Oligomeganephronia in a 29-Year-Old Pregnant Woman

Introduction: Oligomeganephronia (OMN) is a congenital anomaly characterized by reduced nephron number, glomerulomegaly and tubulomegaly. It is a pediatric disease, while late-onset OMN is very rare. We present a case of adult onset OMN at our institute with kidney disease during pregnancy. Case Description: A 29-year-old female with unexplained stage IV chronic kidney disease (CKD) was referred to us for kidney biopsy. Her clinical history dates to 2019, during a pregnancy, when she was noted to have a creatinine of 1.9 with sub-nephrotic proteinuria. Workup done including complement levels, anti-nuclear and anti-neutrophil cytoplasmic antibodies, myeloperoxidase and proteinase-3 antibody were negative. On physical exam, she had height 64", weight 174 lbs, BMI 29.87 kg/m2, blood pressure 116/78 mmHg. Cardiac and pulmonary auscultation were normal. She had no edema. She was started on angiotensin receptor blocker. Her kidney function gradually worsened and a kidney biopsy was done in February 2023 showing moderate chronicity with no evidence of an immune complex-mediated process. Supportive measures were continued. As kidney function continued to decline 1 year later, repeat biopsy was done in March 2024 showing findings consistent with histological diagnosis of OMN (images below). Discussion: OMN is a congenital anomaly characterized by reduced nephron number due to arrested development of metanephric blastema at 14-20-week gestation. Patients are usually born with low birth weight. Early-onset type present at a young age with polyuria, polydipsia, or proteinuria and usually progress to ESRD early in life. Late-onset type is rare; and usually present as asymptomatic proteinuria. Disease pathophysiology is unclear. OMN does not cause any phenotypic characteristics, thus, renal biopsy is crucial for diagnosis. Histologically, OMN is characterized by a reduced number of glomeruli, glomerulomegaly, and tubulomegaly. Over time, histologic changes of fibrosis will be seen. There is no effective treatment for OMN at present. The focus is on supportive measures to reduce glomerular hyperfiltration and delay disease progression.