Annemieke Aartsma-Rus
@oligogirl.bsky.social
Translating science from bench to bedside and from jargon to lay language
So more work is needed, but I appreciated that authors studied the impact of treatment after the onset of symptoms as this is much more clinically relevant than preventing symptoms.
December 11, 2025 at 7:53 AM
So more work is needed, but I appreciated that authors studied the impact of treatment after the onset of symptoms as this is much more clinically relevant than preventing symptoms.
Furthermore, there are also symptoms outside of the kidney for some patients, e.g. hearing loss. This was not studied here. Finally, long term effect of treatment was not studied either (the exon 21 deleted Collagen 4A5 may be less functional than full length protein).
December 11, 2025 at 7:52 AM
Furthermore, there are also symptoms outside of the kidney for some patients, e.g. hearing loss. This was not studied here. Finally, long term effect of treatment was not studied either (the exon 21 deleted Collagen 4A5 may be less functional than full length protein).
They discuss that the background of mouse models plays a big role in how sensitive models are for the development of kidney pathology. Limitations of the study are that it was only a single variant, in one Alport syndrome gene and it is not clear whether this applies also to other in-frame exons.
December 11, 2025 at 7:52 AM
They discuss that the background of mouse models plays a big role in how sensitive models are for the development of kidney pathology. Limitations of the study are that it was only a single variant, in one Alport syndrome gene and it is not clear whether this applies also to other in-frame exons.
Treatment effects were restricted to the glomerulus, as expected due to expression of cre recombinase only in podocytes. Authors discuss their results underline that treatment effects for this variants are possible also after the onset of symptoms, provided there is residual glomerulus function.
December 11, 2025 at 7:52 AM
Treatment effects were restricted to the glomerulus, as expected due to expression of cre recombinase only in podocytes. Authors discuss their results underline that treatment effects for this variants are possible also after the onset of symptoms, provided there is residual glomerulus function.
Authors showed that Col4a5 was not produced in the mutated models, but was produced in a patchy fashion after tamoxifen treatment. Treatment also reduced the amount of fibrosis, even when it was initiated after the onset of pathology.
December 11, 2025 at 7:51 AM
Authors showed that Col4a5 was not produced in the mutated models, but was produced in a patchy fashion after tamoxifen treatment. Treatment also reduced the amount of fibrosis, even when it was initiated after the onset of pathology.
Authors observed kidney injury markers in blood of the mutated mouse. This was prevented when tamoxifen treatment started early. For late treatment, injury markers went up with pathology but upon treatment they went down. This suggests a treatment effect is possible after the onset of symptoms.
December 11, 2025 at 7:51 AM
Authors observed kidney injury markers in blood of the mutated mouse. This was prevented when tamoxifen treatment started early. For late treatment, injury markers went up with pathology but upon treatment they went down. This suggests a treatment effect is possible after the onset of symptoms.
Authors treated mice either before or after the onset of pathology (week 6-10 vs week 14-18). Weight of the mutated mouse model was reduced compared to wild type, but increased with tamoxifen treatment for both start times.
December 11, 2025 at 7:50 AM
Authors treated mice either before or after the onset of pathology (week 6-10 vs week 14-18). Weight of the mutated mouse model was reduced compared to wild type, but increased with tamoxifen treatment for both start times.
This means that if you do not feed the mouse tamoxifen, it will not produce Col4a5, because of the exon 21 nonsense mutation. However, when you feed the mouse tamoxifen, cre recombinase will be expressed in the podocytes and exon 21 will be deleted, thus bypassing the nonsense variant.
December 11, 2025 at 7:49 AM
This means that if you do not feed the mouse tamoxifen, it will not produce Col4a5, because of the exon 21 nonsense mutation. However, when you feed the mouse tamoxifen, cre recombinase will be expressed in the podocytes and exon 21 will be deleted, thus bypassing the nonsense variant.
