Maple Syrup Urine Disease

Maple syrup urine disease is an inherited disease, where a newborn has built up substances in their urine and blood due to incapability to process amino acids. Classic MSUD, the most common form, is caused by the absence of a group of enzymes called “branched-chain ketoacid dehydrogenase” (BCKAD). The job of this enzyme group is to break down three different amino acids called leucine, isoleucine and valine which are called “branched-chain amino acids” (BCAAs) because of their “tree-like” structure. They are found in all foods that contain protein. Large amounts are found in meat, eggs, milk, and other dairy foods. Smaller amounts are found in flour, cereal, and in some vegetables and fruits. As breast milk is usually the staple food for a newborn, the risks are very high as a small baby is very sensitive and MSUD can be therefore life threatening.

MSUD is inherited in an autosomal recessive manner. It affects both boys and girls equally. In children with MSUD, a pair of genes needed to make the BCKAD enzymes is not working correctly. These children inherit one non-working gene for MSUD from each parent. Parents of children with MSUD rarely have the condition themselves. Instead, each parent has a single non-working gene for MSUD. They are called carriers.  Carriers do not have MSUD because the other gene of this pair is working correctly. When both parents are carriers, there is a 25% chance in each pregnancy for the child to have MSUD. There is a 50% chance for the child to be a carrier, just like the parents. Also, there is a 25% chance for the child to have two working genes.

When the amino acids are not broken down, these amino acids build up in the blood  of the baby and cause problems. There are a number of different forms of MSUD. The most common form, “classic MSUD”, which can be life-threatening and must be treated promptly to prevent serious health problems. Other forms, including ‘intermediate’ and ‘intermittent’ forms of MSUD, are less severe. These milder forms are less common. For Classic MSUD symptoms start as soon as a baby is fed protein, usually shortly after birth.  Some of the first symptoms are:
  • Poor appetite
  • Weak suck
  • Weight loss
  • High pitched cry
  • Urine that smells like maple syrup or burnt sugar

Babies with MSUD have episodes of illness called metabolic crisis. Some of the first symptoms of a metabolic crisis are:
  • Extreme sleepiness
  • Sluggishness
  • Irritable mood
  • Vomiting

If not treated, other symptoms can follow:
  • Episodes where muscles tone alternates between being rigid and floppy
  • Swelling of the brain
  • Seizures
  • High levels of acidic substances in the blood, called metabolic acidosis
  • Coma, sometimes leading to death

Symptoms of a metabolic crisis often happen:
  • After going too long without food
  • During illness or infection
  • During stressful events such as surgery
  • Without treatment, brain damage can occur. This can cause intellectual disabilities or spasticity.
  • Some babies become blind. If not treated, most babies die within a few months.

At around 5 days old, babies are offered newborn blood spot screening to check if they have MSUD. This involves pricking your baby's heel to collect drops of blood to test. As soon as MSUD is diagnosed the baby’s doctor will work with a metabolic doctor and dietician to care for the child.Prompt treatment is needed to prevent intellectual disabilities and serious medical problems. Most children need to eat a very low-protein diet and drink a special medical formula. You should start the diet and the formula as soon as you know your child has MSUD. Your dietician can create a food plan that contains the right amount of protein, nutrients, and energy to keep your child healthy.

The following are treatments often recommended for children with MSUD:

1. Medical Formula
In addition to a low-protein diet, children are often given a special medical formula as a substitute for milk. This formula gives them the nutrients and protein they need while helping keep their BCAA levels in a safe range.Your metabolic doctor and dietician will tell you what type of formula is best and how much to use.

2. Diet low in branched-chain amino acids.
The diet is made up of foods that are very low in the BCAAs. This means your child will need to avoid foods such as cow’s milk, regular formula, meat, fish, cheese and eggs. Regular flour, dried beans, nuts, and peanut butter also have BCAAs and must be avoided or strictly limited.Many vegetables and fruits have only small amounts of the BCAAs and can be eaten in carefully measured amounts.There are other medical foods such as special low-protein flours, pastas, and rice that are made especially for people with MSUD. Some states offer help with payment, or require private insurance coverage for medical formula and other special medical foods.Your metabolic doctor and dietician will decide on the best food plan for your child. The exact plan will depend on many things such as your child’s age, weight, and general health. Your dietician will fine-tune the diet over time. Any diet changes should be made under the guidance of a dietician.

Lifelong treatment with the MSUD diet is necessary. Children are at risk for episodes of metabolic crisis when they don’t follow the diet.

3.  Supplements
Children with a rare form of MSUD, called “thiamine-responsive MSUD”, can often be helped by thiamine supplements. Some children with classic MSUD may also benefit from thiamine. Ask your doctor whether your child should take thiamine supplements. Do not use any supplements without checking with your doctor.

4. Tracking BCAA levels
Your child will have regular blood tests to measure amino acid levels. The diet and formula may need to be adjusted based on blood test results.

5.  Call your doctor at the start of any illness
For children with MSUD, even minor illness can cause a metabolic crisis. In order to prevent problems, call your doctor right away when your child has any of the  symptoms listed above.  Children with MSUD need to eat more carbohydrates and drink more fluids during any illness – even if they’re not hungry – or they could have a metabolic crisis. Children who are sick may not want to eat. If they can’t eat, or if they show signs of a metabolic crisis, they may need to be treated in the hospital.Ask your metabolic doctor if you should carry a special travel letter with medical instructions for your child’s care.

6.  Liver transplantation
Liver transplant surgery is an optional treatment for people with MSUD. The BCKAD enzyme that causes MSUD is located in the liver. Because of this, some children with MSUD have had liver transplantation surgery (removal of their liver and replacement with a donor liver) to treat their MSUD symptoms.This major surgical procedure is associated with risks, and individuals who have had a liver transplant must take medication for the rest of their lives to prevent their body from rejecting the donor liver. However, successful liver transplantation cures people of their MSUD symptoms.Many factors must be considered before surgery and this option should be discussed very thoroughly with your child’s physicians.

The sooner found the easier it becomes to treat and the less risk the child is put in, so if your baby's urine smells like pancakes please act quickly and let your physician know as soon as possible.

Thank you for reading :)

Written by Anuja Rajeev 12T
https://rarediseases.org/rare-diseases/maple-syrup-urine-disease/
https://www.nhs.uk/conditions/maple-syrup-urine-disease/
https://en.wikipedia.org/wiki/Maple_syrup_urine_disease

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