DOI: 10.2337/diacare.29.03.06.dc05-1531 © 2006 by the American Diabetes Association
Age at Onset of Childhood-Onset Type 1 Diabetes and the Development of End-Stage Renal DiseaseA nationwide population-based study
1 Department of Public Health and Clinical Medicine, Medicine, Umeå University, Umeå, Sweden Address correspondencereprint requests to Dr. Maria Svensson, Department of Medicine, Umeå University Hospital, SE-901 85 UMEÅ, Sweden. E-mail: maria.svensson{at}medicin.umu.se
OBJECTIVETo analyze the impact of age at onset on the development of end-stage renal disease (ESRD) due to diabetic nephropathy in a nationwide population-based cohort with childhood-onset type 1 diabetes. RESEARCH DESIGN AND METHODSA record linkage between two nationwide registers, the Swedish Childhood Diabetes Registry, including 12,032 cases with childhood-onset diabetes, and the Swedish Registry for Active Treatment of Uraemia was performed. Log-rank test was used to test differences between cumulative risk curves of developing ESRD due to diabetic nephropathy in three different strata of age at onset (04, 59, and 1014 years). RESULTSAt a maximum follow-up of 27 years, 33 patients had developed ESRD due to diabetic nephropathy and all had a diabetes duration >15 years. In total, 4,414 patients had diabetes duration >15 years, and thus the risk in this cohort to develop ESRD was 33 of 4,414 (0.7%). A significant difference in risk of developing ESRD was found between the youngest (04 years) and the two older (59 and 1014 years) age-at-onset strata (P = 0.03 and P = 0.001, respectively). A significant difference in the risk of developing ESRD was also found between children with prepubertal (04 and 59 years, n = 2,424) and pubertal (1014 years, n = 2000) onset of diabetes (P = 0.002). No patient with onset of diabetes before 5 years of age had developed ESRD. CONCLUSIONSWith a median duration of 21 years in this population-based Swedish cohort with childhood-onset diabetes, <1% of the patients had developed ESRD due to diabetic nephropathy, and a prepubertal onset of diabetes seems to prolong the time to development of ESRD.
Abbreviations: ESRD, end-stage renal disease SCDR, The Swedish Childhood Diabetes Registry SRAU, Swedish Registry for Active Treatment of Uraemia
Poor glycemic control is a necessary but not sufficient factor for the development of diabetic nephropathy (13). Other factors, such as perinatal, hormonal, and genetic issues, seem to contribute (4,5). Puberty, in addition to frequently noted deterioration of glycemic control, is characterized by rapid growth and hormonal changes, all factors that could promote the development of chronic diabetes complications (68). Thus, some clinical studies (6,912) but not all (1317) suggest that prepubertal diabetes duration may contribute less to the development of microvascular complications than pubertal and postpubertal duration. In addition, there are studies that have suggested that an onset of diabetes in the youngest age-group, age <5 years, may delay development of chronic diabetes complications such as microalbuminuria and retinopathy (1821). In this large population-based study we assessed the cumulative incidence of ESRD due to diabetic nephropathy in a cohort with childhood-onset diabetes with a median duration of 21 years. In addition, we analyzed the effect of age at onset on the development of ESRD due to diabetic nephropathy using two large nationwide population-based registers.
The Swedish Childhood Diabetes Registry In the Swedish health care system all children aged 014 years with suspected diabetes are referred to pediatric departments. Since 12 July 1977, all children in Sweden with newly diagnosed insulin-treated diabetes are reported to the Swedish Childhood Diabetes Registry (SCDR). This report includes information on personal identification number, sex, county of residence, date of diagnosis (first insulin injection), date of reporting, reporting hospital, and physician. Comparison with external sources has shown that the level of ascertainment in the SCDR is 9699% (22).
The Swedish Registry for Active Treatment of Uremia
The study cohort Among patients who died with a diabetes duration <15 years none had developed ESRD. When linking the SCDR to the SRAU we identified 40 patients that had developed ESRD during this period. Thirty-three (82%) of them had diabetic nephropathy as the primary cause, and of those, 4 had died at follow-up. Among these 33 patients, only 1 received a renal transplant before the start of dialysis. Seven (18%) patients had other renal diseases, i.e., polyarteritis (1), pyelonefritis (2), polycystic renal disease (1), interstitial nefritis (1), and IgA-nefritis (1). In one patient we were not able to specify the primary renal disease. These seven patients were excluded from the analyses. The first patient from the SCDR with ESRD due to diabetic nephropathy was registered in the SRAU in 1993, and all 33 of them were diagnosed with diabetes between 1 July 1977 and 31 December 1985. None of them had diabetes duration <15 years. Thus, all patients diagnosed with diabetes between 1 July 1977 and 31 December 1985 (n = 4,414) comprised the study cohort used in the statistical comparisons of the effect of age at onset, since patients with a duration of diabetes <15 years were not at risk of developing ESRD in this cohort.
