[Latent autoimmune diabetes in adults in Iceland: prevalence, phenotype and relatedness]

Ninety percent of diabetic individuals in Iceland suffer from type 2 diabetes mellitus. Antibodies against ss-cell components characterise type 1 diabetes, but these antibodies are also found in type 2 diabetic individuals, defined as latent autoimmune diabetes in adults or LADA. The purpose of this investigation was to estimate the prevalence of LADA in Iceland and to describe the phenotype and relatedness of these individuals.

A list of individuals diagnosed with type 2 diabetes was generated from outpatient clinic lists and the Reykjavik Study of the Icelandic Heart Association. A genealogy database (Book of Icelanders; deCODE Genetics) was used to identify all individuals related to these index cases within six meioses. This method identified 950 type 2 diabetic individuals during the years 1998-2000. We analyzed their phenotype and measured glutamic acid decarboxylase antibody (GAD). Kinship coefficient was used to compare the relatedness of those with antibodies to GAD to the relatedness of all type 2 diabetic individuals in the study.

10.1% of men and 9.3% women had measurable antibodies against GAD (non-significant difference). The mean age of GAD positive and GAD negative individuals was comparable (67.1 +/- 10.7 and 68.0 +/- 11.3; years +/- SD). Body mass index was significantly lower (p=0,02) for the GAD positive individuals or 28.2 kg/m(2) (27.2-29.2; 95% CI) vs. 29.7 (29.3-30.1). Of the GAD positive individuals, 47% +/- 9% (95% CI) had the metabolic syndrome as defined by WHO compared with 60 +/- 4% of the GAD negative individuals (p=0.02). The kinship coefficient for GAD positive individuals (n=94) was 6.00x10(-4) compared with 3.93x10(-4) +/- 8.3x10(-5) for 500 random samples (each of 94 individuals) of the whole cohort (p=0.008).

About 10% of Icelandic type 2 diabetic individuals have antibodies against GAD, which is comparable to the results of other investigators. Icelandic GAD positive type 2 diabetic individuals have less frequently the metabolic syndrome than other type 2 diabetic individuals and GAD positive individuals are significantly more related to each other than type 2 diabetic individuals in general.