#817 Genetic analysis in a group of patients with persistent isolated microscopic hematuria

Abstract Background and Aims Autosomal dominant Alport syndrome (ADAS) is a genetic disease caused by pathogenic variants in COL4A3 and COL4A4 genes. ADAS is the main cause of isolated persistent microscopic hematuria (PMH). However, other diseases like IgA nephropathy (IgAN) can present with PMH. Establishing a precise genetic diagnosis in this type of patients would avoid invasive studies like kidney biopsies. In this study we performed a comprehensive genetic test in a cohort of patients with isolated PMH to evaluate the frequency of ADAS or other genetic abnormalities and compare the clinical characteristics of patients with or without ADAS Method Fifty-two patients with PMH were included in the study. PMH was defined by the presence of 3 or more dysmorphic red blood cells per field in at least 5 consecutive urine sediments and a time-averaged proteinuria <1 gr/day. Average proteinuria was determined for every 6 months of follow-up and time-averaged (TA) proteinuria represented an average of the mean proteinuria measurements in each 6-month period. A comprehensive genetic study using whole exome next-generation sequencing was performed. One hundred and one genes related to familial hematuria, focal segmental glomerulosclerosis and cystic kidney diseases were analyzed. Patients with known secondary causes of hematuria were excluded. The baseline clinical characteristics of patients with and without ADAS were compared. Patients with pathogenic variants in COL4A5 gene were excluded of this analysis. Results Thirty-one (60%) patients were diagnosed with ADAS (16 patients with pathogenic variants in COL4A3, 15 in COL4A4), 3 (6%) patients (2 women, 1 man) presented pathogenic variant in COL4A5 gene, and the genetic study was negative in the remaining 18 patients (variants of unknown significance in COL4A3 or COL4A4 were found in 3 of the latter). No other genetic abnormalities were detected in the panel of 101 genes. Table 1 shows the baseline clinical characteristics of patients with and without ADAS. Patients with ADAS presented a higher TA proteinuria [0.23 (0.11-0.6) vs 0.08 (0.05-0.16), p = 0.01], and a more frequent familial history of isolated microscopic hematuria (76% vs 40%, p = 0.01) chronic kidney disease (CKD) (44% vs 0%, p = 0.01) or end stage kidney disease (32% vs 0%, p = 0.02). In the multivariate analysis, only a family history of microscopic hematuria was associated with ADAS: OR 5.62 (1.25-25.49, p = 0.02). Conclusion ADAS is the most common cause of PMH. A genetic study should be the first diagnostic step in order to obtain a precise cause of the disease and avoid invasive procedures. A family history of microscopic hematuria and of CKD increases the likelihood of ADAS prior to the performance of genetic test.