Sex differences in secondary attack rate of IDDM to siblings of probands through older ages. Pittsburgh Etiology of IDDM Study

Incidence of new onset type 1 diabetes in siblings of index cases with type 1 diabetes within the first 11 years in Turkish children

AIM

Although newly diagnosed type 1 diabetes mellitus (T1DM) occurs sporadically in childhood, there is an increased risk of T1DM for first-degree relatives of patients that endure into the advanced years. Determination of T1DM incidence in siblings of children with T1DM helps predict the development of new cases. This study focuses on the incidence of the disease in siblings of children with T1DM.

METHOD

A total of 1497 siblings of 850 children (403 female; 447 male) diagnosed with T1DM between 2007 and 2018 years were retrospectively screened for T1DM. The patients were divided into four onset age groups: 0-4, 5-9, 10-14 and ≥15. The annual incidence was calculated for the region.

RESULTS

A total of 34 siblings diagnosed with T1DM were detected. The incidence relating to the years investigated was between 7.42 and 11.73/100 000 for the newly diagnosed indexes while it ranged between 0 and 5.8% for siblings. The 5-9 year group was the most commonly diagnosed onset age group in index (n = 312) and siblings (n = 20). For siblings, the male sex and 5-9 aged at diagnosis of index were significant risk factors for development of T1DM (OR:2.35 and 2.85).

CONCLUSION

This study shows that in the first years following the diagnosis of an index, incidence of T1DM among the siblings can rise up to 5.8%, and the age group of 5-9 in the index and the male sex in the sibling are the most important risk factors. These findings show that the risk for siblings of children with T1DM remarkably increases in the first years after diagnosis in index cases.

Familial clustering of beta-cell autoimmunity in initially non-diabetic children

BACKGROUND

Type 1 diabetes is characterised by familial aggregation. We set out to explore whether beta-cell autoimmunity, which is considered to precede clinical disease, also shows familial clustering.

METHODS

Tests for HLA DQB1 alleles (*02, *0301, *0302, *0602) and islet cell autoantibodies (ICA) were performed on 5836 children from 2283 families. When a child tested positive for ICA, all his/her previous or subsequent samples that were available were also tested for insulin autoantibodies (IAA), antibodies to glutamic acid decarboxylase (GADA) and antibodies to the IA-2 protein (IA-2A).

RESULTS

Forty-four families were observed to have two or more children positive for at least ICA. This proportion (1.9%) was almost five times higher than expected (0.4%; p < 0.001). The frequency of multiple (>/=2) autoantibodies also showed familial aggregation, the observed proportion (0.39%) being three times that expected (0.13%; p < 0.001). In 72.7% of the families with at least two ICA-positive siblings, the children with autoantibodies had the same HLA DQB1 genotype. The median age difference between the ICA-positive children within the same family was 3.3 years (range 0.0-10.5 years), and the median time interval in the appearance of ICA within the family was 1.6 years (range 0.0-3.2).

CONCLUSIONS

beta-cell autoimmunity, as defined by the appearance of ICA, demonstrates familial aggregation, although the antibodies do not appear in close temporal proximity or at an identical age within the same family. The HLA-DQB1 genotypes are more often identical in siblings with autoantibodies than in other siblings.

Increased risk of diabetes among relatives of female insulin-treated patients diagnosed at 15-34 years of age

AIMS

This study aimed to determine the risk of developing diabetes among relatives of patients diagnosed between 15 and 34 years of age who were treated with insulin. Our second aim was to determine whether there was a difference in risk of diabetes between relatives of male and female patients.

METHODS

A questionnaire was sent to patients in the Diabetes Incidence Study in Sweden registry diagnosed between 1983 and 1993 to determine the presence of first-degree relatives with diabetes.

RESULTS

In 3087 index patients treated with insulin, 17.8% (95% confidence interval 16.5, 19.2) had a first-degree relative (excluding offspring) treated with insulin, the frequency being higher in female (19.8%) than in male (16.5%, P = 0.018) patients. A total of 10.7% had a parent treated with insulin. The prevalence of insulin-treated diabetes was higher among parents of female (12.5%) than of male (9.5%), insulin-treated index patients (P = 0.0068). A similar difference was observed using life table analysis (P = 0.0025), which also showed that the risk by 63 years of age was 7.6% for parents of female and 4.9% for parents of male insulin-treated index patients. In insulin-treated index patients, 8.4% had a sibling with insulin-treated diabetes.

CONCLUSIONS

We conclude that the risk for relatives of women with insulin-treated diabetes was higher than for relatives of insulin-treated male patients. We suggest that greater genetic susceptibility is required for females compared with males in the 15-34 age group in order to develop diabetes and hence females might carry more diabetes genes since more of their relatives also develop diabetes.