They made a mouse with the nonsense mutation in exon 21 of mouse Col4a5. Around this, they put sites that will recombine when an enzyme (cre recombinase) is expressed. They also put in the gene for cre recombinase into this mouse model, under a promotor only expressed in podocytes (kidney cell).
December 11, 2025 at 7:49 AM
They made a mouse with the nonsense mutation in exon 21 of mouse Col4a5. Around this, they put sites that will recombine when an enzyme (cre recombinase) is expressed. They also put in the gene for cre recombinase into this mouse model, under a promotor only expressed in podocytes (kidney cell).
However, treatment was prophylactic, while patients are diagnosed due to their symptoms. To test whether exon 21 skipping was also therapeutic after the onset of pathology, authors generated a tamoxifen inducible mouse model.
December 11, 2025 at 7:48 AM
However, treatment was prophylactic, while patients are diagnosed due to their symptoms. To test whether exon 21 skipping was also therapeutic after the onset of pathology, authors generated a tamoxifen inducible mouse model.
The COL4A5 gene is located on the X-chromosome and is the focus of this study. Authors reported a patient with a nonsense variant in exon 21, which is in-frame. Skipping of this exon restored collagen 4A production, which improved renal function in a mouse model.
December 11, 2025 at 7:48 AM
The COL4A5 gene is located on the X-chromosome and is the focus of this study. Authors reported a patient with a nonsense variant in exon 21, which is in-frame. Skipping of this exon restored collagen 4A production, which improved renal function in a mouse model.
Due to the missing collagen filtration does not happen properly, leading to blood and protein in the urine and fibrosis and inflammation in the kidney. Progressive pathology eventually leads to renal failure.
December 11, 2025 at 7:47 AM
Due to the missing collagen filtration does not happen properly, leading to blood and protein in the urine and fibrosis and inflammation in the kidney. Progressive pathology eventually leads to renal failure.
Alport syndrome is a genetic disease characterized by progressive loss of renal function due to glomerulus (kidney filtration units) pathology. The disease is caused by pathogenic variants in the COL4A3,4 or 5 genes, that jointly produce collagen that is present in the glomerular basement membrane.
December 11, 2025 at 7:47 AM
Alport syndrome is a genetic disease characterized by progressive loss of renal function due to glomerulus (kidney filtration units) pathology. The disease is caused by pathogenic variants in the COL4A3,4 or 5 genes, that jointly produce collagen that is present in the glomerular basement membrane.
More work is needed to study the pathomechanism in more detail and also to see how widely applicable this approach is. Furthermore, the question is which part of the disease will be treatable and which will not and what happens when treatment is started AFTER symptom onset (is the case in humans).
December 10, 2025 at 8:18 AM
More work is needed to study the pathomechanism in more detail and also to see how widely applicable this approach is. Furthermore, the question is which part of the disease will be treatable and which will not and what happens when treatment is started AFTER symptom onset (is the case in humans).
However, if you do local treatment in the central nervous system, while this is a problem of the e.g. muscle, likely this will not improve things (note that in 1 day old mice the blood brain barrier is not yet intact, so the ASOs will also go to the muscles/rest of the body).
December 10, 2025 at 8:14 AM
However, if you do local treatment in the central nervous system, while this is a problem of the e.g. muscle, likely this will not improve things (note that in 1 day old mice the blood brain barrier is not yet intact, so the ASOs will also go to the muscles/rest of the body).
This may explain why many animals did not respond with improved survival. Also the improved survival was due to reduction of hypotonia, while the pathomechanism of this is not yet known. If it is of neuronal origin, the ASO treatment may improve things.
December 10, 2025 at 8:13 AM
This may explain why many animals did not respond with improved survival. Also the improved survival was due to reduction of hypotonia, while the pathomechanism of this is not yet known. If it is of neuronal origin, the ASO treatment may improve things.
