Special tribute episode honoring Prof. Dr. Brunhilde Wirth and synthesizing recurring themes across her work on SMN1/SMN2 splicing, variant interpretation, and spinal muscular atrophy.
0:00Welcome to Base by Base, the paper cast that brings genomics to you wherever you are. Thanks for listening, and don't forget to follow and rate us in your podcast app. Yeah, thanks for tuning in, everyone.
0:10So imagine for a 2nd that you are a detective. I like this. Right. But you aren't walking onto a typical crime scene. And you're not looking for a person either. Exactly. You are looking for a ghost hidden deep inside the human genetic code.
0:23You're trying to solve a mystery surrounding the most common lethal genetic childhood motor neuron disease on the planet. Spinal muscular atrophy or um, SMA. Yeah, SMA. So today's Deep Dive is a special mission for us.
0:38We're tracing over 25 years of relentless scientific detective work. Watching the seemingly impossible genetic puzzle unravel. Paper by paper. Discovery by discovery. And we need to say this right up front.
0:50Today, we celebrate Professor Brunhildeworth at the Institute of Human Genetics, University Hospital Cologne, in Germany, and the many teams and trainees who built this body of work with her. It truly is a story of just incredible persistence.
1:04I mean, to understand the sheer stakes of this work. You have to understand what SMA actually does to the human body. Right, it's a devastating disease. It really is. It causes the rapid degeneration of motor neurons in the spinal cord.
1:18And these are the vital cells that serve as the communication wires between your brain and your muscles. And without them, infants experience severe muscle weakness. Progressive loss of motor function, and in its most severe form, it often leads to early death.
1:33But the genetics behind it are absolutely fascinating. They are. Humans have this quirky evolutionary setup. We don't just have one gene responsible for making this crucial neuron protein. We actually have 2 nearly identical genes sitting side by side on our DNA.
1:48SMN1 and SMN2. Exactly. So we have a main gene and a backup gene doing the exact same job on paper, that sounds like a great insurance policy. You'd think so, right? Yeah, if the main gene breaks, shouldn't the backup just seamlessly take over? Why is there a disease at all?
2:02Well, you've just hit on the core mystery that kicked off decades of intense global research. SMA occurs when that 1st gene, the primary one called SMN one is missing or mutated. But the backup gene, S Men 2, fails to step in and save the day.
2:16It turns out SMN one is the gold standard. It produces 100% full length, perfectly healthy, stable protein. And the backup. SMN 2 is a deeply flawed backup. It mostly produces a truncated, unstable protein that quickly falls apart in the cell, only about 10% of the protein that comes from SMN 2 is actually functional.
2:36Wow, only 10%. Yeah. Professor Worth's career alongside her massive network of international collaborators is the story of figuring out exactly why this backup fails, how to accurately measure that failure, and ultimately how to exploit that knowledge to save human lives.
2:52They were essentially the lead detectives mapping the hidden mechanics of these genes. And that brings us to a massive aha moment in the literature. Let's look at a landmark study from 1999. huge year for this field.
3:04They were trying to figure out the difference between the gold standard SMN one and the flawed backup SMN2. What did they find? Right down at the molecular level? The sheer scale of the biological error is staggering. Out of the entire massive genetic code for these genes, the critical difference between SMN1 and SMN2 comes down to a single letter.
3:26Just one tiny typo. Just one. A C in SMN1 is swapped for a T in SMN2, specifically in a region of the gene called Exon 7. But I read that the single letter change is what biologists call a translationally silent mutation.
3:41From my understanding, that means if the cellular machinery were to just read the genetic code and build the protein. That specific letter swap wouldn't actually change the building blocks of the protein at all.
3:51So it should be completely harmless, right? Actually should be harmless, but our cells don't just read genes straight through from start to finish. They edit them first. Oh, right, splicing. Exactly. It's a complex process called splicing.
4:02Think of it like a movie director, cutting together the final film from hours of raw footage. The Exxons are the essential scenes that make the final cut. Okay, I like that analogy. So that tiny CDT typo doesn't change the protein's core recipe, but it completely ruins the splicing instructions.
4:19It disrupts what's called an exotic splacing enhancer, and instead creates a silencer. So the director gets confused. The cellular editing machinery gets completely confused by this typo and accidentally skips Exxon 7 entirely when putting the final instructions together.
4:34And that skip section is crucial. Absolute crucial for the final protein to fold and stabilize. Without that scene in the movie, the plot makes no sense and the protein simply falls apart. That is the ultimate biological absurdity.
4:48We evolved this great backup gene, but a single typo in the editing room ruins the entire production. It really is. And the 1999 paper laid that foundation, but they didn't stop it just understanding the problem.
5:00They turned this knowledge into a powerful clinical tool. Fast forward to 2002. Right. In 2002, the team developed a fast real-time PCR test to accurately count exactly how many copies of SMN1 and SMN2 a person has.
