Passage Bio, Inc.
Q4 2020 Earnings Call Transcript

Published: 3 Mar 2021

[Operator:]

Thank you for holding. Good morning and welcome to the Passage Bio Fourth Quarter and Full Year 2020 Financial and Operating Results Conference Call. At this time all participants are in listen-only mode. Following the formal remarks we'll open the call up for your questions. Please be advised that this call is being recorded at the Company's request. At this time, I would like to turn it over to Stuart Henderson, Vice President of Investor Relations and Strategic Finance. Stuart, please proceed.

[Stuart Henderson:]

Thank you, Operator. This morning we issued a press release that outlines the topics we plan to discuss today. This release is available on the Passage Bio website at investors.passagebio.com under the News and Events section. On today's call, Bruce Goldsmith, President and Chief Executive Officer, and Rich Morris, Chief Financial Officer, will review our fourth quarter and full year 2020 financial results and discuss recent business highlights. Gary Romano, our Chief Medical Officer, and Jill Quigley, our Chief Operating Officer, will also be available for the Q&A portion of the call. Before we begin, please note that today's call may include a number of forward-looking statements, including, but not limited to, comments on our expectations about timing and execution of anticipated milestones, including the initiation of clinical trials and the availability of clinical data from such trials; our expectations about our collaborators' and partners' ability to execute key initiatives; the ability of our lead product candidates to treat the underlying causes of their respective target monogenic CNS disorder; manufacturing plans and strategies; trends with respect to financial performance and cash flows; the Company's ability to fund research and development programs; impacts of the COVID-19 pandemic on the Company's operations; and its ability to manage costs along with uses of the cash and other matters. These forward-looking statements are based on assumptions that are subject to risks and uncertainties that could cause the Company's actual results to differ significantly from those suggested by these statements. Given these risks and uncertainties, you should not place undue reliance on these forward-looking statements. Please refer to the Company's filings with the SEC for information concerning risk factors that could cause the actual results to differ materially from expectations, including any forward-looking statements made on this call, except as required by law the Company disclaims any obligation to publicly update or revise, any forward-looking statement to account for or reflect events or circumstances that occur after this call. It is now my pleasure to pass the call over to CEO, Bruce Goldsmith. Bruce?

[Bruce Goldsmith:]

Thanks Stuart, and thank you all for joining us this morning. Let me begin by remarking on the critical year of accomplishments we had at Passage Bio in 2020 despite the COVID-19 pandemic and other challenges we all faced last year. Our company's work is grounded in the mission to develop life transforming therapies for patients with devastating CNS disorders. We view 2020 as a foundational year in which we focused on preparing for successful transition to a clinical stage company in 2021.

[Rich Morris:]

Thank you, Bruce. And Bruce mentioned we have secured incredible financial security over the past year, which will enable important optionality as we continue to advance and grow our pipeline. As we reported in our press release this morning, we ended the year with cash, cash equivalents and marketable securities of approximately $305 million as compared to $159 million as of December 31, 2019. In addition, we also received $166 million in net proceeds from our recent public offering, which together, we expect to fund our operations for at least the next 24 months. R&D expenses were $81.8 million for the year ended December 31, compared to $29.7 million for 2019. The increase was primarily due to an increase of $24.7 million in clinical manufacturing costs, an increase of $6.6 million in preclinical research and development costs incurred in preparation for our IND filings, a $4.4 million increase in clinical development costs and $3.4 million increase in consulting expense as we prepare for clinical trials to begin in the first half of 2021. We also had a $12.5 million increase in personnel related costs, including share-based compensation due to increases in employee headcount in the R&D function. G&A expenses were $30.1 million for the year ended December 31, compared to $7.0 million for 2019. The increase was primarily due to a $15.3 million increase in personnel related and share based compensation expense due to increases in employee headcount. Our facility costs and professional fees also increased by $4.6 million and $3.3 million respectively as we expanded our operations to support our research and development efforts. Net loss was $112.2 million for the year ended December 31, 2020, compared to $45.6 million for 2019. Now I'll turn the call back to Bruce for closing remarks.

