what is MCAD, frequency, sumptoms, diagnosis,treatment, nutrition intervention

1. Medium Chain Acyl-Coenzyme A Dehdrogenase
( MCAD ) Deficiency
Done by: Dina

2. Introduction:
Medium-chain acyl-coenzyme A dehydrogenase deficiency is the most
common a fatty acid oxidation disorder associated with inborn errors of
metabolism. It is due to defects in the enzyme complex known as medium-
chain acyl dehydrogenase (MCAD) and reduced activity of this complex.
MCAD is an enzyme found in the mitochondria that is responsible for the
metabolism of medium chain fatty acids. When this enzyme is missing, the
body is unable to convert these fatty acids to energy during times of
decreased food intake. (1, 4)
It is recognized as one of the more rare causes of sudden infant death
syndrome (SIDS), although it may be better described as a mimic, rather than
a cause, of SIDS
Overview:
Two main types of fat are found in the body: triglycerides and waxes.
A triglyceride consists of a three-carbon compound known as glycerol to
which three fatty acids (carboxylic acids) are attached by ester bonds. The
length of the fatty acids chains can vary; they may be classified as very long-
chain, long-chain, medium-chain or short-chain depending on the number of
carbon atoms in the chain.
The fatty acids are broken down in stages by the successive removal of
molecules of acetyl-coenzyme A, which contains 2 carbon atoms. Ultimately,
under normal conditions, the fatty acids are converted into carbon dioxide
and water with the liberation of energy during this process. Once a fatty acid
molecule is "activated" (attached to coenzyme A), a series of four reactions,
each catalyzed by a different enzyme, is required to remove each acetyl-
coenzyme A molecule. As the first step involves removal of hydrogen atoms
(i.e. an oxidation) from an acyl group, the enzyme complex is known as an
acyl dehydrogenase. Different enzymes are required to hold fatty acids of
different lengths, and the deficiencies connected with these various proteins
are:
 Very long-chain acyl-coenzyme A dehydrogenase deficiency (VLCAD
deficiency)
 Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency
(LCAD deficiency)
 Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCAD
deficiency)
 Short-chain acyl-coenzyme A dehydrogenase deficiency (SCAD
deficiency)
 3-hydroxyacyl-coenzyme A dehydrogenase deficiency (M/SCHAD
deficiency) (1)

3. Frequency:
 United States
approximately 1 in every 8500 live births.
 International
The average incidence rate among more than 8 million babies was 1 per
14,600 live births, with a range of 1 per 13,500 to 1 per 15,900.(2)
Symptoms:
Clinical presentation is often triggered by a seemingly innocuous illness
(like otitis media). The initiating event is probably due to prolonged
fasting, which may lead to vomiting, lethargy, coma, cardiopulmonary
arrest, or sudden unexplained death. Symptoms often precede the onset
of profound hypoglycemia and are probably related to high free fatty acid
levels. Hypoglycemia occurs from an inability to meet gluconeogenic
requirements during fasting despite activation of an alternate pathway of
substrate production, proteolysis. Physical examination of the acutely ill
child is remarkable for mild to moderate hepatomegaly. Some patients
may also have demonstrable muscle weakness. (3)
Diagnosis:
Initial laboratory examination of blood may reveal hypoglycemia, mild
metabolic acidosis, mild lactic acidosis, hyperammonemia, elevated BUN,
and high uric acid levels. Liver function studies are also usually elevated.
Examination of the urine often shows inappropriately low or absent
ketones.
Biochemical testing of blood and urine for carnitine, acylcarnitines,
acylglycines, and organic acids is diagnostic for this disorder. Low serum
and urine carnitines are consistently found in the untreated patient. A
generalized dicarboxylic aciduria is noted characterized by elevation of
suberylglycine and hexanoylglycine. Plasma or blood spot acylcarnitine
profiles show elevations of medium chain length fatty acid derived
acylcarnitines, especially octanoylcarnitine.(3)
The oxidation of fatty acids occurs within mitochondria. Fatty acids from
the cytoplasm are attached to a molecule called carnitine to transport
them across the mitochondrial membrane. The combination of carnitine
with a fatty acid is known as acyl carnitine. In individuals with MCAD
deficiency, there is an increase in the concentration of medium-chain acyl
carnitines in the cytoplasm of their cells; these acyl carnitines leak into the

4. blood stream. The presence of these acyl carnitines, especially octanoyl-
carnitine, is a major diagnostic characteristic of MCAD deficiency. (1)
Without prior indication of metabolic disease, 20-25 percent of patients
with this disease will die with their first episode of illness. Cerebral edema,
and fatty liver, heart and kidneys are noted at autopsy, often leading to a
misdiagnosis of Reye's syndrome or Sudden Infant Death Syndrome
(SIDS). This disorder accounts for about one of 100 SIDS deaths. (3)
Testing should be initiated in individuals with the following indications:
 Prenatal diagnosis for carrier couples
 Carrier screening in families of affected individuals
 Intermittent hypoglycemia
 Carnitine deficiency
 Urinary excretion of medium chain fatty acids and decreased ketones
 Vomiting, lethargy, and/or coma following fasting
Risk factors include finding fatty infiltration of the liver, family history of
sudden death, Reye's Syndrome, myopathy, and decreased caloric intake
before death. All siblings of individuals with MCAD should be tested even if
they are without symptoms. (4)
Treatment:
Fundamental to the medical management of MCAD is to avoid fasting,
particularly during periods of high metabolic stress, such as illness. Overnight
fasts should last no longer than twelve hours, and infants should continue to
receive nighttime or late evening feedings to reduce this period even further.
High carbohydrate intake should be encouraged during illness, with initiation
of intravenous glucose supplementation if the child is unsuccessful in keeping
down fluids, or unable to take adequate oral feedings. The preventative
efficiency of a low fat diet versus a normal fat diet is unclear, but high intake
of long and medium chain fatty acids should be avoided.
Supplementation with oral L-carnitine at 100 mg/kg/day has been associated
with a reduction in the frequency and severity of episodes in many patients.
We recommend that the dose be increased to 200 mg/kg/day during acute
illness. The continued need for carnitine supplementation post puberty is
uncertain, and has not been adequately studied. The addition of 1-3
tablespoons of food grade cornstarch mixed in liquid at bedtime to some
infants has also helped to decrease the frequency of morning hypoglycemia.(3)

5. References:
(1)
Wikipedia.http://en.wikipedia.org/wiki/Medium_chain_acyl_dehydrogenase_defic
iency
(2)
Emedicine. http://emedicine.medscape.com/article/946755-overview
(3)
MCAD: Medium Chain acyl CoA Dehydrogenase - Information for Clinicians
Charles R. Roe, MD. http://www.fodsupport.org/mcad.htm
(4)
Public Health and Genetics Information Series.
http://www.hgen.pitt.edu/counseling/public_health/mcad.htm