About
What is MSUD?
Maple
Syrup Urine Disease (MSUD) is an inherited metabolic disorder, that,
if untreated, causes mental retardation, physical disabilities and
death. First described as a disease in 1954, it is a rare disorder,
believed to be in all ethnic groups worldwide. The national
incidence is 1 in 225,000 births.
MSUD derives its name from the sweet, burnt sugar, or maple syrup
smell of the urine. The disorder affects the way the body
metabolizes (processes) certain components of protein. These
components are the three branched-chain amino acids leucine,
isoleucine, and valine. These amino acids accumulate in the blood
causing a toxic effect that interferes with brain functions.
Types and Symptoms
The
term, Maple Syrup Urine Disease, includes a range of classic and
variant types of the disorder. The symptoms of classic MSUD are
usually evident within the first week of life. Variant forms of MSUD
are milder, however, the symptoms can be severe during times of
illness.
The first symptoms in an infant are
poor appetite, irritability, and the characteristic odor of the
urine. Within days they lose their sucking reflex and grow listless,
have a high-pitched cry, and become limp with episodes of rigidity.
Without diagnosis and treatment, symptoms progress rapidly to
seizures, coma, and death. In some variant types, failure to thrive
may be the first sign. The earlier these children are diagnosed and
treated, the less risk of permanent damage.
Testing for MSUD
Some states test for MSUD in
their newborn screening programs. MSUD should be included in all
screening programs. Ideally each infant should be tested within 24
hours of birth and the test results available by two to three days
of age. This should be the goal of all testing for MSUD. Early
diagnosis is of paramount importance for the child with MSUD to
develop normally.
Unfortunately some variant types of MSUD may be missed with
screening programs. However, any child at risk or suspected of
having MSUD should be tested. If the result is positive, or
suspected to be positive, treatment should be started immediately.
Testing to identify carriers is only available for the Mennonite
classic type of MSUD. The Mennonite population from eastern
Pennsylvania is at high risk for this classic form of the disorder.
Treatment
Treatment
of children with MSUD must be started as soon as possible,
preferably at birth. It involves a complex approach of maintaining
metabolic control. A special, carefully controlled diet is the focus
of daily treatment. This requires careful monitoring of protein
intake and close medical supervision.
The diet centers around a synthetic formula or "medical food" which
provides nutrients and all the amino acids except leucine,
isoleucine and valine. These three amino acids are added to the diet
with carefully controlled amounts of food to provide the protein
necessary for normal growth and development without exceeding the
level of tolerance.
Various tests are available to monitor the levels of the amino acids
and their keto acid derivatives in the blood and urine. Illnesses
and stress, as well as consuming too much protein, raise these
levels. Even mild illnesses can become life threatening. A metabolic
imbalance requires dietary changes and at times hospitalization.
Each parent of a child with MSUD carries a defective gene for MSUD
along with a normal gene. The defective gene is a recessive gene,
therefore parents are called "carriers" and are not affected by the
disease. Each child receives one gene from each parent.
When both parents are carriers, there is a 1 in 4 chance with each
pregnancy that the baby will receive a defective gene from each
parent and have MSUD; a 2 in 4 chance the baby will receive one
defective and one normal gene becoming a carrier of MSUD; and a 1 in
4 chance the baby will receive two normal genes. Persons with two
normal genes cannot pass MSUD to their offspring.
* If you are interested in learning more about MSUD, please visit the MSUD Support Group. This is a wonderful group, which can put you in contact with individuals and families living with MSUD around the world. They provide a Quarterly newsletter with updates on issues relevant to MSUD as well as running an email group to discuss any questions or issues you may have. the MSUD support group also sponsors a symposium once every 2 years, in which families come together with medical professionals to learn more about new developments in care and research.