SCA3 & life in the countryside: Exploring the interplay between genetics and environment

She's a well-known scientist in Brazil and has a long and prolific journey in the field of neurogenetic diseases, especially spinal cerebellar ataxia. We are going to talk about her recent publication in the Movement Disorders Clinical Practice Journal entitled Rural Environment as a Risk Factor for the Age at Onset of Machado-Joseph Disease.[00:01:00] 

Thank you for joining us today, Professor Laura. 

Dr. Laura Bannach Jardim: Thank you for inviting me and having me today. It's an honor. It'll be a pleasure to respond to your questions. Thank you, Sarah.

Dr. Sarah Camargos: We know for a fact that certain diseases such as Parkinson's disease are more common in rural areas. How did you come across the idea of investigating SCA3? 

Dr. Laura Bannach Jardim: Well, spinocerebellar ataxia type three is rather common here in Southern Brazil. Our state is the souther most place, and we detected the presence of Machado-Joseph Disease, the other name of SCA3 in the late nineties of the 20th century. We have found these families here and they are a huge number.

Indeed they are appearing in our outpatient clinic since then. Exactly at the time when the mutation has been discovered by [00:02:00] 1994. Yeah. So the first families had been diagnosed at Mag U University. Than in 2000 other 60 families has been diagnosed at University of Porto by scales.

And since then we have been doing this diagnosis here in our hospital that is also a place that receives the publics health system individuals that has been seen here in our region in our state and city. And because of that, because we are a public system, we have this easiness to receive so many subjects with this disease.

Because they receive diagnosis and healthcare in our institution. Since then, I think we have collected, I would say 750 patients with Machado-Joseph disease. All of them, or most of them, I cannot say all, but 99% of them [00:03:00] with the same ancestral haplotype and leading us to the understanding that most of them are descendants from the same group that reaches this region of the world. In the 18th century when Brazillian settlers came here, were sent to this place of the world by Portuguese crown to populate, to occupy the space at that time. This is our historic background and that explains this founder effect. The other thing that I need to tell you about Machado-Joseph or SCA3 disease.

Is that this is a rather rare disease in our place . In our region here the the prevalence, the minimal prevalence of this disease is seven subject per a hundred thousand people. Our state has 11 million inhabitants and in this 11 million inhabitants, this [00:04:00] 750 subjects comprises these numbers nowadays.

So this is a rare disease. This is an autosomal dominant disorder, calls it by a mutation. That is correct. Arise it by an expansion of repeat motif inside the gene. This repeat motif is a CAG repeat that when translated, produces an insertion of a glutamine in the protein.

So for this reason, this disorder has been known as a poly Q as a polyglutamine disease, very similar to Huntington's disease. Autosomal dominant with anticipation phenomena, et cetera very similar, as well as SCA1, SCA2, SCA6, and SCA7, et cetera.

Dr. Sarah Camargos: Yes, very interesting. 

Dr. Laura Bannach Jardim: This expanded mutation is the cause of the disease. And at the same time, it explains the variability in the age at onset. I mean the [00:05:00] expanded repeat can be measured. We can count how many CAG repeats you have in the expansion and in part of the world, every researcher have seen that the expanded repeat is the main explanation for the age at onset of the SCA3 as well as Huntington's. For instance, in here if you find a subject from a Machado-Joseph family that carry a 75 CG repeat in his or her mutation. You can estimate that the mean age at onset of the subject will be 38 years of age, for instance. But I'm telling you about the mean age at onset. So we can do the Kaplan-Meier cures per procedure in order to see the mean or the median age and also per repeat.

And that's why it also allow us to present the predicted age at onset, and at the same time to measure the difference in each subject [00:06:00] of his or her actual age at onset compared to the predicted age at onset onset and measure therefore, who were the subjects in which the disease started earlier than expected or later than expected. And we call this the residual age at onset per person, per subject. If you have a negative residual onset, it means that your age onset was earlier than expected. And if you have a positive residual age at onset, it means that you have a later than expected age at onset. 

So for us, this information is helping to find modifiers that are neuroprotective if they are present in subjects with later than expected age at onset. 

Dr. Sarah Camargos: Yes, it's perfect. Very good explanation. But Professor Laura we know for a fact that certain [00:07:00] diseases such as Parkinson's are more common in rural areas. And how did you come across the idea of investigating SCA3 in this context?

Dr. Laura Bannach Jardim: Very good question. Thank you Sarah. As I said before we are trying to find modifier factors. If we discover a modifier factor, we can increase the presence of this neuroprotective factor. So our task is to help finding prevention and therapeutic developments.

But coming back again to the modifier factors. You remember that I said that if you inherited I would say 70 CG repeats. So we expect that you start the disease with 45 years of age, for instance. But we saw that there is a lot of people that starts before, and the other subject that starts later than expected.

So this is telling us how many modifier [00:08:00] factors do act over the pathogenic passway of the Machado-Joseph Disease. Most studies on modifier factors have focused on genetic factors, mostly because from the point of view of design, it's the most easy to do, the most rational to do. I would say you can figure out why you are studying subjects, patients in which the disease already started.