Authors discuss that missplicing of mutually exclusive exons may underlie more epilepsy syndromes and that ASOs could be a way to improve this. However, they also admit that for SCN8A it has been shown that high correct transcript and protein levels are required for a treatment effect.
December 10, 2025 at 8:12 AM
Authors discuss that missplicing of mutually exclusive exons may underlie more epilepsy syndromes and that ASOs could be a way to improve this. However, they also admit that for SCN8A it has been shown that high correct transcript and protein levels are required for a treatment effect.
animals died before the age of 21 days. Intracerebroventricular injection of the 5N targeting ASO at 2 days of age reduced seizures and increased survival at day 30 from 0% to 30%. Surviving animals also showed better motor skills and improved activity.
December 10, 2025 at 8:11 AM
animals died before the age of 21 days. Intracerebroventricular injection of the 5N targeting ASO at 2 days of age reduced seizures and increased survival at day 30 from 0% to 30%. Surviving animals also showed better motor skills and improved activity.
ASO treatment reduced 5N inclusion and reduced the firing (a control ASO was used as a reference). A mouse model with the same 5n variant was made, which showed seizures, less activity and also weight loss due to inability to feed starting from 15 days of age.
December 10, 2025 at 8:09 AM
ASO treatment reduced 5N inclusion and reduced the firing (a control ASO was used as a reference). A mouse model with the same 5n variant was made, which showed seizures, less activity and also weight loss due to inability to feed starting from 15 days of age.
Authors then studied an IPSC cell line differentiated to neuronal cells, where they compared control to a variant that increases exon 5N inclusion. Extra inclusion was confirmed, and multielectrode analysis (MEA) showed more firing of the cells with the 5N inclusion variant.
December 10, 2025 at 8:08 AM
Authors then studied an IPSC cell line differentiated to neuronal cells, where they compared control to a variant that increases exon 5N inclusion. Extra inclusion was confirmed, and multielectrode analysis (MEA) showed more firing of the cells with the 5N inclusion variant.
For exon 5N to exon 5A authors used neuroblastomas while for 5A to 5N they used SH-SY5Y cells as these respective cell lines had high inclusion of exon 5N and 5A so could be used to test. ASOs were identified to shift each way.
December 10, 2025 at 8:07 AM
For exon 5N to exon 5A authors used neuroblastomas while for 5A to 5N they used SH-SY5Y cells as these respective cell lines had high inclusion of exon 5N and 5A so could be used to test. ASOs were identified to shift each way.
Note that they validated this in multiple cell types (which is good because the splicing factors may vary between cell types). They observed that known variants likely cause an increase of 5N inclusion. They then designed antisense oligonucleotides (ASOs) to switch between the 2 exon 5s.
December 10, 2025 at 8:06 AM
Note that they validated this in multiple cell types (which is good because the splicing factors may vary between cell types). They observed that known variants likely cause an increase of 5N inclusion. They then designed antisense oligonucleotides (ASOs) to switch between the 2 exon 5s.
Authors flag that mutually exclusive exons occur in other ion channel genes as well, so this seems to be a conserved mechanism. Authors then studied SCN8A exon 5A/5N in more detail in a minigene to identify splicing enhancer sequences.
December 10, 2025 at 8:03 AM
Authors flag that mutually exclusive exons occur in other ion channel genes as well, so this seems to be a conserved mechanism. Authors then studied SCN8A exon 5A/5N in more detail in a minigene to identify splicing enhancer sequences.
This is a perfect example of how things can go wrong when this is not done as the location in exon 5 does not tell you whether the variant is in 5A or 5N. When this was elucidated, it turned out that seizure onset did not differ but seizure control (with drugs) was easier when variants were in 5N.
December 10, 2025 at 8:02 AM
This is a perfect example of how things can go wrong when this is not done as the location in exon 5 does not tell you whether the variant is in 5A or 5N. When this was elucidated, it turned out that seizure onset did not differ but seizure control (with drugs) was easier when variants were in 5N.