Genotypic analysis of a large cohort of patients with suspected atypical hemolytic uremic syndrome

Implementation of a Kidney Genetic Service Into the Diagnostic Pathway for Patients With Chronic Kidney Disease in Canada

Introduction

Genetic kidney disease (GKD) accounts for 10% to 20% of chronic kidney disease (CKD). Genetic testing using gene panel or targeted exome sequencing (ES) can confirm GKD; however, integration into clinical practice has been hampered by small studies, selective populations, and data predominately derived from research settings. Using prespecified clinical referral criteria and a diagnostic pipeline, we performed a prospective cohort study describing diagnostic efficacy and clinical utility of genetic assessment in patients with CKD.

Methods

We analyzed a prospective cohort of 300 participants (256 families) referred to a kidney genetics clinic, between March 2020 and March 2024. Testing strategies included gene panels, and if negative or unsuitable, targeted ES analysis. Testing was performed for the detection of variants in genes known to cause CKD.

Results

We identified a causative variant in 33% of families (85/256). Diagnostic yield increased from 23% (n = 70/300) from gene panel alone, to 34% (n = 103/300) with comprehensive testing. The median time from first diagnosis of CKD to genetic assessment was long at 10.4 years. Following genetic assessment, the median time to receive a positive genetic result was 2.9 months. Multiple levels of clinical utility were recorded in patients receiving a genetic diagnosis, varying across CKD subtype.

Conclusion

Instituting referral guidelines and a standardized testing algorithm established a genetic diagnosis in one-third of participants, providing insight into the viability of integrating genetic assessment in the CKD diagnostic pathway. Considering the potential for clinical utility, strategies to reduce the time from CKD diagnosis to genetics assessment are needed.

Utility of Genetic Testing in Adults with CKD: A Systematic Review and Meta-Analysis

Key Points

Diagnostic yield of genetic testing in adults with CKD is 40%. Risk factors including positive family history and extra-kidney features associate with higher diagnostic yield, although young age at testing did not. Seventeen percent of patients who received a genetic diagnosis were reclassified into a different phenotype after testing.

Background

Clinical and pathological confirmation of the diagnosis for CKD has limitations, with up to one third of individuals remaining without a formal diagnosis. Increasingly, data suggest that these limitations can be overcome by genetic testing. The objective of this study was to estimate the diagnostic yield of genetic testing in adults with CKD.

Methods

Cohort studies that report diagnostic yield of genetic testing in adults with CKD published in PubMed or Embase between January 1, 2005, and December 31, 2023, were included. The Joanna Briggs Institute critical appraisal tool for prevalence studies was used to assess bias. Duplicate independent data extraction and a meta-analysis of proportions using generalized linear mixed models were completed.

Results

We included 60 studies with 10,107 adults with CKD who underwent genetic testing. We found a diagnostic yield of 40% (95% confidence interval, 33 to 46); yield varied by CKD subtype with the highest yield of 62% (95% confidence interval, 57 to 68) in cystic kidney disease. Positive family history and presence of extra-kidney features were associated with higher diagnostic yield. Reclassification of the before testing diagnosis after a positive genetic testing result occurred in 17% of the solved cohort. Six studies showed the clinical benefits of genetic testing including cascade testing for family members and treatment changes.

Conclusions

Overall, we show that genetic testing is informative in a high proportion of clinically selected adults with CKD. The study was limited by heterogeneity in reporting, testing technologies, and cohort characteristics.

Clinical Trial registry name and registration number:

International prospective register of systematic reviews (CRD42023386880).

Atypical Hemolytic Uremic Syndrome Following Influenza B: A Case Report

Background

Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy that presents with a triad of hemolytic anemia, thrombocytopenia, and acute kidney impairment. It can be attributed to mutations in an array of different complement proteins leading to the overactivation of the complement system, the most impacted being the alternative pathway. Though rare, influenza B has been documented as a potential trigger to the development of aHUS.

Case Presentation

We discuss a 10-year-old girl with a history of aHUS who was found to have a repeat episode of aHUS following an influenza B infection. There have only been a few reports of aHUS triggered by influenza B, making this a unique case. Given the recurrence and atypical features present in this case, a genetic workup was obtained, which showed a heterozygous mutation of complement protein CD46. The presence of mutations in CD46 is a known predisposing factor to aHUS, but influenza B infection is rarely implicated as a trigger to aHUS. The prognosis of aHUS varies and is dependent on the complement mutation specific to the individual.

Conclusion

Patients with CD46 mutations have been shown to have high rates of relapse but less long-term kidney damage, as seen in this case. Clinicians should be aware of the association between influenza B and aHUS to improve patient outcomes.