Familial risks for common diseases: etiologic clues and guidance to gene identification

The Asthma Family Tree: Evaluating Associations Between Childhood, Parental, and Grandparental Asthma in Seven Chinese Cities

Objective: To evaluate the associations between childhood, parental, and grandparental asthma. Methods: We studied 59,484 children randomly selected from 94 kindergartens, elementary, and middle schools in seven Chinese cities from 2012 to 2013, using a cross-sectional survey-based study design. Information on their and their family members' (parents, paternal grandparents, and maternal grandparents) asthma status were reported by children's parents or guardians. Mixed effects logistic regressions were used to assess hereditary patterns of asthma and mediation analysis was performed to estimate the potential mediation effect of parents on the association between grandparental asthma and childhood asthma. Results: The magnitude of ORs for childhood asthma increased as the number of family members affected by asthma increased. Among children who had one family member with asthma, childhood asthma was associated with asthma in maternal grandmothers (OR: 2.08, 95% CI: 1.67-2.59), maternal grandfathers (OR: 2.08, 95% CI: 1.71-2.53), paternal grandmothers (OR: 2.40, 95% CI: 1.93-2.99), and paternal grandfathers (OR: 2.59, 95% CI: 2.14-3.13). Among children who had two family members with asthma, the highest asthma risk was found when both parents had asthma (OR: 15.92, 95% CI: 4.66-54.45). Parents had a small proportion of mediation effect (9-12%) on the association between grandparental asthma and childhood asthma. Conclusions: Grandparents with asthma were associated with childhood asthma and parents with asthma partially mediated the association.

Familial risks between Graves disease and Hashimoto thyroiditis and other autoimmune diseases in the population of Sweden

Genetic and family studies have indicated that Graves disease and Hashimoto thyroiditis have a heritable component which appears to be shared to some extend also with some other autoimmune diseases (AIDs). In the present nation-wide study we describe familial risk for Graves disease and Hashimoto thyroiditis identified from the Swedish Hospital Discharge Register (years 1964 through 2012) and the Outpatient Register (2001 through 2012). Family relationships were obtained from the Multigeneration Register and cancers from the Cancer Registry. Familial standardized incidence ratios (SIRs) were calculated for 29,005 offspring with Graves disease and for 25,607 offspring with Hashimoto thyroiditis depending on any of 43 AIDs in parents or siblings. The concordant familial risks for Graves disease and Hashimoto thyroiditis were 3.85 and 4.75, higher for men than for women. The familial risks were very high (11.35, Graves and 22.06, Hashimoto) when both a parent and a sibling were affected. Spousal familial risks were higher for Hashimoto thyroiditis (1.98/1.93) than for Graves disease (1.48/1.50). For Graves disease, 24 discordant AIDs showed a significant association; for Hashimoto thyroiditis, 20 discordant associations were significant. All significant discordant associations were positive for the two thyroid AIDs, with the exception of Hashimoto thyroiditis with Reiter disease. Overall 8 associations were significant only for Graves disease and 6 Hashimoto thyroiditis. The overall high concordant familial risks for Graves disease and Hashimoto thyroiditis suggest a strong genetic contribution to the familial risk. Significant familial associations among more than half of the 43 AIDs attest to the extensive polyautoimmunity among thyroid AIDs.

Familial associations between autoimmune hepatitis and primary biliary cholangitis and other autoimmune diseases

