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Current time:0:00Total duration:10:49

Neurodevelopmental disorders: Sufficient and necessary causes

Video transcript

so let's take a look at a few of the more common events that can cause neurodevelopmental disorders and maybe let's do that by sort of categorizing them here so let's draw a line down here and pop nature down on this end and nurture on the other end here so now we've got a little spectrum that goes from nature all the way to nurture and you've probably heard these terms before nature and nurture and what we mean when we say nature what we're talking about are things that are innate things that we are born with so for example our DNA our genetic instructions that we have inside of our cells that tells our body what to do and what to make this is part of our nature and let's actually put DNA down here on the nature side of our spectrum of causes of neurodevelopmental disorders so we'll just say genetics here because changes in our DNA like maybe if our mom or our dad or maybe both of them if they pass on mutated genes well this is one of the possible events that can lead to a neurodevelopmental disorder right and I should actually point out here that we're looking at sort of broad causes of neurodevelopmental disorders kind of in general we'll look at some specific examples shortly but right now let's just think broadly just so that we can get a sense of what sorts of overarching causes in general can lead to neurodevelopmental disorders so on the other end of our spectrum here when we say nurture what we're talking about is our environment all of our personal experiences that happen after were born so for example I recently had an infection called meningitis which is when our meninges these protective membranes that cover our brain in our spinal cord they become infected so I developed this infection from my environment rather than something that I was born with and we can actually put infections including meningitis down here on the nurture end of our spectrum as a possible cause of a neurodevelopmental disorder so you might be thinking right now hold on so if she had meningitis and if infections like meningitis can cause neurodevelopmental disorders does that mean that she has a neurodevelopmental disorder and that's actually a really good question and it brings us to a really really important point and that's that all of these different events that we're talking about in order for them to result in a neurodevelopmental disorder they need to occur during the critical periods of development so while the fetus is developing during pregnancy or during the actual birthing process or maybe shortly after birth within the first few months two years of life and that's why we call them neurodevelopmental disorders because when these events occur during these critical periods of development they disrupt development in some way so for me I had meningitis around my mid-20s so I passed these critical periods of development and my meningitis dating results in a neurodevelopmental disorder and let's actually keep this question in the back of our minds because we're going to look at it again shortly when we talk a bit more about this word cause so let's jump back here to our spectrum and while we're here looking at nurture let's pop down something else let's pop down trauma and by trauma what I'm talking about is something like head trauma maybe from a car accident or a fall and we can also put down deprivation and when I say deprivation what I mean is something like temporary hearing loss during the first few years of life maybe from recurrent ear infections in infancy or toddlerhood and let's kind of move to the middle of our line here at the middle of our spectrum to talk about things that kind of fall in between nature and nurture so these are things that might happen before a baby is born so during pregnancy but are due to the environment that the fetus is in so if we're exposed to certain substances or toxins maybe if mom drinks alcohol or smoke cigarettes while she's pregnant this can cause certain neurodevelopmental disorders or maybe if mom doesn't get all of her important vitamins and minerals so for example maybe she doesn't get enough folate one of our B vitamins while she's pregnant so these sorts of nutritional deficiencies can also result in a neurodevelopmental disorder because fetus relies on getting its nutrients the fuel that it needs to grow properly from mom so these are some of the main types of events or conditions that can cause neurodevelopmental disorders and I promised that we would go over some specific examples and talk more about that term cause so let's do that let's put some examples down of some specific neurodevelopmental sorters so how about Down syndrome and cerebral palsy and attention deficit hyperactivity disorder will just put ADHD for that one will use these three disorders in particular because each of them is going to help me demonstrate a particular point that I want to make and let's actually draw a circle for each of these and we'll put the causes of these different disorders in these circles here will kind of make what we call a causal pie chart so if we look at Down syndrome Down syndrome is caused by extra genetic material from chromosome 21 so let's put that in our Down syndrome circle here extra genetic material from chromosome 21 and sorry why would this even happen well this usually happens because