Age-at-onset strata
Statistical methods
Clinical characteristics of the study cohort The crude cumulative incidence of ESRD due to diabetic nephropathy was 33 of 12,032 (0.3%). However, in the population at risk, i.e., with a diabetes duration >15 years, a total of 33 of 4,414 (0.7%) of the patients had developed ESRD due to diabetic nephropathy. The median time of follow-up in this cohort was 21 years (range 1527) and the median time from onset of diabetes to ESRD was 20 years (range 1523). There was no significant difference in median time of follow-up in the three different age-at-onset strata (20.3 [range 1527], 20.5 [1527], 20.4 [1527] years, respectively). Table 1 shows clinical characteristics of patients with and without ESRD due to diabetic nephropathy.
Effect of age at onset on ESRD A significant difference in the risk of developing ESRD was found between the youngest (04 years) and the two older (59 and 1014 years) age-at-onset strata (P = 0.03 and P = 0.001, respectively). No patients with ESRD due to diabetic nephropathy were found in the 04 years age-at-onset group. These results are shown in Fig. 1A. Since our focus is prepubertal onset of diabetes, the two prepubertal age-groups with an onset of diabetes before the age of 10 (04 and 59 years [n = 2,426]) were merged, and a significant difference in the risk of developing ESRD was found between children with prepubertal and pubertal onset of diabetes (P = 0.002). The results are summarized in Fig. 1B.
In this nationwide population-based study <1% of patients with diabetes duration >15 years and a median time to follow-up of 21 years (range 1527) developed ESRD due to diabetic nephropathy. This cumulative incidence is surprisingly low, but comparisons with previous studies are difficult to interpret since most other studies have used microalbuminuria (incipient nephropathy), macroalbuminuria (overt nephropathy), or urinary albumin-to-creatinine ratio as outcome variables and markers of diabetic nephropathy. In addition, the follow-up time varies between studies. The low prevalence of ESRD found in our study may be due to the relatively short time of follow-up, 1527 years, since the peak incidence of diabetic nephropathy previously has been found to occur 2530 years after the onset of type 1 diabetes (9,24). Thus, the most probable explanation of our findings would be a delay in the incidence peak of onset of ESRD. In 1996, a 35-year follow-up study from the Joslin cohort study (from 1959 and onwards) showed a cumulative risk of dialysis treatment (ESRD) of 67% at 20 years duration of type 1 diabetes (25). More recent studies have shown a declining incidence of diabetic nephropathy over time both in the U.S. and in Europe (9,26,27), and similar trends have also been shown in Swedish patient cohorts with respect to both incipient (28) and overt nephropathy (29). A declining incidence of ESRD or a delay in the peak incidence of onset has also been indicated by the fact that the take-on rate for type 1 diabetes in the European Dialysis and Transplant Association registry has remained unchanged through the 1990s despite an increase in prevalence of type 1 diabetes and a longer survival in patients with type 1 diabetes (30). This has also been suggested by findings from the SRAU (31). However, there are other studies from Denmark and Iceland that have indicated an unchanged incidence of diabetic nephropathy (32,33). Only long-term follow-up studies in population-based cohorts may reveal such trends. Many of the previous follow-up studies on chronic diabetes complications involve patients from specialized clinics only (Joslin, Steno, and Linköping), thus not mirroring the general population. On the other hand, population-based cohort studies may be incomplete. Our population-based cohort includes 9699% of the cases with childhood-onset type 1 diabetes during the defined time period in Sweden, and the SRAU includes 95% of cases with ESRD. A concern with population-based prevalence studies is that they might miss patients that have already died and thus underestimate the occurrence of the disease. The death rate in young patients with diabetes is approximately twice the expected rate also at short duration (34). In this study only 70 patients died before a diabetes duration >15 years, all without a diagnosis of ESRD. In the study cohort, 30 of 4,414 patients (0.7%) had died, 4 after having developed ESRD. It is unlikely that the deaths of 26 patients without ESRD would significantly