Autoimmune hepatitis (AH) and primary biliary cirrhosis (PBC) are autoimmune diseases (AIDs) targeting cellular components of the liver. Being rare diseases, limited data are available about familial risks among these AIDs (concordant) or between them and other AIDs (discordant). We aimed to carry out an unbiased study on these AIDs based on medically diagnosed patients. We collected data on patients diagnosed in Swedish hospitals with AH, PBC and other AIDs and calculated familial standardized incidence ratios (SIRs) for concordant and discordant familial relative risks. The number of AH patients was 6,269, of whom 43.0% were male; patient numbers for PBC were 4,269, with 17.8% males. AH accounted for 0.8% and 0.6% of all hospitalized AIDs in Sweden. For AH only the familial risk between siblings was significant (3.83). For PBC the risks for offspring of parents (9.05) and siblings (10.88) were high, but only risk for females was significant. Spousal risks were very high, 5.91 and 6.07 for AH. Risk for AH was 2.21 in families of PBC, and it was 2.47 for PBC in families of AH patients. Among other AIDs, 14 showed a significant association with AH, compared to 16 AIDs with PBC. The surprising finding in this nation-wide family study on medically diagnosed patients was the high risk for AH (6.0) between spouses, which exceed the risk between siblings, suggesting the existence of strong environmental risk factors. AH and PBC were associated with multiple other AIDs. The results call attention to environmental factors in AID etiology which should also be in focus in taking anamnestic data from patients.

Increased risk of hip fracture among spouses-evidence of a homogamy effect

Spouses tend to share habits and therefore have an increased risk of same diseases. We followed all married couples in Sweden, born 1902 to 1942, in hospital records from 1987 to 2002, and found that individuals whose spouse had a hip fracture had an increased risk of hip fracture.

INTRODUCTION

The purpose of this study was to determine whether spouses of hip fracture patients have an elevated risk of hip fracture.

METHODS

We performed a retrospective cohort study of all couples married for at least 5 years in Sweden and born between 1902 and 1942 (n = 904,451) and all patients registered with a hip fracture (n = 218,285) in the National Inpatients Register in Sweden from 1987 to 2002.

RESULTS

During the period 1987 to 2002 hip fractures occurred among spouses in 4212 married couples. The hazard ratio (HR) for hip fracture in a married woman following hip fracture in the husband was 1.11 (95 % confidence interval 1.07 to 1.16) compared to a woman whose husband did not have hip fracture. The corresponding HR for a married man was 1.20 (1.15 to 1.26) compared to a man whose wife did not have hip fracture. The risk was significantly elevated over the age range 60 to 90 years. The increased risk for hip fracture among spouses remained after adjustments for income, education, geographical latitude and urbanisation. In a common model with spouses and their siblings, the HR for spousal effect were 1.63 (1.01 to 2.64) and for sibling effect 2.18 (1.55 to 3.06) compared to married with spouse and sibling respectively without hip fracture.

CONCLUSION

The novel finding of an increased risk for hip fracture among spouses provides evidence indicating that there is a homogamy effect due to common social and lifestyle factors but could also be due to assortative mating.

Association of polymorphisms in the aldosterone-regulated sodium reabsorption pathway with blood pressure among Hispanics

BACKGROUND

Whereas genome-wide association study (GWAS) has proven to be an important tool for discovery of variants influencing many human diseases and traits, unfortunately its performance has not been much of all-around success for some complex conditions, for example, hypertension. Because some of the existing effective pharmacotherapeutic agents act by targeting known biological pathways, pathway-based analytical approaches could lead to more success in discovery of disease-associated variants. The objective of the present study was to identify functional variants associated with blood pressure in the aldosterone-regulated sodium reabsorption pathway using the simulated and real blood pressure phenotypes provided for Genetic Analysis Workshop 19.

METHODS

The present analysis included 1942 samples with exome sequencing data and for whom blood pressure phenotypes were available. Because only odd-numbered autosomes were available, we restricted analysis to 127 quality-controlled single-nucleotide polymorphisms from the aldosterone-regulated sodium reabsorption pathway. We performed pathway-based association analysis using appropriate regression models for single variant, haplotype and epistasis association analyses. To account for multiple comparisons, statistical significance was empirically derived by permutation procedure and Bonferroni correction.

RESULTS

The topmost pathway-based association signals were observed in PRKCA gene for diastolic blood pressure (DBP), systolic blood pressure (SBP), and mean arterial pressure (MAP) in both real and simulated data. The associations remained significant (P <0.05) after multiple testing corrections for the number of genes. Similarly, the pathway-based 2-locus epistasis analysis indicated significant interactions between INSR and PRKCG for SBP and MAP; INS and PIK3R2 for DBP; PIK3CD and ATP1B2 for hypertension in the real data set. We also observed significant within-gene interactions in INSR for SBP, DBP, and hypertension in the simulated data set.