[Bruce Goldsmith:]

Thanks Rich. Looking ahead, we continue to establish Passage Bio as a leading clinical stage company focused on developing life changing therapies for patients with rare monogenic CNS disorders. As a reminder, our key anticipated milestones for the upcoming year are; to dose the first patient in the Phase I/II trial for the treatment of patients with infantile GM1 in the first quarter of 2021; report initial 30 day safety and biomarker data from that trial in mid-year 2021; initiate Phase I/II trials for the treatment of FTD-GRN and for the treatment of early infantile Krabbe disease in the first half of 2021; open our CMC research and development site in the second quarter of 2021 and finally to continue to advance preclinical programs for MLD, ALS, CMT2A and our undisclosed program in adult CNS and bring additional candidates forward. Before taking your questions, I'd like to take this opportunity to recognize and thank the team here at Passage Bio and our partners at Penn's GTP for their hard work and diligence. They set the stage for what is going to be a milestone filled year to come. At this time, we'd like to open the call up for questions. Operator?

[Operator:]

Our first question comes from the line of Anupam Rama from JP Morgan. Your line is now open.

[Anupam Rama:]

Hey, guys, thanks so much for taking my question. Bruce, just wondering what are the gating factors to dosing that first patient in GM1? And can you remind us, I think you mentioned on the call, 10 sites that you're opening up for GM1. Is it going to be site overlap with Krabbe and FTD? Thanks so much.

[Bruce Goldsmith:]

Hi, Anupam, thanks very much for the question and good morning. So I'll talk a little bit and turn it over to Gary for additional remarks. So as we mentioned on the call, we do have the manufacturer - the supply manufacturer and ready to distribute, so that's certainly in place. As we, I think highlighted also and is updated on clinicaltrials.gov, for the trial listing we have - we are starting to recruit with one site open and we're continuing to advance the other sites as well. And maybe Gary, you could talk about just the - what we're going through in terms of additional patient identification and then the comments on overlap between Krabbe and GM1.

[Gary Romano:]

Thanks Bruce. Yeah, so there's - we've seen a lot of interest in the trial, as evidenced by the number of caregivers contacting us to our patient portal to inquire about eligibility and enrollment. And as we've outlined before, we are - have a number of engagement initiatives to help us and enroll them to trial, including engagement with the rare disease community, specific advocacy groups, we have, of course, very strong relationships with sites and study coordinators, investigators, we're decreasing burden to trial participants by having a strategy for remote visits and video - in-home video assessments, as well as enhanced travel services. And we also have a vendor outreach program, working with Invitae to identify patients as rapidly and as early in disease as possible. Regarding the sites, we're planning to open at least seven sites globally. And we currently have, as Bruce mentioned, regulatory clearance in the US, Canada and the UK. We're also looking to open sites in Brazil and Turkey, where there's a higher incidence due to the founder's effect. In Brazil, we're working with Dr. Roberto Giuliani who is a world-renowned expert. It's just one example of our relationships. Regarding overlap of sites, there is some overlap in sites between the Krabbe and GM1 program. But the Krabbe is a leukodystrophy, which is different from GM1 and so we have a concentration of sites that are well known sites that received many referrals for leukodystrophy patients for the Krabbe program.

[Anupam Rama:]

Thanks so much for taking my questions.

[Operator:]

Thank you. Our next question comes in the line of Salveen Richter from Goldman Sachs. Your line is now open.

[Salveen Richter:]

Hello.

[Salveen Richter:]

Yeah, can you hear me?

[Bruce Goldsmith:]

Hi, yes.

[Salveen Richter:]

Hello.

[Bruce Goldsmith:]

Yes. This is Bruce. I was waiting today to take your question.

[Salveen Richter:]

I was so sorry about that.

[Bruce Goldsmith:]

Operator, maybe we've lost Salveen, so.

[Operator:]

Thank you. Our next question comes from the line of Yaron Werber from Cowen. Your line is now open.

[Unidentified Analyst:]

Hi, this is Brandon on for Yaron. Thanks very much for taking the questions and congrats to the team on the solid progress. Just a couple quick ones from us, first, just about the data readout in GM1. Thanks for all the detail on the design. We're just kind of wondering maybe what your plans and maybe the threshold for that release are kind of how many patients that - which dose levels you're hoping to include, whether that would be kind of more of a press release or a medical meeting kind of thing? And then just quickly on the pipeline, wondering if you're planning to release any of the preclinical data from the MLD or ALS programs this year. Thanks very much.