5:15Now, for those of us who aren't in a lab every day, What actually is a PCR test, and why was this such a big deal? PCR stands for polymerase chain reaction. You can think of it like a highly targeted molecular photocopier.
5:27It allows scientists to take a tiny sample of DNA and copy a specific targeted segment 1000000s of times until there's enough of it to easily detect and count. Okay, so it amplifies the signal. Exactly.
5:40And before this PCR test was developed for SMA diagnosis was often agonizingly slow, I want you, the listener, to put yourself in the shoes of a parent back in 2001. That would be terrifying. Your infant is losing muscle tone.
5:53And to figure out why you have to wait weeks for the results of a painful invasive muscle biopsy. Oh, wow. But with this new real-time PCR test, doctors could take a simple blood sample and rapidly safely quantify the exact genetic landscape of a patient in a matter of hours.
6:07That alone changes the landscape of a family's medical journey, but it wasn't just about speed, was it? This test revealed something much deeper about the disease itself. It provided a literal crystal ball for the severity of the disease.
6:19The team analyzed 100s of patients and found a striking correlation based on the number of those flawed SMN 2 backup copies. Because remember, SMN 2 still manages to eke out about 10% functional protein.
6:32Right. So patients with the most severe form of the disease type, I usually have only one or 2 copies of SMN2. Their median survival, tragically, was measured in mere months. But patients with the milder type 3 SMA usually have 3 or 4 copies of SMN2.
6:48So that extra trickle of functional protein from the additional backup copies adds up. Exactly. It allows them to walk and live well into adulthood. By proving this mathematical relationship. Professor Worth's team turned SMN 2 copy counting into a global standard for prognosis.
7:03It's incredible how a simple countenant test allowed doctors to predict the course of the disease and prepare families for what was to come, but science is rarely a straight line. Never a straight line.
7:13Right. Just when you think you have all the rules figured out. Biology throws a massive curveball. And this leads us to what might be the most thrilling plot twist in this entire deep dive, the mystery of the discordant family.
7:25This was a puzzle the team chased relentlessly. They started finding families where siblings had the exact same genetic profile. Like identical DNA for this disease. Yes, both children were completely missing the SMN1 gene, and both children had the exact same number of SMN2 backup copies.
7:42So by all the biological rules we just discussed, they should have had the exact same severity of the disease. But they didn't. One sibling would be severely affected, confined to a wheelchair, while the other sibling was walking around perfectly healthy.
7:55Fully asymptomatic. Completely asymptomatic. You really have to imagine being the detective on that case. The genetic fingerprints at the scene of the crime are identical, but in one room, a tragedy occurs, and in the other, nothing happens at all.
8:09It makes 0 sense on the surface. It suggested that an invisible shield was in play. There had to be a protective genetic modifier somewhere else entirely in the person's genome that was stepping in and overriding the SMA defect.
8:22And in 2008, they found it. They found the very 1st one, yes. In the fully asymptomatic individuals who notably were all females in these initial families, the team discovered unusually high levels of a completely different protein called Plaston 3 or PLS 3.
8:36So having a ton of this plaston 3 protein essentially cured them, even though they were still missing the core motor neuron gene. Yes. What does Plaston 3 actually do to pull off that kind of rescue? PLS 3 is an architect of the cellular skeleton.
8:53It binds to Acton, which are the structural filaments inside a cell, and it stabilizes them. Why is that so important for motor neurons, specifically? Because these cells have massively long arms called axons that stretch all the way from your spinal cord out to your fingertips and toes.
9:09PLS 3 stabilizes those long axons helping them grow and maintain their vital connections to the muscles. So while the underlying SMN defect was actively weakening the motor neurons, this Plaston 3 superpower was stepping in like a structural engineer reinforcing the scaffolding and keeping the neurons alive.
9:26That's a great way to put it. That was 2008, but the hunt didn't stop there. Almost a decade later in 2017, they found another invisible shield. Yes, and this time it required some serious shoe leather epidemiology.
9:37They found a 4 generation Mormon family in Utah. The logistics of finding and studying a massive family tree like that are astounding. It's huge undertaking. In this Utah family, they had healthy individuals missing SMN1 and carrying 4 copies of SMN2.
9:53Normally, 4 cockies gives you type 3 SMA right. It's a milder form, but you still absolutely get the disease. Right. Yeah. These individuals were perfectly healthy. To figure out why the team used a technique called genome wide linkage analysis.
10:08I've seen that term a lot in these papers. Can you break down what genome wide linkage analysis actually looks like in practice? Think of it like playing a massive game of guess who? across an entire family tree's DNA.
