State variations in insertion of long-acting reversible contraception during delivery hospitalization.

OBJECTIVES: This study aimed to describe immediate postpartum long-acting reversible contraception (IPP LARC) insertion rates during delivery hospitalizations at the state level and by payor type. STUDY DESIGN: This is a cross-sectional study of 26 states and District of Columbia using 2020 State Inpatient Database. RESULTS: In 2020, IPP LARC insertion rates varied widely by states, ranging from 2.55 to 637.25 per 10,000 deliveries. Rates were higher for deliveries with Medicaid as primary expected payor than with private insurance in all states but District of Columbia. CONCLUSIONS: Rates of IPP LARC insertion varied in 2020 by state and were higher for deliveries with Medicaid as primary expected payor.

Association of Medicaid Expansion Under the Affordable Care Act With Medicaid Coverage in the Prepregnancy, Prenatal, and Postpartum Periods.

INTRODUCTION: We evaluated how the Affordable Care Act (ACA) Medicaid eligibility expansion affected perinatal insurance coverage patterns for Medicaid-enrolled beneficiaries who gave birth overall and by race/ethnicity. We also examined state-level heterogeneous impacts. METHODS: Using the 2011-2013 Medicaid Analytic eXtract and the 2016-2018 Transformed Medicaid Statistical Information System Analytic File databases, we identified 1.4 million beneficiaries giving birth in 2012 (pre-ACA expansion cohort) and 1.5 million in 2017 (post-ACA expansion cohort). We constructed monthly coverage rates for the two cohorts by state Medicaid expansion status and obtained difference-in-differences estimates of the association of Medicaid expansion with coverage overall and by race/ethnicity group (non-Hispanic White, non-Hispanic Black, and Hispanic). To explore state-level heterogeneous impacts, we divided the expansion and non-expansion states into groups based on the differences in the income eligibility limits for low-income parents in each state between 2012 and 2017. RESULTS: Medicaid expansion was associated with 13 percentage points higher coverage in the 9 to 12 months before giving birth, and 11 percentage points higher coverage at 6 to 12 months postpartum. Hispanic birthing individuals had the greatest relative increases in coverage, followed by non-Hispanic White and non-Hispanic Black individuals. In Medicaid expansion states, those who experienced the greatest increases in income eligibility limits for low-income parents generally saw the greatest increases in coverage. In non-expansion states, there was less heterogeneity between state groupings. CONCLUSIONS: Pregnancy-related Medicaid eligibility did not have major changes in the 2010s. However, states' adoption of ACA Medicaid expansion after 2012 was associated with increased Medicaid coverage before, during, and after pregnancy. The increases varied by race/ethnicity and across states.

Mental health and substance use disorders at delivery hospitalization and readmissions after delivery discharge.

BACKGROUND: The objective was to assess mental health and substance use disorders (MSUD) at delivery hospitalization and readmissions after delivery discharge. METHODS: This is a population-based retrospective cohort study of persons who had a delivery hospitalization during January to September in the 2019 Nationwide Readmissions Database. We calculated 90-day readmission rates for MSUD and non-MSUD, overall and stratified by MSUD status at delivery. We used multivariable logistic regressions to assess the associations of MSUD type, patient, clinical, and hospital factors at delivery with 90-day MSUD readmissions. RESULTS: An estimated 11.8% of the 2,697,605 weighted delivery hospitalizations recorded MSUD diagnoses. The 90-day MSUD and non-MSUD readmission rates were 0.41% and 2.9% among delivery discharges with MSUD diagnoses, compared to 0.047% and 1.9% among delivery discharges without MSUD diagnoses. In multivariable analysis, schizophrenia, bipolar disorder, stimulant-related disorders, depressive disorders, trauma- and stressor-related disorders, alcohol-related disorders, miscellaneous mental and behavioral disorders, and other specified substance-related disorders were significantly associated with increased odds of MSUD readmissions. Three or more co-occurring MSUDs (vs one MSUD), Medicare or Medicaid (vs private) as the primary expected payer, lowest (vs highest) quartile of median household income at residence zip code level, decreasing age, and longer length of stay at delivery were significantly associated with increased odds of MSUD readmissions. CONCLUSION: Compared to persons without MSUD at delivery, those with MSUD had higher MSUD and non-MSUD 90-day readmission rates. Strategies to address MSUD readmissions can include improved postpartum MSUD follow-up management, expanded Medicaid postpartum coverage, and addressing social determinants of health.

