Rare inherited renal disorders, or RIRD, are a genetically diverse group of conditions that include Alport syndrome, nephrotic syndrome, Dent disease, Lowe syndrome, nephrogenic diabetes insipidus and congenital anomalies of the kidney and urinary tract. Individually each is uncommon, but together they contribute substantially to illness and death, particularly among children and young adults. Many patients progress to end-stage renal disease, requiring dialysis or transplantation. Because these diseases are hereditary, a precise molecular diagnosis matters enormously: it can guide treatment, inform family planning, and identify relatives who may carry the same risk.

Next-generation sequencing has transformed the diagnostic landscape for such conditions. Whole-exome sequencing, which reads the protein-coding portions of the genome, can reveal the causative mutation in a substantial fraction of cases. Yet the technology has also created a new bottleneck. Sequencing routinely flags variants of uncertain significance, DNA changes whose effect on protein function is unknown. Under current classification frameworks such as those of the American College of Medical Genetics and Genomics, these variants cannot be used alone to make a diagnosis. Functional evidence, showing that a variant actually disrupts a gene or protein, is often the decisive factor in reclassifying them as pathogenic or benign.

That evidence is scarce for populations that are underrepresented in global genetic databases, and Sri Lankans are a prime example. Variants that are rare or absent in European and East Asian reference cohorts are frequently classified as uncertain simply because nobody has studied them. The Sri Lankan population, with its complex history and distinct genetic architecture, carries variants that may be unique to the island or shared with South Asian neighbors but poorly documented elsewhere. Building population-specific functional data is therefore not an academic luxury; it directly determines whether a family in Colombo receives a definitive diagnosis or an ambiguous report.

The research team, led by K. M. Fathima Rizna and corresponding author Dineshani Hettiarachchi under the senior authorship of Vajira H. W. Dissanayake, set out to functionally characterize variants previously identified through whole-exome sequencing in Sri Lankan patients with clinically diagnosed rare inherited renal disorders. Their strategy had two complementary arms. The first was real-time quantitative polymerase chain reaction, or RT-qPCR, a laboratory technique that measures how actively a gene is transcribed into messenger RNA in patient samples compared with controls. The second was in silico protein modeling, computational methods that predict the three-dimensional structure of a protein and estimate how a specific amino acid change or truncation might destabilize it.

The gene expression results were striking. Several genes showed reduced expression in patient samples: AVPR2, which carries a missense change and encodes the arginine vasopressin receptor 2 central to water balance in the kidney; DAAM2, a gene involved in actin regulation within kidney filter cells; OCRL, mutated in Lowe syndrome and Dent disease; and CLCN5, a chloride channel gene also implicated in Dent disease. In contrast, NPHS2, which encodes the podocin protein essential for the glomerular filtration barrier, and COL4A5, the collagen gene behind X-linked Alport syndrome, showed increased expression. Most notably, DAAM2 expression was strongly downregulated, pointing to a potential functional relevance for the variant of uncertain significance associated with it. DAAM2 variants have previously been shown to cause nephrotic syndrome through disruption of the actin cytoskeleton, making this finding particularly compelling.

The computational modeling told a consistent story. Truncating variants in COL4A5, OCRL and AVPR2 were predicted to cause significant structural disruption, either by removing essential functional domains or by introducing premature stop signals that terminate protein synthesis early. A missense variant in AVPR2 was predicted to affect a transmembrane region of the receptor, the segment that spans the cell membrane and is critical for the receptor to sit correctly in its cellular location and transmit the vasopressin signal. When the team compared these predictions with their laboratory measurements, the two lines of evidence converged: genes whose proteins were predicted to be severely damaged showed absent or reduced expression in patient samples, a pattern consistent with the modeling results.

This convergence is the methodological heart of the study. Neither approach alone is conclusive. Gene expression changes can be secondary consequences of disease rather than causes, and structural predictions depend on the quality of available templates and the assumptions built into tools such as homology modeling and AlphaFold-based structure prediction. But when a predicted structural catastrophe in a protein aligns with measurably reduced transcription of its gene in the tissue of an affected patient, the case for pathogenicity becomes far stronger. Integrating protein modeling with gene expression analysis, the authors argue, provides functional insights that neither method delivers on its own, and supports the potential reclassification of selected variants of uncertain significance.

The clinical implications reach beyond Sri Lanka. For the families enrolled in the study, functional evidence may convert an uncertain result into an actionable diagnosis, enabling cascade testing of relatives, more accurate recurrence risk counseling, and in some cases access to targeted management. For the wider field, the study demonstrates a practical, relatively low-cost workflow, RT-qPCR plus computational modeling, that laboratories in resource-limited settings can deploy to add functional evidence where expensive experimental systems are unavailable. It also adds Sri Lankan variant data to the global pool, gradually correcting the Eurocentric bias that still distorts variant interpretation worldwide.