CONCLUSION

The findings from this study show that pathway-based analytical approach targeting known biological pathways can be useful in identification of disease-associated variants that are otherwise undetectable by GWAS. The approach takes advantage of the assumption of nonindependence of variants within and across pathway genes which leads to reduced penalty of multiple testing and thus less-stringent statistical significance threshold.

Subsequent Type 2 Diabetes in Patients with Autoimmune Disease

Immunological data show that type 2 diabetes (T2D) manifests autoimmune features. We wanted to test the association epidemiologically by assessing subsequent diagnosis of T2D following diagnosis of autoimmune disease (AId) and subsequent AId after T2D in the same individuals. Patients were identified from three Swedish health databases. A total of 32 different AId were included. Standardized incidence ratios (SIRs) were calculated for T2D diagnosis in patients with previously diagnosed AId and compared to those without a previous AId. Among a total of 757,368 AId patients, 15,103 were diagnosed with T2D, giving an overall SIR for T2D of 1.66. T2D risks were increased after 27 AIds; the highest SIRs were noted for chorea minor (8.00), lupoid hepatitis (5.75), and Addison disease (2.63). T2D was increased after 27 of 32 AIds but we were unable to control for factors such as obesity and smoking. However, the clearly increased risks for T2D in most types of AId patients, and in reverse order increased risks for AId after T2D, do not support an overall confounding by life-style factors. Mechanistic links shared by T2D, AId and life-style factors such as obesity, perhaps through chronic inflammation, may drive autoimmune activation of T2D and many AIds.

Pathway analysis supports association of nonsyndromic cryptorchidism with genetic loci linked to cytoskeleton-dependent functions

STUDY QUESTION

What are the genetic loci that increase susceptibility to nonsyndromic cryptorchidism, or undescended testis?

SUMMARY ANSWER

A genome-wide association study (GWAS) suggests that susceptibility to cryptorchidism is heterogeneous, with a subset of suggestive signals linked to cytoskeleton-dependent functions and syndromic forms of the disease.

WHAT IS KNOWN ALREADY

Population studies suggest moderate genetic risk of cryptorchidism and possible maternal and environmental contributions to risk. Previous candidate gene analyses have failed to identify a major associated locus, although variants in insulin-like 3 (INSL3), relaxin/insulin-like family peptide receptor 2 (RXFP2) and other hormonal pathway genes may increase risk in a small percentage of patients.

STUDY DESIGN, SIZE, DURATION

This is a case-control GWAS of 844 boys with nonsyndromic cryptorchidism and 2718 control subjects without syndromes or genital anomalies, all of European ancestry.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All boys with cryptorchidism were diagnosed and treated by a pediatric specialist. In the discovery phase, DNA was extracted from tissue or blood samples and genotyping performed using the Illumina HumanHap550 and Human610-Quad (Group 1) or OmniExpress (Group 2) platform. We imputed genotypes genome-wide, and combined single marker association results in meta-analyses for all cases and for secondary subphenotype analyses based on testis position, laterality and age, and defined genome-wide significance as P = 7 × 10(-9) to correct for multiple testing. Selected markers were genotyped in an independent replication group of European cases (n = 298) and controls (n = 324). We used several bioinformatics tools to analyze top (P < 10(-5)) and suggestive (P < 10(-3)) signals for significant enrichment of signaling pathways, cellular functions and custom gene lists after multiple testing correction.

MAIN RESULTS AND THE ROLE OF CHANCE

In the full analysis, we identified 20 top loci, none reaching genome-wide significance, but one passing this threshold in a subphenotype analysis of proximal testis position (rs55867206, near SH3PXD2B, odds ratio = 2.2 (95% confidence interval 1.7, 2.9), P = 2 × 10(-9)). An additional 127 top loci emerged in at least one secondary analysis, particularly of more severe phenotypes. Cytoskeleton-dependent molecular and cellular functions were prevalent in pathway analysis of suggestive signals, and may implicate loci encoding cytoskeletal proteins that participate in androgen receptor signaling. Genes linked to human syndromic cryptorchidism, including hypogonadotropic hypogonadism, and to hormone-responsive and/or differentially expressed genes in normal and cryptorchid rat gubernaculum, were also significantly overrepresented. No tested marker showed significant replication in an independent population. The results suggest heterogeneous, multilocus and potentially multifactorial susceptibility to nonsyndromic cryptorchidism.