Cost-effectiveness of expanded hepatitis A vaccination among adults with diagnosed HIV, United States.

Hepatitis A virus can cause severe and prolonged illness in persons with HIV (PWH). In July 2020, the Advisory Committee on Immunization Practices (ACIP) expanded its recommendation for hepatitis A vaccination to include all PWH aged ≥1 year. We used a decision analytic model to estimate the value of vaccinating a cohort of adult PWH aged ≥20 years with diagnosed HIV in the United States using a limited societal perspective. The model compared 3 scenarios over an analytic horizon of 1 year: no vaccination, current vaccine coverage, and full vaccination. We incorporated the direct medical costs and nonmedical costs (i.e., public health costs and productivity loss). We estimated the total number of infections averted, cost to vaccinate, and incremental cost per case averted. Full implementation of the ACIP recommendation resulted in 775 to 812 fewer adult cases of hepatitis A in 1 year compared with the observed vaccination coverage. The incremental cost-effectiveness ratio for the full vaccination scenario was $48,000 for the 2-dose single-antigen hepatitis A vaccine and $130,000 for the 3-dose combination hepatitis A and hepatitis B vaccine per case averted, compared with the observed vaccination scenario. Depending on type of vaccine, full hepatitis A vaccination of PWH could lead to ≥80% reduction in the number of cases and $48,000 to $130,000 in additional cost per case averted. Data on hepatitis A health outcomes and costs specific to PWH are needed to better understand the longer-term costs and benefits of the 2020 ACIP recommendation.

Sources of variation in estimates of Duchenne and Becker muscular dystrophy prevalence in the United States.

BACKGROUND: Direct estimates of rare disease prevalence from public health surveillance may only be available in a few catchment areas. Understanding variation among observed prevalence can inform estimates of prevalence in other locations. The Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) conducts population-based surveillance of major muscular dystrophies in selected areas of the United States. We identified sources of variation in prevalence estimates of Duchenne and Becker muscular dystrophy (DBMD) within MD STARnet from published literature and a survey of MD STARnet investigators, then developed a logic model of the relationships between the sources of variation and estimated prevalence. RESULTS: The 17 identified sources of variability fell into four categories: (1) inherent in surveillance systems, (2) particular to rare diseases, (3) particular to medical-records-based surveillance, and (4) resulting from extrapolation. For the sources of uncertainty measured by MD STARnet, we estimated each source's contribution to the total variance in DBMD prevalence. Based on the logic model we fit a multivariable Poisson regression model to 96 age-site-race/ethnicity strata. Age accounted for 74% of the variation between strata, surveillance site for 6%, race/ethnicity for 3%, and 17% remained unexplained. CONCLUSION: Variation in estimates derived from a non-random sample of states or counties may not be explained by demographic differences alone. Applying these estimates to other populations requires caution.

Education and employment as young adults living with spina bifida transition to adulthood in the USA: A study of the National Spina Bifida Patient Registry.

AIM: To describe the education and employment transition experience of young adults with spina bifida (YASB) and investigate factors associated with employment. METHOD: We queried education and employment data from the US National Spina Bifida Patient Registry from 2009 to 2019. We applied generalized estimating equations models to analyze sociodemographic and disease-related factors associated with employment. RESULTS: A total of 1909 participants (850 males, 1059 females) aged 18 to 26 years contributed 4379 annual visits. Nearly 84% had myelomeningocele and, at last visit, the median age was 21 years (mean 21 years 5 months, SD 2 years 10 months). A total of 41.8% had at least some post-high school education, and 23.9% were employed. In a multivariable regression model, employment was significantly associated with education level, lower extremity functional level, bowel continence, insurance, and history of non-shunt surgery. This large, national sample of YASB demonstrated low rates of post-secondary education attainment and employment and several potentially modifiable factors associated with employment. INTERPRETATION: Specific sociodemographic, medical, and functional factors associated with employment are important for clinicians to consider when facilitating transition for YASB into adulthood. Additional research is needed to understand the impact of cognitive functioning and social determinants of health on transition success in YASB. WHAT THIS PAPER ADDS: There were low education attainment and employment rates in a large sample of young adults with spina bifida. Specific sociodemographic, medical, and functional factors are associated with employment. Some employment-associated factors, such as continence and self-management skills, are modifiable.

