Maple Syrup Urine Disease in Infants: Types, Symptoms and Causes

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Maple syrup urine disease (MSUD) is a rare and inherited metabolic disorder in which the body is unable to process certain amino acids (protein building blocks) properly. The disease gets its name from the distinctive sweet odor of affected infants’ urine. Other clinical manifestations seen are  poor feeding, vomiting, lack of energy, abnormal movements and delayed development. If untreated, it can lead to seizures, coma and death.

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maple syrup urine disease

It affects an estimated 1 in 185,000 infants worldwide. This is more common in the Old Order Mennonite population with an estimated incidence of about 1 in 380 newborns. It is found in many countries throughout the world, although it is more common in certain ethnic groups.

In this article:

Types of Maple Syrup Urine Disease in Infants
Symptoms of Maple Syrup Urine Disease in Infants
Signs of Maple Syrup Urine Disease in Infants
Causes of Maple Syrup Urine Disease in Infants
Complications of Maple Syrup Urine Disease in Infants
Treatment for Maple Syrup Urine Disease in Infants

A Guide for Maple Syrup Urine Disease in Infants

MSUD is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated genes but no signs and symptoms are shown by them. It is also known as –

  • BCKD deficiency
  • Branched chain alpha keto acid dehydrogenase deficiency
  • Branched chain ketoaciduria
  • Ketoacidemia
  • Branched chain ketonuria 1

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Types of Maple Syrup Urine Disease in Infants

It is often classified on the basis of signs and symptoms. The types are all inherited genetic disorders and differ by their degree of enzyme activity, severity and the age when the disease appears –

  • Classic MSUD
  • Intermediate MSUD
  • Intermittent MSUD
  • Thiamine responsive MSUD

Classic type which becomes apparent soon after birth is considered as the most common and severe form of the disease. The other variant forms of the disease become apparent later in infancy or childhood and are typically milder but they still lead to delayed development and other health complications if not treated.

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Symptoms of Maple Syrup Urine Disease in Infants

Initial symptoms are –

  • Lethargy
  • Poor appetite
  • Weight loss
  • Weak sucking ability
  • Irritability
  • Vomiting
  • A distinctive maple sugar odor in earwax, sweat and urine
  • Irregular sleep patterns
  • Alternating episodes of hypertonia (muscle rigidity) and hypotonia (muscle limpness) are seen
  • High pitched cry

Signs of Maple Syrup Urine Disease in Infants

  • Seizures
  • Neurological deficiencies
  • Developmental delays
  • Feeding problems
  • Poor growth
  • A distinctive maple sugar odor in earwax, sweat and urine

Causes of Maple Syrup Urine Disease in Infants

It is caused by mutations in the BCKDHA, BCKDHB and DBT. These three genes provide instructions for making proteins that work together as part of a complex. The protein complex is essential for breaking down the amino acids such as leucine, isoleucine and valine which are found in many kinds of food particularly protein-rich foods such as milk, meat and eggs.

Mutations in any of these three genes reduce or eliminate the function of the protein complex and therefore prevent the normal breakdown of leucine, isoleucine and valine. As a result of this, these amino acids and their byproducts build up in the body. Because high levels of these substances are toxic to the brain and other organs, their accumulation leads to the serious health problems associated with MSUD.

Complications of Maple Syrup Urine Disease in Infants

Complications from undiagnosed and untreated MSUD can be severe and fatal too. Even the babies in a treatment plan can experience incidents of extreme sickness called metabolic crises. This occurs when there is a sudden and intense increase of branched chain amino acids in the system. If untreated it can lead to serious physical and neurological damage. A metabolic crisis is usually indicated by –

  • Extreme fatigue or lethargy
  • Loss of alertness
  • Irritability
  • Vomiting

If MSUD is undiagnosed or metabolic crises are untreated, the following severe complications can occur –

  • Seizures
  • Swelling of the brain
  • Lack of blood flow to the brain
  • Metabolic acidosis
  • Coma

When these conditions occur, they may lead to –

  • Severe neurological damage
  • Intellectual disability
  • Blindness
  • Spasticity or uncontrolled muscle tightness

Treatment for Maple Syrup Urine Disease in Infants

If the infant is diagnosed with MSUD, prompt medical treatment can avoid serious medical problems and intellectual disability. Initial treatment involves reducing the levels of branched chain amino acids in the infant’s body.

Typically, this involves intravenous (IV) administration of amino acids that don’t contain branched chain amino acids, combined with glucose for extra calories. The treatment promotes the utilization of existing leucine, isoleucince and valine in the body. At the same time it will reduce the branched chain amino acid level and provide necessary protein.

The physician will create a long-term treatment plan for the child with MSUD in conjunction with a metabolic specialist and a dietitian. The goal of the treatment plan is to provide the child with all the protein and nutrients needed for healthy growth and development. The plan will also avoid allowing too many branched chain amino acids to collect in their blood.

Conclusion

MSUD is a condition in which the body is unable to break down certain amino acids. Infants with MSUD should have regular medical monitoring and careful attention to dietary restrictions will help to avoid potential complications. However, even after dietary restrictions, a metabolic crisis can erupt. Tell the doctor if there are any MSUD symptoms.

References

https://ghr.nlm.nih.gov/condition/maple-syrup-urine-disease#diagnosis

https://www.healthline.com/health/maple-syrup-urine-disease#treatment

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