LIMITATIONS, REASONS FOR CAUTION

The present study failed to identify genome-wide significant markers associated with cryptorchidism that could be replicated in an independent population, so further studies are required to define true positive signals among suggestive loci.

WIDER IMPLICATIONS OF THE FINDINGS

As the only GWAS to date of nonsyndromic cryptorchidism, these data will provide a basis for future efforts to understand genetic susceptibility to this common reproductive anomaly and the potential for additive risk from environmental exposures.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by R01HD060769 (the Eunice Kennedy Shriver National Institute for Child Health and Human Development (NICHD)), P20RR20173 (the National Center for Research Resources (NCRR), currently P20GM103464 from the National Institute of General Medical Sciences (NIGMS)), an Institute Development Fund to the Center for Applied Genomics at The Children's Hospital of Philadelphia, and Nemours Biomedical Research. The authors have no competing interests to declare.

Clinical implications of genomics for cancer risk genetics

The study of human genetics has provided substantial insight into cancer biology. With an increase in sequencing capacity and a reduction in sequencing costs, genomics will probably transform clinical cancer genetics. A heritable basis for many cancers is accepted, but so far less than half the genetic drivers have been identified. Genomics will increasingly be applied to populations irrespective of family history, which will change the framework of phenotype-directed genetic testing. Panel testing and whole genome sequencing will identify novel, polygenic, and de-novo determinants of cancer risk, often with lower penetrance, which will challenge present binary clinical classification systems and management algorithms. In the future, genotype-stratified public screening and prevention programmes could form part of tailored population risk management. The integration of research with clinical practice will result in so-called discovery cohorts that will help identify clinically significant genetic variation.

Phenotype specific association of the TGFBR3 locus with nonsyndromic cryptorchidism

PURPOSE

Based on a genome-wide association study of testicular dysgenesis syndrome showing a possible association with TGFBR3, we analyzed data from a larger, phenotypically restricted cryptorchidism population for potential replication of this signal.

MATERIALS AND METHODS

We excluded samples based on strict quality control criteria, leaving 844 cases and 2,718 controls of European ancestry that were analyzed in 2 separate groups based on genotyping platform (ie Illumina® HumanHap550, version 1 or 3, or Human610-Quad, version 1 BeadChip in group 1 and Human OmniExpress 12, version 1 BeadChip platform in group 2). Analyses included genotype imputation at the TGFBR3 locus, association analysis of imputed data with correction for population substructure, subsequent meta-analysis of data for groups 1 and 2, and selective genotyping of independent cases (330) and controls (324) for replication. We also measured Tgfbr3 mRNA levels and performed TGFBR3/betaglycan immunostaining in rat fetal gubernaculum.

RESULTS

We identified suggestive (p ≤ 1× 10(-4)) association of markers in/near TGFBR3, including rs9661103 (OR 1.40; 95% CI 1.20, 1.64; p = 2.71 × 10(-5)) and rs10782968 (OR 1.58; 95% CI 1.26, 1.98; p = 9.36 × 10(-5)) in groups 1 and 2, respectively. In subgroup analyses we observed strongest association of rs17576372 (OR 1.42; 95% CI 1.24, 1.60; p = 1.67 × 10(-4)) with proximal and rs11165059 (OR 1.32; 95% CI 1.15, 1.38; p = 9.42 × 10(-4)) with distal testis position, signals in strong linkage disequilibrium with rs9661103 and rs10782968, respectively. Association of the prior genome-wide association study signal (rs12082710) was marginal (OR 1.13; 95% CI 0.99, 1.28; p = 0.09 for group 1), and we were unable to replicate signals in our independent cohort. Tgfbr3/betaglycan was differentially expressed in wild-type and cryptorchid rat fetal gubernaculum.

