Insulin gene (
INS) mutations have recently been described as a common cause of permanent neonatal diabetes (PNDM) and a rare cause of diabetes diagnosed in childhood or adulthood [
1‐
4]. Heterozygous mutations in
INS account for 15 - 20% of cases of PNDM [
4,
5]. Gene discovery can lead to recognition of novel phenotypes [
6] and recognition of novel clinical subgroups. For example, MODY was initially clinically defined as autosomal dominantly inherited, non insulin dependent, early-onset diabetes, but now there are at least eight distinct genetic subgroups of MODY, most of which have a discrete phenotype and specialized treatment needs [
6]. An R46Q
INS mutation was recently described in a Norwegian study of 62 probands fulfilling conventional MODY criteria. In addition, they examined 223 patients from the population-based Norwegian Childhood Diabetes Registry and found an R55C
INS mutation. One hundred blood donors were screened negative for these mutations [
7]. The Italian study group on early onset diabetes has detected two
INS mutations (A23S and G23S) in children negative for 5 type 1 diabetes (T1D) autoantibodies [
1]. In addition, an R6C mutation was identified in an English MODY family and a L68M mutation was described in a family of Turkish origin with young-onset type 2 diabetes [
3]. Furthermore, a recent screening for
INS mutations in 252 patients diagnosed clinically with T1D between 6 months and 17 years of age identified 2 de novo heterozygous mutations G32S and R89C among the 25 (8%) antibody-negative patients [
8]. To our knowledge, no studies have screened women with gestational diabetes mellitus (GDM) for
INS mutation. GDM was defined as an abnormal glucose tolerance diagnosed for the first time in pregnancy.