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Depression and Heart Disease

The Genetics of Huntington’s Disease


hello my name is Gene and I’m a strand
of DNA and I’m here to explain the genetics behind Huntington’s disease
whoa whoa whoa why do I look like a pair of jeans seriously guys you had one job
I’m meant to look like a genetic strand of DNA not a pair of denims I guess you
want me to do the whole video looking like this don’t you
oh sorry Gene we can’t change it now uh-huh hello my name is Cody and I’m a
CAG repeat me and gene our co-presenters today gene hey why are you dressed like
jeans for hi Cody thank this guy over here amateur I see you got Cody’s outfit
right though hey gene can you explain DNA to the viewers and give me a call
when you are ready to teach them about CAG repeats that’s my part sure Cody so
HD is a genetic neurodegenerative condition which means it can be
inherited through a family to understand the genetics of HD you need to first
understand DNA genes and chromosomes DNA is something we inherit from our parents
it’s like a recipe on how to make each of us DNA is a genetic code which hello
again everyone you call Gene are you done with DNA already
that was real quick hi Cody no I was talking about the
genetic code oh my bad I thought you called my name
my hearing is not so good I don’t have any ears so where were we
yes DNA is a genetic code which decides things like our hair color height and
aspects of our personality DNA is made up of things called genes oh that’s real
funny you should be a comedian Thanks you know very well it’s not those kind
of genes it’s a gene there are around 23,000 genes in the cells in our bodies
each gene is like a set of instructions for cells in our body to help it work
properly Gene’s are packed into things called
chromosomes we have 46 chromosomes in our DNA
23 for Mom and 23 from dad we know that HD is caused by a gene on
the fourth chromosome that’s not fair I don’t have any control over any of the
genes in me dude okay as I was saying HD is caused by a mutation on a gene in
chromosome four oh here’s the comedian again stop it stop drawing the x-men
mutation does not have to mean mutants in this case one gene is chromosome four
is longer than it should be and that causes HD this long gene is caused by
something called CAG repeats maybe I should call Cody now as he likes to do
this part Cody hello again everyone I’m at the CAG
repeat part Cody well I’m Cody the CAG repeat so I got
this buddy so you may or may not know that our DNA is made up of four bases
which are known as adenine abbreviated a Cystosine C guanine G and Thmine T
these bases are the code behind all our DNA if we were to write a gene code down
it would look like each letter stands for one of the four DNA bases the gene
that causes HD has a CAG repeat on it this is normal everyone has a CAG repeat
on this team usually about 16 or 17 repeats but people with HD have more
repeats than usual thanks G hi Cody you’re an expert in explaining this
how many CAG repeats does it take to get HD thanks gene people with HD usually
have over 40 CAG repeats but there are actually four ranges that CAG repeats
may fall into as I said everything over 40 is going to cause HD for that person
and there is a risk of passing HD on to their children something between 36 and
39 repeats means you may or may not get HD but there is still risk of passing HD
on anything between 27 and 35 means that person won’t get HD but there is a very
small chance HD could be passed on finally anything below 27 means no HD
for you and no risk for future generations amazing I can see why they
hired you Cody I hope they are paying you well
for this job you know your CAG repeats Gene, it’s for charity I’m doing it for
free oh wow how nice of us remind me to thank my agent next time I see him all
right moving on so how do you inherit HD from someone and what risks does that
give people of getting HD great questions Cody I have a question for the
audience how many copies of a gene do we have inside us the answer is two copies
of each gene you might think it would be one but if you remember we said that you
get one chromosome of genes from your mother and another from your father
giving you two of everything so people actually have two copies of
the gene that causes HD one from their mom and another from dad because HD is
what we call autosomal dominant it only takes one gene that has HD to cause
someone to get HD so in this example this person has one gene that is 40 plus
CAG repeats and will cause HD they have another which is completely normal but
because they have one gene with HD the person will unfortunately develop HD
gene so what happens if someone who has HD wants to have a child is there a risk
of inheriting HD yes there is Cody let’s use this guy as an example he has the
gene that will cause HD but he doesn’t have any symptoms so he is healthy right
now let’s say he is a married man his wife comes from a family of know HD and
has two normal versions of the gene that causes HD so she has no risk of getting
HD or passing it on if they were to have a child together the child would inherit
one gene from Dan and another from mom we don’t know what gene they would
inherit from mom or dad but they must have one from each this leads to four
possible outcomes for the child one the child inherits dad’s normal gene and
mums first normal gene equaling know HD 2 the child inherits dads HD gene and
mom’s first normal gene equaling HD 3 the child inherits dads HD gene and mums
second normal gene equaling HD or the child inherits dad’s normal Jian
mums second normal gene equaling no HD if you are good at math you will realize
that out of those four possibilities two cause HD and two don’t which means the
child would have a 50% risk of inheriting HD from their parents
nice work Gene what about if your grandparent has HD but you don’t know if
your parent does what kind of risk do people have in that situation thanks
Cody well in this case we could say that the grandparent has HD so the risk is
100% and we don’t know if their adult child the parent has HD so they are
still at risk 50% of inheriting HD if they had a child then we would have the
risk of their parent to give a probability that the child would get HD
in this case 25% but this probability could change over time because this
probability was done with no knowledge of the parents HD status so if the
parents HD status becomes known at some point that would change the child’s risk
if the parent did have HD and the child’s risk would increase to 50% but
if the parent didn’t have HD then the child’s risk would disappear to 0% okay
folks that’s it we are at the end of this video hope you understand how the
inheritance of HD works a bit better now please if you have any questions just
ask us at hdyo support at hdyo dot org thank you
everybody hopefully next time we meet and i’m dressed correctly i’m going off
now to say hello to my dear agent

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