Molecular Review of Suspected Alport Syndrome Patients—A Single-Centre Experience

<b>Background:</b> Alport syndrome (AS) is a clinically and genetically heterogeneous glomerulopathy resulting from pathogenic variants in <i>COL4A3, COL4A4,</i> and <i>COL4A5</i>. Genetic diagnosis is increasingly being conducted using next-generation sequencing (NGS). <b>Methods:</b> Within eight years, we examined a group of 247 Polish individuals and found in total 138 unrelated probands suspected with AS based on clinical course, laboratory findings, and/or family history, as well as the total of 109 family members. We applied a targeted NGS panel to identify the genetic spectrum of AS. Known and novel variants were revealed, and detailed evaluation was performed according to ACMG/AMP guidelines to classify them as pathogenic/likely pathogenic/VUS changes. Identified genotypes were compared with clinical manifestations: hematuria, proteinuria, chronic kidney disease, sensorineural hearing impairment, ocular abnormalities, and hypertension. <b>Results:</b> The molecular background was established in 109/138 probands. Overall, 79 different <i>COL4A3-COL4A5</i> changes (56 known and 23 novel) were revealed. About 97% were SNVs, and only two <i>COL4A5</i> CNVs were identified. In total, 11 recurrent <i>COL4A3-COL4A5</i> variants were observed, including the most frequent <i>COL4A5</i>:p.Gly624Asp, accounting for 31% of X-linked AS. <b>Conclusions:</b> The use of NGS panel has shown considerable promise in the field of AS, increasing diagnostic rate to 79% and reducing time to diagnosis. The phenotype-driven gene panel, specific for genetic diseases in the pediatric population, is an affordable alternative to WGS and WES, offering comparable diagnostic efficacy and supporting its implementation as a first-line genetic test in rare diseases, including AS. Based on the obtained genotype-phenotype correlation, we assessed that NGS allows us to avoid invasive renal biopsy in AS diagnosis. It provides AS confirmation/exclusion, atypical AS identification, symptomatic/asymptomatic monoallelic <i>COL4A3-COL4A5</i> carrier (especially <i>COL4A5</i> females) determination, and inheritance pattern establishment. AS diagnosis confirmation enables clinical course prediction and is crucial for the early introduction of renoprotective treatment with renin-angiotensin-aldosterone system blockade, aimed at slowing the disease progression and estimating the risk in family members, which is important for genetic counselling.