They already have the disease. So modifier factors already had acted over them beforehand, before you have seen them. If you study genetic factors, there is no confusion. There is no confusion variable because genetic factors are present since you had been born or before it. So their effects are present since you have been concepted by your parents. In contrast, environmental factors are quite hard to be, [00:09:00] studied in the past because of course the modifier factors were present in the past history of your patients. So they are quite hard to be studied and as far as I know nobody had done it before or with other diseases.

The thing that I know for sure is those studies, ecological studies, relating prevalence rates. I would say. In rural environments, the prevalence of Parkinson's disease, of Alzheimer's, of cognitive decline, of lateral myotrophic sclerosis are higher than in urban places. And then this made me and my group to think, how could we do that with Machado-Joseph?

We could not. It wouldn't never be the same because to have Machado-Joseph is enough and sufficient to inherited the mutation. And there this is nothing to do with environment, but the age at [00:10:00] onsets on the other hand, can be studied. And in relation to the urban environment versus rural environment.

That's why we decided to focus this scientific question and present these results.

Dr. Sarah Camargos: Yeah, it's very interesting because your population is homogeneous because they have the same background and the same sample types, and you could examine the environmental factors in a very good population. 

Dr. Laura Bannach Jardim: Right. I do agree with you. Moreover, we had that advantage of having the public data related to the demographic densities of our municipalities. We had this information about consumption of untreated waters as well of our municipalities. And at the same time we have our large database about our patients that have [00:11:00] been seen in our public institution for more than 20 years.

So we converge this information and it was easy to identify. Moreover I need to say, nobody knows about, how is our state Mato Grosso do Sul state have a lot of cities, large cities with high demographic densities, but most part of the territory of the land is countryside. And it's nowadays almost empty because majority of our countryside has been used to soybean acquisition as well as, pecuaria and I don't know if I need to, say this in English.

So quite a few people living there. So we have several municipalities with very low demographic densities and with high proportion of rural populations as well in these places. But you need to think, okay. You have a lot of [00:12:00] municipalities with low demographic densities, but because of that, you have a small number of subjects living there, and we need comparison to have any statistical effect. You need to have numbers of patients. Yeah, in both groups in urban versus rural groups.

Dr. Sarah Camargos: And this comes to my question, how did you measure the country side effect on these patients based on the demographic issues and what else.

Dr. Laura Bannach Jardim: Of course it's not demography the cause or the modifier factor. It's just a proxy. A proxy variable, because we are unable to measure, for instance, the exposure to pesticides or whatever. Then we read a lot and we saw that other authors have already used demographic density as a proxy of exposure to pesticides and rural areas as well as the opposite way. 

[00:13:00] In high density places you are expecting pollution exposure and industrial factors exposures as well. And I need to say to you that before studying these factors in neurodegenerative diseases, I have the prejudice that, I would think that Machado-Joseph patients will go worse in cities than in the countryside.

It was a prejudice, a romantic way of seeing rural life nowadays. Yeah. It was exactly the opposite way actually. I dunno if I replied to you, but the other thing that I saw it was very interesting was how to study the consumption of untreated water. Yeah. As a factor. And again it has been one of the very interesting results of this observational study I would say that we have published in our very, very prestigious journal.

Dr. Sarah Camargos: Very nice. The rationale behind the country side effects [00:14:00] are, what grounds for the pesticides do you think for the untreated water. And do you have more ideas about it.

Dr. Laura Bannach Jardim: Yeah we speculated a lot. In the discussion part of our paper, but it's rather risky to do that. That when I told you five minutes ago that my preconception way of what I was expecting was the opposite. It reveals that when we speculate a lot, we maybe we are, we lose the focus of the reality.

But of course, nowadays, the most important candidates that we know as neurotoxic in the countryside, in rural life would be the use of pesticides. One hand, and the other that I can remember was exposure to  gastrointestinal viruses that are more common in untreated water as well as the presence of this [00:15:00] dines. It's produced by cyanobacteria present in untreated waters that have been shown in bench studies and I don't remember the model, if it was it was a cellular model that it increases the presence of this dines products of this bacteria and enhances neurodegeneration in cellular models.

So it was quite distant from our data. Our data was just an association data. In summary, I don't know if the listeners are aware of that, but what we have seen that people that lives in places with low demographic densities and at the same time in places with higher consumption of untreated waters have a significant earlier age at onset when compared to the other subjects after controlling for the mutation because we are measuring this residual age at onset, so we are controlling for the mutation and also [00:16:00] after controlling for family effects because of course you supposed that your relatives will be near you, so everybody's living in order or in countryside or in the cities.

I do say that it's not the case because families migrate are prone to exodus, inside exodus. But we control also for that. And what we have seen was that. Especially when we compared the real extremes of the distribution because you see from the point of view of mathematics of the algebraic findings, we needed to divide our sample size into two groups.

Those with higher demographic density, I will say demographic density for a while. Okay. And those with lower demographic densities. 