Cumulative incidence of type 1 diabetes in 10,168 siblings of Finnish young-onset type 1 diabetic patients

The aims of our analysis were to obtain the empirical risk estimates for type 1 diabetes in the siblings of a Finnish population-based cohort of childhood-onset diabetic patients and search for demographic and other factors predicting the risk of type 1 diabetes in siblings. We defined the diabetes status of all siblings of all probands who are included in the nationwide register of Finnish cases for whom type 1 diabetes was diagnosed before age 18 years between 1965 and 1979. Siblings' diabetes status was ascertained by a record search of nationwide registries through 2001, and the type of diabetes and date of its manifestation were obtained from medical records. The total number of person-years during the follow-up was 405,685. Of the 10,168 siblings at risk, 647 (6.4%) had been diagnosed with type 1 diabetes by 2001. The cumulative incidence of type 1 diabetes by ages 10, 20, 30, 40, and 50 years in all siblings was 1.5, 4.1, 5.5, 6.4, and 6.9%, respectively. A young age at diagnosis in the index case, paternal young-onset diabetes, male sex, and older parental age at delivery considerably increased the risk of type 1 diabetes for siblings. This large prospective family study of type 1 diabetes in siblings of childhood-onset diabetic patients provides reliable empirical estimates for the sibling recurrence risk.

HLA-DQB1-defined genetic susceptibility, beta cell autoimmunity, and metabolic characteristics in familial and nonfamilial insulin-dependent diabetes mellitus. Childhood Diabetes in Finland (DiMe) Study Group

Familial aggregation of insulin-dependent diabetes mellitus (IDDM) is a common phenomenon, but the reasons behind it are poorly understood. To investigate whether there is heterogeneity between familial and nonfamilial forms of IDDM we compared genetic, immunological, and clinical characteristics of diabetic children with and without an affected first-degree relative in a population-based series of Finnish children with IDDM. The frequencies of HLA-DQB1 genotypes known to be associated with high (DQB1*0302/0201) or moderate (*0302/x) IDDM risk in the Finnish population were increased, while the proportions of DQB1 genotypes associated with low or decreased risk for IDDM were reduced in the 121 familial cases as compared with the 574 nonfamilial cases (32.7 vs. 21.3%, 41.3 vs. 35.9%, 18.3 vs. 31.4%, and 7.7 vs. 11.4%, respectively; P = 0.002). The frequencies and serum concentrations of islet cell antibodies, insulin autoantibodies, and antibodies to the 65-kD isoform of glutamic acid decarboxylase were similar at diagnosis in the familial and nonfamilial cases. The 31 first-affected cases in the multiple case families were younger at diagnosis than the nonfamilial cases (6.9 vs. 8.5 yr; P < 0.05). The 90 second-affected familial cases had less severe metabolic decompensation at diagnosis than either the first-affected familial or nonfamilial cases. In conclusion, familial aggregation of IDDM in Finland is at least partly explained by a higher frequency of IDDM susceptibility genes in families with multiple affected individuals. The lack of differences in autoantibody levels between the familial and nonfamilial cases indicates homogeneity rather than heterogeneity in the pathogenetic process of beta cell destruction.

Long-term risk of IDDM in first-degree relatives of patients with IDDM

Due to a short observation period previous studies may have underestimated prevalence and recurrence risk of IDDM in relatives of IDDM patients. To obtain a more exact life-time risk estimate we identified 310 probands, representative of Danish IDDM patients, characterized by current age more than 50 years, age at onset 40 years or less and diabetes duration of more than 30 years. Family data were obtained from 291 probands. Mean "observation" times (age) (+/- SD) for siblings (n = 553) and offspring (n = 359) were 59.4 +/- 16.1 years and 33.8 +/- 8.8 years, respectively. Of the probands 73 (25.1%) had at least one first-degree relative with IDDM. Seventeen percent had at least one affected sibling. An increase from 10.4% to 22.4% of having first-degree relatives with IDDM among probands with age at onset below 20 years was observed during the period from proband at age 21 years up to 1 September 1992. Among affected siblings 48% of the second cases were affected more than 10 years after the first affected sibling. Using the life-table method cumulative recurrence risks from time of birth were calculated for siblings up to age 30 years of 6.4% and up to age 60 years of 9.6%. For offspring the risk up to age 34 years was 6.3%. In addition, we present a life-table method evaluating the cumulative recurrence risk from time of onset in the proband, as this is the most relevant when giving genetic counselling. In conclusion, the long-term risks of IDDM in siblings and offspring are high compared to that shown in previous reports.