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

Background

Alport syndrome (AS) is a clinically and genetically heterogeneous glomerulopathy resulting from pathogenic variants in COL4A3, COL4A4, and COL4A5. Genetic diagnosis is increasingly being conducted using next-generation sequencing (NGS).

Methods

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.

Results

The molecular background was established in 109/138 probands. Overall, 79 different COL4A3-COL4A5 changes (56 known and 23 novel) were revealed. About 97% were SNVs, and only two COL4A5 CNVs were identified. In total, 11 recurrent COL4A3-COL4A5 variants were observed, including the most frequent COL4A5:p.Gly624Asp, accounting for 31% of X-linked AS.

Conclusions

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 COL4A3-COL4A5 carrier (especially COL4A5 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.