MCAD Deficiency and SIDS
Wed, 28 Jul 1999
If a medical examiner sent out tissues to be tested, how long would it take to get them back? Is there a time frame that this testing needs to be done (for instance, if they parents had a second opinion on the autopsy, would it still be identifiable?)
There is no strong link between SIDS and metabolic diseases. Fatty acid disorders have been linked with sudden death, but these occur primarily in children older than 1-2 years of age, and should be associated with fatty changes in the liver at autopsy. These disorders can be identified from tissue samples (liver) or with urine, and would likely take several weeks for results.
Hope this is helpful.
By: Piero Rinaldo, MD
13 May 1997
In reply to the question about whether or not
13 May 1997
I would agree that if a child died
Date: Wed, 30 Apr 1997
MCAD deficiency is a rare "inborn error of metabolism". In this
A number of years ago, the late Professor David Read for Sydney, Australia, a prominent researcher in respiratory control with interests in SIDS, hypothesized that SIDS might be caused by a group of metabolic disorders, of which MCAD Deficiency (MCADD) is the most common. MCAD is a naturally occurring enzyme in cells which breaks down fats so that can be used for energy. The absence of this enzyme is only a problem in relative fasting or starving states, when there is not enough sugar to nourish the cells of the body. Ordinarily, the cells would break down fats to convert them to sugar, but MCADD prevents this from happening. It has been suggested that if an infant has a fever (high metabolism) and is sick (not eating), then MCADD may result in an apneic episode, and possibly even death. MCADD is inherited as an autosomal recessive disorder. This means, IF each parent is a carrier, there is a one-in-four chance of each baby having MCADD. However, the chance of a person being an MCADD carrier is very low. MCADD is uncommon (about 1 in 7500) as opposed to SIDS, which is very common.
There are a few problems with the theory that MCADD explains most SIDS.
We were able to perform a study of all the babies who died from SIDS in Los Angeles County over a 6-year period of time, about 1300 babies. We were able to obtain a small piece of liver tissue which was stored from the autopsy of each infant and run DNA testing for MCADD. None of the infants who died from SIDS had MCADD. Therefore, we believe that MCADD is not a common cause of SIDS.
Presumably, pathologists should be able to distinguish these types of metabolic disorders from SIDS at autopsy because they would result in increased fat stored in the liver. However, the distinction may not be obvious, especially if the pathologist doing the autopsy is not thinking of this as a possibility.
Consequently, I do not think that performing MCADD testing will be helpful in the classical SIDS infant, as your child is unlikely to have died from MCADD.
When is MCADD testing indicated? If there is any family history of SIDS besides your own child, MCADD testing may be more likely. Similarly, if there is a family history of apnea, seizures, etc., MCADD testing may be helpful. We did find an increased incidence of metabolic disorders in infants who presented with severe apnea (ALTE) which required full CPR and which did not resolve like the usual clinical course. This would be another indication.
Finally, a note to physicians: In this latter study, we found that the serum ammonia level was an excellent screening test for the presence of metabolic errors of beta oxidation of fatty acids (of which MCADD is the most common). If the serum ammonia is normal, none of the ALTE babies we studied had a metabolic disorder.
Thomas G. Keens, M.D.
Reprinted with permission
Has anyone heard about the gene testing done at Washington University in St. Louis? After our son died, my husband and I were approached about taking a genetic test. I don't remember which gene it was. We haven't done anything about it. Supposedly *they* have linked 5% of SIDS deaths to a mutation of this particular gene. We had a copy of a paper done on this research, but have misplaced it. We are interested to have more info. on this research. Please respond if you have any info. that might help.
Not all SIDS infants undergo extensive genetic testing. These researchers have reported the result of extensive genetic testing on 100 or so infants that died of SIDS and found that some of these actually had this genetic abnormality called MCAD deficiency or medium chain acyl diglyceraldehyde deficiency. This is a fatty acid disorder that can result in the sudden unexpected death of an infant. Infants who have been identified as having this disorder and have died from it have not died of SIDS. They died from MCAD deficiency and subsequent pregnancies can be tested. The total number of infants that may have died from MCAD deficiency but mistakenly called SIDS was initially felt to be as high as 5% but I think this number is too high.
J D DeCristofaro, MD
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