Abstract
BackgroundThere is great heterogeneity on geographic and temporary Huntington disease (HD) epidemiological estimates. Most research studies of rare diseases, including HD, use health information systems (HIS) as data sources. This study investigates the validity and accuracy of national and international diagnostic codes for HD in multiple HIS and analyses the epidemiologic trends of HD in the Autonomous Community of Navarre (Spain).MethodsHD cases were ascertained by the Rare Diseases Registry and the reference Medical Genetics Centre of Navarre. Positive predictive values (PPV) and sensitivity with 95% confidence intervals (95% CI) were estimated. Overall and 9-year periods (1991–2017) HD prevalence, incidence and mortality rates were calculated, and trends were assessed by Joinpoint regression.ResultsOverall PPV and sensitivity of combined HIS were 71.8% (95% CI: 59.7, 81.6) and 82.2% (95% CI: 70.1, 90.4), respectively. Primary care data was a more valuable resource for HD ascertainment than hospital discharge records, with 66% versus 50% sensitivity, respectively. It also had the highest number of “unique to source” cases. Thirty-five per cent of HD patients were identified by a single database and only 4% by all explored sources. Point prevalence was 4.94 (95% CI: 3.23, 6.65) per 100,000 in December 2017, and showed an annual 6.1% increase from 1991 to 1999. Incidence and mortality trends remained stable since 1995–96, with mean annual rates per 100,000 of 0.36 (95% CI: 0.27, 0.47) and 0.23 (95% CI: 0.16, 0.32), respectively. Late-onset HD patients (23.1%), mean age at onset (49.6 years), age at death (66.6 years) and duration of disease (16.7 years) were slightly higher than previously reported.ConclusionHD did not experience true temporary variations in prevalence, incidence or mortality over 23 years of post-molecular testing in our population. Ascertainment bias may largely explain the worldwide heterogeneity in results of HD epidemiological estimates. Population-based rare diseases registries are valuable instruments for epidemiological studies on low prevalence genetic diseases, like HD, as long as they include validated data from multiple HIS and genetic/family information.
Highlights
There is great heterogeneity on geographic and temporary Huntington disease (HD) epidemiological estimates
HD case ascertainment (HIS and Medical Genetics Centre (MGC)) health information systems (HIS) captured a total number of 119 potential HD cases between 2000 and 2017: 40 from Minimum Basic Data Set at Hospital Discharge (MBDS), 51 from Electronic Clinical Records in Primary Care (ECRPC), 7 from Temporary Work Disability Registry (TWDR), and 21 from Mortality Statistics (MS)
2/3 of HD cases identified across all four HIS were confirmed by review of clinical/genetic records, with individual dataset Positive predictive values (PPV) ranging from 76% for hospital discharges data to 100% for temporary working leave information
Summary
There is great heterogeneity on geographic and temporary Huntington disease (HD) epidemiological estimates. Huntington disease (HD) is a rare, autosomal dominant neurodegenerative disorder caused by the abnormal expansion of a CAG repeat sequence in the Huntingtin (HTT) gene. Some studies among Caucasians have reported a substantial increase in prevalence, incidence and/or mortality rates, which might indicate a time variation in HD epidemiology [6,7,8,9,10]. Whether it is, a true trend or secondary to an improved ascertainment process in post molecular years has not been fully investigated
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