[Bruce Goldsmith:]

Hi, Brandon, thanks very much for the question. Yes. So the first question on the on the readout in mid-year for GM1, which focuses on 30-day safety and biomarker data, in particular beta-galactosidase enzyme activity. What we've said is that it'll be available in the middle of the year. I don't think there's a medical conference that's completely aligned with that. So we may release that via press release. I think we have to determine the final form of that as we approach. And then the second part of that question was what - basically what kind of patient data in terms of numbers? The way we've always positioned this is that we really desire to release data on a complete cohort. And in this particular trial design for GM1 in the late infant - the late onset infantile patients, cohort is two patients. And so we would expect, to report on those two patients. And obviously, that would also be contingent on bringing that data to DSMB and then also thinking about expanding both to a higher dose for the late onset patients, and then the lower dose for early onset patients later this year as well. So that's how we think about the release of the initial data. And on your - can you repeat your second question? Apologies.

[Unidentified Analyst:]

No, that's alright. Thanks very much. It's really just about if you're have any plans to release any of the preclinical data from the MLB or ALS programs?

[Bruce Goldsmith:]

Yeah, that'll be dependent on both Congress availability and abstracts that were submitted. And that might be submitted, as well as any papers that are written by Jim Wilson and his team at GTP. As you know they're responsible for the preclinical data. So until those become public, in terms of any potential papers et cetera, we're not commenting on when those data would be released.

[Unidentified Analyst:]

Okay, great. Thanks very much.

[Bruce Goldsmith:]

Thank you.

[Operator:]

Thank you. Our next question comes from the line of Salveen Richter from Goldman Sachs. Your line is now open.

[Salveen Richter:]

Good morning. Thanks for taking my question. I'm sorry, the technical difficulties earlier. Maybe you could just talk about the Natural History work that you're doing for these indications and how that's playing out in cadence with running your clinical trials. And then also as you look at the pipeline that's coming from Penn, how you're thinking about prioritization of that on the board?

[Bruce Goldsmith:]

Sure. So why don't I make a brief introductory comment and I'll give it to Gary to talk about how we're approaching kind of Natural History and maybe we can focus on both GM1 and Krabbe disease. The basic idea that we're approaching - how we're approaching this is, is looking at both studies that we're running, for example in GM1 we're running a study with the Orphan Disease Centre at Penn to create our own Natural History data. But we're also looking at sites that might have data and we could pull that information in. And the whole idea is to have this as a potential competitor, once the study in terms of the expansion cohorts could read out. So we don't necessarily need that data any time in the near term. But we certainly want to generate it and make sure that there's a high-quality data for potential comparison. And maybe Gary you can talk a little bit about in more detail about how we're approaching this with GM1 and Krabbe.

[Gary Romano:]

Yeah, thanks, Bruce. So in GM1 we're conducting our own a - through the Orphan Disease Centre at Penn, a prospective Natural History Study that matches our cohort very closely, - sorry, our interventional trial protocol very closely. And it's also being conducted at the same sites as the study - as the interventional study. This is to ensure compatibility of the data. That study is enrolling and we've seen enrollment pick up recently. So we're very happy to see that. We're also planning to access other sources of data and we've had conversations with FDA about this strategy. What I mean by that is, is other data that exists either from academic cohorts or even publications. In Krabbe, thanks to the fact that there are a number of academic longitudinal observational studies in Krabbe infants and a wealth of Natural History data as a result. There, we don't feel that it's necessary to initiate an independent prospective Natural History Study, instead, we're engaged with those centers who've collected that data and working with them to gain access to the data to use in comparison to our interventional trial.

[Bruce Goldsmith:]

Great, thanks Garry. And then on prioritization, as we think about new potential indications, we essentially look at a number of different attributes. The one really critical driving factor that is underlying the foundation of a company is, can we produce a program that is highly differentiated? And the way we think about this in GM1, Krabbe and FTD is, are there reasons to believe that this - that the capsid, the vector, the combination of those, or the administration, for example, can lead to a highly differentiated and potentially best in class approach. And that's certainly the driving factor behind selection of new potential additions to our pipeline through the 10 remaining options that we have. And then we look at things like feasibility, develop ability, and obviously also commercial potential at some level as well. And we put those together. And when we think about develop ability and feasibility. We also think about other animal models that are somewhat predictive or highly predictive, can we overcome any technical challenges to reach the clinic. And we do this in very close collaboration with Jim Wilson and his group, ranging from the manufacturing and vector core group to the preclinical scientists as well. And so it really is an integrated effort to think about which new indications we could bring in. And that's resulted obviously, in one additional indication that we brought in last fall, which is in an unnamed adult CNS neurodegenerative disease that we're highly interested in. And Jim and his team are now progressing from a preclinical perspective. And we're certainly interested in growing our pipeline more this year as well.

