clinical features in the index children previously identified as risk factors for cancer in their first degree relatives. Overall there was a non-significant deficit of cancers in the second degree relatives (RR = 0.88) and cancer risk was unrelated to type or site of cancer, type of relative, or to risk factors in the index case. The findings indicate that although the families investigated may include a proportion with the Li-Fraumeni cancer family syndrome, the increased cancer risk already reported in the first degree relatives does not extent to second degree relatives in general.

Genetic epidemiology utilizing the adoption method: studies of obesity and of premature death in adults

Genetic epidemiology gives no priority to genes or environment in the search of disease causation. However, a major problem in this field is the disentangling of the effects of environment and genes. The study of subjects separated very early in life from their biologic parents and adopted by unrelated parents provide a strong tool for estimation of genetic and familial environmental influences. The degree to which the trait or disease frequency of the adoptees is similar to that seen among the biologic relatives is an indication of the strength of the genetic influence. Similarity to the adoptive relatives suggests influences of the family environment shared between them. Adoption studies of adult obesity show that it is genes, and not the family environment, that is responsible for the familial aggregation of obesity. A study of the mortality of adult adoptees and their biologic and adoptive parents indicates a genetic influence on the risk of premature death from all causes, from natural causes, infections, and cardio- and cerebrovascular conditions, and suggests familial environmental influences on death from the vascular causes and from cancer.

Abdominal aortic aneurysm: results of a family study

Data pertaining to abdominal aortic aneurysm among first-degree relatives of 91 patients with abdominal aortic aneurysm are presented. The percentage of families with at least one affected first-degree relative of the proband (multiplex families) was 15.4%. In 21.4% of multiplex families parent-offspring transmission of abdominal aortic aneurysm was noted; in the remaining families only siblings were affected. The mean age at onset among probands was 67.3 years; that among all affected was 67.4 years. No statistically significant difference in the mean ages at onset between genders was noted. Among affected siblings of probands, the sex ratio, male:female, was 1.33:1, which is not significantly different from 1:1. The relative risk of developing an abdominal aortic aneurysm was 3.97 for fathers, 4.03 for mothers, 9.92 for brothers, and 22.93 for sisters.

Familial occurrence of inflammatory bowel disease

BACKGROUND AND METHODS

We assessed the familial occurrence of inflammatory bowel disease in Copenhagen County, where there has been a long-term interest in the epidemiology of such disorders. In 1987 we interviewed 662 patients in whom inflammatory bowel disease had been diagnosed before 1979, asking whether their first- and second-degree relatives had this disorder. Ninety-six percent of the patients (504 with ulcerative colitis and 133 with Crohn's disease) provided adequate information.

RESULTS

As compared with the general population, the first-degree relatives of the 637 patients with ulcerative colitis or Crohn's disease had a 10-fold increase in the risk of having the same disease as the patients, after standardization for age and sex. The risk of having the other of the two diseases was also increased, but less so, and the increase in the risk of having Crohn's disease was not significant in the relatives of patients with ulcerative colitis. The risk of ulcerative colitis in first-degree relatives of patients with ulcerative colitis appeared to be virtually independent of the generation to which the first-degree relative belonged and of the sex of the patient and the relative. The risk of ulcerative colitis in first-degree relatives tended to be higher if the disease had been diagnosed in the patient before the age of 50, but the risk seemed to be independent of the current age of the relatives. The prevalence of the same disease as that of the patient (either ulcerative colitis or Crohn's disease) among second-degree relatives was increased; the prevalence of the other disease was not increased.

CONCLUSIONS

The 10-fold increase in the familial risk of ulcerative colitis and Crohn's disease strongly suggests that these disorders have a genetic cause.

The Biodemography of Variation in Human Frailty

A population is composed of individuals who are heterogeneous in their susceptibility to death and disease. This heterogeneity is reflected in the age-specific incidence or mortality (hazard) function. This variation has typically been hidden—that is, not measured directly—and has generally been modeled in a purely empirical statistical way, because there is no theory in demography for the distribution of frailty. A substantial fraction of variation in frailty, however, has an underlying genetic basis, for which there is a formal theory. This theory, based on evolutionary biology and on the nature of mendelian transmission, provides prior constraints on the distribution of variation in the population as well as providing methods for identifying genes involved in many important diseases. The accumulating effects of environmental exposures with age are another major component of variation in frailty. In some important instances, this variation and its effect on the age-specific hazard function can also be understood in terms of cause-specific biological processes. These biological considerations may enable demographers to model frailty, and thus mortality, in a better way.

Coronary risk associated with age and sex of parental heart disease in the Framingham Study

Data from the Framingham Study, a population-based prospective study of 5,209 persons, were analyzed to determine whether a parental history of death by coronary artery disease (CAD) before or after 65 years of age was an independent risk factor for CAD of early onset (age younger than 60 years) or late onset (age 60 years or older) among the men and women in the cohort. Death due to CAD in parents was associated with a 30% increase in the risk of CAD. The effect was apparently stronger for an early CAD outcome, with adjusted relative risks of 1.5 for early and 1.2 for late outcome CAD. The effect of parental CAD death on risk was not mediated by other shared risk factors for CAD. These findings were similar for those with either a mother or a father with CAD, if CAD onset in the offspring occurred before the age of 60 years. For persons with CAD at age 60 years or older, maternal CAD death was a stronger predictor of CAD than paternal CAD death. The association with parental history of CAD was similar among men and women in the cohort, with adjusted relative risks of 1.3 and 1.2, respectively. However, early age of parental CAD death may account for the association among women (RR = 1.6), whereas late age of CAD death for either parent was associated with the risk of CAD among men (RR = 1.4).

