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  #1  
Old 03-07-2012
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Biochemistry The cause of this non-ketotic hypoglycemia

A 3-year-old Caucasian boy of Scandinavian descent, who had been developing normally, contracted otitis media. Because he had not felt well, he missed two meals. Suddenly, he became lethargic, started vomiting, had a violent seizure, and became comatose. His parents called 911, and he was put on a saline IV drip and taken to the emergency department. There, his physician immediately ordered a complete blood count, a liver panel, a chemistry panel, and a urinalysis.
A finger prick test showed that the child was hypoglycemic but not ketonic. In taking a history from the mother, the attending physician finds that an older sibling died mysteriously in her sleep as an infant. He immediately orders the saline IV drip to be changed to a 10% glucose solution, and shortly thereafter, the patient starts to recover. Several hours
later, when the laboratory results become available, it is determined that the boy’s serum glucose value had been 35 mg/dL and that he had slightly elevated serum blood urea nitrogen (BUN), ammonia, and uric acid levels; an anion gap metabolic acidosis; and his liver enzyme values were also elevated. However, both his serum and urine ketone levels were zero.
The child most likely has which one of the following?
(A) Glucose 6-phosphatase deficiency
(B) Medium chain acyl-CoA deficiency
(C) Carnitine acyltransferase deficiency
(D) Primary hyperinsulinemia
(E) Acute intermittent porphyria
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Ans is B, but did you miss the word dehydrogenase in the name of Medium chain Acyl Coenz A dehydrogenase deficiency?
Thanks.
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Quote:
Originally Posted by patho2012 View Post
Ans is B, but did you miss the word dehydrogenase in the name of Medium chain Acyl Coenz A dehydrogenase deficiency?
Thanks.
how do you know its B over C?
both B and C are involved in this B-oxidation pathway, which is the pathway at fault here.
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Correct Answer

My answer is

(B) Medium chain acyl-CoA deficiency

R
ecall that Fatty Acyl CoA dehydrogenase exist in 3 forms
- LCAD= long chain acyl coA dehydrogenase : chains > 10 carbon atoms
- MCAD= Medium chain ..... ..................... : chains 8-9 carbon atoms
- SCAD= short chain .............................. : Chains <8 carbon atoms


They all act in B oxidation in mitochondria to make ketones.
Deficiency in Fatty acyl CoA dehydrogenase : Hypoglycemia, hypoketonemia,

Treatment: IV Glucose
Prevention: frequent feeding with high carbohydrate diet
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Quote:
Originally Posted by Dr.NickRiviera View Post
how do you know its B over C?
both B and C are involved in this B-oxidation pathway, which is the pathway at fault here.
The way I figure it out:
First, there is the buzz word hinting at his brother 's sudden death at night. The most common cause of SCID is median chain Acyl Coenzyme A dehydrogenase defect.
Carnitine acyl transferase is not the right answer, because if there was such, it would result in no fatty acid degradation at all and the clinical consequence is much severe. Fatty acids are not able to enter the mit matrix.
In this case, the child 's symptoms only come to attention when glucose/glycogen resource is depleted, ie after an infection, a stressful event, long time fasting, ...etc. Feeding the child with glucose is fine, so he has no problem with glycolysis pathway. Regarding the fatty acid after being transported into the matrix, the long chain of it will be chopped down gradually until all of it becomes acetyl CoA. The first enzyme (out of 4 enzymes responsible for each execution cycle) is acyl CoA dehydrogenase. Due to an autosomal recessive defect, the enz Acyl CoA Dehydrogenase able to recognize the median size of the fatty chain is not there, so the fatty acid degradation is, lets say, half completed. So the baby is at risk of cardiac arrest, leading to SCID.
He is not ketogenic while hypoglycemic, also.

Does it makes some sense? Lol C:
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Quote:
Originally Posted by Desos View Post
My answer is

(B) Medium chain acyl-CoA deficiency

R
ecall that Fatty Acyl CoA dehydrogenase exist in 3 forms
- LCAD= long chain acyl coA dehydrogenase : chains > 10 carbon atoms
- MCAD= Medium chain ..... ..................... : chains 8-9 carbon atoms
- SCAD= short chain .............................. : Chains <8 carbon atoms


They all act in B oxidation in mitochondria to make ketones.
Deficiency in Fatty acyl CoA dehydrogenase : Hypoglycemia, hypoketonemia,

Treatment: IV Glucose
Prevention: frequent feeding with high carbohydrate diet
Nice explanation, but why it's not C? because in carnitine deficiency, you also get hypoglycemia and hypoketonemia
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Default Mcad def

Hints...
Sudden infant death syndrome
Hypoglycemia
No ketones
Hypoglycemia
Patient got better after glucose infusion
Tm..
Frequent feeds
Glucose provision
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Quote:
Originally Posted by patho2012 View Post
The way I figure it out:
First, there is the buzz word hinting at his brother 's sudden death at night. The most common cause of SCID is median chain Acyl Coenzyme A dehydrogenase defect.
Carnitine acyl transferase is not the right answer, because if there was such, it would result in no fatty acid degradation at all and the clinical consequence is much severe. Fatty acids are not able to enter the mit matrix.
In this case, the child 's symptoms only come to attention when glucose/glycogen resource is depleted, ie after an infection, a stressful event, long time fasting, ...etc. Feeding the child with glucose is fine, so he has no problem with glycolysis pathway. Regarding the fatty acid after being transported into the matrix, the long chain of it will be chopped down gradually until all of it becomes acetyl CoA. The first enzyme (out of 4 enzymes responsible for each execution cycle) is acyl CoA dehydrogenase. Due to an autosomal recessive defect, the enz Acyl CoA Dehydrogenase able to recognize the median size of the fatty chain is not there, so the fatty acid degradation is, lets say, half completed. So the baby is at risk of cardiac arrest, leading to SCID.
He is not ketogenic while hypoglycemic, also.

