An international HBOP Variant Curation Expert Panel developed PALB2-specific specifications of the 2015 ACMG/AMP variant-interpretation guidelines by tailoring, limiting, or removing existing codes and tested them on 39 pilot variants to improve ClinVar concordance and harmonize classification.
0:15I'm staring down a string of letters in the dark Welcome 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 write us in your podcast app.
0:28Usually when you go to the doctor, um, and take a medical test, you really expect a clear binary answer. Right. Yeah, yes or no. Exactly. You know, you take a strip test, it's positive or it's negative, your arm hurts, the x-ray shows, it's broken, or, well, it's just a sprain.
0:43We just crave that definitive certainty. Oh, absolutely. I mean, we rely on that certainty to make decisions, right? tells you what to do next. But if you step into the world of clinical genetics, suddenly that certainty can just vanish.
0:56It really can. Imagine taking a genetic test because you want to understand your risk for a severe cancer. You're sitting there waiting for the result, you know, bracing yourself for high risk or hoping for safe.
1:07And instead, the result comes back as a variant of uncertain significance of VUS. Of the US. It is essentially the genetic equivalent of a medical shrug. I mean, the laboratory is looking at your DNA and basically saying, we see a change here, like a typo in the code, but we genuinely have no idea if it is dangerous or completely harmless.
1:27It's like, imagine your genome is this incredibly long, complex, 1000000000 word manuscript. We are reading through it, and we find a single swapped letter. Just one letter out of billions. Right. And what we're trying to figure out is, does that one swap letter change the entire plot of the story? Or is it just a harmless typo that the reader's brain skips right over?
1:49And when scientists genuinely don't know the answer, well, you get a VUS. And this ambiguity, it's a massive real world hurdle in clinical genetics right now, especially for genes linked to severe cancers.
2:01So our deep dive today asks, how could changing the rulebook for reading these genetic typos suddenly give 1000s of patients clear answers? Well, answering that requires looking at a monumental effort and variant interpretation, which is a specialized branch of genetics that operates largely behind the scenes.
2:18Today, we celebrate the work of the hereditary breast, ovarian, and pancreatic cancer variant curation expert panel, or uh, the HBOP VCP for short. Yes. Specifically researchers, Marcy E. Richardson, Fergus J.
2:34Couch, and their incredible international team of experts. Right, who have really advanced their understanding of how to accurately classify variants in the POB2 gene. The HBOP VCAP. It operates as this massive international assembly.
2:47I mean, you have specialists in clinical genetics, molecular biology, biostatistics and epidemiology, all coming together for a singular purpose. I love thinking about this group almost like a genetic Supreme Court.
2:59Oh, that's a great way to put it. Right, because they convene to hash out the absolute best legal precedence for interpreting these DNA typos. It's not just, you know, a lone scientist in a lab making a judgment call.
3:10No, at all. It's a global consensus. They're trying to build the most robust legal framework possible to judge a variant. And that level of consensus is absolutely critical when the gene on trial is POB2.
3:21So, um, let's lay the groundwork for you, the listener. What exactly is the pal B2 gene? And I mean, what happens when it breaks down? Okay, so Pal B 2 stands for a partner and localizer of BRCA 2? And to grasp its importance?
3:37We really need to look at how our cells handle catastrophic damage. Like DNA damage. Exactly. Our DNA is constantly under assault, right, from ultraviolet light, environmental toxins, even just the normal metabolic processes of the cell.
3:50It's a rough environment there. It really is. And sometimes this damage causes a double strand break. The DNA double helix literally snaps into. Wow. And if the cell tries to divide with a broken chromosome, it leads to massive genomic instability.
4:05which is of course, the hallmark of cancer. So it sounds like a structural collapse at a construction site. You need an emergency crew to come in and perfectly weld those steel beams back together. That is exactly what happens.
