Miguel Servet, Zaragoza (Marta Ferrer, Gracia M Lou), H. addition to the classical IAA, GADA and IA2A autoantibodies to improve the accuracy of type 1 diabetes analysis. Methods Four hundred Spanish pediatric individuals with recent-onset diabetes (mean age 8.9 3.9 years) were analyzed for IAA, GADA, IA2A and ZnT8A pancreatic-autoantibodies and HLA-DRB1 alleles. Individuals without autoimmunity and those with only ZnT8A positive were screened for 12 monogenic diabetes genes by next generation sequencing. Results ZnT8A screening improved the number of autoantibody-positive individuals from 373 (93.3%) to 377 (94.3%). An isolated positivity for ZnT8A allowed diagnosing autoimmune diabetes in 14.8% (4/27) PP242 (Torkinib) of pediatric individuals negative for the rest of the antibodies tested. At least 2 of the 23 individuals with no detectable autoimmunity (8%) carried heterozygous pathogenic variants: one previously reported missense variant in the gene (p.Gly32Ser) and one novel frameshift variant (p.Val264fs) in the gene. One variant of uncertain significance was also found. Service providers of pathogenic variants experienced HLA-DRB1 risk alleles for autoimmune diabetes and medical characteristics compatible with type 1 diabetes except for the absence of autoimmunity. Summary ZnT8A determination enhances the analysis of autoimmune diabetes in pediatrics. At least 8% of pediatric individuals suspected of type 1 diabetes and with undetectable autoimmunity have monogenic diabetes and may benefit from the right diagnosis of the disease by genetic study. Intro Type 1 diabetes (T1D) is an organ-specific autoimmune disorder caused by the damage of insulin-producing pancreatic -cells leading to an absolute insulin deficiency. Although T1D can be diagnosed at any age, it is probably one of the most common chronic diseases of child years. Peaks in demonstration happen between 5C7 years of age and at or near puberty [1]. The presence of autoantibodies against several pancreatic islet molecules in response to the autoimmune process is, to day, the best predictive and diagnostic marker for T1D [2]. The autoantibodies that have been of most interest from a medical and study perspective are islet-cell cytoplasmic autoantibodies (ICA), those against the 65kD isoform of glutamic acid decarboxylase (GADA), the pancreatic tyrosine phosphatase-like molecule IA-2 (IA-2A) and insulin autoantibodies (IAA). More recently, Zinc transporter 8 protein islet autoantibodies (ZnT8A) have also been recognized [3]. Nevertheless, not all individuals with suspected T1D display evidence of autoimmunity on the basis of the above-mentioned markers [4]. The result in of the autoimmune process associated with T1D is determined by complex relationships between several genetic loci (nearly 40 loci explained so far) and environmental factors [1]. Susceptibility to and PP242 (Torkinib) safety against the development of autoimmune diabetes are primarily associated with the highly polymorphic sequences of the HLA class II genes on chromosome 6p21. In Caucasians, HLA haplotypes DRB1*03:01-DQA1*05:01-DQB1*02:01 and DRB1*04-DQA1*03:01-DQB1*03:02 confer the greatest susceptibility, while the DRB1*15:01-DQA1*01:02-DQB1*06:02 haplotype provides disease safety [5]. Monogenic diabetes (MD) is definitely a clinically and genetically heterogeneous disease that includes maturity onset diabetes of Tmem9 the young (MODY) and infancy-onset and neonatal diabetes mellitus, which are characterized by practical problems of pancreatic -cells resulting in insulin deficiency and moderate to severe hyperglycemia in early existence [6]. It accounts for at least 1C2% of all instances of diabetes. MODY, the most common type of monogenic diabetes, is an autosomal-dominant form of non-autoimmune diabetes, typically diagnosed before 25 years of age. More than 12 different genes have been associated with MODY. Pathogenic variants in and genes account for approximately 80% of all MODY instances followed by and genes representing about 10% and 6% respectively, although percentages can differ dramatically country-to-country due to different recruitment biases. Pathogenic variants in the remainder of the genes are rare forms of MODY [7]. Given that the medical features of MD are often non-specific, it is estimated that around 80% of MD instances remain undiagnosed or are misdiagnosed as type 1 or type 2 diabetes [7]. Recognition of the correct etiology of diabetes is vital for medical management, therapeutic choice and prognosis, as well as for genetic counseling, when relevant [8]. The main PP242 (Torkinib) objective of this study was to search, in a cohort of Spanish pediatric patients suspected of T1D, whether a monogenic form of diabetes could be recognized in cases with absence of immunological markers at the onset of the disease. We also aimed to assess the further value of ZnT8A screening in addition to the classical IAA, GADA and IA2A autoantibodies for the diagnosis of autoimmune diabetes. Methods Patients We recruited 400 unrelated pediatric patients with recent-onset type 1 diabetes diagnosed according to the International Society for Pediatric and Adolescent Diabetes (ISPAD) criteria [9] who were less than a week on insulin replacement therapy. Participants were recruited from seven referral hospitals in Spain between 2012 and 2017 (mean onset age 8.9 3.9 years, 47.3% female). In all cases HLA-DRB1 alleles.