Does it makes some sense? Lol C:
awesome, thanks!

but i never knew there was a connection between MCAD deficiency and SCID.
could you direct me to where in FA it says that?
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Quote:
Originally Posted by Poonam aslam View Post
Hints...
Sudden infant death syndrome
Hypoglycemia
No ketones
Hypoglycemia
Patient got better after glucose infusion
Tm..
Frequent feeds
Glucose provision
whats the connection with sudden infant death syndrome?
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Quote:
Originally Posted by Dr.NickRiviera View Post
whats the connection with sudden infant death syndrome?
It is written in Devlin's textbook of Bch or PubMed or FA p112.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1793557/
(There are many causes of sudden infant death but from the biochemistry point of view, only MCAD is important )

The key point in distinguishing the Carnitin Acyl Transporter def and MCAD def is that in the latter there is increased dicarboxylic acids in the blood. It is also in FA, just so you know.

Please call it SIDS, I call it SCID to remind me of the other two things, I have prob with memorizing names (
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Quote:
Originally Posted by patho2012 View Post
It is written in Devlin's textbook of Bch or PubMed or FA p112.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1793557/
(There are many causes of sudden infant death but from the biochemistry point of view, only MCAD is important )

The key point in distinguishing the Carnitin Acyl Transporter def and MCAD def is that in the latter there is increased dicarboxylic acids in the blood. It is also in FA, just so you know.

Please call it SIDS, I call it SCID to remind me of the other two things, I have prob with memorizing names (
oh by SCID you meant SIDS, i thought you meant severe combined immunodeficiency.
ok cool, thanks.
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This is the way I know it:

LCAD: hypoketotic hypoglycemia WITH muscle weakness, hypotonia and eventually cardiomyopathy.

MCAD: hypoketotic hypoglycemia.


LCAD is the 1st step in B-oxidation...so if it's not present then the effects will be more severe...hence the hypotonia and muscle weakness. If you notice in the stem they make no mention of hypotonia/muscle weakness so we can rule it out.


I know its a little more complex than this description, but I try to simplify everything to remember it more easily.
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thanks for nice expln. ans is MCAD def.[hypoglycemia hypoketonemia SIDS]
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Medium chain acyl-coA dehydrogenase deficiency (MCAD deficiency) is the answer. Patient can also present with vomiting or already in coma. It is marked with raised medium chain fatty acid in the blood and dicarboxylic acidemia. Inherited as AR.
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Originally Posted by patho2012 View Post
The way I figure it out:
First, there is the buzz word hinting at his brother 's sudden death at night. The most common cause of SCID is median chain Acyl Coenzyme A dehydrogenase defect.
can you mention source saying MCAD is mcc of SIDS? i have online cant find so...

Quote:
Originally Posted by patho2012 View Post
so the fatty acid degradation is, lets say, half completed. So the baby is at risk of cardiac arrest, leading to SCID.
how come its true ? cant get it? fatty acids causes cardiac arrest?

please reply
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Originally Posted by tyagee View Post
can you mention source saying MCAD is mcc of SIDS? i have online cant find so...


how come its true ? cant get it? fatty acids causes cardiac arrest?

please reply
okay, I got this during the Bch course years ago...Maybe there has been more publications since then, so keep me updated with your reference source.

In SIDS children, when forensics finds nothing abnormal, like toxins, ketoacidosis, airway obstruction, present infections, tissue damage ... etc, there are still explanations for the unexected death like MCAD, infants' habit to hold their breath, brain defect, sleeping position... If you read the Pub Med link above, you will see that 1/4th of children with MCAD have SIDS or Reye's syndrome.

Cardiomyocytes rely heavily on fatty acid degradation for energy. If there is no fatty acid degradation at all, the heart becomes dilated and hypertrophic by 3 years of age. If MCAD is present, and known, the heart will be fine if you supply enough glucose to it and avoid fasting. Btw, myocytes use mainly glucose, fatty acids, and ketones to produce energy for its vigorous activity. Cardiac arrest or arrythmia happens because there is insufficient mus contraction and possibly excitation-contraction uncoupling. Hope it helps.

Last edited by patho2012; 03-07-2012 at 09:40 PM. Reason: Cardiac myocytes
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Default this is what kaplan says...

Quote:
Originally Posted by tyagee View Post
can you mention source saying MCAD is mcc of SIDS? i have online cant find so...


how come its true ? cant get it? fatty acids causes cardiac arrest?

please reply
It is now believed that some cases of sudden infant death syndrome were due to MCAD deficiency.

It's in KLN Biochemistry 2011 edition on page 242. I am not sure if other editions have similar discussion on MCAD deficiency.

Hope it helps...
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Quote:
Originally Posted by patho2012 View Post
It is written in Devlin's textbook of Bch or PubMed or FA p112.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1793557/
(There are many causes of sudden infant death but from the biochemistry point of view, only MCAD is important )

The key point in distinguishing the Carnitin Acyl Transporter def and MCAD def is that in the latter there is increased dicarboxylic acids in the blood. It is also in FA, just so you know.

Please call it SIDS, I call it SCID to remind me of the other two things, I have prob with memorizing names (

Great explanation. Was wondering what part of the question stem indicated dicarboxylic acid?
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