4:16That emergency crew is a cellular pathway called homologist recombination repair. And Bellby 2, well, it is the foreman of that crew. Okay, the foreman. like that. When a double strand break occurs, PB2 physically bridges the gap between 2 other famous proteins, BRCA1 and BRCA2.
4:33Oh, right. The BRCA genes, we hear a lot about those. Exactly. So PB2 acts as a structural scaffold. It holds these crucial repair proteins exactly where they need to be. So they can use a pristine copy of the DNA to perfectly stitch the broken strands back together.
4:48But if that pay will be too foreman is missing or defective, the repair crew is uncoordinated. Right. The brakes don't get fixed properly. And errors just pile up and a cell can turn malignant. That brings us to the clinical stakes here.
5:00If a person inherits one broken copy of Paley 2 from their parents, like a heterozygous pathogenic variant, There are a lifetime risk for certain cancers just skyrocket. Specifically breast, ovarian, and pancreatic cancers.
5:12Those patients, they need intense surveillance or even preventative care. But the stakes change drastically if a child inherits 2 broken copies of pale B2, right? One from each parent. They do. That leads to a rare, devastating pediatric condition called Fancone anemia, specifically subtype N, or FAM.
5:30It is. Because the child has 0 functional Pal B2 protein. Their cells literally cannot handle even basic DNA stress. It manifests severe congenital malformations, catastrophic bone marrow failure, and childhood leukemias.
5:46So the gene is incredibly important. But interpreting whether a variant is actually broken is the hard part here. It's the hardest part Because the foundational rule book for clinical genetics is the 2015 ACMG variant interpretation guidelines, and that rule book established 28 different evidence codes to help scientists weigh if a variant is benign or pathogenic.
6:06Right, that was the baseline. But here is my question. If the 2015 guidelines were already established, why do we need a specialized case law just for pal B2. Well, think of the 2015 guidelines at a broad national constitution.
6:17It was a monumental achievement for standardized medicine. Okay. But every single gene has entirely unique biology. And every genetic disease manifests differently. So applying a broad constitutional law to every specific genetic scenario, it just leads to blind spots.
6:32Oh, I see. A law written to govern a tiny town might cause absolute chaos if you applied it to a massive metropolis. Exactly. And the defining biological factor here is incomplete penetrance. Unpack that for us.
6:45What does that mean? So with Pelby 2, carrying a pathogenic variant elevates your wrist for breast cancer, but it does not guarantee you will develop it. Oh okay. The penetrance is incomplete. You might live to be 90 and never get cancer.
6:57But contrast that with the pediatric disease we just mentioned, Fancone anemia. If a child has 2 broken pal B2 copies, that disease is almost fully penetrant. It appears early and appears severely. Wow, okay.
7:10So you simply cannot use the exact same logic and statistical waiting to judge a common adult onset cancer gene with incomplete penetrance, as you would for a rare, fully penetrant pediatric disease. You really can't.
7:22The context completely changes the evidence. Which is exactly why the Supreme Court, the HPOP, VCEP, had to sit down and write highly specific case law solely for the Pell B2 gene, just modifying that original 2015 Constitution.
7:36So if I'm trying to rewrite this genetic case law. I assume I can't just, you know, throw darts at a board and hope my new rules work. Definitely. I need to take my newly drafted legal precedence and apply them to past cases to see if the outcome actually makes sense.
7:50Is that how they approach the methodology? Yeah, that's pretty much it. They started by meticulously reviewing all 28 existing ACM jam evidence codes, but through the lens of Pal B 2 biology. They debated the literature, analyzed internal laboratory databases, and used their collective expertise to decide which rules needed tailoring and which just needed to be scrapped.
8:13And then they conducted a rigorous pilot test. They took their newly drafted rule book for a test drive. Exactly. They selected a diverse set of 39 PalB2 variants. And this set included the entire spectrum.
8:25You know, variants known to be highly pathogenic, variants universally agreed to be benign, and variants that were complete mysteries. The VUS's. Right? those stubborn V US's. So they apply their new tailored rules to these 39 variants and compare the outcomes against the existing classifications sitting in Kernvar.