CONCLUSIONS

These data suggest complex or phenotype specific association of cryptorchidism with TGFBR3 and the gubernaculum as a potential target of TGFβ signaling.

Quality of family history collection with use of a patient facing family history assessment tool

Background

Studies have shown that the quality of family health history (FHH) collection in primary care is inadequate to assess disease risk. To use FHH for risk assessment, collected data must have adequate detail. To address this issue, we developed a patient facing FHH assessment tool, MeTree. In this paper we report the content and quality of the FHH collected using MeTree.

Methods

Design: A hybrid implementation-effectiveness study. Patients were recruited from 2009 to 2012. Setting: Two community primary care clinics in Greensboro, NC. Participants: All non-adopted adult English speaking patients with upcoming appointments were invited to participate. Intervention: Education about and collection of FHH with entry into MeTree. Measures: We report the proportion of pedigrees that were high-quality. High-quality pedigrees are defined as having all the following criteria: (1) three generations of relatives, (2) relatives’ lineage, (3) relatives’ gender, (4) an up-to-date FHH, (5) pertinent negatives noted, (6) age of disease onset in affected relatives, and for deceased relatives, (7) the age and (8) cause of death (Prim Care31:479–495, 2004.).

Results

Enrollment: 1,184. Participant demographics: age range 18-92 (mean 58.8, SD 11.79), 56% male, and 75% white. The median pedigree size was 21 (range 8-71) and the FHH entered into MeTree resulted in a database of 27,406 individuals. FHHs collected by MeTree were found to be high quality in 99.8% (N = 1,182/1,184) as compared to <4% at baseline. An average of 1.9 relatives per pedigree (range 0-50, SD 4.14) had no data reported. For pedigrees where at least one relative has no data (N = 497/1,184), 4.97 relatives per pedigree (range 1-50, SD 5.44) had no data. Talking with family members before using MeTree significantly decreased the proportion of relatives with no data reported (4.98% if you talked to your relative vs. 10.85% if you did not, p-value < 0.001.).

Conclusion

Using MeTree improves the quantity and quality of the FHH data that is collected and talking with relatives prior to the collection of FHH significantly improves the quantity and quality of the data provided. This allows more patients to be accurately risk stratified and offered appropriate preventive care guided by their risk level.

Trial number

NCT01372553

Personalizing prenatal care using family health history: identifying a panel of conditions for a novel electronic genetic screening tool

In the age of genomic medicine, family health history (FHH) remains an important tool for personalized risk assessment as it can inform approaches to disease prevention and management. In primary care, including in prenatal settings, providers recognize that FHH enables them to assess the risk for birth defects and complex conditions that not only affect the fetus health, but also the mother’s. However, many providers lack the time to gather FHH or the knowledge to confidently interpret the data. Electronic tools providing clinical decision support using FHH data can aid the busy provider with data collection and interpretation. We describe the scope of conditions included in a patient-entered FHH tool that provides clinical decision support and point-of-care education to assist with patient management. This report details how we selected the conditions for which it is appropriate to use FHH as a means to promote personalized medicine in primary prenatal care.

Sibling risk of anxiety disorders based on hospitalizations in Sweden

AIMS

This study used nationwide hospital records to examine sibling risk of any type of anxiety disorder in Sweden over a 40-year period.

METHODS

This study, carried out between 1 January 1968 and 31 December 2007, of the entire population of Sweden, linked information on family relationships from the nationwide Multi-Generation Register with information from the nationwide Swedish Hospital Discharge Register on first diagnosis of anxiety disorder. A total of 42,602 persons hospitalized for anxiety disorders and 2093 affected siblings were identified. Standardized incidence ratios (SIR) were calculated by comparing risk in siblings of persons hospitalized for anxiety disorders with risk in persons whose siblings had no hospital diagnosis of anxiety disorders.