[Salveen Richter:]

Thank you. That's very helpful.

[Operator:]

Thank you. Our next question comes from the line of Neena Bitritto-Garg from Citi. Your line is now open.

[Neena Bitritto-Garg:]

Hey, guys, thanks for taking my question. So I just had a question about the Krabbe disease study. I saw on clinicaltrials.gov some of the inclusion criteria. And I guess, can you just talk a little bit about how well the criteria that you're using to screen patients kind of correspond with what's generally screened for under some of the newborn screening programs in terms of, like GALC activity and things like that, since I noticed that I think you are allowing pre-symptomatic patients into the study as well.

[Bruce Goldsmith:]

Sure. Thanks Neena. Thanks for your question. And I'll probably turn it over to Gary to highlight several of the inclusion criteria that we think are important and kind of talk through those considerations. Gary?

[Gary Romano:]

Sorry, for mute, yes. Yeah, so for the Krabbe study, we're going to enroll early infantile Krabbe disease, this is patients who have onset before six months of age, and we're enrolling patients who are ages one to nine months of age. Your question was around what goes on in screening and there, there are enzyme activity screening for GALC where our inclusion criteria include GALC activity. Also, importantly, whole blood cytosine levels, we have a threshold there. That's to - that is because cytosine levels, the threshold we're using 10 nanomolar, is been shown to be predictive of in the early infantile form of disease and rapidly progressive early infantile form of disease. They'll also have to have biological, pathogenic GALC mutations or big gene variants, as described. And as you mentioned, we are enrolling both symptomatic and pre-symptomatic patients in this trial. So that's - that they have to - will have to have a minimum level of neurological and developmental exhibit, a minimum level of neurological developmental function. That is they can't be too far progressed to be in the trial. We're going to be enrolling in the study in two separate cohorts. We're going to start with cohorts that are the older base children who are four to nine months of age, and then with acceptable safety, initiate dosing in the younger infants, one to four months of age and also dose escalate in the older infants.

[Bruce Goldsmith:]

Yeah. Thanks Gary. And I think to bring it back to, I mean to your - to those screening criteria and how that links to newborn screening. It's a little bit variable because this is state-by-state on the on the nine or 10 states that have newborn screening in place for Krabbe disease. But all do start with I believe, GALC enzyme tests. And then what if there's a - and it's also possible to look for mutations first. But those all would then precipitate a more quantitative look at either the mutations or the GALC enzyme levels, and then also potentially cytosine. So it lines up fairly well. But obviously, the screening by any state level newborn screening would obviously be followed by our own screening criteria as well. So it does line up at least at the beginning quite well. And obviously it requires additional testing for entry into the study.

[Neena Bitritto-Garg:]

Okay. Thank you.

[Operator:]

Thank you. Our next question comes from the line of Gbola Amusa from Chardan. Your line is now open.

[Gbola Amusa:]

Great, thanks for taking my call. So you've shown that you can get three IND's cleared up very recently. I'm curious about your sort of next cluster of indications in MLD, ALS, CMT2A and the adult CNS indication. Question is whether there are any unique device related issues on those programs or other issues that you're focused on to move them forward and get cleared.

[Bruce Goldsmith:]

Yeah, thanks. And thanks for the question. We're really not commenting on the other approaches. We haven't kind of talked about the - even the vector selection or the potential target population at this point. So we'll have to wait to talk about this, as we define the programs. I think the first three indications were a little bit different because they were far advanced at the time, we went public and really had a lot more detail in those as we progressed towards both filing and then obviously for the IND approvals. And we're likely to follow that same pattern, which is, as the program moves through, for example, IND enabling studies, as well as potentially showing activity in various models of - disease models, we'll give more and more detail as those progress. But right now, we're not willing to kind of give that information publicly because it just hasn't been completely defined at this point until we have a candidate.

