María del Mar Del Águila García
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Antonio M Poyatos Andújar
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Ana Isabel Morales García
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Margarita Martínez Atienza
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Susana García Linares
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Abstract
Background and Aims
Hereditary renal disease (HRD) is still underdiagnosed: although we know aspects related to autosomal dominant polycystic kidney disease (ADPKD), we know little about the incidence and prevalence of other entities such as Alport syndrome. Altogether, HRD can represent 15% of individuals undergoing renal replacement therapy (RRT) or could even be higher.
The advancement of genetics at the healthcare level let to achieve accurate and early renal diagnoses, as well as the incorporation of genetic counseling to families, all of which will result in better management of the disease in its initial stages and the possibility of offering reproductive options that avoid transmission to offspring.
Our objective is to know the performance offered by the implementation of the ERH panel through Next Generation Sequencing (NGS) in our healthcare area.
Method
Observational-descriptive study of 259 probands (141 men / 118 women), mean age of 46 years (30 pediatric / 123 over 50 years), with chronic kidney disease and suspected hereditary cause attended in the specialized consultation of our centers from October 2018 to October 2020. The DNA extracted from leukocytes obtained by venipuncture was processed with Nephropathies Solution version 3 panel (SOPHiA Genetics) according to the manufacturer's protocol. This panel covers the coding regions and splicing junctions of 44 HRD-related genes such as nephrotic syndromes, polycystic kidney diseases, Bartter syndromes, Alport syndrome, CAKUT or tubulopathies (table 1).
The sequencing of the libraries was done in a MiSeq (Illumina Inc), the bioinformatic analysis of the data and annotation of variants was performed using the SOPHiA DDM 5.8.0.3 software, and the revision of variants by consulting the main databases (ClinVar, Exac, HGMD, NCBI, PKD Foundation, LOVD).
Results
The panel was informative (pathogenic or probably pathogenic) in 80/259 patients (31%) and 56/259 cases (21.66%) of variants of uncertain significance (VSI) were detected.
Autosomal dominant polycystic kidney disease accounted for 76.2% of the variants identified (56.2% PKD1, 20% PKD2), following Alport syndrome with 15% and the alterations in the PKHD1 gene associated with renal polycystic disease in its recessive form with about 4% (Figure 1). We have also identified a case of autosomal dominant tubulointerstitial kidney disease associated with the UMOD gene that was not suspected until the genetic study was performed. We highlight that 45% (36/80) of the variants identified as responsible for the renal disease are not yet described. Overall, the most prevalent type of mutation is that which produces displacement in the reading frame or frameshift (Figure 2). Individually, frameshift is the most frequent alteration in PKD1, PKD2 and COL4A5, while for PKHD1, COL4A3 and COL4A4 it is missense.
Conclusion
Our NGS HRD panel a) offers an adequate diagnostic performance at the healthcare level, with definitive results in 1 out of 3 cases and has also allowed the performance of many carrier studies among family members b) is able of diagnosing the most frequent disease, ADPKD and Alport syndrome, as well as unresolved or poorly characterized cases, and c) opens the horizon for new diagnoses, all without increasing costs by outsourcing services. All this makes the genetic study of renal pathology a useful and efficient strategy.
These results encourage us to enhance the resources in this area that we consider to be of strategic value.
Molecular Pathophysiology of Autosomal Recessive Polycystic Kidney Disease