8:42And just for you listening, Clinvar is the massive public database where genetic labs around the world share their variant interpretations. Yes, it's essentially the public record of genetic verdicts. But wait, how exactly do you pilot test a rule book like that?
8:56If Clinbar already has an answer, aren't you just trying to match it? What does a success rate even look like when you are dealing with unknown genetics? Well, success requires a really nuanced look at the data.
9:08For the variants that the scientific community universally agrees upon, like the clearly benign or clearly pathogenic ones, the new rule book must reach that same established conclusion. Oh, I see. You need to prove that your new rules haven't accidentally broken the system.
9:23Right. You don't want your new legal framework to suddenly start convicting innocent variants. Exactly. But the true test of success is looking at the variants where Clinvar shows conflicting interpretations between labs or list them as a VUS.
9:38Does your new rule book provide enough rigorous clarity to finally tip the scales and resolve those mysteries? Let's dig into those findings then? Because this pal B2 rule book ended up being a massive overhaul of the original constitution.
9:51It really was. Out of the original 28 codes, the VCEP throughout 13 entirely. They strictly limited the use of another 6 codes, and they highly tailored 9, throwing out almost half of the foundational rules is a huge shift.
10:05It is, and it reveals profound insights into the biology of Pal B 2. The VCEP eliminated those 13 codes, primarily for two critical reasons. What's the first one? The 1st reason involves common phenotypes.
10:18Several of the original 2015 codes allow scientists to weigh the patient's clinical presentation as evidence. The logic goes, if you find a genetic variant in a large group of patients who all have the same disease, that variant is likely the cause.
10:32Wait, I need to push back on this. If a patient comes into the clinic with breast cancer, Andy, they carry a variant in their pal B2 gene, isn't that a smoking gun? Why wouldn't a geneticist use that as evidence?
10:42I mean, it sounds like a smoking gun. But you have to consider the broader epidemiological picture. Breast cancer is exceptionally common. Approximately one in 8 women will develop it in their lifetime.
10:55Wow, okay. Because the baseline risk in the general population is so incredibly high. A patient having both breast cancer and a random Pam Latu variant could easily be a sheer coincidence. Ah, they could have developed sporadic breast cancer due to environmental factors, age, or just bad luck.
11:14Right. entirely independent of their genetics. And they just happen to also carry a completely harmless typo in their pound me 2 genes. Exactly. In genetics, this phenomenon is actually called a phenocopy.
11:25It's when a trait or disease appears to be driven by genetics, but is actually caused by environmental or non-genetic factors. Oh I see. Because breast cancer has so many fanoc copies, you cannot just count pro bands.
11:37You know, the 1st affected individuals identified in a family and assume the variant is guilty. Circumstantial evidence isn't enough for a conviction when the crime happens this frequently. Exactly. To legally prove a variant is guilty in a high background rate disease, you need immense statistical rigor.
11:53You need massive case control studies comparing 1000s of patients with the variant against 1000s of healthy controls. Just to prove the variant actually elevates risk above that one in 8 baseline. Yes, because simple pro band counting is statistically flawed here, the VCEP eliminated codes like PS4 that rely on it.
12:13Okay, throwing out rules because the disease is too common makes perfect statistical sense. But you mentioned a 2nd major reason, they toss so many rules. I did. And this one revolves around a massive challenge in genetics, misense ambiguity.
12:25Why would swapping a single letter in the DNA be treated with such suspicion? Well, returning to your manuscript analogy, A mis sense variant doesn't rip a whole chapter out of the book. It just swaps a single letter, changing a single word.
12:37Biologically means the DNA code swaps out one single amino acid building block in the final PLB2 protein chain. So why is it so hard to judge if one swapped word ruins the plot? It comes down to protein structure.
12:51Some proteins act like rigid, complex locks. If you change even a single atom, the key won't turn and the protein is destroyed. Right. But the pale V2 protein seems to be largely tolerant of these single amino acid swaps.