[Gbola Amusa:]

Sure. I may get the same response to the next question. So forgive me, but in ALS, we've seen for example, I think one preclinical program has been sitting there for five years elsewhere. Can you talk to conceptually about what issues you're trying to overcome to ensure that your program moves to clinic in a reasonable amount of time?

[Bruce Goldsmith:]

Yeah, I think - yeah, it's - without going into a lot of the details, I think, what Jim and his team are looking at are both the expression of the particular enzyme as well as suppression of the mutation in CNI and in the balance of that, as well as readouts in potential disease models, as well as permanent dynamic models. And those would kind of give us the clear pathway forward, or the decisions that we have to make to revisit the constructs. And I think that that's what some of the other companies have also faced that you're alluding to. So we're being very, I think, careful and judicious in our in our preclinical work that again, Jim is conducting to diverse this as much as possible before we move forward.

[Gbola Amusa:]

Great. Thanks. And congrats on the progress, look forward to biomarker data in the year ahead.

[Bruce Goldsmith:]

Thank you.

[Operator:]

Thank you. Our next question comes from the line of Laura Chico from Wedbush Securities. Your line is now open.

[Laura Chico:]

Good morning, thanks for taking the call. I guess, first question, certainly looking forward to the safety biomarker data for GM1 in the middle of this year, but wondering if you could elaborate a little bit further on potential timing to clinical data. And kind of given the size of the cohorts, just trying to understand what would you need to see at this stage from the clinical data to advance to further studies and then I have one quick follow up after that.

[Bruce Goldsmith:]

Yeah. No, thanks very much for the question, and thanks for joining us. So the way we're thinking about this for GM1 and Krabbe and also for FTD are all trying to look at as much Natural History diseases - of the disease as we can to think about what could trigger the expansion. And obviously, the primary goal of all of the initial cohorts is clearly safety. But then we're going to look at either enzymatic activity or in the case of FTD, to looking at progranulin levels, and then potentially, in those early stages we're only going to have 30 days of those samples, is really to move forward to the higher dose in order to then progress to potential expansion, expansion arms and looking at longer term follow up for potential biomarkers of disease progression, or disease modification. So the early decisions, I think, and I'll turn this over to Gary as well, if he ever has any additional comments, but the I think the early decisions are really about safety and initial view of the enzymatic activity or protein levels that we're able to achieve. Gary, is that a fair summary or do you have any other?

[Gary Romano:]

Yeah, well, I think you covered that very nicely around the biomarker data. I think part of the question was also around when we're getting over to clinically effective? And I just make a couple comments here, maybe overall, depending on the age of onset for these patients' therapeutic effect on developmental trajectories is driven what are our clinical objectives or outcomes are. Will take - can take up to 24 months. So the primary efficacy endpoint is therefore 24 months, so that will certainly evaluate clinical changes throughout the study at defined points. I think it's important to remember that children with this GM1 show rapid developmental progression, they have lots of developmental milestones starting at six to 12 months of age. And after we, as Bruce mentioned, look at enzyme activity and disease progression markers, with longer term follow up and expansion of the cohort we'll then assess impact on patient developmental trajectories, demonstrating that the treatment is restored developmental potential, and as positive effects on patient's quality of life.

[Laura Chico:]

That's really helpful, Gary and Bruce, thank you very much. And then one quick follow up. You mentioned the Invitae LSD collaboration and wondering if you could talk a little bit how that complements or fits into your own in-house strategies to identify patients. And I guess if you could walk through the mechanics on how that information is conveyed from Invitae to Passage that would be helpful. And I guess, basically, just could there be ways to further extend this collaboration to the other disease settings outside of GM1 that Passage is working on? Thanks very much.

[Bruce Goldsmith:]

No, great question and yeah, maybe I can turn it over to Jill to kind of highlight how the programs work together and how we're thinking about both distributing information and integrating that information into in-house and again, to your point, how it works, not only with GM1, but how we're thinking about the future as well. Jill?