the person has three copies of chromosome 21 rather than two and you may have heard this being referred to as trisomy 21 try meaning three and saw me referring to chromosome and 21 because we're talking about the 21st chromosome so when someone has this extra genetic material from chromosome 21 they will develop Down syndrome so we call this type of cause this extra genetic material a sufficient cause where sufficient means that every time this happens so in this case the extra genetic information from chromosome 21 the outcome Down syndrome will always follow so a totally different example of a sufficient cause is if I throw water on you right you will definitely get wet each time I throw water on you you'll get wet so me throwing water on you is a sufficient cause of you getting wet whereas an insufficient cause of you getting wet would be maybe like walking past a sprinkler it's there but you may or may not get wet now if we come back to down syndrome here in order for someone to develop Down syndrome they must have extra genetic material from chromosome 21 in other words every person with Down syndrome has this extra material from chromosome 21 so because of this because this is a requirement for the development of Down syndrome we also call this a necessary cause necessary meaning that we need this to happen in order for our event down syndrome to occur so extra genetic material from chromosome 21 is is sufficient and a necessary cause of Down syndrome sufficient because it alone will always cause Down syndrome and necessary because you can't have Down syndrome without extra genetic information from chromosome 21 so with these definitions in mind let's check out cerebral palsy next well there are actually quite a few different events that can each result in cerebral palsy let's draw another pie chart here and let's say that each of these represents a different person with cerebral palsy and we could potentially draw a hundred more circles here to write down all of the causes of cerebral palsy but I'm just going to use two examples for now so in this first one here one cause of cerebral palsy is trauma so maybe this person was in a car accident when they were just a few months old and let's make our other example here an infection so maybe this person had an infection like meningitis a few days after they were born now this brings us back to that thought that I wanted you to hold on to when we were wondering why I don't have a neurodevelopmental disorder even though I've had meningitis because that question leads us really nicely into how we can use the word cause in different ways so while both of these people here have cerebral palsy because of these events like trauma or infection these events don't always cause cerebral palsy so because they don't always cause cerebral palsy these are insufficient causes right there the sprinkler and let's see if any of these events are necessary causes in in other words does cerebral palsy require one of these events well this person here they develop cerebral palsy but they never had an infection like meningitis so meningitis isn't a necessary cause right we don't need meningitis in order for cerebral palsy to occur and this person they develop cerebral palsy but they haven't sustained any head trauma so head trauma can't be a necessary cause either so none of the causes of cerebral palsy are necessary causes right remember our example where I caused you to get wet because I threw water at you well there are other ways I could get you wet right I could spray you with a hose or push you into a pool both of these will leave you pretty soaked as well so me through in water at you isn't a necessary cause of you getting wet because I can accomplish my goal of soaking you without it and it's the same kind of idea for these different causes of cerebral palsy here for both of these people these events for them have caused cerebral palsy but remember that there are lots of potential causes of cerebral palsy so infection or trauma aren't necessary causes of cerebral palsy so let's look at ADHD and with ADHD well we haven't quite figured out all the details behind the causes of ADHD but we have discovered some events that increase a person's chance of developing ADHD so we think that these events sort of come together and form a sufficient cause of ADHD so let's make up an example of what this might look like so maybe for this person ADHD runs in the family maybe mom or a dad have ADHD themselves so let's put genetic predisposition down here as one wedge in our pie chart and maybe mom smoked while she was pregnant with our kid here with ADHD so let's put maternal cigarette exposure here is another wedge and let's make our last wedge exposure to toxins may be something like exposure to lead from old school lead paint while the person was a young kid maybe he used to eat paint chips from his bedroom wall when he was little I know at least one person who's done this so we know that these events increase the chance of ADHD developing but alone might not be sufficient enough to cause ADHD but if we combine them together like we have here we think that the combination might be enough making them together a sufficient cause of ADHD and none of these individual events is a necessary cause of ADHD because not everyone with ADHD has a genetic predisposition or was exposed to lead or cigarette toxins so we don't need any one of these individual events in order for ADHD to develop