13:04Large sections of the protein act more like flexible scaffolding. Okay. If you swap a building block in a flexible pether, usually continues to function just fine. So, the primary way pal B2 actually causes disease is through what we call loss of function.
13:18The mutation doesn't just swap a letter. It introduces a stop sign too early, truncating the protein, or it completely destroys its ability to bind to BRCA1 and BRCA2. Yes, the page is ripped out entirely.
13:31Now, it is absolutely possible that some specific misence variants are pathogenic. Like, if they swap an amino acid right at a critical binding junction. Right. Right. But to date, there is no universally accepted solid proof of specific misinperience actually causing disease in this gene.
13:48So because we lack concrete proof that these single letter swaps are actually dangerous in Palbi 2, the VCEP essentially said, we cannot use rules that assume mis sense variants can be used as evidence of pathogenicity.
14:01Exactly. They struck down or heavily restricted any code relying on misense evidence. For instance, the 2015 guidelines feature a rule stating that if you find a new misans variant, at the exact same location as a known established pathogenic variant.
14:16That serves as strong evidence, the new one is also bad. Right. But the VCP threw that out for Pelvy too, because we do not have those established pathogenic misins variants to benchmark against in the 1st place.
14:27They just refuse to let past assumptions influence new verdicts. They did. So what happened when they took this highly tailored, rigorously stripped down case law and ran their 39 pilot variants through it?
14:38Well, the results validated their rigorous approach. Out of the 39 pilot variants, 37 were already catalogued in Clinbar, and the new palbi 2 rules achieved an 84% concordance with Clinbar's established classifications.
14:51So for the variants, the scientific community was already confident about. The new rules arrived at the exact same correct conclusions. Exactly. But the true breakthrough happened with the uncertain variants.
15:02The 14 variants in the pilot group that Clinvar had labeled as a V US or where different laboratories were actively disagreeing on the verdict. Yes. Applying the new VCP guidelines, the panel successfully resolved 4 of those 14 mysteries.
15:18Wow. Two variants were definitively downgraded to benign, clearing those patients of genetic risk. And 2 were upgraded to likely pathogenic or pathogenic, finally giving those patients a clear medical answer.
15:30Now, resolving 4 out of 14 might not sound like a sweeping revolution to an outsider, but in the context of the entire database, It represents a 5% overall increase in classification certainty. And in the agonizingly slow world of clinical genetics, I mean, moving the needle by 5% is a massive victory.
15:47It is a profound shift, and this brings us to the deeper implications of this new framework. The defining characteristic of the HBOP VCV's case law is that it is incredibly conservative. Conservative, meaning the burden of proof is extraordinarily high.
16:01They require an overwhelming mountain of evidence before they will officially label a variant as pathogenic. And that high barrier is deliberately designed to protect patients from false positives. Let's focus on that human element for a moment because it's so important.
16:17Imagine being a patient receiving these test results. If a genetic rule book is too loose. A lab might accidentally label a harmless typo as a pathogenic killer. And the clinical consequences of that falls positive are life altering.
16:31Based on that inaccurate genetic report, a perfectly healthy patient might choose to undergo extreme prophylactic measures, like the surgical removal of healthy breasts or ovaries, just to prevent a risk they never actually possessed.
16:44That's terrifying. It's the ultimate application of 1st do no harm. Absolutely. The VCEP determined that it is medically safer to leave a variant stranded as a V US than to falsely convict it and trigger unnecessary irreversible surgeries.
16:58Exactly. But that strict conservative stance leaves us facing a rather daunting reality, doesn't it? It does. The scale of the remaining problem is vast. The Clinvar database currently holds about 6,300 unique variants for the Powell B2 gene.
17:13Okay. And despite this new optimized framework, roughly 44% of those variants are still classified as a variant of uncertain significance. At 44%. Yes, and here is the truly staggering statistic of that massive pile of unresolved VUSs, 90% of them are miscents variants.