[Jill Quigley:]

Yeah. So Invitae has - is providing a great service for patients. So essentially, what we're sponsoring here in detail is pre-genetic screening. So when a patient is identified with GALC levels or other things and they're sent through genetic screening that is paid for, it's free, and they get results through Invitae. The way that that feeds into Passage, we obviously do not get patient specific information. But importantly, the patient now has a diagnosis and hopefully earlier than they may have otherwise received it. And they receive clinical trial information through Invitae, through their physician. So they'll be notified about our study and about other studies, and then we'll be able to funnel through the system in that way. So we're excited about Invitae coming on board. It's definitely important for early patient identification, and a longer-term view towards identifying patients as you're moving into a commercial product.

[Laura Chico:]

Thanks very much.

[Operator:]

Thank you. Our next question comes from the line of Debjit Chattopadhyay from Guggenheim Securities. Your line is now open.

[Unidentified Analyst:]

Hi, guys. Good morning. Thanks for taking my questions. This is Aaron on for Debjit. So I just had a question on how much should we read through on the risk to the basal ganglia from the GM1 study to the FTD study, since they're using - you're using different vectors? And I know that AAV1 was selected for its transduction of the ependymal cells, but how well does it transduse neuron especially relative to AAVhu68?

[Bruce Goldsmith:]

Yeah, thanks very much. So the GM1 and adjacent Krabbe program both use hu68. And if I was to interpret your question, you're talking about the DRG neurons, is that what you're referring to?

[Unidentified Analyst:]

Yeah.

[Bruce Goldsmith:]

Yeah. So yeah, we've - and maybe I'll have Gary comment a little bit about the AAV1, both at new born and other transduction as well. But let me first back up and say that we've reported and been very clear that all of the all of the programs do see some DRG neuronal death in axonopathy. However, in all of our studies, we have not seen this results in any gross symptomology. Obviously, you can't ask non-human primates. But we can we can assess the behavior and, in the study, there was not any clinical manifestations that we could see. We did see a decrease in the sensory neuron action potentials and conduction velocity, we're going to be monitoring that and we'll continue to do that, because we think it's important to investigate this in patients as well. And it's also important to note that Jim put out a paper last summer that essentially across multiple different studies routed to the administration, and also different, different AAV's, that he did see this dorsal root ganglia toxicity in basically across different studies in non-human primates. So it seems to be somewhat agnostic as to the both capsid as well as they are to route of administration, although certainly is influenced by the levels achieved in CNS. So we're going to monitor this, but we haven't seen anything clinically to date in terms of our natural non-human primate studies. So maybe I'll turn over to Gary to talk - to give any more detail, but also to talk about the AAV1, you mentioned ependymal cells, that's not the only thing that gets transduced, So Gary, maybe you can talk about anything that I missed on DRG and the AAV as well.

[Gary Romano:]

Thanks. Yeah, I think you covered the DRG. I'm happy to take any follow up questions here. Regarding the question about - I think you're asking about the bio distribution of those vectors. So we see broad brain bio distribution with both hu68, which is the variant of a benign and with AAV1. And it's really - very, very comparable, the difference is with AAV1 is that we also see very high transduction of ependymal cells, the cells that line the CSF spaces and secrete progranulin into the CSF, you see that with AAV1, whereas so with much less with the hu68. So with AA1, you see about 50% of the ependymal cells are transduced, where it's about 1% to 2% with hu68. So in a disease like progranulin - like FTD progranulin, where we believe that supraphysiological levels of CSF progranulin are going to be required to correct the intracellular deficiency progranulin, we are using AAV1 because we really want to drive progranulin levels up in the CNS. Of course, we don't know that we're going to require 50-fold normal levels, which is what we've achieved in non-human primates that AAV1 vector. But we're very happy to be able to dose escalate and determine empirically the levels of progranulin dose of our product that will need to the modified disease pathophysiology. In contrast, in GM1, we expect that our doses there, which may achieve - just so let me just put that in perspective in GM1, we don't expect to need super physiological levels. But if we can bring levels back to the levels of heterozygotes, which are 50%, they're completely - they have no phenotype and even patients with 20% of normal activity have a very mild adult form of the disease. So we feel like the bar is much lower there. And that's the rationale for the different vectors in those two different programs.

[Unidentified Analyst:]

Right. Okay. Yeah, that makes sense. All right. Thanks for the answers.

[Bruce Goldsmith:]

Thank you.

[Operator:]

Thank you. Our next question comes from a line of Yasmeen Rahimi from Piper Sandler. Your line is now open.

