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by Neff DM

Inherited Metabolic Diseases—Overview

Definition

Inherited metabolic diseases are a group of disorders that result in missing or defective enzymes. The enzyme problems can lead to:
  • A build up of harmful substances that the enzymes would otherwise breakdown
  • An inability to fully breakdown food for use in the cells
There are thousands of inherited metabolic diseases.

Causes

These diseases are caused by a problem with the genes that determine how specific enzymes are made. The genes are passed on from parent(s) to child.
Genetic Material
Chromosome DNA
Copyright © Nucleus Medical Media, Inc.

Risk Factors

Inherited metabolic disease is more common in families with
  • Ashkenazi Jewish, Finnish, or Dutch heritage
  • A family history of metabolic disorders
  • Sibling with unexplained neonatal death or sudden infant death syndrome
  • Parents that are related to each other

Symptoms

Most inborn errors of metabolism are found as a result of newborn screening tests. If no screening tests are available or the disease is not detected on screening test, symptoms develop.
Symptoms can be severe and appear shortly after birth. Tell your doctor if your infant has any of these:
  • Excessive sleepiness
  • Weak muscles
  • Persistent vomiting
  • Feeding problems
  • Rapid breathing
  • Muscle spasms or twitches
  • Developmental delays
  • Seizures
  • Problems with hearing or sight
  • Problems with the liver, including jaundice
  • Problems with the heart or kidney
Symptoms can also be mild and detected later in life. Children 1 year old and over can have additional neurologic symptoms. Tell your doctor if your child has any of these:
  • Trouble with balance
  • Involuntary movements
  • Loss of sensation or mevement
  • Muscle tightening
  • Behavior or psychiatric problems
  • Loss of developmental skills, language, or physical skills

Diagnosis

You will be asked about your child's symptoms and medical history. A physical exam will be done.
Blood tests will be done to help identify which of the many possible causes it might be. This will help narrow the possibilities to a few specific conditions. Further testing of skin and blood will be done to confirm the diagnosis and/or look for the specific enzyme that is causing the problem.
Other tests may be done to look for any problems that may have developed. Tests may include:
  • Screening tests for vision and hearing
  • Eye exams
  • Neuropsychological testing—measures mental function
  • MRI scan
  • Lumbar puncture —fluid is taken from the spine and examined
  • Tissue biopsy —a sample of tissues is taken and examined
  • Electromyogram (EMG)—measures electrical impulses in the muscles
  • Other special tests of the heart, liver, and kidneys
Prenatal testing and newborn screening may help with early detection.

Treatment

Some infants and children will need immediate support with intravenous fluids and medications. Ongoing treatment will depend on the type of condition a child has.
Treatment options may include:

Nutrition

Dietary changes that may be required include avoiding certain foods, avoiding long periods of not eating, or taking vitamins.

Ongoing Symptom Management

The following may be needed to manage symptoms and other conditions:
  • Dialysis
  • Physical therapy
  • Surgery
  • Medications

Enzyme Therapy

  • Substrate synthesis inhibition therapy (SSI)—Medication that decreases the item that build up in the cells due to missing enzymes.
  • Enzyme replacement therapy (ERT)—Working enzymes are delivered through an IV to do the job of the defective enzymes.
  • Stem cell transplant—Stem cells are transplanted through IV to encourage the body to make the missing enzyme.

Ongoing Monitoring

For some conditions, regular annual screening tests will be needed, such as:

Prevention

There are no current guidelines to prevent these disorders.

RESOURCES

Children Living with Inherited Metabolic Disorders
http://www.climb.org.uk
Society for Inherited Metabolic Disorders
http://www.simd.org

CANADIAN RESOURCES

The Canadian Society for Mucopolysaccharide & Related Diseases
http://www.mpssociety.ca
Health Canada
http://www.hc-sc.gc.ca

References

Ezgu F. Inborn Errors of Metabolism. Adv Clin Chem. 2016;73:195-250.
Inherited Metabolic Disorders. National Information Center for Metabolic Diseases (CLIMB) website. Available at: http://www.climb.org.uk/inherited-metabolic-disorder/. Accessed August 23, 2017.
Mak CM, Lee HC, Chan AY, Lam CW. Inborn errors of metabolism and expanded newborn screening: review and update. Crit Rev Clin Lab Sci. 2013 Nov;50(6):142-62.
Rice GM, Steiner RD. Inborn Errors of Metabolism (Metabolic Disorders). Pediatr Rev. 2016 Jan;37(1):3-17

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