Background
and Aim: Latent autoimmune diabetes in adults (LADA)
is a slowly progressive form of adult-onset type 1 diabetes characterized by
the presence of circulating islet autoantibodies, classically glutamic acid
decarboxylase antibody positivity (GADA). Even though in newly detected
autoimmune diabetes, GADA concentration is reported to inversely correlate with
beta-cell function, in classical type 1 diabetes, the islet autoantibody
concentration is recognized to decrease over time due to loss of beta cell mass
and associated antigenic drive. Over time in patients with LADA, we hypothesize
the GADA concentrations may decrease due to declining beta-cell mass. We
therefore aimed to compare GADA concentration in LADA diagnosed early versus
late. Methods: One hundred patients with LADA diagnosed at
the Royal Melbourne Hospital were analysed for GADA concentration and the
timing of detecting islet autoimmunity. GADA concentration was compared in LADA
detected ‘Early’ (within 10 years of diabetes diagnosis) compared to ‘Late’
(after 10 years of diabetes diagnosis).
Results: The median age of the entire cohort of LADA
was 47.5 years (n=100, M=54, F=46).
In the ‘Early’ detection group (n=51) the median time to detection of
islet autoimmunity 0.7 years) whilst in the ‘Late’ group (n=49) the median time
to detection of islet autoimmunity 12.9 years. There was no difference in the median age at diagnosis of
diabetes in the ‘Early’ group (median age 47.5 years) versus the ‘Late’ group
(median age 47.6years). (GADA concentration was significantly lower in the ‘Late’
group compared to the ‘Early’ group (median IQR 61 [42-89] vs. 38 [12-78],
P=0.033). There was no significant difference in IA2 Ab positivity or
concentration between the two groups.
Conclusion:
Immunity to GAD may lessen with longer duration
LADA. In long standing diabetes in adulthood lack of islet autoantibody
positivity may not preclude the possibility of autoimmune diabetes.