affect our results. The SRAU started in 1991, initially also collecting prevalent cases of ESRD, and none of the patients in the SCDR then had a duration >13 years. Therefore, our study should cover the vast majority of all potential cases in the defined time period and thus represents the Swedish population at large. To the best of our knowledge, we show, for the first time in a nationwide population-based study, that onset of diabetes before the age of 10 years, and thus prepubertal, significantly influenced the time to development of ESRD due to diabetic nephropathy. This suggests, not that the early ages of onset are protective but rather that "the clock does not run as fast" for the years before pubertal onset. A similar impact of age at onset has been indicated in a population-based study in an American and a Japanese cohort where a positive correlation between age at onset and risk of ESRD was found (35). Other studies have indicated that the prepubertal years with diabetes involve a reduced risk or a longer time to development of diabetic nephropathy and other microvascular complications, e.g., retinopathy (6,9,11,3638). Our study and others (1821) may also suggest that an onset of diabetes before the age of 5 years may have an additional impact on risk or the time to development of microvascular complications. The mechanism behind this effect of age at onset is not clear, but it has been speculated that puberty, characterized by both rapid growth, hormonal changes, and worsening in glycemic control, may accelerate the processes leading to chronic diabetes complications such as ESRD. Hyperglycemia is crucial and promotes early glomerular hyperfiltration and, in addition, stimulates pathways that may influence the development of diabetic nephropathy (39,40). A role of growth hormone has been indicated (41); however, the postpubertal susceptibility to diabetic nephropathy seems to be persistent during adulthood (9). In addition, sex hormones may be of importance (4244), with studies indicating a higher prevalence of diabetic nephropathy in men (45,46). In this study we could not confirm an association between male sex and ESRD; however, the number of patients with ESRD due to diabetic nephropathy is low and the follow-up time is limited. In summary, at a median of 21 years of follow-up, <1% of patients with childhood-onset type 1 diabetes had developed ESRD due to diabetic nephropathy in this nationwide population-based study. A prepubertal onset of diabetes seems to prolong the time to development of ESRD. These results should be confirmed in studies with longer follow-up, preferably including also patients with a postpubertal onset of diabetes.
Members of the Swedish Childhood Diabetes Study Lars Skogsberg (Luleå), Agne Lindh (Borås), Karin Segnestam (Eskilstuna), Kalle Snellman (Falun), Åke Stenberg and Christer Nilsson (Gällivare), Gunilla Kördel-Engberg (Gävle), Bengt Lindblad (Göteborg), Nils Östen Nilsson (Halmstad), Jan Neiderud (Helsingborg), Herje Hörnell and Åke Lagervall (Hudiksvall), Lars Ivar Hardell (Kalmar), Hans Edenwall (Karlskrona), Gudrun Jonsell (Karlstad), Karin Larsson (Kristianstad), Bengt Hansing (Lidköping), Sture Sjöblad (Lund), Lars Stenhammar (Norrköping), Lennart Hellenberg (Nyköping), AnnaTrela (Skellefteå), Marie Bourdin (Skövde), Britta Björsell (Sollefteå), Susanne Rudberg and Ingemar Zachrisson (Stockholm), Torunn Torbjörnsdotter (Huddinge), Leif Blom (Stockholm), Eva Landgren (Sundsvall), Ragnar Hanås (Uddevalla), Jan Gustafsson (Uppsala), Margareta Blomgren (Visby), Nils Wramner (Trollhättan), Björn Eriksson (Västervik), Björn Jönsson (Ystad), Carl Göran Arvidsson (Västerås), Stig Edvardsson (Växjö), Ulf Ståhle (Ängelholm), Jan Åman (Örebro), Stellan Sjögren (Örnsköldsvik), and Anna-Lena Nilsson (Östersund).
Members of the board of the SRAU
This study was supported by grants from the Swedish Research Council (project no. 07531), the Faculty of Medicine at Umeå University, the Lundström foundation, The Swedish Association for Patients with Kidney Disease, the Swedish Society for Medicine, and the Västerbotten County Council. We thank Lena Mustonen for valuable assistance in processing data from the SCDR.
* Complete lists of Swedish Childhood Diabetes Study members and SRAU board members appear in the APPENDIX. A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Received for publication August 16, 2005. Accepted for publication December 1, 2005.
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