10:20Researchers look at the DNA of the family members who have the disease and compare it to the DNA of the family members who were protected. Scanning across all the chromosomes. Exactly, looking for a specific genetic marker that is always inherited by the healthy people, but never by the sick people.
10:35And through this massive computational matching game, they discovered that this time the protective shield wasn't an increase in a protein like we saw with Plaston 3. No, it was a severe reduction in a completely different one.
10:46A neuronal calcium sensor. called NCALD. Wait, I need to wrap my head around this. Boosting a structural protein helps, but lowering a calcium sensor also helps. On the surface, those sound totally unrelated.
10:59They really do. How does lowering NCLD protect against SMA, and does it even connect to the Plaston 3 discovery? This is where the genius of this research really shines. It wasn't just about cataloging random genes.
11:12It was about connecting the dots to understand the underlying machinery of the disease. The team prove that both of these mechanisms, having more plastin 3 are having less NCLD actually rescue the exact same cellular process.
11:27Which is that? It's a biological process called endocytosis. Endocytasis. If I recall my high school biology, that's essentially how cells absorb materials from their outside environment, right? Kind of like a cellular supply chain bringing in cargo.
11:39That is a perfect analogy. Think of the motor neuron like a bustling city that suddenly loses its ability to receive cargo shipments. The roads are blocked, the supply chain is broken, and everything grinds to a halt.
11:50Because of the low SMN levels. Yes. The team discovered that the core problem caused by low SMN levels in these motor neurons was a failure in endocytosis. But if you randomly happen to have the genetic luck that boosts Plaston 3 or the genetic luck that lowers in CLD, your body creates a bypass.
12:10It forces the supply chain to work again. Exactly. This proved that SMA isn't just about a missing protein. about a specific cellular transport failure, that the body can actually fix itself. That is profound.
12:23The cure wasn't sitting in a pet traditional lab. It was already walking around inside the protective mutant genetics of healthy family members. incredible. And this brings us into the modern era of treatments.
12:34There's a massive 2020 review paper in our stack of sources celebrating 25 years of SMA research. It outlines how this field moved from giving families a definitive death sentence to ushering in an era of groundbreaking treatments.
12:48Real tangible treatments. But how do we actually fix the core issue? I've seen things about new drugs, but how are they actually addressing that original splicing error? Because the research is understood exactly how that single C to T letter swap in SMN 2, caused the skipping of Exxon 7 pharmaceutical companies, could design drugs specifically tailored to fix that exact biological typo?
13:11We now have treatments known as anti-sense oligonucleotides, or ASOs. Anti-sense oligonucleotides, that is a mouthful. Yeah, it is. How does an ASO actually fix a broken gene? You can think of an ASO as a tiny, custom designed piece of genetic whiteout.
13:29It's a synthetic molecule designed to enter the cell, find the flawed SMN 2 gene and physically stick to that exact spot where the splicing silencer is located. So it just covers it up. By covering it up, it forces the cellular editing machinery to stop skipping Exon 7.
13:43The machinery reads right through it, and suddenly the flawed backup gene starts churning out full-length healthy protein. It's brilliant. You are literally masking the typo so the cell can read the manual properly.
13:53Exactly. But Professor Worslev didn't just sit back and watch these new therapies roll out. They kept pushing the boundaries. A 2019 paper shows. They started exploring combinatorial therapies and severe mouse models of SMA.
14:05The reality is that while these new ASO drugs are absolute miracles, They aren't always perfect, especially if they're administered after a patient has already started showing severe symptoms. So they needed a multi-layered approach.
14:17Right. So the team decided to tackle the problem from multiple angles at once. They gave the severe SMA mice a low dose of the SMN boosting ASO drug, but they also administered a drug specifically designed to lower NCLD.
14:32They were chemically mimicking that protective shield they found naturally occurring in the Utah family. Yes, a 12 punch. Fixing the protein deficiency at the genetic level while simultaneously forcing the cellular supply chain to reopen.
14:45And the results. Stunning. They proved that hitting the disease from 2 completely different angles worked significantly better than just one treatment alone. It opens the door for entirely new multi-layered therapeutic strategies for patients who might not fully respond to the baseline genetic therapies.
15:01It's amazing how quickly the science moves from observing a family pedigree in a clinic to developing a tangible multi-layered therapy, which brings us right up to the present day with a fascinating paper published in 2026.
15:14A very recent and important one. This paper highlights the real world modern challenges of this genetic revolution. We are now in a reality, where universal newborn screening for SMA is happening in places like Germany and Australia.
15:27Every baby gets a heel prick, and their DNA is tested for SMA right at birth. And this screening is crucial. With these modern therapies, if you can treat a baby before they show any symptoms, you can often save their motor neurons entirely.
15:41But newborn screening relies on standard algorithmic tests. And standard tests are programmed to look for the most common genetic signatures. This 2026 paper tells a gripping story about 2 newborns, one in Germany, and one in Australia.
