SUMMARY Maturity-onset diabetes of the young (MODY) is a heterogeneous group of monogenic forms of diabetes mellitus with distinct clinical features. Clinical dermatological phenotypes in MODY patients are very rare in literature. This report describes a patient with HNF1A-MODY presenting with necrobiosis lipoidica (NL) and granuloma annulare (GA). A 39-year-old asymptomatic woman, with atypical diabetes diagnosed at age 17, has a confirmed HNF1A mutation on exon 2 (c.392G>A, p.R131Q), classified as Pathogenic by the ACMG guidelines. She has reasonable metabolic control using oral anti-diabetic medications and has no chronic diabetic complications. Clinical and histologic diagnoses of both NL and GA were made. We discuss these conditions and their association with MODY.

SUMMARY Identification of the correct etiology of diabetes brings important implications for clinical management. In this report, we describe a case of a 4-year old asymptomatic girl with diabetes since age 2, along with several individuals in her family with different etiologies for hyperglycemia identified in youth. Genetic analyses were made by Sanger sequencing, laboratory measurements included HbA1c, lipid profile, fasting C-peptide, pancreatic auto-antibodies (glutamic acid decarboxylase [GAD], Islet Antigen 2 [IA-2], and anti-insulin). We found a Gly178Ala substitution in exon 5 of GCK gene in three individuals co-segregating with diabetes, and type 1 diabetes was identified in two other individuals based on clinical and laboratory data. One individual with previous gestational diabetes and other with prediabetes were also described. We discuss difficulties in defining etiology of hyperglycemia in youth in clinical practice, especially monogenic forms of diabetes, in spite of the availability of several genetic, laboratory, and clinical tools.