Aim: To analyse the fasting proinsulin levels in first degree relatives of patients with insulin-dependent diabetes mellitus (IDDM) with different risk for developing the disease.
Patients and methods: Non siblings first degree relatives, 33, of IDDM patients were separated into three groups with different risk for developing IDDM: Group 1, 14 first degree relatives (eight male/six female), aged from 18 to 57 years, normal first phase insulin release (FPIR) in the intravenous glucose tolerance test, negative ICA; Group 2, 11 first degree relatives (six male/five female), aged from 16 to 62 years, normal FPIR and ICA < 20 JDF U; Group 3, eight first degree (six male/two female), from 16 to 52 years, FPIR diminished and ICA > 20 JDF U. All patients had normal oral glucose tolerance test at the initiation of the study. We tested fasting proinsulin (PRO) and insulin (IRI) levels by radioimmunoassay (RIA) and the PRO/IRI ratio.
Results: Four first degree from the group 3 developed IDDM after 2-32 months. No differences were observed in-fasting PRO levels and PRO/IRI ratio between the groups. However, the PRO (21.7 +/- 5.8 pmol/l) and PRO/IRI ratio (0.29 +/- 0.10) levels of the subjects who developed IDDM were significantly higher (P < 0.05) than those values obtained in subjects who did not developed the disease.
Conclusion: these data indicate that fasting PRO levels and the PRO/IRI ratio may be an additional marker in post-puberty first-degree relatives of IDDM patients with immunological and metabolic evidence of high risk for developing the disease.