RESULTS

The sibling risk was 2.26, which was independent of sex and age differences between siblings. The SIR was highest in siblings <20 years of age (2.83). Analysis of risk by subtype showed that having a sibling diagnosed with any anxiety disorder resulted in increased risks of a number of disorders; the highest increased risk was of social phobia (SIR 3.68, 95% confidence interval, 1.68-7.69). Risk of panic disorder, generalized anxiety disorder, mixed anxiety and depressive disorder, and obsessive-compulsive disorder was raised in female but not male siblings.

CONCLUSIONS

Heritable effects likely play an important role in the cause of anxiety disorders, but the extent of their role remains to be established. Important contributions could be made by studies of gene-environment interactions that have sufficient sample sizes to produce reliable results.

The behavioral response to personalized genetic information: will genetic risk profiles motivate individuals and families to choose more healthful behaviors?

This report describes the use of information emerging from genetic discovery to motivate risk-reducing health behaviors. Most research to date has evaluated the effects of information related to rare genetic variants on screening behaviors, in which genetic risk feedback has been associated consistently with improved screening adherence. The limited research with common genetic variants suggests that genetic information, when based on single-gene variants with low-risk probabilities, has little impact on behavior. The effect on behavioral outcomes of more realistic testing scenarios in which genetic risk is based on numerous genetic variants is largely unexplored. Little attention has been directed to matching genetic information to the literacy levels of target audiences. Another promising area for research is consideration of using genetic information to identify risk shared within kinship networks and to expand the influence of behavior change beyond the individual.

Familial melanoma: a meta-analysis and estimates of attributable fraction

Melanoma commonly clusters in families, and the recent identification of numerous genotypes predicting higher risks of melanoma has led to the widespread perception that this cancer is predominantly a genetic disease. We conducted a systematic review of the literature and meta-analysis to quantify the contribution of familial factors to melanoma, estimated by the population attributable fraction (PAF). Eligible studies were those that permitted quantitative assessment of the association between histologically confirmed melanoma and family history of the disease; we identified 22 such studies using citation databases, followed by manual review of retrieved references. We calculated summary RRs using weighted averages of the log RR, taking into account random effects, and used these to estimate the PAF. Overall, family history was associated with a significant 2-fold increased risk of melanoma (odds ratio, 2.06; 95% confidence interval, 1.72-2.45); however, there was significant heterogeneity (P = 0.01). The pooled estimate for population-based studies (n = 11) was 2.03 (1.70-2.43), and 2.51 (1.55-4.07) for clinic/hospital-based studies (n = 11), both with significant heterogeneity (P = 0.049 and P = 0.013, respectively). Two studies used record linkage to verify family history in relatives; the pooled risk estimate from these two studies was 2.52 (2.11-3.00) with no evidence of heterogeneity (P = 0.258). Estimates of PAF associated with a positive family history ranged from 0.007 for Northern Europe to 0.064 for Australia (0.040 for all regions combined). Our findings suggest that only a small percentage of melanoma cases (always <7%) are attributable to familial risk; the majority of melanomas are presumably attributable to other factors.

Familial association of inflammatory bowel diseases with other autoimmune and related diseases

OBJECTIVES

Familial risk estimates are useful for genetic counseling, etiological understanding, and design of gene identification studies. We wanted to estimate the associations of ulcerative colitis (UC) and Crohn's disease (CD) with 32 autoimmune and related diseases among parents and offspring, singleton siblings, twins, and spouses.

METHODS

The Multigeneration Register in Sweden provides reliable access to information on families among 11.5 million individuals throughout the last century. The diseases in individual family members were obtained through linkage to the Hospital Discharge Register. Standardized incidence ratios (SIRs) and 95% confidence intervals were calculated as relative risks for UC/CD in family members of patients diagnosed with any of the 34 diseases compared with those lacking affected family members through years 1964-2004.