Hypertensive Disorders in Pregnancy and Mortality at Delivery Hospitalization - United States, 2017-2019.

Hypertensive disorders in pregnancy (HDPs), defined as prepregnancy (chronic) or pregnancy-associated hypertension, are common pregnancy complications in the United States.* HDPs are strongly associated with severe maternal complications, such as heart attack and stroke (1), and are a leading cause of pregnancy-related death in the United States.† CDC analyzed nationally representative data from the National Inpatient Sample to calculate the annual prevalence of HDP among delivery hospitalizations and by maternal characteristics, and the percentage of in-hospital deaths with an HDP diagnosis code documented. During 2017-2019, the prevalence of HDP among delivery hospitalizations increased from 13.3% to 15.9%. The prevalence of pregnancy-associated hypertension increased from 10.8% in 2017 to 13.0% in 2019, while the prevalence of chronic hypertension increased from 2.0% to 2.3%. Prevalence of HDP was highest among delivery hospitalizations of non-Hispanic Black or African American (Black) women, non-Hispanic American Indian and Alaska Native (AI/AN) women, and women aged ≥35 years, residing in zip codes in the lowest median household income quartile, or delivering in hospitals in the South or the Midwest Census regions. Among deaths that occurred during delivery hospitalization, 31.6% had any HDP documented. Clinical guidance for reducing complications from HDP focuses on prompt identification and preventing progression to severe maternal complications through timely treatment (1). Recommendations for identifying and monitoring pregnant persons with hypertension include measuring blood pressure throughout pregnancy,§ including self-monitoring. Severe complications and mortality from HDP are preventable with equitable implementation of strategies to identify and monitor persons with HDP (1) and quality improvement initiatives to improve prompt treatment and increase awareness of urgent maternal warning signs (2).

Direct costs of adhering to selected Duchenne muscular dystrophy Care Considerations: Estimates from a midwestern state.

INTRODUCTION/AIMS: The multidisciplinary Duchenne muscular dystrophy (DMD) Care Considerations were developed to standardize care and improve outcomes. We provide cumulative cost estimates for selected key preventive (ie, excluding new molecular therapies and acute care) elements of the care considerations in eight domains (neuromuscular, rehabilitation, respiratory, cardiac, orthopedic, gastrointestinal, endocrine, psychosocial management) independent of completeness of uptake or provision of nonpreventive care. METHODS: We used de-identified insurance claims data from a large midwestern commercial health insurer during 2018. We used Current Procedural Terminology and national drug codes to extract unit costs for clinical encounters representing key preventive elements of the DMD Care Considerations. We projected per-patient cumulative costs from ages 5 to 25 years for these elements by multiplying a schedule of recommended frequencies of preventive services by unit costs in 2018 US dollars. RESULTS: Assuming a diagnosis at age 5 years, independent ambulation until age 11, and survival until age 25, we estimated 670 billable clinical events. The 20-year per-patient cumulative cost was $174 701 with prednisone ($2.3 million with deflazacort) and an expected total of $12 643 ($29 194) for out-of-pocket expenses associated with those events and medications. DISCUSSION: Standardized monitoring of disease progression and treatments may reduce overall costs of illness. Costs associated with these services would be needed to quantify potential savings. Our approach demonstrates a method to estimate costs associated with implementation of preventive care schedules.

Variations in Low-Risk Cesarean Delivery Rates in the United States Using the Society for Maternal-Fetal Medicine Definition.

