Progressive deterioration of insulin secretion in Japanese type 2 diabetic patients in comparison with those who carry the S20G mutation of the islet amyloid polypeptide gene: A long-term follow-up study.
Aims/Introduction:  In order to clarify the enhanced β-cell dysfunction in type 2 diabetic patients carrying the S20G mutation of the islet amyloid polypeptide gene (S20G-patients), we first estimated the decline of insulin secretion in Japanese type 2 diabetic patients without the S20G mutation (non-S20G-T2D-patients) by long-term observation, and then compared it with that of the S20G-patients.


METHODS
We followed 70 non-S20G-T2D-patients (body mass index <30 kg/m(2)) for more than 10 years and six S20G-patients for more than 5 years. We measured fasting C-peptide (F-CP) every 1-2 years and carried out a glucagon test at least once during the follow-up period. F-CP and a 5-min value of C-peptide after glucagon injection (5'-CP) were used as the indices of insulin secretion. We excluded patients who had renal dysfunction and/or anti-insulin antibodies in the insulin-treated patients. The individual annual declines were calculated from the slopes of the regression lines between C-peptide levels and duration (years after diagnosis).


RESULTS
The mean individual annual declines of both F-CP and 5'-CP were significantly greater in the S20G-patients than the non-S20G-T2D-patients (F-CP; 0.047 ± 0.026 vs 0.011 ± 0.037 nmol/L/year, P = 0.025, 5'-CP; 0.139 ± 0.055 vs 0.022 ± 0.012 nmol/L/year, P = 0.008).


CONCLUSIONS
We established the annual decline of insulin secretion in the Japanese type 2 diabetic patients by the long-term observation. The results show that the decline of insulin secretion is more rapid in the S20G-patients than the non-S20G-T2D-patients. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00102.x, 2011).
Department of Clinical Laboratory Medicine, Wakayama Medical University, Wakayama, Japan.
Shuhei
S
Morita
Department of Clinical Laboratory Medicine, Wakayama Medical University, Wakayama, Japan.
Setsuya
S
Sakagashira
Department of Clinical Laboratory Medicine, Wakayama Medical University, Wakayama, Japan.
Minoru
M
Ueyama
Department of Clinical Laboratory Medicine, Wakayama Medical University, Wakayama, Japan.
Yoshinori
Y
Shimajiri
Department of Clinical Laboratory Medicine, Wakayama Medical University, Wakayama, Japan.
Machi
M
Furuta
Department of Clinical Laboratory Medicine, Wakayama Medical University, Wakayama, Japan.
Tokio
T
Sanke
Insulin secretion; Islet amyloid polypeptide; Type 2 diabetes