RESULTS

Among a total of 441,642 patients diagnosed with autoimmune and related conditions, 25,846 were diagnosed with UC and 18,885 with CD. Familial cases amounted to 5.4% of all UC patients and 6.5% of CD patients. SIR for UC was 3.9 (95% confidence interval 3.5-4.3) in offspring of affected parents, 4.6 (3.0-7.4) in siblings, 10.4 (6.5-15.8) in families of affected parents and siblings, and 6.3 (1.9-17.7) for monozygotic twins. The respective SIRs for CD were 6.0 (5.4-6.7), 6.3 (4.1-9.8), 34.0 (24.9-45.3), and 23.4 (10.1-51.1). All discordant associations, i.e., those between CD and other diseases, were also found for UC, including ankylosing spondylitis, asthma, polymyalgia rheumatica, psoriasis, and sarcoidosis. For UC, six additional associations were observed. No correlations between specific diseases were found among spouses, but between UC or CD and any disease it was 1.1 (1.0-1.1).

CONCLUSIONS

The concordant familial risks for UC and CD were lower than those commonly cited. Both diseases are associated with several autoimmune and related diseases, suggesting genetic sharing.

Familial association between type 1 diabetes and other autoimmune and related diseases

AIMS/HYPOTHESIS

In the era of genome-wide association studies, familial risks are used to estimate disease heritability and success in gene identification. We wanted to estimate associations between type 1 diabetes mellitus and 33 autoimmune and related diseases in parents, offspring, singleton siblings and twins.

METHODS

The availability of a Multigeneration Register in Sweden provides reliable access to families throughout the last century. The diseases in individual family members were obtained through linkage to the Hospital Discharge Register. Standardised incidence ratios (SIRs) were calculated as relative risks of contracting type 1 diabetes in family members of affected patients compared with those lacking affected family members.

RESULTS

Among a total of 450,899 patients, 21,168 were diagnosed with type 1 diabetes. Familial cases amounted to 10.3% of all type 1 diabetes patients. SIR for type 1 diabetes was 8.23 in offspring of affected parents, 11.92 in singleton siblings, 39.22 in multiplex families and 21.88 in twins; the calculated risk for monozygotic twins was 32.33. Type 1 diabetes in offspring was associated with 13 diseases in parents, including Addison's disease (SIR 2.41), asthma (1.38), coeliac disease (2.73), Graves' disease/hyperthyroidism (1.86), Hashimoto disease/hypothyroidism (2.35), pernicious anaemia (3.09), primary biliary cirrhosis (3.63), rheumatoid arthritis (2.12), sarcoidosis (1.62), systemic lupus erythematosus (2.04), ulcerative colitis (1.23) and Wegener's granulomatosis (2.12).

CONCLUSIONS/INTERPRETATION

The concordant familial risks for type 1 diabetes were high and the calculated risk for multiplex families and monozygotic twins may be explained by epistatic gene x gene or gene x environment interactions. Familial associations with several autoimmune and related diseases suggest genetic sharing and challenge to gene identification.

Familial associations of rheumatoid arthritis with autoimmune diseases and related conditions

OBJECTIVE

In the era of genome-wide association studies, familial risks are used to estimate disease heritability and the likelihood of candidate-gene identification. This study was undertaken to estimate associations of rheumatoid arthritis (RA) with any of 33 autoimmune diseases and related conditions among parents and offspring, singleton siblings, twins, and spouses.

METHODS

The Multigeneration Register in Sweden was used as a reliable source of information on Swedish families throughout the last century. Data on autoimmune diseases in individual family members were obtained through linkage to the Hospital Discharge Register. The standardized incidence ratio (SIR) was calculated as a measure of the relative risk of RA in family members of patients with RA or any of 33 other autoimmune diseases or related conditions, as compared with the relative risk of RA in those lacking an affected family member.

RESULTS

Among a total of 447,704 patients, 47,361 were diagnosed as having RA. The SIRs for RA were 3.02 in offspring of affected parents, 4.64 in siblings, 9.31 in multiplex families, 6.48 in twins, and 1.17 in spouses. Significant associations with the familial risk of RA in offspring according to parental proband were observed for ankylosing spondylitis (SIR 2.96), localized scleroderma (SIR 2.40), Sjögren's syndrome (SIR 2.25), systemic lupus erythematosus (SIR 2.13), systemic sclerosis (SIR 1.65), Hashimoto thyroiditis/hypothyroidism (SIR 1.54), pernicious anemia (SIR 1.53), sarcoidosis (SIR 1.40), psoriasis (SIR 1.36), Wegener's granulomatosis (SIR 1.34), and asthma or polymyalgia rheumatica (SIR 1.32).

