The incidence, sex, seasonal and geographical patterns of juvenile-onset insulin-dependent diabetes mellitus (j.i.d.m.) were studied retrospectively on one third of the Danish population 1970-1974. The j.i.d.m. incidence remained fairly constant during the study period, the average being 13.2 per 100000 per year. The total number of boys exceeded the number of girls by 27%. A marked peak of incidence was found at 12-14 years, earlier for females than for males. A seasonal variation in onset (diagnosis) of j.i.d.m. was observed with the lowest number of new cases in May-July. The j.i.d.m. incidence seemed to show socioeconomic differences, being highest in those parts of the survey area with lower status.

The incidence of IDDM in the age group over 30 years was estimated in a historical prospective study, using clinical and biochemical measurements at onset as criteria for classification. The study population, nearly one million, represents 20% of the Danish population. The degree of ascertainment was > 99%. One thousand two hundred and forty patients were treated with insulin during the study period (1973-77). Based on the clinical and biochemical variables, the patients were classified into three groups: insulin-dependent diabetes mellitus (IDDM) accounted for 16.2%, insulin-treated diabetes mellitus for 54.1% and short-term treated diabetes mellitus for 29.6% of the total insulin-treated group. The incidence of IDDM in the age group over 30 years at onset was 8.2 100,000(-1) year-1. The cumulative incidence rate (0-90 years) was 1.5-1.6 per cent. The present study indicates that IDDM may develop at any age. Thus the life-time risk of developing IDDM is higher than hitherto expected.

The relationship between the HLA system and insulin-dependent diabetes mellitus (IDDM) is reviewed. Data compiled by the HLA and Disease Registry reveal that HLA-B8 and/or Dw3 are associated with IDDM in all populations studied so far, but further population studies in non-Caucasian populations should be performed. In Caucasians, HLA-Dw2 renders protection against IDDM while HLA-Dw3 and Dw4 are associated with susceptibility to IDDM. The exact mode of inheritance of susceptibility to IDDM remains to be established. Involvement of at least two genes is likely. Heterogeneity of IDDM is highly possible and should be a matter of major interest in diabetes research.

OBJECTIVE—The incidence rate of childhood type 1 diabetes is thought to be increasing; however, Danish studies have not confirmed this. Using a national diabetes register initiated in 1996 and two previous regional incidence studies, we studied the age-specific incidence of type 1 diabetes over 30 years. Here, we describe the incidence rates of type 1 diabetes in Danish children from 1996 to 2000 and evaluate trends in age-specific incidence rates from 1970 to 2000. RESEARCH DESIGN AND METHODS—A nationwide registration of all newly diagnosed cases of type 1 diabetes among children under the age of 15 years was established in Denmark in 1996. Incidence rates of type 1 diabetes in Denmark were obtained from this register. Age-specific incidence rates were compared with data collected from 1970 to 1976 and from 1980 to 1984, both population-based studies using existing national routine registration of hospitalizations within the survey areas. Population data were obtained from Statistics Denmark. RESULTS—During the study period, 1,421 Danish children developed type 1 diabetes before the age of 15 years. The incidence rates by age-groups were: 12.7, 19.4, and 26.3 for the 0–4, 5–9, and 10–14 years age-groups, respectively, and 19.5 for the 0–14 years age-group per 100,000 in the period 1996–2000. An age-period-cohort analysis showed a modest drift effect (yearly increase) of 1.2% (0.7–1.8) from 1970 to 2000, and a significant birth cohort effect with an increased risk for children born after 1985 was observed. CONCLUSIONS—The incidence rate of type 1 diabetes is rising in children living in Denmark. The steep increase in the youngest age-group was explained by the increased risk for cohorts born at the beginning of the 1980s.

Sixty-one juvenile, insulin-treated diabetics below 50 years of age with a duration of diabetes mellitus longer than 10 years underwent impedance audiometry with determination of stapedius reflex thresholds at 500 Hz, 1, 2, and 4 kHz, conventional pure tone and speech audiometry, and high-frequency audiometry up to 20 kHz. The results were compared with a normative material of non diabetic subjects selected after exactly the same criteria. No significant differences in hearing or stapedius reflex thresholds were found. Among half of the subjects there was a diabetic retinopathy. A comparison between those with and those without retinopathy did not reveal any significant difference in audiological findings. Even subjects with severe diabetic complications and almost life-long diabetes had normal hearing. Recent investigations on plasma-lipoids have discussed the possibility that insulin might prevent a premature ageing of hearing which has been reported by other authors. It is concluded that no statistical data exist that confirm a correlation between hearing impairment and diabetes.