well welcome to another MedCram comm board vitals question this question
comes from the USMLE step one and comlex level one question banks an 11 year old
boy complains of sore muscles muscle cramps and severe fatigue following
exercise your analysis shows myoglobin urea which of the following enzymes is
this patient most likely deficient in alpha one six glucose 'days
glucose-6-phosphatase hepatic glycogen phosphorylase lysosomal alpha one for
glucose I'd ace or my o phosphorylase now we've talked about these glycogen
storage diseases in the past and I would recommend looking back on a couple of
questions that we've done regarding this and if again if you review those
differences specifically Pompeii's von Guericke
the cartel's these are the ones that it get tested over and over again the thing
I want you to aware of is the fact that the patient is 11 years old so you know
he lived out of infancy and toddlers and he's only having muscle cramps so this
is one of the more mild types of diseases so you should know which that
one is and again let's go over that and review that so let's take a look here at
the glycogen storage diseases so I've got them listed there's about eight of
them actually there's nine if you can count the zero each glycogen storage
disease is a problem with an enzyme in the process of making the glycogen and
specifically storing it so there's only one that's actually for making glycogen
and all the other ones are storing it so what happens is the glycogen accumulates
in the liver and it can accumulate in different compartments and that causes
different problems interestingly type 0 which is very rare is a problem with
actually making it and so what happens is that the liver is actually pretty
small in these cases and it's actually quite mild but all of the other ones
that you would be tested on is one through eight and let's go through those
so there's von Gierke which is a problem with glucose-6-phosphatase and this is
pretty severe they usually have problems very early in life there's liver
enlargement because the storage of the glycogen and the
glucose is very very low pretty severely low so these people have problems very
early on that's one of the things that you'll see with von gierek's disease
Pompey's disease which I have here in red is a problem with maltase and it's
an alpha 1-4 alpha one six glucoside ace and the key to remember what this is it
is number two and there are two types there's a pediatric and there's an adult
type the pediatric is pretty severe and they're usually dead by 2 from
cardiomyopathy and all organs are affected because of this with the adult
however there is less of a deficiency and they actually do fine up until later
in life maybe 20s or 30s and what they start to get is lower extremity weakness
which sounds familiar here right so there's less of an accumulation and what
you'll see is you'll see these lysosomes in the cells that are full of this stuff
so lysosomal accumulation is key for pompes disease which is type 2 and
remember there are two types of the type 2 there's pediatric and adult Corey is
the debranching enzyme it's a milder form of type 1 whereas anderson is a
branching enzyme that's very severe so think of the branching as severe and the
debranching is not so severe I don't know if it'll be helpful to memorize mlo
1/6 glucose I days for the debranching or alpha 1-4 alpha 1 6 for the branching
but you may need to know these although Corey and Anderson are probably not
tested as often one that is however is McArdle's disease phosphorylase you
should know that they just get muscle cramps not really weakness just some
muscle cramps so we see a big diversity here with hers it's also phosphorylase
but it's a much milder form of type 1 and phosphofructokinase is very similar
to type 5 which we've got up here and then finally phosphorylase kinase again
it's like type 1 if you do have an enlarged liver you do have decreased
glucose like you do in type 1 which we have here but it's also a milder form so
the key here is understanding that McArdle's disease which is a type 5
gives you this muscle glycogen phosphorylase that you
see here so this is a glycogen muscle phosphorylase otherwise known as my o
phosphorylase is going to basically prevents the glycogen from being
phosphorylated so it can be metabolized anaerobically into glucose and this is
going to cause accumulation of glycogen and that's going to cause muscle cramps
so the key with this question is understanding that first of all this
kids a little bit older and there's muscle cramps so obviously this is not
something where people are dying in there you know two or three years of age
this is a less severe type of disease and it's very classic for McArdle's
disease which is my o phosphorylase okay so it can't be a which is the alpha one
six right because we get cirrhosis by the age of two here
Pompey is the alpha one six glucose adays and there's a type one there's a
pediatric and there's an elderly not elderly but the adult one leads to
accumulation and affects the lower limbs typically it's in terms of weakness not
just muscle cramps but actual weakness and the pediatric is dead by two so that
can't be it so in this situation a is actually
referring to the debranching enzyme of the one six glucoside ace it's a milder
form of type one which remembers von Gierke and von Couric's gives you liver
enlargement things of that nature so that's not what it is that's going on
here this is a debranching enzyme and a is Corey's disease and that's not what
we're dealing with here so B is glucose-6-phosphatase which is von
garrix disease and it's a much more severe form so you get liver enlargement
decrease glucose problems with uric acid hepatomegaly lactic acid things of that
nature that's certainly way more severe than
what we're seeing here in the question so that's not it
so C is hers disease or type six again a phosphorylase it's milder like type one
again this is not what we're seeing here we're not seeing liver enlargement in
the question stem we're seeing something like muscle cramping pain especially on
exercise so it's much much more mild and finally the last one is pompes disease
most of these are pediatric they're dead by two this is the alpha one for the
lysosomal where things are just not broken down and they get all sorts of
problems with a Patou megali and and again it's almost always fatal in the
pediatric population certainly not something we're dealing with here well
thank you very much for joining us