New high-throughput assay enhances diagnosis of Alagille syndrome

The development and application of a high-throughput assay to measure JAG1 membrane expression significantly improves the classification of JAG1 gene variants, reducing diagnostic uncertainty for Alagille syndrome and enhancing molecular diagnosis, according to a study.

Currently, up to 85% of JAG1 missense variants have uncertain or conflicting classifications.

To address this issue, a comprehensive library of 2832 JAG1 nucleotide variants within exons 1-7, a region rich in reported missense variants, was created. A high-throughput assay was designed to measure JAG1 membrane expression, a key factor for normal function. Calibration with 175 known or predicted pathogenic and benign variants allowed for precise functional classification.

The study characterized 486 variants as functionally abnormal, with 439 (90.3%) being missense variants. The results highlighted specific residues where divergent membrane expression occurs, suggesting that the loss of the wild-type residue itself does not solely drive pathogenicity.

Of 144 uncertain variants reported in patients, 27 exhibited functionally abnormal membrane expression. Inclusion of these data led to the reclassification of 26 variants as likely pathogenic.

Reference
Gilbert MA, Keefer-Jacques E, Jadhav T, et al. Functional characterization of 2,832 JAG1 variants supports reclassification for Alagille syndrome and improves guidance for clinical variant interpretation. Am J Hum Genet. 2024;S0002-9297(24)00218-0. doi: 10.1016/j.ajhg.2024.06.011. Epub ahead of print. PMID: 39043182.

Rare Disease 360® is the Official Media Partner and Official Publication of The Alagille Syndrome Alliance (Alagille.org).