OBJECTIVE: To assess variations in low-risk cesarean delivery rates in the United States using the Society for Maternal-Fetal Medicine (SMFM) definition of low-risk for cesarean delivery and to identify factors associated with low-risk cesarean deliveries. METHODS: From hospital discharge data in the 2018 National Inpatient Sample and State Inpatient Databases, we identified deliveries that were low-risk for cesarean delivery using the SMFM definition based on the International Classification of Diseases, Tenth Revision, Clinical Modification codes. We estimated national low-risk cesarean delivery rates overall and by patient characteristics, clinically relevant conditions not included in the SMFM definition, and hospital characteristics based on the nationally representative sample of hospital discharges in the National Inpatient Sample. Multivariate logistic regressions were estimated for the national sample to identify factors associated with low-risk cesarean delivery. We reported low-risk cesarean delivery rates for 27 states and the District of Columbia based on the annual state data that represented the universe of hospital discharges from participating states in the State Inpatient Databases. RESULTS: Of an estimated 3,634,724 deliveries in the 2018 National Inpatient Sample, 2,484,874 low-risk deliveries met inclusion criteria. The national low-risk cesarean delivery rate in 2018 was 14.6% (95% CI 14.4-14.8%). The rates varied widely by state (range 8.9-18.6%). Nationally, maternal age older than 40 years, non-Hispanic Black or Asian race, private insurance as primary payer, admission on weekday, obesity, diabetes, or hypertension, large metropolitan residence, and hospitals of the South census region were associated with low-risk cesarean delivery. CONCLUSION: Approximately one in seven low-risk deliveries was by cesarean in 2018 in the United States using the SMFM definition and the low-risk cesarean delivery rates varied widely by state.

Labor market participation and productivity costs for female caregivers of minor male children with Duchenne and Becker muscular dystrophies.

INTRODUCTION/AIMS: Duchenne and Becker muscular dystrophies (DBMD) are X-linked neuromuscular disorders characterized by progressive muscle weakness, leading to decreased mobility and multisystem complications. We estimate productivity costs attributable to time spent by a parent caring for a male child under the age of 18 y with DBMD, with particular focus on female caregivers of boys with Duchenne muscular dystrophy (DMD) who have already lost ambulation. METHODS: Primary caregivers of males with DBMD in the Muscular Dystrophy Surveillance and Research Tracking Network (MD STARnet) were surveyed during 2011-2012 on family quality of life measures, including labor market outcomes. Of 211 respondents, 96 female caregivers of boys with DBMD were matched on state, year of survey, respondent's age, child's age, and number of minor children with controls constructed from Current Population Survey extracts. Regression analysis was used to estimate labor market outcomes and productivity costs. RESULTS: Caregivers of boys with DBMD worked 296 h less per year on average than caregivers of unaffected children, translating to a $8816 earnings loss in 2020 U.S. dollars. Caregivers of boys with DMD with ≥4 y of ambulation loss had a predicted loss in annualized earnings of $23,995, whereas caregivers of boys with DBMD of the same ages who remained ambulatory had no loss of earnings. DISCUSSION: Female caregivers of non-ambulatory boys with DMD face additional household budget constraints through income loss. Failure to include informal care costs in economic studies could understate the societal cost-effectiveness of strategies for managing DMD that might prolong ambulation.

Rates of hospitalization for urinary tract infections among medicaid-insured individuals by spina bifida status, Tennessee 2005-2013.

BACKGROUND: Individuals with spina bifida are at increased risk for urinary tract infection (UTI), however there are few population-based investigations of the burden of UTI hospitalizations. OBJECTIVE: We assessed rates and risk factors for UTI hospitalization in individuals with and without spina bifida. METHODS: We conducted a retrospective cohort study to estimate rates of UTI hospitalization by spina bifida status. We included individuals enrolled in Tennessee Medicaid who lived in one of the Emerging Infections Program's Active Bacterial Surveillance counties between 2005 and 2013. Spina bifida was primarily defined and UTI hospitalizations were identified using International Classification of Diseases, Ninth Revision diagnoses. We also studied a subset without specific health conditions potentially associated with UTI. We used Poisson regression to calculate rate ratios (RR) of UTIs for individuals with versus without spina bifida, adjusting for race, sex and age group. RESULTS: Over the 9-years, 1,239,362 individuals were included and 2,493 met criteria for spina bifida. Individuals with spina bifida had over a four-fold increased rate of UTI hospitalization than those without spina bifida-in the overall study population and in the subset without specific, high-risk conditions (adjusted rate ratios: 4.41, 95% confidence intervals: 3.03, 6.43) and (4.87, 95% CI: 2.99, 7.92), respectively. We detected differences in rates of UTI hospitalization by race and sex in individuals without spina bifida that were not seen among individuals with spina bifida. CONCLUSIONS: Individuals with spina bifida had increased rates of UTI hospitalizations, and associated demographic patterns differed from those without spina bifida.