Limitations remain, and the authors are careful about what their data can and cannot show. Expression measurements were performed on available patient samples rather than in purpose-built disease models, and computational predictions, however sophisticated, ultimately require experimental validation through approaches such as model organism studies or cellular assays before variants can be definitively reclassified. Patient data could not be deposited in public repositories for ethical and privacy reasons, though it is available from the corresponding author on reasonable request. Nevertheless, the study marks a meaningful step toward diagnostic precision for rare inherited kidney disease in a population that has long waited for its genomes to be read on their own terms, and it offers a template other underrepresented populations can follow.

Subject of Research: Functional characterization of genetic variants associated with rare inherited renal disorders in the Sri Lankan population

Article Title: Functional characterization of genetic variants associated with rare inherited renal disorders in the Sri Lankan population

Article References: Rizna, K. M. F., Noordeen, N., Bandara, W. M. M. S., Hewavitharana, H., Hendalage, B., Neththikumara, N., Hettiarachchi, D., & Dissanayake, V. H. W. (2026). Functional characterization of genetic variants associated with rare inherited renal disorders in the Sri Lankan population. Molecular Genetics and Genomics, 301(1), Article 201. https://doi.org/10.1007/s00438-026-02524-x

Image Credits: AI Generated

DOI: 10.1007/s00438-026-02524-x

Keywords: rare inherited renal disorders, whole-exome sequencing, variants of uncertain significance, RT-qPCR, in silico protein modeling, Sri Lanka, kidney genetics, Alport syndrome, nephrotic syndrome, DAAM2, AVPR2, COL4A5

The tool, described in the journal BMC Bioinformatics, is a command-line Java application with a companion web interface that jointly optimises the many interacting variables that determine whether a primer panel succeeds or fails. It balances primer melting temperatures and thermodynamic stability, evaluates linguistic sequence complexity to reject primers drawn from low-complexity or repetitive sequence, models primer-dimer interactions across the entire panel, and applies multiplex-aware, reference-guided specificity screening and repeat masking to prevent off-target amplification. The developers report that the software can produce ultra-high-plex panels containing hundreds of amplicons within seconds to minutes on standard hardware, with a worst-case runtime of about fifteen minutes when the full human reference genome must be screened for specificity.

The scope of the software is deliberately broad. PCRpanel supports workflows from a simple two-primer assay up to designs with hundreds of amplicons, and its authors say it accommodates targets ranging from complete viral genomes and eukaryotic gene families to structural-variant breakpoints and environmental metagenomes. Both gene-specific and universal designs are supported across homologous gene families, a capability that matters when the targets are evolutionarily related genes with highly similar exons. The application requires only Java SE 26 or higher, carries no external dependencies, and is distributed under the GNU General Public License, making it freely available to academic and commercial users without registration or licensing fees.

To demonstrate the tool in a demanding real-world setting, the team turned its attention to Alport syndrome, a hereditary kidney disease most commonly caused by pathogenic variants in the collagen IV genes COL4A3, COL4A4 and COL4A5, with the adjacent COL4A6 also included in the design. These genes present a formidable challenge for primer design: they are large, GC-rich in places, riddled with repetitive elements, and members of a homologous family in which a primer intended for one gene can easily amplify a paralogous sequence from another. Using PCRpanel, the researchers designed 237 primer pairs, comprising 474 individual primers, tiled across all exonic regions of the four genes.

Experimental validation on DNA from four clinical Alport syndrome samples confirmed successful amplification for all 237 primer pairs, a striking result for a fully computational design in a gene family notorious for primer cross-reactivity. Because the exercise was structured as a pilot run aimed at initial validation of the design workflow, sequencing was performed on one representative patient sample. Each primer pool was amplified separately and sequenced at two template dilutions, generating fourteen libraries on the Illumina MiSeq platform; one pool was additionally run as a 50-primer sub-pool during protocol optimisation. Reads were aligned to the GRCh38 human reference genome using the DRAGEN Bio-IT Platform, and coverage was quantified over a 45,372-base-pair exon-restricted target interval derived from the GENCODE v49 annotation. Duplicate marking was deliberately disabled, since amplicon molecules generated by a common primer pair are positionally indistinguishable from PCR duplicates.