CONCLUSION

This is the first study to compare the familial risks of RA in relation to a large number of autoimmune diseases and related conditions using data from a single population. The high discordant familial risks in this population suggest that there is extensive genetic sharing between RA and the associated diseases.

Familial risks for hospitalization with endocrine diseases

CONTEXT

Familial clustering of a disease is an indicator of a possible heritable cause. In the era of genome scans, the consideration of data on heritability should be important in the assessment of the likely success of the scans.

OBJECT

The objective of the study was to carry out a family study on nonthyroid endocrine diseases to search familial clustering of these diseases beyond the known syndromes.

DESIGN AND SETTING

The Swedish Multigeneration Register on 0- to 72-yr-old subjects was linked to the Hospital Discharge Register from years 1964 to 2004.

MAIN OUTCOME MEASURE

Standardized incidence ratios were calculated for offspring of affected parents and siblings by comparing with those whose relatives had no hospitalization for nonthyroid endocrine diseases.

RESULTS

A total of 11,948 hospitalized cases and 443 familial cases were identified. The familial standardized incidence ratios were increased for parathyroid, pituitary, and adrenal hyperfunctions and hypofunctions, some findings consistent with known syndromes, most clearly that for adrenal cortical hypofunction showing recessive inheritance described for autoimmune polyendocrine syndrome 1. The sibling risks were very high for many diseases, but some of these affecting young individual may be due to bias caused by selective hospitalization. A high sibling risk observed for anterior pituitary hypofunction may represent a yet-unknown recessive syndrome.

CONCLUSIONS

To our knowledge this is a first population-based study on nonthyroid endocrine diseases. The results call for further studies to sort out the challengingly high sibling risk for many individual nonthyroid endocrine diseases, whether they are due to bias or possible recessive effects.

Risk for multiple sclerosis in relatives and spouses of patients diagnosed with autoimmune and related conditions

In the era of complex disease genetics, the consideration of familial risks is important in the assessment of the likely success of these studies. In the present article, we study familial risks for multiple sclerosis (MS) among parents and offspring, singleton siblings, twins, and spouses when a family member was diagnosed with MS or any of 33 other autoimmune diseases. The availability of a Multigeneration Register in Sweden provides a reliable access to families throughout the last century. The diseases in individual family members were obtained through linkage to the Hospital Discharge Register. With a total patient population of 425,102 of whom 11,154 were diagnosed with MS, this is the largest population-based family study on these diseases to date. Standardized incidence ratio (SIR) was calculated for family member of MS patients compared to those lacking an affected family member. SIR for MS was 5.94 (6.12 when parents were aged <73 years) in offspring of affected parents, 6.25 in singleton siblings, 9.09 in twins, and 1.50 (nonsignificant) in spouses; the SIRs did not depend on the gender. The SIRs for MS were 1.84 when a parent was diagnosed with amyotrophic lateral sclerosis and 1.14 with parental asthma. The overall risk of MS was 1.21 when a parent was diagnosed with any autoimmune disease. The genes, so far associated with MS, explain little of the familial aggregation of MS, calling for further efforts in gene identification. The shared familial risks of MS with amyotrophic lateral sclerosis and asthma suggest shared genetic basis.

The 'common disease-common variant' hypothesis and familial risks

The recent large genotyping studies have identified a new repertoire of disease susceptibility loci of unknown function, characterized by high allele frequencies and low relative risks, lending support to the common disease-common variant (CDCV) hypothesis. The variants explain a much larger proportion of the disease etiology, measured by the population attributable fraction, than of the familial risk. We show here that if the identified polymorphisms were markers of rarer functional alleles they would explain a much larger proportion of the familial risk. For example, in a plausible scenario where the marker is 10 times more common than the causative allele, the excess familial risk of the causative allele is over 10 times higher than that of the marker allele. However, the population attributable fractions of the two alleles are equal. The penetrance mode of the causative locus may be very difficult to deduce from the apparent penetrance mode of the marker locus.