MAPLE SYRUP URINE DISEASE
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ALTERNATE NAMES
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BCKD; DeficiencyBranched-Chain Alpha-Ketoacid Dehydrogenase Deficiency; Branched-Chain
Ketoaciduria; MSUD
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DESCRIPTION |
Maple
syrup
urine
disease
(MSUD) is an inherited metabolic disorder in which the body is unable to process certain
protein building blocks (amino acids) properly. Because these amino acids are not
metabolized, they, along with their various byproducts, abnormally accumulate in the
cells and fluids of the body. The condition gets its name from the distinctive sweet
odor of the affected infant’s earwax, sweat, and urine.
Mutations in the BCKDHA, BCKDHB, DBT, and DLD genes cause MSUD. Individuals with this condition cannot break down the branched
chained amino acids (BCAA) leucine, isoleucine, and valine . This leads to a buildup
of these chemicals in the blood.
There are four common forms:
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1.
Classic
MSUD In the classic form, the disorder presents after the infant has had milk containing
protein. This causes an increase in the offending amino acids which become toxic to
the brain. Classic MSUD tends to impair intellectual development and bone growth.
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2.
Intermediate
MSUD Onset of symptoms of intermediate MSUD is later than in the classic form, typically
between six months and seven years of age.
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3.
Intermittent
MSUD
In the intermittent form, growth and intellectual development are normal. Stressors
such as infections, fever, or hunger can cause brain damage, leading to episodes of
metabolic decompensation. Such episodes are potentially catastrophic and fatal.
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4.
Thiamine-Responsive
MSUD This form has shown favorable response to treatment with thiamine (vitamin B1) along
with diet restrictions.
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DIAGNOSTIC TESTING, PHYSICAL FINDINGS, AND ICD-9-CM/ICD-10-CM CODING
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Diagnostic testing: Diagnostic testing for MSUD includes blood and urine amino acid tests that measure
the levels of leucine, isoleucine, alloioleucine, and valine. If MSUD is found, there
will be signs of ketosis and excess acid (acidosis). These are measured in the usual
newborn screening test.
Physical findings: Symptoms include:
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Hypotonia (low muscle tone) or hypertonia (increased muscle tone);
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Dystonia (uncontrolled muscle contractions); and
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ICD-9: 270.3
ICD-10: E70.1
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PROGRESSION
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If the disease is not treated, MSUD can lead to seizures, coma, and death at any age.
In the intermittent type symptoms become apparent later in infancy or childhood and
are typically milder. Long-term sequelae may include developmental delays, learning
problems, seizures, and motor difficulties. Even with dietary treatment, stressful
situations, and illness can still cause high levels of certain amino acids. Death
may occur during these episodes.
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TREATMENT
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When the condition is diagnosed and during episodes, treatment involves eating a protein-free
diet and correction of the metabolic consequences of the elevated amino acid levels.
A special intravenous solution decreases the leucine level (the most toxic) and corrects
the energy deficits.
In the intermittent form a special diet containing low levels of the offending amino
acids is required. Even with treatment affected individuals remain at risk for developing
episodes of acute illness (metabolic crisis), often triggered by infection, injury,
failure to eat (fasting), or psychological stress. During these episodes there is
a rapid, sudden spike in amino acid levels necessitating immediate medical intervention.
For acute toxic episodes the management is the same as in the classic form.
In the Thiamine-responsive form, administration of thiamine and consumption of a low
protein diet results in a reduction of amino acid levels to normal. Withdrawal of
thiamine treatment results in a rapid rebound in the elevation of plasma amino acid
concentration.
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SUGGESTED PROGRAMMATIC ASSESSMENT*
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Suggested MER for Evaluation:
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Clinical examination with a description of findings;
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Plasma amino acid test, and urine amino acid test; and
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Lab reports documenting signs of increased leucine, isoleucine, allioleucine, and
valine. There may also be ketosis and acidosis.
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Suggested Listings for Evaluation:
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DETERMINATION
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LISTING
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REMARKS
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Meets
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111.17
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112.02
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Equals
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* Adjudicators may, at their discretion, use the Medical Evidence of Record or the
listings suggested to evaluate the claim. However, the decision to allow or deny the
claim rests with the adjudicator.
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