The analytical performance reported for that representative sample was strong. Read alignment rates ranged from 94.2 to 99.3 percent, between 77.8 and 96.1 percent of aligned reads fell within the exonic target, and mean target depth per library reached 149.1 to 273.7 times. Critically, the fraction of target bases receiving coverage far above the thresholds needed for confident genotype calling was essentially complete: between 97.9 and 100 percent of target bases reached at least 20-fold depth, and all of those also reached at least 50-fold depth. Measured against the genomic footprint each primer pool was designed to cover, the coverage breadth of each library corresponded to roughly 60 to 130 percent, and the authors note that because each library carried only a single pool, coverage normalised to the complete four-gene target reflects the pooling design rather than amplification performance.

The results also offered an instructive lesson in how parameter choices shape outcomes in repetitive genomic terrain. Under the amplicon-size window and genome-wide specificity screen used for the deposited panel, in silico exonic coverage reached 65.6 percent for COL4A3, 41.4 percent for COL4A4 and 64.4 percent for COL4A6, but only 30.8 percent for COL4A5. A systematic sweep of 1,688 design runs, however, raised coverage to 92.8 percent of the exonic target in a single configuration with repeat masking enforced in full and the genome-wide specificity screen omitted, and placed an amplicon over all 53 exons of the gene across the sweep. The authors argue that this shortfall therefore reflects the specific parameters used for the deposited panel together with the stringency of the specificity screen, not an inherent limit of the method. They provide a step-by-step gap-filling procedure that restricts redesign to uncovered intervals and merges rescue primers into the panel under dimer control, allowing regions that initially fail to be recovered at a stated and explicitly accepted off-target risk.

PCRpanel was benchmarked in silico against two existing tools, NGS-PrimerPlex and Olivar, positioning it within a growing ecosystem of amplicon design software but distinguishing itself by the joint optimisation of sequence complexity, thermodynamic stability, dimer interactions and off-target risk in a single computational pass. That integrated approach is what allows the tool to remain robust even in repetitive or homologous regions, the environments where conventional pipelines most often surrender. The practical consequence is a substantial compression of the design cycle: what previously required iterative manual refinement by an experienced practitioner can now be generated on a desktop computer while the user waits.

The clinical implications of the work extend well beyond Alport syndrome. Targeted amplicon sequencing is a mainstay of molecular diagnostics because it concentrates sequencing capacity on the regions that matter, keeping costs low and interpretation straightforward, but building custom panels has been a bottleneck for laboratories facing rare diseases, local pathogen surveillance, or rapidly evolving viral genomes. The study’s authors emphasise that PCRpanel offers a scalable, platform-agnostic solution for ultra-multiplex PCR panel construction, and the software’s design range, from complete viral genomes to metagenomes, suggests applications in infectious disease genomics, biodiversity monitoring through environmental DNA, and routine diagnostic resequencing alike. Because the tool supports both short-read and long-read sequencing platforms, including Oxford Nanopore Technologies instruments, laboratories are not locked into a single sequencing ecosystem when adopting a panel design.

For the Alport syndrome community specifically, the demonstration that a single computational design can amplify every exon across three established disease genes and a fourth homolog, verified experimentally in patient DNA with sequencing depth far exceeding the requirements for variant calling, offers a template for genetic testing programs in settings where commercial capture kits are financially out of reach. The study was approved by the Ethics Committee of the National Center for Biotechnology in Astana and conducted under the Declaration of Helsinki with written informed consent from all participants. Funded by the Committee of Science of the Ministry of Science and Higher Education of the Republic of Kazakhstan and supported by open access funding from the University of Helsinki, the work reflects a growing effort to move advanced genomic tooling out of well-resourced centers and into broader clinical and research practice. With PCRpanel freely available on GitHub, the barrier to building a custom, several-hundred-amplicon sequencing panel has shifted from weeks of specialist labor to a single afternoon of computation, and the resulting panels, the authors show, hold up under the unforgiving scrutiny of real patient genomes.

Subject of Research: Automated design software for ultra-multiplex PCR primer panels used in targeted amplicon sequencing

Article Title: PCRpanel: automated design of ultra-multiplex PCR panels for targeted amplicon sequencing

Article References: Kalendar, R., Daniyarov, A., Serikzhan, A., Kairov, U., Basharova, D., Toleuzhanova, A., Bekbayeva, A., Romanova, A., & Zholdybayeva, E. (2026). PCRpanel: automated design of ultra-multiplex PCR panels for targeted amplicon sequencing. BMC Bioinformatics. https://doi.org/10.1186/s12859-026-06648-0

Image Credits: AI Generated

DOI: 10.1186/s12859-026-06648-0

Keywords: PCRpanel, primer design software, ultra-multiplex PCR, targeted amplicon sequencing, next-generation sequencing, Alport syndrome, COL4A3, COL4A4, COL4A5, sequence complexity, off-target prediction, bioinformatics tool