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 items that the enzymes would normally breakdown
• The body not being able to fully breakdown food for use in the cells

There are thousands of these disorders.

Causes

These diseases are caused by a problem with the genes that determine how specific enzymes are made. The genes are passed on to a child from one or both parents.

Genetic Material.

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Risk Factors

These diseases are more common in people with:

• Ashkenazi Jewish, Finnish, or Dutch ancestry
• A family history of metabolic disorders
• A brother or sister who died at birth or who had sudden infant death syndrome
• Parents who are related to each other

Symptoms

Problems in infants happen shortly after birth and can be severe. They may be:

• Being very sleepy
• Weak muscles
• Feeding problems
• Vomiting
• Rapid breathing
• Muscle spasms or twitches
• Problems with hearing or sight
• Not meeting milestones
• Seizures
• Problems with the liver, such as a yellowing of the skin or the whites of the eyes
• Problems with the heart or kidney

Problems can also be mild and found after 1 year of age. A child may have:

• Trouble with balance
• Movements that they cannot control
• Loss of feeling or movement
• Muscle tightening
• Behavior or mental health problems
• Loss of developmental skills or language

Diagnosis

Most disorders are found during prenatal testing and newborn screening. In others, the doctor will ask about your child's symptoms and health history. A physical exam will be done.

Blood tests will be done to look for causes. Skin, blood, and urine tests will be done to confirm the diagnosis and look for the enzyme that is causing the problem.

Other tests may also be done, such as:

• Eyesight and hearing tests
• Neuropsychological testing to measure brain function
• MRI scan to take pictures
• Lumbar puncture to test the fluid around the brain and spine
• Tissue biopsy
• Electromyography (EMG) to measure the electrical activity of the muscles
• Other special tests of the heart, liver, and kidneys

Treatment

Some infants and children will need care right away, such as IV fluids and medicines. Ongoing treatment will depend on the type of disorder. Some choices are:

• Dietary changes, such as taking vitamins and not eating certain foods
• Physical therapy to help with strength, flexibility, and range of motion
• Medicine to:
  • Decrease the harmful items that the missing enzymes would normally breakdown
  • Replace missing enzymes
• A stem cell transplant to encourage the body to make the missing enzyme
• Dialysis to filter blood when the kidneys are not able to do so

Infants and children who are not helped by these methods may need surgery.

Prevention

There are no current guidelines to prevent these diseases.