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Charles R. Roe, MD
Medium chain acyl CoA dehydrogenase deficiency, or
'MCAD,' is a disorder in which your body is unable to breakdown fats
to make energy. Normally, fat is broken down into energy by "enzymes."
This energy keeps your body running whenever it runs out of its
main source of energy, a sugar called 'glucose.' In MCAD, a very
important enzyme for breaking down fat, the medium chain acyl CoA
dehydrogenase enzyme (MCAD) is missing or does not work correctly.
This means that people with MCAD can't break down fat for energy
when they run out of glucose.
Children with MCAD usually get sick for the first
time between two months and two years of age but some children get
sick as early as two days old or as late as six years old (**be
aware that asymptomatic and symptomatic adults are now also being
diagnosed, some after having their own MCAD children diagnosed or
after an episode). They usually have an illness that makes them
not want to eat, like the flu, an ear infection, or a cold. We get
worried if children with MCAD have: vomiting. diarrhea, are very,
very sleepy or hard to wake up, seizures, or have difficulty breathing.
Sometimes a child with MCAD will stop breathing, have seizures,
or their heart will stop. Doctors usually check for MCAD deficiency
because a child has had these kinds of problems and they can't find
another cause.
MCAD deficiency may be the cause of one out of 100
infant deaths thought to be Sudden Infant Death Syndrome (SIDS).
About one fifth of children with MCAD die with their first illness,
before anyone knows that they have MCAD deficiency. These children
are often completely well until right before they become ill and
die. After they die, autopsy often shows brain swelling, a big fatty
liver, and too much fat in their heart and kidneys. Some children
who die are diagnosed incorrectly as having Reye's syndrome and
sudden infant death (SIDS).
MCAD passes from parent to child through 'genes.'
Genes are the instructions that our bodies use to make us and to
keep us running right. Several genes string together like a necklace
and makes a bigger instruction 'booklet' called a 'chromosome.'
Normally we have two copies of our genetic material. We have 22
pairs of chromosomes numbered from largest to smallest, 1 to 22.
The23rd pair is special because they are different in men and women.
The 23rd pair, the X- and the Y- chromosomes, is called the 'sex
chromosome' because they decide whether a child will be a boy or
a girl.
The gene that causes MCAD is chromosome number one.
For a child to have MCAD, both chromosome number 1's must have an
abnormal MCAD gene. This is why MCAD is called an 'autosomal recessive'
disease. Autosomal means it is a condition that affects both boys
and girls. Recessive means that both copies of the gene must be
abnormal to get the disease. Most parents of affected children only
have one abnormal gene for MCAD, and the other gene is normal, so
they do not get sick. We call people with only one abnormal gene
'carriers,' because they 'carry' one copy of a gene that does not
work properly on their # 1 chromosome, but do not get sick themselves
since their other gene is normal. If both parents are carriers for
MCAD, they have a one in four chance of having another child with
MCAD. There is also a one in four chance that brothers and sisters
of the child with MCAD might also have MCAD, even if they are older
and have not been sick.
We test for MCAD by looking for abnormal substances
in the blood or urine. Our tests are very good, and almost always
right. Some of these tests let us test children for MCAD at birth,
before they get sick, on a very small amount of blood, like a finger
stick. We can even find out who carries the MCAD mutation, but are
not affected with the disease, by looking directly at each family
member's DNA. If a child in the family has died, a piece of tissue
or a blood specimen from their autopsy can be used to see if they
had MCAD deficiency, When we find out that one person in a family
has MCAD deficiency, it is very important that other members of
the family be tested for the disease too. Knowing if other children
in the family have MCAD is important because with treatment the
severe problems from MCAD deficiency can be prevented.
The main treatment is to avoid going without food
for more than ten or twelve hours (ie., an overnight fast when well). Children should eat high carbohydrate
meals like sugar-containing drinks, cereals, and pastas when they
are ill. A low fat diet may be helpful, and a high fat diet should
be avoided. Infants less than one year old should continue to have
at least one night-time feeding, or a late night snack, as they
should not go even twelve hours without eating. Please read 'MCAD
Information for Clinicians' (on this site) to understand important
emergency room procedures for the MCAD child.
Some doctors who take care of children with MCAD use
a drug called L-Carnitine, which helps them keep from getting low
blood sugar when they have infections or when they don't eat. In
general, experience in taking care of patients with MCAD suggests
that L-Carnitine is very useful in preventing problems with low
blood sugar. L-Carnitine is a substance made by the body that carries
wastes out of your body's cells and into your urine. People with
MCAD make more toxic wastes than normal people so they need more
L-Carnitine than their body can make. When people with MCAD deficiency
get sick, are pregnant, or they need to have an operation, they
may need even more L-Carnitine than usual. You should never give
your child Carnitine that you can buy at the health food store unless
you talk to your doctor first. This type of Carnitine may not be
L- Carnitine@ and could cause a problem. Please talk with your child's
doctor if you have questions about MCAD or any questions about his
or her medications.
A support group for parents and families of children
with the medium chain acyl CoA dehydrogenase deficiency and other
inherited disorders affecting fat breakdown has been formed by parents
of these children. The purpose of the FOD (Fatty Oxidation Disorders)
Family Support Group is to allow parents and children (and some
adults) with the disorder to talk with each other to provide emotional
support and practical information about living with MCAD deficiency
(and the other FODs), and to keep families informed regarding new
developments in treatment of the disorder.
For more information about this support group, contact
Deb Lee Gould (2041 Tomahawk, Okemos MI 48864.
She may be reached at (517) 381-1940 or deb@fodsupport.org.
Or visit the FOD Family Support Group's website at www.fodsupport.org.
The Baylor Institute of Metabolic Disease provides
supplemental newborn screening for MCAD and other disorders. For
information and test kits you can call 800-4-Baylor
If you have questions regarding the treatment or course
of MCAD, and would like to speak with someone, you are welcome to
contact Dr. Charles Roe at the Institute of Metabolic Disease at
Baylor University Medical Center in Dallas. Telephone (214) 820-4533
or fax (214) 820-4853.
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