17:33So they've basically built an incredibly accurate sorting machine for genetic variants. The Supreme Court has built an unassailable legal framework for judging the obvious crimes, you know, the completely torn pages in the completely harmless typos.
17:44But there is still this massive pile of maybe mis sense cases, just sitting in the docket waiting for forensic technology to catch up. Precisely. Because the VCEP demanded empirical proof before convicting a mis sense variant.
17:57The vast majority of them will remain in that V. US. backlog for now. The rule book is functioning exactly as intended. It is refusing to guess. So how does the scientific community eventually clear that backlog?
18:08How do we definitively prove whether a swapped amino acid in that flexible scaffolding actually breaks the PLB2 foreman's ability to repair DNA? Well, the solution lies in the laboratory. The scientific community must develop highly calibrated high throughput functional assays.
18:24What does that look like in practice? We need specialized cellular tests. Capable of rapidly introducing 1000s of specific single letter swaps into the PLB 2 G? And then we have to empirically measure exactly how each swap impacts the protein's ability to perform homologous recombination repair?
18:42Okay, so once scientists can physically observe a specific mis sense variant, failing to repair a double strand break in a Petri dish that provides the hard empirical evidence the rule book demands. Exactly.
18:53Once those functional assays are validated. The VCEP can reconvene, update the specifications to accept that new line of evidence, and finally begin moving those 1000s of miss ends variants out of the VUS pile and into definitive clinical categories.
19:07It's a powerful reminder that science is an inherently iterative process. This new Palabi 2 rule book isn't a stagnant document etched in stone. It is a living framework designed to evolve in tandem with our technological capabilities.
19:21The work of the HBOP VCP has set a rigorous new gold standard, ensuring that the genetic verdicts delivered to patients today are as accurate, protective, and scientifically sound as possible. It really is an incredible step forward for patient care.
19:35The HBOP MCEP has successfully tailored ACM JamKit guidelines for the Palbutu gene, creating a conservative, evidence-based framework that improves classification accuracy. By limiting the use of certain evidence codes, especially those relying on common cancer phenotypes or unproven misense pathogenicity, these specifications reduce clinical uncertainty.
19:56What does this mean for the 1000s of patients currently sitting with a variant of uncertain significance in their medical files? It means we are getting closer to the truth step by step. This episode was based on an open access article under the CCBY 4.0 license.
20:10You can find a direct link to the paper and the license in our episode description. If you enjoyed this, follow, or subscribe in your podcast app, and leave a 5 star rating. If you'd like to support our work, use the donation link in the descriptions.
20:23Now stay with us for an original track created especially for this episode and inspired by the article you've just heard about. Thanks for listening and join us next time as we explore more science face by base.
20:50Staring down a string of letters in the dark A family's future balanced on a single mark Some changes shout in silence. Frames that fall apart And some just drift like static never hit the heart. We need a rule that doesn't bend with every tide.
21:08A map of what to trust. What to set aside, fit, break still repair, we name it. No disguise. It's only a sure, we won't sell it as a sign. Cut the noise, cut the signal, clean and bright. Draw the line where the ending turns to switch off at night.
21:26If it's loss of function, we can call it what it is. It's missing smoke, we all pretend it's fire in the wind. We lay the crowds of databases of frequency hum Not too common to be dangerous. Not too rare.
21:54To be none, cold get tighten, some get muted, some are thrown away. So the same variant means the same thing, day after day. There's a boundary in the tail where the cutoff lives. A last safe fetch before the verdict shifts start, and they whisper spicy shadows say still unproved.
22:12So we hold the claims to what the evidence can move. Cut the noise, put the signal clean and bright. Draw the line where the ending turns to switch off at night. We harmonize. The labels make the hardcores kind.
22:26So uncertain. Take it smaller and the care gets back in time. Uh, uh, uh, uh, uh, uh, uh, uh, uh, uh, uh, uh,