[Yasmeen Rahimi:]

Hi, team. Thank you so much for the great updates. I have a lot of very tedious questions around beta-gal measurements. It's critically important data readout on med this year, so maybe we could spend some time talking about the beta-gal assay, how it works, variability associated with it. Is there a certain consideration and blood or CSF collection that we should be aware to contribute or reduce their ability in the essay? And then secondly, maybe also help us understand, what are substrates for beta-gal that you're going to be measuring and hopefully sharing with us at day 30, the significance of those biomarkers as proof of concept? And thank you for taking my questions.

[Bruce Goldsmith:]

Hi, thanks very much for the question as well. Yeah, in terms of the details of the of the beta-gal assay, certainly turn that over to Gary to talk through. And I think you were asking not only the details, but also are their idiosyncrasies in terms of blood and CNS kind of measurements. I guess, Gary can maybe address that two or I can jump back in and then -

[Gary Romano:]

Yeah, I'm happy to do that. Yeah, so just first, as I think you understand, we're planning to measure safety and 30-day biomarker data in the program as our first data readout. And that will include levels of beta-gal activity in both CSF and serum. And we certainly hope to see treatment related increases in beta-gal activity in those fluids. And that will depend, of course, on the magnitude of the increase rates we observed, and our ability to detect it. To speak to some of your questions about the intricacies of the beta-gal assay, we're using a form metric assay. And that's what's used across the field. One challenge is that in normal subjects, beta-gal activity in the spinal fluid is much lower. It's about 20-fold lower than it is in serum. And another challenge to this assay is that beta-gal activity is very labile. So requires very careful sample collection and storage. We've worked through a lot of the analytical methods to optimize this. So these factors can make detecting CSF - levels in CSF where it's much lower a challenge. But as I said, we've developed the analytical methods to do so. And we're confident we're going to be able to measure activity in serum and probably CSF. But we're not - we're also planning to use not just beta-gal, measure beta-gal directly, but also indirectly by looking at substrates, measuring various substrates with beta-gal and also by looking at other indicators of lysosomal function. So hexosaminidase which shows a compensatory increase in the presence of the lysosomal storage, we'll be looking at that as well as another indicator. So we'll be looking at the totality of the data, the beta-gal activity, but also these other biomarkers to understand the impact of our treatment on beta-gal activity and lysosomal function.

[Bruce Goldsmith:]

Yeah, and I would just add one thing. I think we've mentioned this before. This is obviously an ICM injection. And while there are specific technical challenges of measuring potential CSF levels, just because of the low indulgence levels of both patients without - people without the disease and people with the disease, it's going to be very low. But since we're doing ICM injection, and we're measuring both CSF and serum we'll be very happy to see increases in serum for beta-gal independently of CSF, just simply because for injecting into the brain, we see blood levels increase, that would also be a very positive outcome. And then as Gary said, we're also looking at the downstream hexosaminidase and I think, keratan sulfate is another downstream markers as well. So again, the way we're thinking about this is the totality of the data, as well as the different compartments both CSF as well as serum.

[Yasmeen Rahimi:]

Thank you, Bruce, for the color, maybe one follow-up question. Do we have a good understanding the day-to-day variability and beta-gal activity and blood in these patients, I guess what I'm trying to understand is, is there going to be a fluctuation between day 30 versus maybe day 60 or even day 30 versus day 31?

[Bruce Goldsmith:]

One of the things we're - so I'm not sure day-to-day, but I know that Gary and I have talked about that we're going to try to account for any circadian rhythm changes like by asking for collection at similar times during the day. I'm not sure if there are in these children for example, monthly cycles. It's a great question. But I don't know Gary, if you know the answer to that either.

[Gary Romano:]

Yeah, there is - we will certainly anticipate some biological variability. But it can save the planet from our preclinical studies with the mice and NHPs we see we see durability of effect on beta-gal activity. And so we think that we were able to still measure a treatment effect over and above that biological variability.

[Yasmeen Rahimi:]

Great, thank you so much for taking my questions, and we're looking forward to the data.

[Bruce Goldsmith:]

Thanks Yasmeen.

[Operator:]

Thank you. Ladies and gentlemen, this concludes today's conference call. Thank you for participating. You may now disconnect.