15:53Both babies tested positive for severe SMA on the standard newborn screen because they were missing the standard SMN one gene. So you have 2 families who are given this terrifying news right after the birth of their child.
16:05And because they are missing SMN one, these babies were slated to receive intense, highly expensive treatments. We're talking about gene therapies that can cost upwards of $3500000 per child. The medical machinery was ready to move.
16:21But when the secondary standard tests were run to check their backup SMN 2 copies, the clinical picture didn't perfectly align. something was off. The clinical teams reached out and Professor Worth's teams stepped in to do some precision genetic sleuthing.
16:35They bypass the standard algorithms and sequence the entire region base by base. What did they find? They discovered a completely new anomaly. They found a tiny 4 letter deletion right near the very end of the SMN1 gene.
16:47Now you'll have to help me out here. I've read that a 4 letter deletion throws off something called the reading frame of a gene. Why is losing just 4 letters such a massive deal to a computer algorithm?
16:57To understand a reading frame, imagine reading a sentence made entirely of 3 litter words. Let's say the cat ate the rat. That makes perfect sense. But if you delete just one letter, say the E in the HE, and keep reading in groups of three, the sentence becomes THC 88 Tet her at.
17:17It turns into complete gibberish. Complete gibberish. Our genetic code is read in 3 letter chunks. A 4 letter deletion shifts everything out of alignment and usually results in a broken, useless protein.
17:28That's exactly how the standard screening algorithms interpreted it. The computer flagged it, essentially saying broken genes, severe SMA, initiate $3.5 million therapy. Exactly. But I'm guessing the team didn't just blindly trust the algorithm.
17:43They absolutely did not. In clinical genetics, this kind of newly discovered anomaly is called a variant of uncertain significance. It's the genetic equivalent of a massive maybe. You don't know if it causes disease or if it's harmless.
17:55So the team took cells from these patients and ran rigorous functional studies to see what the protein was actually doing. And the results flip the script entirely. The functional studies proved that this specific tiny deletion didn't destroy the protein at all.
18:08Instead, it somehow produced a completely stable, highly functional previously undiscovered version of the SMN protein. Wow. It was a genetic variant of uncertain significance that turned out to be completely 100% benign.
18:22The tests were throwing a false positive. Because of this rigorous base-by-base genetic detective work, the clinical teams realized these babies were actually fine. They were naturally producing enough functional protein on their own.
18:35The children were spared unnecessary extreme medical interventions. The paper notes that today, at 24 months of age, both children are fully healthy and thriving, over $7000000 in medical costs were saved, but so much more importantly, 2 families were spirit unimaginable anxiety and unnecessary medical procedures for their tiny infants.
18:54It perfectly encapsulates the signature of Professor Worth's career. It's a relentless drive to ensure that basic genetic discovery zooming all the way down to single letters of DNA are translated into tangible clinical consequences that protect and save human lives.
19:09But as you look through these 10 papers spanning decades, there is another recurring theme that is impossible to ignore. What's that? The massive lists of co-authors on every single one of these papers.
19:22The incredible number of trainees, lab techs, and international collaborators from all over the world. Oh, absolutely. This deep dive isn't just about one brilliant mind sitting alone in a room. It's about the orchestration of a massive global community.
19:37The sheer scale of the experimental work is staggering. Over the years, they studied the mechanics of these genes in yeast and microscopic worms in zebra fish, swimming in tanks and mouse models, and crucially by sitting down and working intimately with patient families across the globe.
19:52From Germany to Utah to Australia. You simply cannot map a disease from a single letter mutation all the way to a global therapy without a dedicated community. You really can't. When you look at the entirety of this timeline.
20:04What does this all mean for the listener and for the families affected by this disease? It means that today SMA is no longer just a clinical mystery, or an inevitable tragedy, thanks to Professor Brunhildeworth and her dedicated teams.
20:18It has been transformed into one of the greatest success stories of modern neurogenetics. To Professor Worth and to everyone who played a part in this journey, we owe you great and many thanks. You're enduring impact has literally rewritten the fate of 1000s of children.
20:32The scientific legacy here is profound. It teaches us that the answers to our most devastating diseases aren't always found by inventing something completely new in a laboratory. Sometimes the answers are hiding in plain sight.
20:45Tucked away in the protective viewed in genetics of healthy family members. We just have to be curious enough and persistent enough to find them. Which leaves you the listener with a final thought to mull over.
20:56As we enter an age where everyone's DNA might eventually be sequenced right at birth, how many other seemingly broken genetic variants are actually secret protective superpowers waiting to be discovered.
21:07Could the cure for the next great medical mystery be hiding in your own DNA right now? Think about it. And don't forget to subscribe and rate the show in your podcast tab so you never miss a deep dive.
21:16Catch you next time.