On the measurement of susceptibility to genetic factors

Geneticists usually measure the phenotypic effects of a single gene trait in terms of penetrance and recurrence risks in relatives of affected individuals, while epidemiologists usually compute measures of relative and attributable risks. These concepts can be merged to measure the proportion of individuals "susceptible" to a genetic factor. In the context of a sufficient cause model, susceptibility can be defined as the underlying factor(s) sufficient to make a person develop disease because of the genetic factor in the absence of other causes. The proportion of susceptibles to the genetic factor in the population differs conceptually and often arithmetically from the penetrance of the genotype especially for common diseases with etiologic heterogeneity. For a wide range of disease and allele frequencies, it can be shown that the proportion of susceptibles can be approximated by the risk difference measure (i.e., difference between penetrance with the genotype and penetrance without the genotype). We also apply the concept of susceptibility to estimate familial recurrence of disease due to a genetic factor. This measure of familial recurrence differs conceptually from simple recurrence risk and can be approximated by the familial risk difference measure (i.e., difference between recurrence risks in relatives of cases and relatives of controls) for a wide range of disease and allele frequencies.

Genetic and environmental influences on premature death in adult adoptees

To assess genetic and environmental influences on adult mortality, we followed 960 families that included children born during the period 1924 through 1926 who were placed early in life with adoptive parents unrelated to them. We evaluated the risks of dying from all causes or from specific groups of causes between the ages of 16 and 58 years for adoptees with a biologic or adoptive parent who died of the same cause before the age of either 50 or 70. We compared these risks with the adoptees' risk of dying from the same causes between the ages of 16 and 58 when either the biologic or adoptive parents were still alive at the ages of 50 and 70. The death of a biologic parent before the age of 50 resulted in relative risks of death in the adoptees of 1.71 (95 percent confidence interval, 1.14 to 2.57) for all causes, 1.98 (1.25 to 3.12) for natural causes, 5.81 (2.47 to 13.7) for infections, 4.52 (1.32 to 15.4) for cardiovascular and cerebrovascular causes, and 1.19 (0.16 to 8.99) for cancers. The death of an adoptive parent resulted in relative risks of death in the adoptees that were close to unity for all causes, natural causes, and infections, 3.02 (0.72 to 12.8) for vascular causes, and 5.16 (1.20 to 22.2) for cancers. A similar but weaker pattern was observed when either a biologic or adoptive parent died before the age of 70. We conclude that premature death in adults has a strong genetic background--especially death due to infections and vascular causes.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessing familial aggregation of congenital cardiovascular malformations in case-control studies

Recent data indicate that the familial aggregation of congenital cardiovascular malformations (CCVM) varies with the type of defect in the index case. Using a logistic regression model that allows for dependence among family members, we calculated the risk of any CCVM to case relatives compared with relatives of controls. Data from 3,908 first-degree relatives of 570 matched cases and controls identified from 1981 through 1985 by the Baltimore-Washington Infant Study were used in the analyses. Overall risk for any CCVM in case relatives was increased four-fold over that of control relatives. While relatives of cases with flow lesions (including right and left heart defects, as well as perimembranous ventricular septal defect [VSD]) had a five-fold increase in risk, the risk to relatives of nonflow lesion cases did not differ significantly from the risk to relatives of controls. Sex, maternal age, miscarriage history in the mother, and birth order had no apparent effect on risk among siblings. However, there was an indication of increased risk in relatives of nonwhite cases with VSD compared to relatives of matched controls. However, with these data it was not possible to distinguish between environmental and genetic sources of this familial aggregation.

Relationship of epithelial ovarian cancer to other malignancies within families

The relationship of family history of cancer of the breast, colon/rectum, cervix, endometrium, lung, and thyroid to the risk of epithelial ovarian cancer was investigated in a large population-based case-control study. The data consisted of family histories from 493 epithelial ovarian cancer cases and 2,465 controls aged 20-54 years. After controlling for potential confounders, risk for epithelial ovarian cancer was found to be significantly elevated among women reporting breast cancer and colo/rectal cancer in a first-degree relative. Adjusted odds ratios were 1.5 (95% CI = 1.1-2.1) and 1.9 (95% CI = 1.1-3.3), respectively. None of the remaining four types of cancer was found to be statistically associated with the risk of epithelial ovarian cancer. However, when histologic subtypes of epithelial ovarian cancer were considered, a family history of breast cancer was found to be associated with an elevated risk of endometrioid ovarian cancer (odds ratio = 2.3; 95% CI = 1.1-4.7), as was a family history of endometrial cancer (odds ratio = 2.7; 95% CI = 1.0-6.9). The results are considered in the context of other studies of familial patterns of cancer and are compared with published findings concerning the occurrence of multiple primary cancers in the same individual. The findings indicate that further study is warranted regarding possible genetic relationships between epithelial ovarian cancer and cancers arising in other organs.