Abstract Disclosure: D. Taha: None. R. Thirunagari: None. A. Adhikari: None. Background: The BLK gene is a tyrosine protein kinase involved in cell proliferation and differentiation. It has been identified as a modulator of beta cell function and plays a role in the regulation of insulin synthesis and secretion. We describe the case of a patient presenting with prediabetes associated with a heterozygous c.1366 C>T of the BLK gene. Case Report: We report a 10 year old Asian female who presented with a hemoglobin A1c (HbA1c) level of 6.1% (4.0-5.7), within prediabetes range. Her weight was 44 kg (Z score 1.34), height 148.2 cm (Z score 1.52) and BMI was 20 kg/m2 (85th percentile; Z score 1.06). She had no acanthosis nigricans by exam and she was at early Tanner stage 2 of puberty. Initial evaluation revealed normal C-Peptide level of 2.1 ng/mL (0.9-6.9), normal insulin level of 21.1 mcUnits/mL (3 - 25). She had normal complete blood count and comprehensive metabolic profile, and normal thyroid function tests. Glutamic acid decarboxylase (GAD65) antibodies and islet cell antibodies were negative. She had an oral glucose tolerance test which revealed a fasting glucose level of 101 mg/dL and a 2-hour glucose level of 158 mg/dL. Lipid profile was normal. She was advised regarding healthy lifestyle changes and her HbA1c level was stable. She was lost to follow-up until 16 years of age when she presented with irregular menstrual cycles and was diagnosed with polycystic ovary syndrome. Her HbA1c was elevated at 6.3% with a normal insulin level. Cortisol and thyroid function tests were normal. Pancreatic antibodies including GAD65, IA-2, insulin antibodies, islet cell antibodies, and zinc transporter 8 antibodies, were negative. C-peptide level was normal at 4.3 ng/mL (1.1-4.4). Family history was significant for patient’s father and paternal grandmother having diabetes and taking Metformin. Patient’s father was diagnosed with diabetes at 13 years of age. Maturity onset diabetes of the young (MODY) panel/ sequencing and deletion/duplication analysis was performed at GeneDx and revealed that she is heterozygous for a c.1366 C>T; p.Arg456Cys (R456C) variant in exon 13 of the BLK gene. This variant has not been previously published as a pathogenic or benign variant to our knowledge. No additional variants were identified in any of the MODY genes on this panel (ABCC 8, APPL1, CEL, GCK, GLUD1, HADH, HNF1A, HNF 1B, HNF4A, INS, KCNJ11, KLF11, NEUROD1, PAX4, PDX1). Conclusion: Variants of the BLK gene have been reported in association with autosomal dominant MODY, type 11. We report a pediatric patient presenting with MODY prediabetes associated with a heterozygous c.1366 C>T; p.R456C variant in the BLK gene. To our knowledge, this variant has not been previously reported in MODY patients. We propose that this is a pathogenic variant and review this rare MODY form. Presentation: Saturday, June 17, 2023
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