Summary

A medRxiv preprint maps a COL4A5 intronic mutation hotspot and reports that one antisense oligonucleotide restored normal RNA splicing and collagen expression for multiple variants in patient-derived cells. The work is a preclinical study, with no treatment of patients reported.

Researchers have identified a region of the COL4A5 gene where several disease-causing intronic variants disrupt RNA splicing, and report that a single antisense oligonucleotide (ASO) corrected the resulting defect in cells from affected patients. The findings appear in a medRxiv preprint posted on September 15, 2026.

The study used X-linked Alport syndrome as a proof-of-concept model. Its evidence is preclinical and cellular: the ASO was tested in patient-derived cells rather than administered to people.

Contents

Why deep intronic variants matter

Introns are stretches of DNA removed from a gene's initial RNA transcript before mature messenger RNA is produced. Variants located deep inside introns can create or strengthen cryptic splice sites—sequences that resemble the signals used to process RNA. This can cause the cell to insert an abnormal segment called a pseudoexon into the mature transcript.

Such variants are difficult to interpret because they are outside the protein-coding regions commonly examined by exome sequencing and gene panels. The researchers proposed that pathogenic deep intronic variants might cluster in genomic regions that are especially prone to pseudoexon activation, rather than being distributed randomly.

In X-linked Alport syndrome, changes in COL4A5 affect production of the alpha-5 chain of type IV collagen, a structural protein important to basement membranes, including those in the kidney. The study focused on a defined section of COL4A5 intron 6 and screened unsolved cases from several European diagnostic centres.

A shared splice defect across multiple variants

The researchers identified eight independent variants in more than 35 affected individuals from 10 unrelated families. These variants produced two pseudoexon-inclusion events, both involving the same strong cryptic splice donor site.

RNA sequencing and minigene assays confirmed abnormal splicing for all of the variants examined. A minigene assay uses an engineered DNA construct containing the relevant gene segment to test how a variant changes RNA processing. The study reports that experimental confirmation was obtained even when computational prediction tools disagreed or produced scores below clinical interpretation thresholds.

This shared mechanism provided a common molecular target. Instead of designing a separate treatment for each variant, the researchers developed an ASO directed at the cryptic donor site. ASOs are short nucleic-acid molecules designed to bind a selected RNA sequence and influence how that RNA is spliced.

From computational hotspot to ASO candidate

In patient-derived cells, the single ASO restored normal COL4A5 messenger RNA and expression of the alpha-5 type IV collagen protein, regardless of which of the causative variants was present. The result links several genetically different variants to one correctable splicing defect.

The researchers then extended the analysis across the gene using AlphaGenome, described in the preprint as a sequence-to-function model. This computational analysis supported intron 6 as one of the most critical COL4A5 splicing hotspots and identified additional regions containing novel predicted spliceogenic variants.

The significance of the approach is that it shifts the search from individual rare variants to recurrent functional regions. If the same splice-control site is affected by multiple mutations, one ASO could potentially serve a genetically broader group of patients than a variant-specific design. In this study, that possibility was demonstrated at the level of patient-derived cells.

The current evidence remains preclinical. Clinical evaluation would be needed to determine whether an ASO can reach the relevant tissues, remain effective and produce a meaningful benefit safely in people. The additional hotspots identified by AlphaGenome are computational predictions and require experimental validation.

Sources