Kidney Function Surveillance in the National Spina Bifida Patient Registry: A Retrospective Cohort Study.

PURPOSE: Chronic kidney disease affects 25% to 50% of patients with spina bifida. Guidelines recommend kidney function surveillance in these patients but practice patterns are unknown. Variations in kidney function surveillance were assessed in patients with spina bifida based on the hypothesis that the treating clinic and spina bifida type would be associated with kidney function surveillance. MATERIALS AND METHODS: A retrospective cohort study was conducted of U.S. patients in the National Spina Bifida Patient Registry from 2013 to 2018. Followup was anchored at the 2013 visit. Participants with either an outcome event within 2 years of followup or more than 2 years of followup without an outcome event were included. Primary outcome was kidney function surveillance, defined as at least 1 renal ultrasound and serum creatinine within 2 years of followup. Primary exposures were clinic and spina bifida type, which were analyzed with covariates including sociodemographic and clinical characteristics in logistic regression models for their association with the outcome. Sensitivity analyses were performed using different kidney function surveillance definitions. RESULTS: Of 8,351 patients 5,445 were included with a median followup of 3.0 years. Across 23 treating clinics kidney function surveillance rates averaged 62% (range 6% to 100%). In multivariable models kidney function surveillance was associated with treating clinic, younger patient age, functional lesion level, nonambulatory status and prior bladder augmentation. Treating clinic remained a significant predictor of kidney function surveillance in all sensitivity analyses. CONCLUSIONS: Within the National Spina Bifida Patient Registry wide variation exists in practice of kidney function surveillance across treating clinics despite adjustment for key patient characteristics.

Fragile X Syndrome-Associated Emergency Department Visits in the United States, 2006-2011.

Using national data, we examined emergency department (ED) encounters during 2006-2011 for which a diagnosis code for fragile X syndrome (FXS) was present (n = 7,217). Almost half of ED visits coded for FXS resulted in hospitalization, which is much higher than for ED visits not coded for FXS. ED visits among females coded for FXS were slightly more likely to result in hospitalization. These findings underscore the importance of surveillance systems that could accurately identify individuals with FXS, track healthcare utilization and co-occurring conditions, and monitor quality of care in order to improve care and reduce FXS-associated morbidity.

Philosophy of care delivery for spina bifida.

The multidisciplinary model (MCM) is described as one that utilizes skills and experience from practitioners belonging to various disciplines, each treating patients from a specific clinical perspective.1 The Spina Bifida Association (SBA) supports and recommends that clinical care for people with Spina Bifida (SB) be provided in specialty clinics of which the MCM is an example; that care be coordinated; and that there be a plan for transitional care.2 This paper explores the challenges the MCM faces with a transitioning and aging population in a care system that calls for a positive patient experience, engaged health care professionals, desired outcomes, with consideration of cost.

Summary of Selected Healthcare Encounters among a Selection of Patients with Myotonic Muscular Dystrophy.

OBJECTIVE: Research has not examined the use of health care by patients with myotonic muscular dystrophy (MMD), but it would provide insights into this population, which is prone to comorbidities and high service needs. This study is an analysis of this understudied subgroup, using a unique linked dataset to examine the characteristics and healthcare utilization patterns for people with MMD. METHODS: This analysis used 3 South Carolina datasets (2009-2014). The subjects included individuals with at least 1 encounter with an International Classification of Diseases, Ninth Revision, Clinical Modification code of 359.21. The variables included sex, race, visit type, payer, and diagnoses. The analyses examined characteristics and number of encounters. RESULTS: The subjects were predominately female, white, and 45 to 64 years old. A total of 44.6% of the study population had at least 1 inpatient visit, whereas 64.2% had at least 1 emergency department visit. A majority of the subjects had at least 1 office visit (55.0%), and most (85.3%) did not have a home health encounter. CONCLUSIONS: Investigation of the reasons for these inpatient and emergency department encounters may be helpful in identifying ways to deliver high-quality care.

Differences in Length of Stay and Costs Between Comparable Hospitalizations of Patients With Spina Bifida With or Without Pressure Injuries.