If you use the median, and you remember that most people are living in high demographic densities. By the way, they are causing high demographic densities because they're [00:17:00] there.

You can see that the median is very close to the urban demographic density, so it's not that good.

But when we move it to the 25% of subjects living in those lower demographic densities when compared to the 75% of those living in the high demographic densities. Then the change was of more than three years of age. So I mean that people that are really in the countryside, started the disease 3.5 to almost four years before the other ones.

Defect size again is not that large, but it was significant. And I do believe that our patients would be happy if they can postpone for at least four years. But this is not the point. The point is that the defect size can be small because we are not measuring the real idio factor. And then moving to your question, what would be the real [00:18:00] factor?

We had already speculated about pesticides and about virus. I need to tell you that Brazil is one of the most important consumers of pesticides nowadays because our regulatory laws relaxed the use of them. There are lots of things that can be used here, even paraquat and other stuff.

But the data about consumption, it's quite controlled here. Consumption of pesticides. The data about the concentration of pesticides in rivers is also known, but it's recent. We have this data from 10 to 20 years from here. So this data cannot be used to as a factor for a disease that or had already started in so many people with nowadays their forties and fifties and sixties here is ages of year.

So [00:19:00] I would say that this data will be useful for the future studies because we have nowadays, so for the next 10 to 20 years. They can be used as risk factors.

Dr. Sarah Camargos: And professor, do you foresee the replication of your results in other cohorts?

Dr. Laura Bannach Jardim: Very nice question because we need it to confirm an association. We need to have the confirmatory cohort. Yeah. This is just an exploratory cohort. Maybe this is very, specific, very peculiar to our cohort and then something else, and not exactly the things that I'm saying.

That's why it's so important to have a confirmatory cohort where to confirm that you need to have a territory with variable demographic densities. One. Second thing. You need to have a cohort of well known disease. I would say, for instance, SCA3 [00:20:00] or maybe Huntington's disease, it would be a very good candidate to be studied in which you need to have large number of subjects because you need to remember, you need to have a large number of subjects coming from low density lands. So I. 

Dr. Sarah Camargos: And living there. 

Dr. Laura Bannach Jardim: And living there until now. Because the exposure you need to control. People changes a lot. People moves, people meet grades. So in our paper the inclusion criteria was to have been born and living, still living in the same place. To guarantee that exposure was the thing that we are measuring.

Dr. Sarah Camargos: But still, you had a lot good number of patients on this.

Dr. Laura Bannach Jardim: Yeah, I do agree. But then I can figure out this happening for Huntington's in some places like us, but Machado-Joseph or SCA3. The thing can be done, I would say in China. 'cause they had a lot of subjects there [00:21:00] and they had very controlled data as well. I was just remembering also SCA1 in Russia because Russia is also again a place in which pesticides should be in use, I would say.

Yeah. And in our country, maybe Huntington's as well. Yeah. I don't know if SCA3 is common in other places, maybe in Eastern Canada, in Toronto. I don't know actually if they can do that, but my hope was that scientists that had already been studying similar models in which pesticide effects can be measured, or animal models in which pesticides or viral things, anything has been tested now. Read this paper and maybe be inspired to do transgenic studies as well together with their models on pesticides or whatever.

Dr. Sarah Camargos: And maybe finding that they [00:22:00] can modulate genetic factors as you already demonstrated in SCA3.

Dr. Laura Bannach Jardim: Yeah, I actually, I wouldn't say I demonstrated, I raised the high possibility of that. But we need to confirm first and second. We need to find out what was this factor in order to avoid it.

Dr. Sarah Camargos: And what are your next steps to help move this field forward? 

Dr. Laura Bannach Jardim: I think I would say that in our country. Sarah, in Brazil. As well as in other underdeveloped or inequalities inside the populations because of course we have a high technologies, high people, very rich in Brazil as well.

But we have also people very poor in now in our countries. I think that, most important thing nowadays is to increase the awareness of families about the disease, to increase access to diagnosis in healthcare, and to increase genetic [00:23:00] counseling for one hand. For the other hand, we need to try to change the reality of families that are unable to interrupt their pregnancies in differently from Europe, differently from US. Why interruption of pregnancies are allowed there. There's no problem there. Whereas here, it is. People need to have access to prevention of the disease. Moreover, in secondhand, we need to also to increase access to registries and access to studies, access to clinical trials. When they come. 

And then this move is also our thoughts. Your thoughts and my thoughts to this very important issue of the price of this new therapies that are arriving in now in our horizons. Prices sometimes are impossible and first of all, [00:24:00] even in the richest country in the world.

So there is something wrong with this crisis. We know this is wrong.

Yeah, we need to change this reality. This is my thoughts about the future. 

Dr. Sarah Camargos: Okay, Laura. Thank you very much for sharing your thoughts with us and for giving your time with us. Thank you very much and have a very nice day.

Dr. Laura Bannach Jardim: Thank you, Sarah. I thank you for the same reasons. Yeah. I thank you very much for having the proclivity to talk about this disease too and maybe to reach more people and to think about these issues as well. Thank you very much. [00:25:00]