MSUD is a genetic disorder. Children with this disorder cannot use the BCAA (branched-chain amino acids) in the normal way. The outcome in these children is affected by several factors. These include age of diagnosis, degree of enzyme impairment, time at which diet therapy is begun and adequacy of management. Management requires an aggressive protocol to reduce plasma BCAA to avoid central nervous system changes. Goals of long-term nutrition support are:
a) Normal plasma amino acid concentrations
b) Urine free of branched-chain keto acids (BCKA)
c) Normal growth, development and status.
Nutritional management requires initiation of nutrition support immediately with BCAA free medical foods (formula). Depending on clinical status, patients are fed by nipple, nasogastric (N-G) tube, intravenous infusion (IV), or a combination of these methods. When plasma leucine reaches the upper limit of treatment range, leucine is added back gradually using infant formula or whole cow's milk depending on the child's age.
Over restriction or imbalance of BCAAs has adverse effects. These include anemia, desquamation (shedding of the skin) and failure to thrive. Free isoleucine and valine can be used to correct some imbalances. It is very important to provide protein-free sources to meet energy requirements. In addition 100 to 500 mg of oral thiamine per day may be provided for three months to evaluate the response. Guidelines used for fluid requirements in treating these children include:
- Less than one month of age:100-150 ml/kg/day
- 0-10 kg in weight:100ml/kg/day
- 11-20 kg in weight:1000ml+50ml/each kg over 10kg
- Over 20kg in weight:1500ml+20ml/each kg over 20kg
It was emphasized that energy requirements during acute illness/surgery increase. Therefore aggressive nutrition support becomes necessary to prevent catabolism which could be caused by poor oral intake or the stress of infection itself. Suggested nutrition protocol during illness:
- As soon as the child shows any signs of being sick, natural protein should be reduced by half or eliminated.
- Adjust energy intake (kilo-calories) through medical food (protein-free) to at least maintenance levels. Try to add 10-20% above maintenance levels.
- All fluid needs could be provided through the medical food mixture.
- Give feedings and drinks every 1 to 2 hours in small amounts to children less than 5 years old and older than three.
- Continue all vitamins and medications at the same dosage.
- Minimum volume intake of 75% of prescribed intake for two consecutive feedings and 85% of prescribed intake during 24 hours should be acceptable.
- If decreased intake continues for 24 to 48 hours, make an effort to maintain intake by nasograstic tube using enteral pump. The oral regimen is preferable to intravenous therapy.
- If nausea or vomiting persists and the gut cannot be used, peripheral venous alimentation can be used for patients whose needs are likely to be short term (2 to 5 days). Central hyperalimentation should be implemented for patients requiring long term support.
In conclusion, immediate adequate energy and fluid intake become important during acute episodes.