Ketosis-prone diabetes (KPD) is a heterogeneous syndrome characterized by patients who present with diabetic ketoacidosis or unprovoked ketosis but do not necessarily have the typical phenotype of autoimmune type 1 diabetes. In this case report, we expose the difficulties in the diagnosis aetiology of A- β- ketosis-prone diabetes (KPD) in a 22-year-old North-African woman presenting with diabetic ketoacidosis. Her initial glycaemia was at 17.2 mmol/L and glycated haemoglobin (HbA1c) was moderately increased at 7.6% with no clinical evidence of other precipitating illnesses or stressful events. Her baseline and glucagon-stimulated serum C-peptide levels were below the detection limit at the time of admission. All anti-pancreatic antibodies were negative and pancreatic imaging was normal. Direct sequencing of HNF1A, HNF4A, INS, IPF1, NEUROD1 and PAX4 genes were performed and showed three mutations in HNF1A (I27L), NEUROD1 (A45T) and PAX4 (H321P). HLA typing showed the genotype DQB1*03- DRB1*11/DQB1*03-DRB1*13. Based on that data, type 1A diabetes mellitus (DM) could be excluded. However, criteria of fulminant type 1 DM are mostly filled but difficult to be confirmed and the MODY (Maturity Onset diabetes of the young) hypothesis could not be ruled out as other genes may be involved. Our observation highlights the difficulties of understanding the aetiology of A- β- KPD with sudden-onset although clinical, imaging, immunologic and genetic data are available.