OBJECTIVE: To estimate differences in the length of stay and costs for comparable hospitalizations of patients with spina bifida (SB) with and without pressure injuries. DESIGN: Retrospective, cross-sectional, observational study. SETTING: Nationwide Inpatient Sample from years 2010-2014. PARTICIPANTS: Hospitalizations of patients with SB (N=7776). Hospitalizations among patients with SB and pressure injuries (n=3888) were matched to hospitalizations among patients with SB but without pressure injuries (n=3888). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Differences in length of stay and total costs between the 2 groups. RESULTS: After successful matching, multivariate modeling of costs and length of stay on matched sample showed that hospitalizations with pressure injuries had an increased 1.2 inpatient days and excess average costs of $1182 in 2014 dollars. CONCLUSIONS: The estimated average cost of hospitalization increased by 10%, and the estimated average length of stay increased by 24% in the presence of pressure injuries among hospitalized patients with SB, compared with their peers without these injuries. These results highlight the substantial morbidity associated with pressure injuries, which are potentially preventable before or during hospitalizations among persons with SB.

Gender difference in clinical conditions among hospitalized adults with myotonic dystrophy.

INTRODUCTION: In this study we examined gender differences in adult hospitalizations with myotonic dystrophy (DM). METHODS: From the Nationwide Inpatient Sample (NIS) 2010-2014, we identified 1,891 adult hospitalizations with a DM diagnosis and constructed a comparison group of hospitalizations without DM using propensity score matching. We calculated relative risk by gender for 44 clinical diagnoses that each accounted for at least 5% of DM hospitalizations. RESULTS: Hospitalizations with DM were longer (4.8 vs. 4.1 days, P < 0.0001) and more costly ($13,241 vs. $11,458, P < 0.0001) than those without DM. More than half (25 of 44) of the conditions co-occurring with DM hospitalizations did not differ in their relative risks by gender. For those that differed by gender, only 5 were specific to DM, compared with hospitalizations without DM. DISCUSSION: Our findings highlight the importance of comprehensive and coordinated care for DM rather than gender-oriented care in the inpatient setting. Muscle Nerve 59:348-353, 2019.

30-day all-cause readmission rates among a cohort of individuals with rare conditions.

BACKGROUND: There is a need to examine health care utilization of individuals with the rare conditions muscular dystrophies, spina bifida, and fragile X syndrome. These individuals have a greater need for health care services, particularly inpatient admissions. Prior studies have not yet assessed 30-day all-cause readmission rates. OBJECTIVE: To estimate 30-day hospital readmission rates among individuals with three rare conditions. HYPOTHESIS: Rare conditions patients will have a higher 30-day all-cause readmission rate than those without. METHODS: Data from three sources (2007-2014) were combined for this case-control analysis. A cohort of individuals with one of the three conditions was matched (by age in 5 year age groups, gender, and race) to a comparison group without a rare condition. Inpatient utilization and 30-day all-cause readmission rates were compared between the two groups. Logistic regression analyses compared the odds of a 30-day all-cause readmission across the two groups, controlling for key covariates. RESULTS: A larger proportion in the rare condition group had at least one inpatient visit (46.1%) vs. the comparison group (23.6%), and a higher 30-day all-cause readmission rate (Spina Bifida-46.7%, Muscular Dystrophy-39.7%, and Fragile X Syndrome-35.8%) than the comparison group (13.4%). Logistic regression results indicated that condition status contributed significantly to differences in readmission rates. CONCLUSIONS: Higher rates of inpatient utilization and 30-day all-cause readmission among individuals with rare conditions vs. those without are not surprising, given the medical complexity of these individuals, and indicates an area where unfavorable outcomes may be improved with proper care coordination and post discharge care.

Utilizing Combined Claims and Clinical Datasets for Research Among Potential Cases of Rare Diseases.

With data quality issues with administrative claims and medically derived datasets, a dataset derived from a combination of sources may be more effective for research. The purposes of this article is to link an EMR-based data warehouse with state administrative data to study individuals with rare diseases; to describe and compare their characteristics; and to explore research with the data. These methods included subjects with diagnosis codes for one of three rare diseases from the years 2009-2014; Spina Bifida, Muscular Dystrophy, and Fragile X Syndrome. The results from the combined data provides additional information that each dataset, by itself, would not contain. The simultaneous examination of data such as race/ethnicity, physician and other outpatient visit data, charges and payments, and overall utilization was possible in the combined dataset. It is also discussed that combining such datasets can be a useful tool for the study of populations with rare diseases.