MODY caused by a mutation in the insulin gene

Abstract

MODY10 is a rare subtype of MODY diabetes, which caused by heterozygous mutations in the insulin gene INS. There are single descriptions of families with MODY-INS or MODY10 in the literature, its clinical course is not well understood. We present a case of MODY10 in a boy with a history of diabetes mellitus (DM) in three generations (father and paternal grandmother). Proband was diagnosed with diabetes mellitus at the age of 7 years. The glycaemia at the onset of the diabetes was 10.2 mmol/l, HbA1c — 7.6%, islet cell autoantibodies (ICA), insulin autoantibodies (IAA), glutamic acid decarboxylase antibodies (GADA) and islet tyrosine phosphatase 2 (IA2) antibodies (IA2) were not detected. According to the results of the oral glucose tolerance test, fasting blood glucose was 6.5 mmol/l, in 120 minutes 10.3 mmol/l, which corresponded to the diagnosis of impaired glucose tolerance. Diet with restriction of easily digestible carbohydrates was recommended, than gliclazide was added to the therapy, which the proband received for 3 years. At the age of 10, a deterioration in the parameters of carbohydrate metabolism was noted, which insulin therapy was added. Examination at the age of 12 revealed a decrease in C-peptide secretion. The child’s father has a similar phenotype — slowly progressive disorders of carbohydrate metabolism from 6 years old, from 10 years old — insulin therapy. A genetic test was provided, in the child and his father was detected a previously undescribed heterozygous mutation in the INS p.C31W. Thus, in our clinical case, MODY10 was characterized by a milder course than T1DM, but eventually leading to the development of insulin demand, which distinguishes it from the most common forms of MODY. Currently, there is no specific therapy, and the detection of a mutation in the INS gene does not affect therapeutic tactics, however, a correct genetic diagnosis makes it possible to predict the course of diabetes and provide genetic counseling to the family.